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ANALYSIS OF OPTIONS FOR TIDAL POWERDEVELOPMENT IN THE SEVERN ESTUARY -

INTERIM OPTIONS ANALYSIS REPORT

VOLUME 1

DECC

December 2008

Prepared byParsons Brinckerhoff Ltdin association withBlack & Veatch LtdQueen Victoria HouseRedland HillRedlandBristolBS6 6US

Prepared forDECC1 Victoria StreetLondonSW1 0ET

Final iDecember 2008

CONTENTSPage

EXECUTIVE SUMMARY IV

SECTION 1 1

INTRODUCTION 1

SECTION 2 6

ASSESSMENT FRAMEWORK 62.1 Overview of Process 82.2 Fair Basis Evaluation 82.3 Assessment Framework 92.4 Assessment Framework Spreadsheet 13

SECTION 3 15

LONG LIST OF PROPOSALS 153.1 Identification of Potential Options 163.2 Proposals taken from the SDC research 163.3 Responses to the Call for Evidence 183.4 Other Strategically Selected Proposals 213.5 Long-Listed Proposals 223.6 Tidal Lagoon Concept 243.7 Initial Screening 25

SECTION 4 32

COMPARISON OF ENERGY OUTPUT 324.1 Estimation of Energy Output 334.2 Comparison with Call for Proposal Submissions 414.3 Tidal Fence 434.4 Optimisation of Energy 46

SECTION 5 48

ENVIRONMENTAL, SOCIAL, ECONOMIC AND REGIONAL CONSIDERATIONS 485.1 Introduction 505.2 Qualitative environmental review of long-list options 525.3 Environmental Issues Relevant for All Options 525.4 Modes of Operation 845.5 Mitigation and compensation issues 855.6 Ecosystem goods and services 865.7 Conclusion 86

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SECTION 6 87

CIVIL, MECHANICAL AND ELECTRICAL ENGINEERING CONSIDERATIONS 876.1 Civil Engineering 886.2 Lagoon Construction 936.3 Tidal Fence Construction 996.4 Tidal Reef Construction 996.5 Navigation Issues 1006.6 Adaptability for Sea Level Rise 1046.7 Turbines and Generating Equipment 1056.8 Grid Connection and Reinforcement 112

SECTION 7 119

ESTIMATED FIRST YEAR OF OPERATION 1197.1 Overview 1207.2 Innovation Risks 1217.3 Construction Programmes and Estimated First Year of Operation 122

SECTION 8 125

SCHEME COST AND COST OF ENERGY 1258.1 Pre-Construction Cost Estimates 1268.2 Barrage and Lagoon Civil Engineering Cost Estimates 1278.3 Barrage and Lagoon Mechanical and Electrical Cost Estimates 1288.4 Tidal Fence Civil, Mechanical and Electrical Cost Estimate 1298.5 Tidal Reef Civil, Mechanical and Electrical Cost Estimate 1298.6 Grid Reinforcement 1318.7 Compensatory Habitat 1318.8 Ancillary Works Costs 1328.9 Cost per Unit Energy 1378.10 Risk Assessment 143

SECTION 9 149

ASSESSMENT SCREENING 1499.1 Application of the Assessment Framework 1509.2 Summary of Analysis 151

SECTION 10 162

CONCLUSIONS 16210.1 Conclusions 16410.2 Overall Summary 166

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APPENDIX A 171

FINANCIAL ANALYSIS DATA 171

VOLUME 2

APPENDIX B ASSESSMENT FRAMEWORK MODEL OUTPUTS

APPENDIX C LOCATION PLANS FOR OPTIONS

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EXECUTIVE SUMMARY

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EXECUTIVE SUMMARY

Objectives and ContextThe Government has set ambitious targets to reduce carbon emissions by 80% by 2050 andincrease renewable energy. The draft EU Renewable Energy Directive will require 15% ofthe UK’s energy to come from renewable sources in 2020. Both, alongside the goals ofenergy diversity and security, will require significant investment in low carbon energysources including many different forms of renewable electricity which may have to accountfor around 32% of the UK’s electricity mix by 2020. It is in this context that generation ofelectricity from the tidal range of the Severn is again being examined to assess how it maycontribute to the UK’s renewable energy strategy. The Severn Estuary has the second orthird largest tidal range in the world and is the most significant tidal range resource in theUK by some distance. In addition, the Severn represents one of the largest single projectpotential contributors of low carbon energy with the largest options being capable ofcontributing up to 7% of the UK’s total electricity demand.

The objective of this report is to analyse, from a technical perspective, potential tidal rangepower options in the Severn Estuary to inform Government in developing a draft short-listof options. Government will also take account of non-technical issues which could impact onthe overall feasibility of an option. The assessment to form the short-listed options has beenundertaken having regard to the identification of options that are able to:

generate electricity from the renewable tidal range resource of the SevernEstuary in ways that will have an acceptable overall impact on theenvironment and economy both locally and nationally, will meet ourstatutory obligations and provide benefit to the UK

deliver a strategically significant supply of renewable electricity, which isaffordable and represents value for money compared to other sources ofsupply in the context of the UK's commitments under the forthcoming EURenewable Energy Directive and Climate Change Act and our goal to delivera secure supply of low-carbon electricity.

Other studies undertaken by the Government are considering related technical issues such asgrid reinforcement and financing / procurement options.

Assessment of OptionsA common set of principles and associated assumptions has been applied to the analysis ofeach option to enable a “fair basis” assessment of costs (the application of commonassumptions and principles across all options). As a result, the information contained in thisreport is of sufficient accuracy as is necessary for differentiating between options.

The options studied by this report are summarised in the table ES1 at the end of thissummary. This provides an executive summary for each of the options studied. Figuresquoted are based on a discount rate of 8% and exclude the costs of providing compensatoryhabitat or grid reinforcement. Inclusion of compensatory habitat costs increases the capitalcosts by between 6% and 20% for larger barrage options and typically between 10% and 35%

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for the other options (dependent upon replacement ratios). In addition, the relativedifferences between the larger barrage options and the other, smaller options become smallerand, in some cases are reversed. This is because the loss of inter-tidal areas as a percentageof energy yield is smaller for the larger options. It should, however, be noted that the fairbasis assessment of loss of inter-tidal areas, which is based on Admiralty Chart data, is anindicator and may over or under-estimate areas of loss when compared with outputs fromdetailed analyses which take account of hydrodynamic effects upstream and downstream ofeach option. If a decision is taken by Government to proceed to the next stage of this study,such analyses will be undertaken for all options selected by Government to be on the short-list. As a comparison the SDC report "Turning the Tide" estimated losses of inter-tidalhabitat of up to 14,500 hectare (ha) on a Spring tide for a Cardiff-Weston barrage and up to5,500 ha for an English Stones barrage rather than the 20,000 ha and 5,000 ha respectivelydetermined by the fair basis methodologies used in this report. Subsequent analyses, usingcomplex hydrodynamic models, will be critical in providing more definitive estimates ofinter-tidal habitat loss, as well as addressing a key issue for all options, specifically, how theywould affect the geomorphological response of the estuary.

ConclusionsEngineering The study has evaluated the engineering performance and requirements of all options. TidalBarrages have been assessed on the basis of the same recommendations made in previousstudies updated to suit present day requirements. Engineering for tidal barrages is wellunderstood and the main issues relate to the selection of gates and turbine types to maximisepower generation whilst adequately mitigating environmental effects. Tidal lagoons involvesimilar engineering components as barrages although, due to the longer lengths of wallconstruction required to form an impoundment, different forms of wall construction have beenproposed to reduce costs by comparison with a conventional rock armoured embankment.These, more innovative, forms of wall construction involve greater risk in terms of engineeringdesign, estimation of costs and durability. Embryonic technologies such as the tidal fence andthe tidal reef present the greatest engineering challenges and this is likely to be reflected inincreased development times to reduce the risks associated with such technologies.

Energy Yields and Carbon Dioxide SavingsThe larger barrage options (B1 to B3) have the potential to contribute the most significantreductions in carbon dioxide emissions with the ability to generate renewable energyaccounting for between 4.5 and 7% of the UK’s electricity requirements. All other optionsare smaller in output contributing up to 1% of the UK’s electricity requirements but with theadvantage that the electricity they produce during the late night / early morning tides ismore likely to be fully utilised. In terms of contributing to the UK’s climate change targets of80% reduction by 2050, those technologies that are already deployed in projects around theworld can be implemented in the short term and thus be capable of making a greatercontribution to the offsetting of carbon emissions compared with less developedtechnologies such as those used in the tidal fence and tidal reef proposals.

CostsThe lowest cost per unit energy is achieved by smaller barrages located at the point wherethe tidal range is greatest. Larger tidal barrages are between 24 and 34% more expensive on

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a cost per unit basis, whilst land connected tidal lagoons have similar energy costs to largebarrages but smaller output. Offshore lagoons represent the most expensive option.Embryonic technologies such as the tidal fence and the tidal reef are more difficult to predictin terms of cost but even allowing for a significant reduction in costs compared with currentdemonstration projects, the tidal fence option is more than double the unit cost of the lowestcost option (B4 the Shoots Barrage).

In terms of affordability, all options represent significant construction projects in their ownright with the larger barrage options costing upwards of £18bn and the smaller optionscosting up to £5bn although those with the lowest cost per energy are between £1.8bn and£3bn. Costs of compensatory habitats would be additional and there would also need to beinvestment to reinforcing the national grid although similar investments would be requiredfor other renewables if no Severn tidal power option was pursued. Combinations of options,such as a Barrage and a Tidal Lagoon could also be considered.

Impacts on HabitatsAll options would impact inter-tidal habitats including offshore lagoons. Although anoffshore lagoon does not directly lead to loss of inter-tidal habitats, resultant changes in tidalcurrents and geomorphology will affect adjacent habitats. Following appropriate assessmentwhich involves consideration of alternatives, and subject to the requirements of the Habitatregulations, should a decision be taken to proceed on the basis of the over-riding publicinterest, compensatory measures would be required including habitat compensation for lostintertidal habitat. Not all compensation would necessarily be located in the Severn. For thisreport, these costs have been assessed in headline terms only using a range of possiblereplacement ratios and an indicative cost per ha.

Environmental EffectsClimate change is already affecting the Severn Estuary and any environmental effects haveto be seen in the light of this changing baseline. The most significant environmental effectsof a scheme will be those relating to the geomorphological response of the estuary to anytidal power structure, loss of inter-tidal habitat, changes to habitats including feedinggrounds available to birds, salt marsh and sedimentation, effects on fish and changes inwater quality. For some of the smaller options, whilst the effects will continue to besignificant, the scale of impact may be smaller (for example availability of feeding groundsfor birds). Other effects include changes to water quality and turbidity. Fish behaviour willbe changed by all options and where fish navigate upstream or downstream throughturbines, significant mortality rates will be experienced.

Social, Economic and Regional EffectsThe construction of any tidal power project in the Severn will result in significantemployment opportunities both during and after construction. There is also potential forjobs to be lost from industries whose operations are compromised by a Severn tidal powerdevelopment. Impacts during construction will require careful management but will resultin benefits for local service industries.

Transportation links have not been considered by this study as there is no policy at presentto increase the number of transportation links across the Severn. The activities of

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commercial ports will be affected by tidal barrages in particular and will entail navigationthrough an additional set of ship locks (increasing transit times) and modification of existingfacilities to accommodate changed water levels. A potential benefit for impacted ports willbe increased high water standing times and a significant increase in low water level. Nonbarrage options will impact ports in different ways – tidal reefs and tidal fences will presentchallenges in time of entry / exit through their navigation provision because of the increasedtidal currents that will prevail. Tidal lagoons may have less impact on ports althoughchanges to dredging regimes may result from all options. The numbers of ports impacteddiffers depending upon the location of options

The extent of flood benefits and impacts remains uncertain from a Severn tidal powerscheme. Whilst flood defence should be enhanced (by protecting communities locatedupstream of a barrage or the Bridgwater Bay land connected lagoon from storm surges andsea level rise), this would only be effective if mitigation of adverse effects is achieved (forexample submerged tide locked land drainage outfalls) so that existing standards of floodprotection are maintained. Other regional effects include impacts on fisheries.

SummaryTidal barrage options offer the greatest degree of certainty in relation to energy yields, costs,timescales and technology. Tidal lagoons use similar turbines and generating equipment butinvolve less traditional forms of construction for the lagoon walls. Whilst, in engineeringterms, there are examples of tidal power barrages in existence (La Rance, France andAnapolis Royal, Canada and Sihwa, South Korea – under construction) there are, as yet notidal lagoons. Both tidal barrages and tidal lagoons will result in significant changes to theSevern Estuary although the real extent and nature of these changes is dependent upon thelocation of the specific option.

More embryonic technologies have potential (albeit unproven) benefits but will also result insignificant changes to the Severn Estuary. As they are located in the outer part of theestuary, the extent of these changes, although smaller at any one location than an equivalentbarrage, will extend through a greater area. In addition, their development cycle (noexamples of tidal fences or tidal reefs currently exist) will delay implementation on theSevern with the consequent impact in contributing to the Government’s energy and carbonreduction targets. As this is a specific objective of the Government’s Feasibility Study, thissuggests that embryonic technologies will be less able to meet the Government’s requiredtimescales compared with tidal barrages and lagoons. However, for the purposes of thisreport, where adequate data are available on which to assess energy yields and costs,assessment of embryonic technologies has been analysed assuming that they and the otheroptions follow similar timescales for planning, designing and achieving consents to enablecosts to be compared on an equivalent basis.

Consideration of options operating in conjunction with each other may also be relevant, andthe combination of one or more lagoons with a barrage located upstream will also beconsidered in Phase 2 if the decision is taken to proceed.

Generation of power using the tidal range from the Severn is technically feasible andpreliminary costs have been determined for each option. All options considered have

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impacts and benefits relating to the environment, social, economic and regional effects. Thescale of these impacts and benefits varies across options and further work is needed toquantify and assess these to determine the extent of benefits and technical and financialfeasibility of mitigation and compensation. The purpose of this report is to differentiatebetween options and provide a high level indication of their respective benefits and impacts.In accordance with current normal practice, a precautionary approach has generally beenadopted for identifying potential environmental impacts. In subsequent stages, afterconfirmation of a short-list of feasible options, more detailed work will be undertaken toassess significant benefits and impacts to a level commensurate with the strategic nature ofthis study.

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Table ES1- Executive Summary for Each of the Options

Option Option Name Key Conclusions

B1 Outer Barrage fromMinehead to Aberthaw

Largest producer of energy (25TWh/a) but with highest capital cost (£29bn);Cost of energy is 13.94p/kWh excluding compensatory habitat costs ;Largest environmental impact footprint, and will result in reduction of water levels andtidal range, loss of inter-tidal habitats and impacts on bird and fish populations in theSevern; Benefits include protection from effects of storm surges, sea level rise and reducedturbidity;Severn Ports upstream will be affected, primarily Barry, Bristol, Cardiff, Newport andSharpness.

B2 Middle Barrage fromHinkley to LavernockPoint (Shawater concept)

Longest barrage option - based on the B3 option but with additional embankmentextending the barrage to Hinkley Point - Energy output of 19TWh/a;Although the capital cost is less (£22bn), the cost of energy is similar to Option B1 at13.96p/kWh;Environmental effects are similar to those for B1 as this option seeks to provide similar flooddefence benefits by crossing Bridgwater Bay;Severn Ports upstream will be affected, primarily Bristol, Cardiff, Newport and Sharpness.

B3 Middle Barrage fromBrean Down toLavernock Point(commonly known asthe Cardiff to WestonBarrage)

Most studied of any of the options and reported on in Energy Paper 57;Annual energy output of 17TWh and a capital cost of £18bn;The cost of energy is the best of all the “large” options at 12.94p/kWh excludingcompensatory habitat costs ;Environmental impacts are potentially significant, as with other large barrage options, andwill result in reduction of water levels and tidal range, loss of inter-tidal habitats andimpacts on bird and fish populations in the Severn; Benefits include protection from effectsof storm surges, sea level rise and reduced turbidity.

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Severn Ports upstream will be affected, primarily Bristol, Cardiff, Newport and Sharpness.

B4 Inner Barrage (ShootsBarrage)

Significantly smaller than the large barrage options, this option is located just downstreamof the Second Severn Crossing co-incident with the highest tidal range in the Severn;Generates 2.77TWh per year at a capital cost of £2.6bn and achieves the lowest cost per unitenergy at 10.4p/kWh;Environmental impacts are similar in type (although not necessarily scale) to other barrageoptions although there is an increased risk of sedimentation;This option does not impact the Ports of Bristol or the ABP Ports on the Welsh coast.

B5 Beachley Barrage Located upstream of the Wye, smallest barrage option studied (£1.8bn) and has similarcharacteristics to Option B4;Annual energy output is 1.59TWh/a, 57% of Option B4 whilst the cost per energy is12.58p/kWh;Similar environmental effects as Option B4 except that the Wye is not impounded andsedimentation risk is higher;This option affects ports in the Gloucester Harbour Trustees administered waters.

F1 Tidal Fence Proposalssubmitted by SevernTidal Fence Group

Initially, proposed between Cardiff and Weston but a more feasible alignment wassubsequently considered between Minehead and Aberthaw;Annual energy output of 3.3TWh is achievable at a cost of £6.3bn. Cost of energy is morethan double the lowest cost option at 22.72p/kWh;Assumes future development costs will reduce significantly from the current demonstrationproject costs for tidal stream technology. This implies a significant period of furtherdevelopment and experience before large scale implementation could be achieved. Unlikelythat a decision to proceed with a tidal fence could be made in the short-term;It does offer the possibility of less significant environmental effects than barrage options

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although the area affected is as large as the biggest barrage option.

L2 Tidal Enclosure on theWelsh Groundsproposed by FlemingEnergy

Land connected lagoon located on the relatively high Welsh Grounds just downstream ofthe Shoots Barrage (B4);It has an annual energy output (2.3TWh/a) achieved at a cost of £3.1bn. Cost per unitenergy is 15.46p/kWh and is thus more expensive than the larger barrage options, althoughdevelopment alongside B4 would reduce energy cost. Additional energy output could beachieved from the Welsh Grounds if the materials used in construction were excavated fromwithin the basin to achieve greater live storage. This would marginally increase energyyield and thus reduce the cost of energy;Land connected lagoons, like barrages, result in loss of inter-tidal habitats because of thesignificant reduction in tidal range within the impounded area. Other environmental effectsare similar to smaller barrages except that impacts on fish and navigation are expected to beless because they do not form a barrier across the estuary.

L3 Tidal Lagoon Concept(which has beensubsequently modelledas four land-connectedlagoons and threeoffshore lagoons basedon various generalsubmissions receivedfrom the Call forEvidence)

Various land connected and offshore lagoon configurations have been studied usingdifferent forms of lagoon wall construction;As lagoon costs are influenced by the length and depth of wall forming the impoundedbasin, innovative methods of wall construction are required and the lowest cost option,(apart from the wall design proposed by Fleming Group for Option L2) comprises ageotextile solution using material dredged from the estuary and protected by rock armour(externally) and revetment (internally);Aside from the L2 Welsh Grounds proposal, Bridgwater Bay offers the most cost effectivelagoon option with a higher energy yield (2.64TWh/a) and slightly reduced capital coststhan L2 giving a cost per kWh of 13.02p/kWh.An offshore lagoon, located below the low water contour (and reduced impact on habitats),has been modelled to produce a similar energy output using the same forms of construction.Because of the much deeper wall construction required, it is more expensive with a capital

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cost of £5.8bn for almost the same energy output of 2.6TWh/a as the £3bn Bridgwater Bayland connected option. This is also reflected in the cost of energy which is more than doublethe land connected lagoon alternative.

R1 Tidal Reef proposed byEvans Engineering.

Entirely new concept that has continued to evolve during the study period.Studied and reported on to a level commensurate with the information available but theassessment has not been able to provide as definitive estimates as other options on which todevelop reliable cost base and energy yields. Outline estimates provide a capital cost of£18.1bn with an energy yield of 13TWh/a with a preliminary estimated cost of energy of20.30p/kWh.Development period would be greater than other options and require demonstrationprojects to test the concept – this would take between 10 and 15 years if tidal streamtechnology is taken as a benchmark.

U1 Severn Lakes (promotedby Gareth Woodham)

Originally included because one of its objectives is to produce power using the tidal rangeof the Severn.The cost of constructing a 1km wide causeway 16km in length would be significantly morethan a conventional tidal barrage and clearly requires additional investment streams tojustify its cost. On the basis of the information within the public domain, this is alsorecognised by the proposer who envisages other revenue streams from land, recreationaland other energy developments as part of this scheme.This study is only examining potential options from an energy perspective. For this reasonthis option is not considered specifically by the Study.Should tidal power development from the Severn form part of Government’s future energypolicy, a privately proposed option such as Severn Lakes could be considered in the future.

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SECTION 1

INTRODUCTION


1 INTRODUCTION

The objective of this report is to analyse potential tidal range power options in theSevern Estuary and confirm quantitative and qualitative data to enable Governmentto recommend a draft short-list of options that have the technical potential to formthe reasonable alternatives for the Strategic Environmental Assessment (SEA). Thedraft short-list will be finalised following examination by Government of non-technical issues which could impact on the overall feasibility of an option andpublic consultation. The assessment to form the short-listed options has beenundertaken having regard to the identification of options that are able to:

generate electricity from the renewable tidal range resource of theSevern Estuary in ways that will have an acceptable overall impacton the environment and economy both locally and nationally, willmeet our statutory obligations and provide benefit to the UK

deliver a strategically significant supply of renewable electricity,which is affordable and represents value for money compared toother sources of supply in the context of the UK's commitmentsunder the forthcoming EU Renewable Energy Directive and ClimateChange Act and our goal to deliver a secure supply of low-carbonelectricity.

A common set of principles and associated assumptions have been applied to theanalysis of each option to enable a fair basis assessment across all options. As aresult, the information contained in this report is only of sufficient accuracy as isnecessary for the comparison of options. The accuracy of the data also reflects thelimited understanding of some of the projects and technologies. Cost assessmentsused in this report are therefore based on sources common to all options and directcomparison with previously published cost data for some options is not appropriatedue to the differences in assumptions required to apply a fair basis approach acrossall options.

The short-listed options will be worked up in subsequent phases of this study inorder to develop a more detailed assessment of cost and energy yield, includingmodifying option configurations to achieve the optimal results having regard toconstruction/operating costs, value of energy produced and environmental/regionalimpacts.


ObjectivesThe Government has launched a Feasibility Study to consider whether theGovernment could support a project which exploits the major energy generationpotential of the tidal range of the Severn Estuary, and if so, on what terms. TheTerms of Reference of the Feasibility Study were published on 22 January 2008.

The Severn Estuary has the most significant tidal range resource in the UK1. Thetidal stream resource in the Severn Estuary is not nationally significant (only 4% ofthe potential of UK waters2). As such, the Feasibility Study scope considers all tidalrange technologies, but not tidal stream technologies unless in combination withtidal range.

In recognition of the importance of the natural environment of the Severn Estuary,the feasibility study has commissioned a Strategic Environmental Assessment whichwill assess a plan whose purpose is:

generate electricity from the renewable tidal range resource of the SevernEstuary in ways that will have an acceptable overall impact on theenvironment and economy both locally and nationally, will meet ourstatutory obligations and provide benefit to the UK

deliver a strategically significant supply of renewable electricity, which isaffordable and represents value for money compared to other sources ofsupply in the context of the UK's commitments under the forthcoming EURenewable Energy Directive and Climate Change Act and our goal to delivera secure supply of low-carbon electricity.

In order to define the plan for the strategic environmental assessment, theGovernment seeks to identify a short list of potential tidal power schemes on theSevern from the long list that has been drawn up following a call for proposalsissued in May 2008. The final decision on whether to support a Severn tidal powerproject will take into account the feasibility and cost of other non-Severn basedoptions to meet our renewable energy objectives and goals on low-carbon electricityand carbon reductions.

This report covers the analysis of the candidate projects that form the long list andthe process that has been used to appraise to inform selection of a draft short list ofoptions that have the technical ability to meet the objectives of the plan. Wider issues

1 Sustainable Development Commission “Turning the Tide” Report published in October 2007 http://www.sd-commission.org.uk/publications/downloads/Tidal_Power_in_the_UK_Oct07.pdf]

2 http://www.sd-commission.org.uk/publications/downloads/TidalPowerUK1-Tidal_resource_assessment.pdf.

http://www.sd-/

http://www.sd-commission.org.uk/publications/downloads/TidalPowerUK1-Tidal_resource_assessment.pdf.


such as affordability for the public purse will be considered by Government outsideof this study prior to finalising the draft short-list for public consultation.

Report StructureThis report is structured as follows:

Assessment FrameworkSection 2 describes the assessment screening method used to derivethe short list;

Identified Potential OptionsSection 3 describes all the potential development options identifiedand presents a long list of options assessed in this report;Section 4 provides an estimate of the energy output of the long listedoptions;Section 5 provides an analysis of the environmental effects of the longlisted options;Section 6 provides an appraisal of the civil, mechanical and electricalengineering components of each long listed option;

Programme and Fair Basis Cost AnalysisSection 7 provides an estimate of the earliest feasible year for firstenergy production for each long list option;Section 8 provides an estimate of construction cost and the cost ofenergy for each long listed option;

Application of the Assessment FrameworkSection 9 presents the assessment screening method worksheets andtheir subsequent analysis, including the comparison to plan objectives;Section 10 presents conclusions and a summary of the options.

Appendices A Cost Assumptions and Analyses B Assessment Framework Outputs C Location Plans

MethodologiesThe methodologies used in the initial analyses are intended to enable the comparisonof options on a fair basis to inform the selection of the draft short list of options withthe technical ability to meet the plan objectives. Results from previous studies onsome options have been used to provide the baseline data for comparison as it wasnot practical nor indeed necessary to study all options to the same level of detail as isavailable in previous studies. However, where possible, methods have been adoptedwhich apply a common set of principles to the analysis of each option and all costshave been developed to a first quarter 2008 base. Appendix A provides further detailon this.


Although the core information contained in this report has been developed withsufficient accuracy to enable comparison of options on a fair basis, the resulting costsdo not necessarily reflect the anticipated out-turn cost for a specific option. This is toprevent one option being disadvantaged by comparison with another if the latter hasthe benefit of more accurate data being available. An example would be thedetermination of loss of inter-tidal habitats – whilst more accurate data are availablefor some of the previously studied barrage options, in order that the same datasource is used for all options, areas have been derived from Admiralty Charts whencomparing options. More accurate estimates will be produced following detailedmodelling studies using the most up to date bathymetric models of the Estuaryduring subsequent stages of the study. As a consequence, cost data from this phaseof the study is indicative and comparative and should not be used on an absolutebasis without first confirming that the data are appropriate.

Similarly, levelised cost data has been used to derive cost of energy on a per kWhbasis. The levelised costs are calculated by discounting the stream of generationcosts over the lifetime of the asset (120 years) and dividing this value by the amountof electricity generated over this period to calculate the price at which the generatorwould have to sell the electricity generated in order to break even over theperiod. Calculating levelised costs over the lifetime of the asset illustrates the cost ofgeneration if the lifetime of the asset is the same as the financial lifetime of theproject. If the financial lifetime of the project is shorter than this, the levelised costswould be higher than those shown here but would exclude the residual value of theasset beyond the financing period of the project.

A disadvantage of net present value calculations when applied to long life renewableenergy projects is that, because of the high initial capital cost compared with theearly revenue yields, revenues from energy beyond 40 years or so add very littlecalculated value except at very low discount rates. As this report is comparingdifferent options with similar characteristics, the use of net present value analysis toproduce levelised costs for comparison purposes is reasonable and fair. However,using such costs to compare tidal energy with other forms of generation requirescareful application both because of the less accurate nature of fair basis assumptionsand the long project lifespan. Comparison of different types of generation projects istherefore best undertaken using project life carbon dioxide emission savings inaddition to the more conventional means of financial assessment.


SECTION 2

ASSESSMENT FRAMEWORK


2 ASSESSMENT FRAMEWORK FOR INITIAL APPRAISAL OF OPTIONS

The assessment framework comprises a number of actions. It is an appraisal of allproposals against the objectives contained in this report and outside of it and anassessment of whether any issues exist that would prevent an individual or allproposals coming forward. This includes cost of energy, affordability (how aproject may be financed and what position the Government will want to take) andrisk of delivery. This will lead to a draft short-list of proposals that will form thereasonable alternatives for the SEA subject to public consultation.

The aim, in this report, is to provide sufficient information to identify proposals thathave the technical capability to meet the plan objectives. Each proposal is assessedagainst key criteria within the objectives:

Volume of energyCost of energyAmount of Carbon savingsTimingCostCompensatory habitat requiredAssessment of environmental and regional impact

This can be broken into three areas;

a. scientific, technical and/or commercial credibilityb. quantitative (energy yield, carbon reduction, cost etc.)c. qualitative (impact on environment, region etc.)

The high level qualitative assessment is important to ensure that proposals that mayhave additional benefits either in terms of the environment or economy are notmissed. It provides a high level assessment of issues that help inform on aproposal’s ability to meet the EU legislation. Outside of this report, widerquestions will be asked as to whether there are issues beyond technical capabilitywhich may negatively impact on a proposal’s overall feasibility. For example a lowconfidence on the technology will attract greater levels of risks in terms ofdeliverability, costs and financing.

The short-listing process is a pre-cursor to the SEA. It will help define the planthe SEA will assess and help define the list of feasible options that meet theobjectives of the plan to utilise the tidal range of the Severn Estuary


2.1 Overview of Process

Identification of options for the generation of tidal power using the tidal range of theSevern has been undertaken using inputs from three sources:

Call for Proposals, issued as part of the Call for Evidence issued on 12May 2008. The Call for Evidence invited interested parties to submit (a)evidence based proposals for development which will generate electricityfrom the tidal range of the Severn Estuary, and (b) other information,which either exists or is under development, which could potentiallycontribute to the evidence base for the assessment of schemes and theSEA.

The options studied by the Sustainable Development Commission in‘Turning The Tide’

Other strategic options which were not covered by proposals in i) and ii)above.

The core component of the methodology for evaluation of options proposed for tidalpower generation in the Severn Estuary is a high level screening process comparingoptions on the information available and the objectives of the plan. Groups ofoptions which could operate in combination with each other have also beenconsidered although the analyses have been undertaken on an project by projectbasis.

The outputs from the initial screening process have been revisited further as moredetailed information from proposals has been determined following analysis and thedevelopment of the environmental, social, regional and economic data and analysis.

Recommendations on the proposals to include in the draft Short List that have thetechnical capability of meeting the objectives and are considered feasible will then bemade by officials to Ministers in the autumn. A do nothing option is included but isnot covered specifically by this report.

The shortlisting process is a pre-cursor to the SEA. It will help define the plan theSEA will assess and help define the list of feasible options that meet the objectivesof the plan to utilise the tidal range of the Severn Estuary.

2.2 Fair Basis EvaluationIn order that options are not disadvantaged by differing levels of previous researchand study into their feasibility, a methodology has been adopted to evaluate the costand energy production on a “fair” basis. In essence, this involves applying aconsistent set of cost rates and assumptions across all options. The cost estimates havebeen produced by an independent firm of cost consultants working on engineeringdata that has either been prepared or reviewed as part of this study.


Energy yield estimates have been prepared on a similar basis using a parametricapproach supplemented by 0-D and 1-D modelling3. Estimates of losses of inter-tidalhabitats have been taken from Admiralty Charts with the same cost rate applied to alloptions for the compensation of lost habitats. Construction and operation assumptionsare also consistently applied. Where different assumptions apply because of scaleissues, these are clearly stated. It is important to note that in some cases (for exampleestimates of loss of inter-tidal areas), fair basis assumptions may differ from those ofmore detailed studies undertaken on specific options. Using the latter data on oneoption when it could not be applied to all options could place that option at an unfairdisadvantage. There are also some options which have unique components (forexample a Tidal Fence) and in these circumstances, cost estimates have beendeveloped which are consistent with the above principles.

The fair basis assessments of planning, construction and operation costs, together withthe energy yields and the project timeline all contribute to a discounted cash flowmodel that calculates costs in terms of pence per kWh for each option using differentdiscount rates. The project timeline is taken to the full project life although foranything but the lowest discount rates, the net present values calculated by thediscounted cash flow model have negligible impact for energy and costs incurred after35 to 50 years. This may be an issue in comparing unit costs with other forms ofgeneration but is of no relevance in differentiating between options which have similarcharacteristics – namely high capital costs but low running costs. For similar reasons,the cost of decommissioning is not taken into account because it has been assumedthat all options have similar operational lives of 120 years (with regular replacement ofequipment during this period). Discounting decommissioning costs back over 120years has a negligible (in terms of differentiating between options) effect on the costper unit.

2.3 Assessment Framework

The assessment framework comprises a number of actions which, bar the first, havebeen applied iteratively over the period July to November 2008 with the aim toidentify which proposals could, taken individually, be feasibly built. This involves atechnical assessment of each of the options.

The first step of the assessment process in this report is applied to all optionsidentified through the three sources above. It has the objective of identifying thoseoptions which do not meet the objectives of the plan as:

they are not within the Severn Estuary; or

3 0-D modelling estimates energy yield from the head generated at the turbines and the volume offlow through the turbines. It does not model the tidal range along the estuary and is limited tomodelling a single basin. 1-D modelling estimates energy by modelling the tidal range and flowalong the estuary. It can be used to model combinations of options and multiple basins and modelsthe effects of schemes on the tidal range.


they lack scientific, technical or commercial credibility for the purposes ofthe plan.

An example might be a new technology that has never been tested, even at a smallscale, and that may not give investors confidence in committing money to the project;another example is where the electricity output cannot be guaranteed. Proposals thatdo not pass through this stage are not considered further. There may be proposals thatare marginal on these issues and in particular may represent other benefits – as suchthey may be included in the further analysis in this report on the understanding thatrisks surrounding their ability to deliver and confidences around costs and time arelikely to be larger than other options.

The next stage is an iterative assessment to provide the information as to whether theproposals have the technical ability to meet the objectives of the plan in terms of thequantitative (energy yield, carbon reduction, cost etc.) and qualitative (impact onenvironment, region etc.) data available with sensitivity testing included.

The quantitative assessment provides the data required to “inform broad comparison”for the quantifiable data listed in the Call for Evidence4. It looks at each proposal ona basis of the cost and amount of energy they are likely to produce, their financialfeasibility, timescales for power generation, degree of technical risk, and theirpotential contribution to the UK’s commitments under the forthcoming EURenewable Energy Directive and Climate Change Act and goal to deliver a securesupply of low-carbon electricity. This is the primary criterion of the assessment andaims to help identify those which are significantly more favourable as an energyproject. In addition, other quantitative data such as timeframes, CO2 outputs andcapital cost are included here5. The criteria are not set in absolute terms orthresholds but instead reflect the merits of each option with the aim of establishingwhether the individual proposal could be taken forward and be developed to meetthe plan objectives. Optimism bias is not included in the technical comparison ofoptions but risk and contingency allowances of 15% are included.

The qualitative assessment provides the “interim appraisal on a qualitative basis” and“This initial appraisal will also act as a precursor to, and will inform, the full strategicassessment of short-listed options to be undertaken within the SEA process6.” It aims toidentify projects which may be marginal in terms of the energy criterion but whichappear, on the information currently available, to be relatively attractive whenenvironmental, grid compatibility and regional economic and construction impact, orlack of, are considered. Proposals that do not perform well on firstly the quantitativeand then also on the qualitative screen will not be considered further subject to

4 http://www.pbworld.co.uk/index.php?doc=627

5 Carbon emissions were initially included as an environment criterion but as they can be quantified they have been includedwithin the quantitative action for assessment purposes

6 Italicised text represents extracts from the Call for Evidence

http://www.pbworld.co.uk/index.php?doc=627


sensitivity testing. It is not the intention to use any results from the qualitativeanalysis to screen out proposals that meet the quantitative objectives at this stage,particularly as more work is being undertaken to determine environmental impacts.

The factors that are considered in the high level qualitative assessment build on thelist outlined in the Call for Evidence and are informed by the SEA Directive;

i) Environment:

Surface, Marine and Ground Water QualitySoilsHistoric EnvironmentLand and SeascapeResource Efficiency and WasteHydrodynamics (including tides), Geomorphology and SedimentationClimatic Factors (Embedded Carbon (e.g. carbon emitted during construction)Changes to Sources (e.g. low carbon generation), Changes to Sinks (e.g.sedimentation))Habitats, biodiversity, fauna & flora (Effects on Designated Sites, Wider Effects toHabitats and Biodiversity, Birds, Fish, Other (e.g. mammals and molluscs)Ability to be compliant with EU environmental legislation

ii)) Economic /Social /Regional

Material Assets:Flooding and Land DrainageFisheriesPorts and Commercial ShippingConstruction (e.g. Supply Chain pressures, sourcing of materials etc)Other (e.g. dredging and marine aggregates)

Population and Health:Tourism and LeisureConstruction ImpactsOther (e.g. ancillary benefits, global benefits of reduced GHG emissions etc)

The process for evaluating each of these issues uses a qualitative scale against whichassessments are graded. A crucial element to note is that at this screening stage, theinformation available may not be able to inform a judgment as to the impact of aproposal, this will be noted within the assessment framework by a ? category. Thishelps identify areas where information is not available in sufficient detail so that incan be examined within the SEA framework.


Scale Definition

++ The proposal may have a major positive effect in relation to assessment criterion.

+ The proposal may have a positive effect in relation to assessment criterion.

0 The proposal is unlikely to have any effect in relation to assessment criterion.

- The proposal may have a negative effect in relation to assessment criterion.

-- The proposal may have a major negative effect in relation to assessment criterion.

? The proposal may have both positive and negative effects in relation to assessmentcriterion and the balance cannot be determined at this stage.

A model has been developed to apply the assessment framework and the results ofthis assessment are described in Section 9 and the model outputs are included inAppendix B.

The assessment for each option has been taken against a common baseline. Theassessment itself has been determined by issue area experts and subject to peerreview. Whilst it would be desirable to assess against a baseline that accuratelyrepresented the changes in the estuary that are likely to take place over the nexthundred years, the reality is that qualitative assessment is more readily undertakenagainst the baseline conditions that exist today. However, the impact of climatechange and how it may affect today's baseline conditions and the subsequentevaluation of the option for each of the criteria has been considered by the issue areaexperts in their application of the qualitative assessment.

It is recognised that at this stage that more detailed analysis will be included in theSEA framework and any subsequent environmental impact assessment (EIA). Theassessment contributes to identifying areas that will merit further study within theSEA framework for short-listed options.

Sensitivity tests on proposals which have been compared on ebb-only generationhave also been performed to assess whether a different configuration or combinationwith other proposals would allow for a proposal to reach the short list. Othersensitivities for all proposals that come through the initial sift include discount rates,robustness of data on energy yield and costs and the commercial risk. At this point,further qualitative and quantitative assessment may be performed as part of theiterative assessment framework adopted.

The final step of the assessment is performed outside this report, and determineswhether it is reasonable to take proposals forward to the short list of options forpublic consultation. This step will include the outputs of this report and factor in


other wider issues that may impact on the feasibility of an option – such as the abilityto provide sufficient compensatory habitat, ability of project to be financed and valuefor money. There is no pre-determined number of proposals that will come forwardon to the short list.

2.4 Assessment Framework Spreadsheet

Concept

The assessment model itself has been designed as a series of integrated ExcelSpreadsheets which follow the principles of the flow chart in Figure 2.1. The modelcomprises the following spreadsheets

0. Summary

1. Initial Screening

2. Quantitative (primarily energy and cost)

3. Environmental

4. Economic / Social / Regional

The Assessment Framework outputs have also been reviewed using sensitivity testson the following:

a. Different compensatory habitat ratios

b. Increases in capital cost estimates (+10%)

c. Reduction in energy yields (-10%)

d. Application of discount Rates

e. Potential Combinations, Pumping and Two Way Generation

The model outputs are summarised in Section 9 of this Report with the associatedspreadsheets being incorporated in Appendix B to this report.


SECTION 3

LONG LIST OF PROPOSALS


3 LONG LIST OF PROPOSALS

Identification of options for the generation of tidal power using the tidal range ofthe Severn has been undertaken using inputs from three sources:

Call for Proposals, issued as part of the Call for Evidence on 12 May2008. The Call for Proposals invited interested parties to submitevidence-based proposals for development which will generateelectricity from the tidal range of the Severn Estuary.

The options studied by the Sustainable Development Commission in‘Turning The Tide’

Other strategic options which were not covered by proposals in i) and ii)above.

This section describes the process used to identify and review the options forinclusion on the long-list, and the summary details for each of the options includedon the long-list.

3.1 Identification of Potential OptionsAn initial objective of the study was to assess the potential tidal power candidateprojects in the Study Area. This was initially undertaken by reference to previousstudies – particularly the studies published as Energy Papers (EP46 (Bondi) and EP57(STPG/ETSU)) in the 1980’s and the more recent report on tidal power in the UK by theSustainable Development Commission (Turning the Tide – October 2007). Thesereports covered both tidal barrage and tidal lagoon locations. A Call for Proposalswas also launched to identify if there were any further proposals being considered byorganisations. This provided a number of additional specific proposals, includingvariants on previous barrage proposals, a Tidal Fence, a specific design for a tidallagoon on the Welsh Grounds, a conceptual design for a tidal reef, some generallocations for offshore tidal lagoons and proposals for alternative wall designs to beused with tidal lagoons. Finally a strategic overview was undertaken to see if therewere any options not previously studied or not identified within the Call forProposals, which could potentially meet study objectives with different characteristicsto those options already proposed. This resulted in the addition of a proposed barrageat Beachley to assess the effects on energy generation if the Wye was not impounded.

3.2 Proposals taken from the SDC research

The SDC’s research in 2007 identified a number of schemes for barrage and non-barrage options for developing power from the tidal range in the Severn Estuary aslisted below7.

7 Sustainable Development Commission “Turning the Tide” Report published in October 2007 http://www.sd-commission.org.uk/publications/downloads/Tidal_Power_in_the_UK_Oct07.pdf]

http://www.sd-/


(i) Barrage Proposals

Cardiff-Weston scheme: often known as the main ‘Severn Barrage’ proposal,this would run from Lavernock Point, west of Cardiff, to Brean Down, south-west of Weston-Super-Mare

Cardiff-Weston Scheme with second basin: similar to the Cardiff-Westonscheme above, but with a second basin on the seaward side, thus enablingutilisation of nearly the full estuary resource and also providing some floodprotection benefits to the Somerset Levels

Minehead-Aberthaw scheme: often referred to as the ‘Outer Barrage’, thisalignment would make maximum use of the Severn Estuary tidal resource, and isone of the longest barrage proposal because of its downstream location

Dawson continuous power scheme: a barrage in the outer estuary fromMinehead (as the Minehead to Aberthaw barrage above), but with anembankment extending to Brean Down, thus creating a second basin andenabling greater availability of power over the tidal cycle

English Stones or Shoots scheme: the currently proposed alignment would runclose to the two Severn Crossings and has been designed to facilitate a high-speed rail link to replace the aging Severn Tunnel

Hooker scheme: similar to above but with a second basin to seaward, enablingout of phase operation on both the ebb and flood tides

Severn Lake scheme: a 1 km wide causeway adopting a similar alignment to theCardiff-Weston scheme, designed to allow the construction of a number ofadditional features, including a wave farm on the seaward side, and four marinas

Shaw two-basin energy storage scheme: similar to the above, but with deep-setpump turbines to enable out of phase operation .

The barrage proposals can be divided into single basin and twin basin schemes.Twin basin schemes would enable the delivery of power to the grid more frequentlythan a single basin scheme operating only on the ebb tide. All the twin basinschemes incorporate a barrage which would occupy a similar alignment to one of theequivalent single basin schemes. Conversely, all single basin schemes could intheory be varied to include secondary basins.


Single basin schemes which are relatively less economic than other single basinschemes will not become relatively more economic with the addition of a secondarybasin. This is because, as highlighted in the SDC’s research 8, studies haveconsistently shown that schemes requiring long lengths of embankment result inrelatively high unit costs of energy than equivalent schemes with embankmentlengths kept to a minimum.

The long-listing of barrage proposals has therefore only considered single basinschemes to differentiate between options; the appraisal of short listed schemes willthen consider variations in the operating regime, including the addition of secondarybasins. This is necessary because the variations in operating regime may haveimportant implications in terms of the delivery of power to the grid, value of energyand environmental effects.

(ii) Land Connected and Offshore Impoundment Proposals

o Russell Lagoons: two land-bordered tidal lagoons on the Welsh coast, onthe Peterstone Flats and Welsh Grounds, and one land-bordered tidallagoon on the English coast on the English Grounds

o Swansea Bay Lagoon: a smaller (in comparison to the Russell Lagoons)offshore tidal lagoon but not located within the proposed study area; assuch this option may be promoted independently of any strategic tidalpower development in the Severn.

3.3 Responses to the Call for Evidence

Call for Proposals SubmissionsTable 3.1 below lists the proposals that have been submitted in response to the Callfor Proposals.

Proposal Name Proposer(s) and/orAssociations/Status

Brief Description

TidalImpoundent onthe WelshGrounds

Fleming Group A variant on the Russell Welsh Groundslagoon comprising an infilled precastconcrete wall solution to enclose thelagoon.

New Build Tidal Rubicon Marine New build tidal lagoons and the creation

8 Sustainable Development Commission “Research Report 3 - Severn Barrage Proposals” published in September 2007http://www.sd-commission.org.uk/publications/downloads/TidalPowerUK3-Severn_barrage_proposals.pdf

http://www.sd-commission.org.uk/publications/downloads/TidalPowerUK3-Severn_barrage_proposals.pdf



Brief Description

Lagoons of high tidal flow channels.

Outer Barrage The Burnham andSomerset LevelsSea Flood StudyGroup

Minehead to Aberthaw scheme asdescribed in 3.1 above but with a view tomaximising variation in water levels tominimise loss of inter-tidal habitats

Severn Barrage toHinkley andBrean

Tom Shaw(Shawater)

A barrage crossing between LavernockPoint and Hinkley Point (via SteepHolm). The additional enclosed waterarea would increase the annualgenerating potential of the project by upto 10% depending on the exact alignmentchosen for the barrage. The plan alsoshows provision for traffic (road and rail)to continue by viaduct to the coastlinesouth of Weston-super-Mare. Thebarrage link to Hinkley Point would offera third outlet for the electrical connectionof the project. This is the longest barrageproposal.

Severn Tidal Reef Evans Engineering A barrage that would include fixed flowturbines operating on a very lowconstant head difference maintained byfloating caissons or movable ‘crest gates’.Minehead to Aberthaw suggested as theoptimal alignment.

Tidal FenceProposal

Severn Tidal FenceGroup

A barrier constructed over part of theCardiff to Weston alignment, with opensections in the ship canal and at thecoastal fringes, incorporating tidalstream turbines to capture energy duringboth the ebb and flood tides.

Tidal Lagoons Tidal ElectricLimited (TEL) andBCP.

A schedule of various tidal lagoons bothwithin and beyond the estuary submittedby TEL and the offshore Swansea BayLagoon submitted by BCP. The TELsubmission did not include specific



Brief Description

designs but suggested the use of multiplecells within the lagoon to increase theavailability of energy. The Russelllagoons sites have been used to assessland connected tidal lagoons and anoffshore lagoon close to Bridgwater Bayhas been used in this study to assessoffshore proposals

Tidal PowerDevelopment inthe SevernEstuary

Mr FrankGoldsmith

Barriers built across the estuary withvalving at the base to provide controlledwater flow through turbine or paddledriven generators. Valve controls wouldlimit the water differential to 1m at thebarrier. No specific location referenced.

Table 3.1 Summary of Call for Proposals Submissions

Pre- Screening of the Call for Evidence Submissions

The following proposals were conceptual proposals which were not location specific orwere specified for locations outside of the area covered by the Feasibility Terms ofReference. As a consequence, they were considered as information (under the Call forInformation) that could potentially be used in the optimisation and/or more detailedstudy rather than as specific proposals:

New Build Tidal Lagoons submitted by Rubicon Marine (this covered a newembankment construction method using shipbuilding techniques and will bereviewed as an alternative form of construction for lagoon proposalsIn response to the Call for Information, Halcyon Marine Hydroelectricsubmitted proposals for a pile supported/modular barrier construction to beapplied to the impoundment of lagoon basins. In the submission, Halcyonpresented a lagoon alignment between Minehead and Hinkley Point, notingthat this was just one possibility among many which could include larger orsmaller lagoons, either offshore or connected to land. This form will bereviewed as an alternative form of construction for lagoon proposals.Tidal Power Development in the Severn Estuary proposals submitted by Mr FGoldsmith (this proposed a combination of different operatingequipment/modes and new construction concepts)Swansea Bay Tidal Lagoon – this is outside the study area and any conclusionreached by this study is unlikely to impact proposals to develop a tidal lagoon


in Swansea Bay. However, the information and research undertaken by theSwansea Bay promoters may be relevant to similar concepts within the studyarea.

All other submissions have been brought forward to a long-list, reviewed and theirdetails are summarised in this report together with detailed independent analysis oftheir design, costs and energy yields with the exception of those that are have beenscreened out during the initial stage of the Assessment Framework.

3.4 Other Strategically Selected Proposals

Beachley Barrage

Previous studies of the Severn have considered alignments throughout the Estuarybut other than a causeway proposal in the 19th century, there have been few, if any,studies of proposals upstream of English Stones, the location of the Shoots Barrage.The Shoots proposal adopts a position which coincides with the highest tidal rangein the Estuary and as a result has been reported to operate more efficiently with alower cost of energy than other barrages. A barrage further upstream wouldhowever, have potentially fewer environmental effects, including less of an effect onthe estuary habitats and would not act as a barrier to the River Wye. To enable areview of these relative benefits and disbenefits, a barrage alignment has been addedto the long list upstream of the Shoots Barrage at Beachley Head, by the originalSevern Bridge, where the estuary naturally narrows. This alignment also enables areview of the merits of barrage construction landward of the Wye. A more optimumalignment of a barrage landward of the Shoots Barrage could be determined if theBeachley Barrage is selected for the shortlist.

Other Strategic Proposals

Other potential strategic proposals are the optimal arrangement of twin basin and /or combination of options based on maximising the value of energy by allowinggeneration of more energy during periods of higher demand and less energy atnight. Although the cost per kWh is likely to be higher and/or the total amount ofenergy produced is less, if the timing of generation can produce an enhancement toenergy value, such arrangements could offer a better return than ebb only or singlebasin options. These strategic options will be examined in detail followingdetermination of the short list of options. Although single basin ebb-only generationoptions do not produce the highest energy values, nevertheless, adapting suchoptions to two way flow or two basin operation will generate better returns oninvestment compared with the same adaptation applied to less economic ebb onlygeneration options. The adoption of ebb only generation for the purposes of initialassessment therefore remains the most effective means of assessing all options


initially with optimisation of energy value studies being undertaken subsequently onthe short-listed options.

3.5 Long-Listed Proposals

The long list of proposals is as set out in Table 3.2 below and their alignmentsillustrated in Figure 3.1.

Option No Option Name

B1 Outer Barrage from Minehead to Aberthaw

B2 Middle Barrage from Hinkley to Lavernock Point

B3 Middle Barrage from Brean Down to Lavernock Point (commonlyknown as the Cardiff to Weston Barrage)

B4 Inner Barrage (Shoots Barrage)

B5 Beachley Barrage

F1 Tidal Fence Proposal (see 3.7 below)

L2 Lagoon Enclosure on the Welsh Grounds (Fleming Lagoon)

L3 Tidal Lagoon Concept (see 3.6 below)

R1 Tidal Reef (see 3.7 below)

U1 Severn Lake Scheme (see 3.7 below)

Table 3.2 Long Listed Proposals


Figure 3.1 Location Of Options


Tidal Lagoon Concept

The tidal lagoon concept can be applied to a number of locations using differentforms of construction to impound the lagoon basin. These forms of constructionwould include those submitted by TEL, the Fleming Group, Rubicon and Halcyon,together with traditional forms of marine embankment and/or construction of similarform to barrage construction as applied in the designs available for the B3 and B4barrages.

The lagoon concept can be either a completely artificial offshore enclosure(hereinafter termed an offshore lagoon) or an enclosure formed by an artificialbarrier constructed into the estuary from two points on the shoreline (hereinaftertermed a land connected lagoon).

For the purpose of this study, the tidal lagoon concept has been applied to the landconnected Russell lagoon alignments in order to update the early Bondi work (1981)and recent SDC study.

In addition, the tidal lagoon concept has been applied to Bridgwater Bay as both aland connected and offshore lagoon form. Bridgwater Bay has been selected for anumber of strategic reasons:

It was listed as having the highest energy generating potential of all lagoonsin the TEL submission,It enables consideration of the specific environmental effects of impoundmentof Bridgwater Bay, andIt enables consideration of the compatibility of a lagoon seaward of allbarrages, except B1 Outer Barrage, and the F1 tidal fence.

It should be noted the lagoon concept has been applied to these locations in order toconsider a representative sample of lagoon schemes, to update previous work on theRussell Lagoons and to build upon the previous studies undertaken for the SwanseaBay lagoon scheme. Studying the concept at these locations provides an improvedunderstanding of performance of the lagoon concept, in terms of its energy yield,together with the relative performance characteristics of different forms ofconstruction. The lagoon concept has required appraisal at specific locations basedon specific construction forms and operating regimes to inform the analysis ofoptions and to further understand the technical feasibility of different configurations.


Lagoon Location ImpoundedArea (km2)

Installed Capacity(MW)

Bridgwater Bay 91 1360

English Grounds(Russell Lagoon)

40 760

Welsh Grounds(Russell Lagoon)

72 1360

Peterstone Flats(Russell Lagoon)

72 1120

Table 3.3 Long Listed Lagoon Proposals

3.6 Initial Screening

The initial screening stage of the Assessment Framework is designed to evaluate thecredibility of options in relative risk terms so that detailed assessment is notundertaken on those options which, in technology or financial risk terms, areunlikely to be developed sufficiently to mitigate those risks within theimplementation period envisaged by the Feasibility Study. The implementationperiod commences with the necessary design, planning and environmental impactassessments proceeding soon after the conclusion of the Feasibility Study providingthat the Study concludes that tidal power generation from the Severn is feasible ineconomic and environmental terms and that these conclusions are endorsed by theGovernment.

It therefore follows that proof of concept for any proposal in its use of technology hasto have been established for the Feasibility Study to correctly evaluate its economiccredentials. As all proposals for the Severn represent some of the largest tidal powerprojects in the world, it is also logical that they do not offer opportunities for pilot orprototyping. Those submissions which require some form of pilot or prototypeapplication, to increase confidence in the proof of technological concept and reducefinancial and/or technology risks, may therefore be screened out at the initialassessment phase on the basis that pilot or prototype trials will, in themselves, takemany years before conclusions can be reached. However the options that potentiallyfall into this category are innovative and have exploitable advantages that may beapplicable to tidal power generation in this country and internationally in futureyears if proof of concept can be satisfactorily demonstrated to reduce thetechnological and financial risks typically associated with emerging technologies.


The main proposal that potentially falls into this category comprises a completelynew technology concept based on a tidal reef with turbines that generate using aconstant two metre head differential over the tidal cycle except as the tide transitionsfrom the ebb to flood and vice versa (the Severn Tidal Reef).

A second proposal that is based on new technology that would require moreresearch and possible pilot testing is the Severn Tidal Fence. This utilises tidalstream technology configured to provide increased resistance (by virtue of thestructure supporting the turbines and proximity of adjacent turbines) to concentrateand increase flow velocities through the turbines driven, in part by the tidal range.

Both these options are more “permeable” than conventional tidal range technologyas used in a barrage or a lagoon and thus offer less loss of inter-tidal areas as theirimpact on the natural tidal range is reduced. However, the technologies andassociated energy yields in both cases are not well established.

A third option, Severn Lakes (U1) is different from the above options in that itdoesn’t rely as much on new tidal range technology, but nonetheless is a candidatefor exclusion following initial screening because its current shape and form cannot besustained solely by exploiting tidal range energy. Severn Lakes is a mixeddevelopment proposal involving the construction of a 1km wide causeway withdifferent forms of energy generation and other forms of development. Theconstruction of such a large causeway clearly requires other forms of income tosupport its business case by comparison with a tidal barrage in the same location.

Further detail is provided below:

Severn Tidal Reef

The concept includes fixed flow turbines operating on a two metre constant headdifference. In the words of the proposer, “The Reef is a complex engineering conceptthat is underpinned by established engineering designs and technology.”

The Reef is essentially a structure extending between Minehead andAberthaw comprising embankments, caissons and piled structural walls. Alarge number of relatively low capacity turbines are located in siphonmodules mounted on the structure. The objective is to maintain a constant 2metre head between upstream and downstream levels and generate electricalpower using this head. This results in a longer period of generation but withreduced electrical output by comparison with a conventional tidal barrage. Ifachievable, this also has the advantage of reducing the loss of inter-tidal areas.There is claimed to be a reduction in fish mortality rates by comparison with a


conventional barrage. Figure 3.2 is an artist’s impression of the tidal reef providedby the proposer.

Figure 3.2 Artist’s impression of the Tidal Reef (courtesy of Evans Engineering)

Several different types and layout of turbine have been considered by the proposerin various technical submissions. Originally a system of floating turbine modulesinto place during construction and removing them to a dry-dock for maintenancewas considered but subsequently replaced by a fixed design that is set higher out ofthe water and uses a siphon arrangement to stop and start the turbines. These wouldbe constructed as modules, each housing two turbines and capable of being rotatedthrough 90 degrees to allow increased water passage and cleaning of screens. Theturbines themselves are based on low specific speed mixed-flow turbines of a typeused extensively in the early days of hydropower engineering using a vertical shaftarrangement.

The proposer is also assuming that the deep water navigation gates, each weighingaround 15,000 tons each and made of reinforced concrete, include turbines. The useof rotating turbine modules, navigation gates incorporating turbines and therequirement to impound the estuary to create the head differential provides anindication of the magnitude of this option and the development challenges.

In energy yield terms, the reef would operate on both the ebb and flood tides. Thehead attained at the reef would be controlled by the rate of flow through the reef andthe head differential across the turbines. No evidence is available to support costing


or derivation of energy yield, indicating the very early stage of development of thisproposal.

The original proposal suggests the use of 1000 no. 10m diameter, 5MW, turbines,giving an annual power output of 20 TWh/year, for a constant head of 2m. Ananalysis of the tide curve for Ilfracombe indicates that a 2m head could, in theorydeliver approximately 13 TWh/year. The proposer has subsequently also revisitedpotential yield and is now indicating an energy yield between 11 and 14TWh perannum delivered for a capital cost between £10bn and £15bn. However, thepredominant risks are associated with the cost of construction and the application ofthe technology, as no specific design information has accompanied the proposal. Ithas therefore been more difficult to model this option financially on the same termsas the others. The development work in relation to the rotating turbine modules anddevelopment of the siphon is however the major challenge and, if the developmenttimeframe for tidal stream technology (itself based on established wind generationtechnology) is taken as a benchmark, the development timeframe could be between10 and 15 years. Consequently, this option will be less able to contribute to theGovernment’s climate change targets than other equivalent tidal range options.Nevertheless, this option has been reviewed and analysed using fair basisassumptions to assess how well, in relative terms such an option performs bycomparison with existing forms of tidal power. Such an approach has involveddevelopment of some design and costing assumptions given the lack of technicaldata available for this option.

RSPB commissioned an independent report, published in November 2008, to reviewthe feasibility of the Tidal Reef proposal. This report has been considered by theParsons Brinckerhoff consortium so that it can be taken into account in the appraisalof the reef. The report (produced by Atkins Ltd) focuses on three key issues: turbinetechnology, power output and cost estimates. These are discussed below.

Turbine Technology

The Atkins report reviewed the Armstrong Evans reef concept and, because it wasconcluded that it contains too many unknowns for a like for like comparison with abarrage, the turbine caissons are vulnerable to effects of wave loading and theshallow turbines likely to suffer from cavitation effects. Therefore Atkins took adifferent approach and varied the Armstrong Evans concept. This variation hasadopted the same core principle as Armstrong Evans that the reef generates powerusing a controlled constant 2 metre differential head during the ebb and flood tides.This variation takes the form of a line of concrete caissons housing a new concept ofsubmerged bi-directional very low head hydro turbine, which at present are notknown to be in development. The report makes reference to a prototype very lowhead 410kW uni-directional hydro turbine installed at Millau, France, but this is notconsidered a relevant analogue as developing bi-directional turbines of this form,


scaled up from 0.4MW to 5MW for application in a tidal power development wouldrequire a fundamental change in the turbine concept. The report also makesreference to the potential use of tidal stream technology which would cause the TidalReef to behave more similarly to a Tidal Fence. This concept would require theupscaling of tidal stream technology from its current 1.2MW level to 5MW whichwould be a significant extrapolation of existing technology and not consideredfeasible. This has been discussed in relation to the Tidal Fence in Section 4.3. TheAtkins report did not address the issue of how the constant 2 metre head would becontrolled.

Power Output

The RSPB report estimates that the power output of the scheme is 20TWh/yr (if it isable to generate on the ebb and flood tides). This estimate assumes the availability ofvery low head bi-directional turbines for which there is no existing technology (asreferred to above). This estimate also assumes that the 2 metre head differential isavailable at all times, however a review of the tidal range at Ilfracombe indicates thatthe 2 metre tidal range is only available from between one third and half the timeand therefore the energy yield would be 10 to 15TWh/yr, which supports the EvansEngineering’s revised estimated output of 11 to 14TWh/yr. This study has taken a13TWh/yr estimate as a median.

Cost Estimate

The RSPB consideration of capital cost has focussed primarily on the cost of the reefcaisson structures and has identified opportunities to reduce the caisson costcompared to barrage caissons using the Cardiff to Weston barrage caissons as abenchmark. These opportunities include reducing the volume of concrete requiredon account of the smaller differential head, by simplifying the caisson design, byseating the caissons on inflatable grout mattresses and improving caissonsinstallation techniques. Atkins estimates that if a reef were deployed on the Cardiffto Weston line, these measures could result in an overall £2bn saving in caissonconstruction compared to the equivalent barrage caisson cost reported in the SDCResearch Report 3, £1bn of which is due to the reduced head differential. Apart fromthe head differential, the cost saving opportunities are not unique to the Tidal Reefand can be applied across the short list of options. Within this study, all caisson costshave been estimated on a fair basis (as described in section 8) and opportunities toimprove the cost efficiency are due to be considered in Phase 2.

The £1bn reduction in caisson cost arising from the reduced head differentialrepresents a 40% reduction in the SDC caisson cost. The reef caisson cost estimate inthis study has also taken into account the effect of the reduced differential head and,applying assumptions which are favourable to the reef, a 55% saving on the outerbarrage caissons have been taken for the Tidal Reef constructed on the outer line.


The Atkins report concludes that the tidal reef turbine cost will be similar to theCardiff to Weston barrage turbine cost if constructed on the Cardiff to Weston line.A discussion on reef turbine costs is included in Section 8.5

Severn Tidal Fence

The Severn Tidal Fence concept has been developed in more depth than the TidalReef option and the first proposal envisaged an alignment between Cardiff andWeston. It is an extrapolation of an embryonic technology and has been developedto outline design stage including preliminary assessments of costs and energy yield.This option has therefore been reviewed on the basis of the information provided,verified where possible by other sources of data and knowledge. The submission bythe proposer acknowledges that a number of their conclusions are subject to furtherresearch. Their methodology applies wind engineering techniques for turbine designto tidal stream applications with adjustment applied to reflect the increased marinevs wind application costs for the sub-marine plant. The original proposal (shown inFigure 3.3 overleaf) has been assessed in modified format using smaller 1MWturbines than those envisaged in the original submission. In addition, a furtheralignment between Minehead and Aberthaw has been proposed utilising 800 nr1.6MW turbines. This does not have the development disadvantages of the initialproposal although 1.6MW turbines represent a 25% increase in capacity bycomparison with the largest existing operating unit. This alternate option still has anumber of risk factors associated with it, including cost of turbine units, and theeffects on sedimentation (arising from the high rate of change in currents at thefence). Of more concern is the general acknowledgement that currents in the Severnestuary are generally lower than desirable for tidal stream generation except in themain navigation channels. Although a fence created by an array of turbines willincrease velocities, the extent to which this is possible and the variability of velocitiesthroughout the estuarine cross section and at different states of the tide, are notknown and the assumptions made by the proposer may thus be optimistic. Theseissues are discussed in more detail in Section 6 of the report. As tidal streamtechnology is currently at demonstration project stage, this option has passedthrough the initial screen but it should be recognised that, although for the purposesof fair basis comparison the tidal fence has been assessed on the basis thatconstruction started in 2014 in common with the other options, in reality, the tidalfence would be unlikely to be sufficiently developed by 2014 to permit commercialdeployment of a 1280MW installation. Consequently, this option may be less able tocontribute to the Government’s climate change targets than other equivalent tidalrange options. However, it has been analysed using the fair basis approach todetermine its’ relative performance against other forms of tidal power. Figure 3.3shows an artist’s impression of the tidal fence provided by the proposer.


Figure 3.3 Artist’s impression of the Severn Tidal Fence (courtesy of SevernTidal Fence Group (STFG) Tidal)

Severn Lakes (U1)

The Severn Lakes concept was originally included because one of its objectives is toproduce power using the tidal range of the Severn. Tidal power is part of thebusiness plan which also relies on many other economic drivers to substantiate thecost of building a 1km wide causeway across the Severn, including developmentland, marinas, landfill and other renewable energy technologies. This isacknowledged by the proposer. The information relating to this option comes fromthe proposer’s web site and provides details of the general conceptual details. It isunderstood that specific design elements are being worked on but are not availablefor consideration by this study.

The construction of a wide causeway could not result in a lower cost of energycompared to an equivalent barrage because of the increased civil engineering worksrequired. Therefore, for the scheme to be justifiable on commercial grounds, thevalue of the mixed development would need to offset the opportunity cost of theincrease in energy cost.

As this study is only examining potential options from an energy perspective thisoption will not considered specifically by the Study. However, should tidal powerdevelopment from the Severn form part of Government’s future energy policy, aprivately proposed option such as Severn Lakes could be considered in the future.For this reason, this report will reference information relevant to Severn Lakes forinformation.


SECTION 4

COMPARISON OF ENERGY OUTPUT


4 COMPARISON OF ENERGY OUTPUT

A comparison of the energy output has been undertaken on the schemes identifiedwithin the long-list and analysed to provide a fair basis of comparison.

Energy yields have initially been calculated statistically using the detailedinformation contained in Energy Papers 46 and 57 and applying the principles ofthis information to all long-list options based on the available characteristics of theimpoundments. The energy yield modelling has been updated to take account ofrecent improvements in turbine and generator efficiency. Reviews of previousstudies have then been verified and amended as appropriate using preliminary 1-Dmodelling incorporating the latest bathymetric data from the Severn. This hasproduced largely similar results to the statistical approach although there are someoptions where the bathymetry has influenced a change in the energy yield. Resultsfrom both methods are provided in this section and the preliminary 1-D energyoutputs have been carried forward to the financial analysis.

For the purposes of the initial evaluation, energy yields have been calculated on thebasis of ebb only generation (except the F1 Tidal Fence and R1 Tidal Reef which areconfigured only to operate in ebb and flood generation mode) as this has beendemonstrated to achieve the most favourable cost per unit energy (see Section 3.2).Recent improvements in turbine design have not overcome the historic technicallimitations on ebb and flood generation efficiency that make this option lessattractive economically. Optimising the most cost effective schemes to achieve themost favourable energy value will be undertaken on short-listed options as theoptimisation methodologies can be applied equally to all options.

4.1 Estimation of Energy OutputPrevious energy yield estimates, available for some long listed schemes frompublished reports, have been collated and reviewed as a benchmark for thecomparison. This includes modelling work undertaken for EP46 by the SevernBarrage Committee (the Bondi schemes) and later by STPG between 1985 and 1990on the then favoured schemes, much of which has been reported in EP57. These laterstudies on energy yield are the most accurate available. Energy predictions in thesubmissions in response to the Call for Proposals have also been reviewed.

Based on a reinterpretation of past estimates, the predicted annual energy, whereavailable, for the long-list schemes have been plotted to provide a relationshipbetween impounded area (applied in conjunction with average depth to provide animpounded volume) and annual energy yield. Impounded areas and average depthshave been estimated initially from Admiralty Charts for consistency across all


options. Points have been plotted in Figure 4.1 distinguishing between those derivedfor the Bondi schemes and the post-Bondi work.

Other factors apart from impounded area that have a significant effect on annualenergy output include:

The number and diameter of turbines and the electrical capacity of theattached generators. .The tidal range at the site. Within the Severn Estuary and Bristol Channel,tidal range increases up estuary and so the larger schemes which are locatedfurther west in the lower estuary experience a lower tidal range. This factoris taken into account implicitly within Figure 4.1 as the size of the majority ofschemes used to establish the relationship is related to their location withinthe estuary. However, if a small scheme is located further west in an area oflower tidal range, this method of energy assessment is likely to overestimateannual energy output. For example, a lagoon at Bridgwater Bay is likely tohave a smaller energy output because of the lower tidal range in that areathan a lagoon of similar area on the English or Welsh grounds.

Nevertheless, the data provided gives an acceptable and robust first assessment ofthe relative potential of the schemes. At this stage, no attempt has been made tooptimise the various schemes to identify the lowest unit cost of energy for eachalignment by varying the number of turbines, installed capacity and sluice area.

1

10

100

1000

10000

0.1 1.0 10.0 100.0

Average annual energy output (TWh)

Impo

unde

d ar

ea (k

m2)

Energy from BondiEnergy post BondiBest fit line

P = 0.0398 * A ^ 0.97

Figure 4.1 – Correlation between energy yield and impounded area


STPG’s most recent estimates for the Cardiff-Weston barrage increased significantlyover the Bondi 1981 estimate for this site and so the best fit line included in Figure 4.1is based on the post-Bondi results to reflect the increased energy output that has beenreported post-Bondi. The results quoted in Table 4.1 for the current study are eitherbased on reported previous work or derived from the best fit line. The notes columnin Table 4.1 indicates the source of these estimates.

The current study energy output for the Minehead to Aberthaw (Outer) Barrage isassessed as 30% greater than the Bondi estimate in line with the improvementreported for the Cardiff Weston line by STPG. The installed capacity for the OuterBarrage has also been increased from 12GW to 14.8GW to achieve this. The best fitline extrapolation of Figure 4.1 predicts a higher annual energy output for the outerline that we consider unlikely to be realised in practice because of declining tidalranges in the outer estuary.

In estimating the design annual energy output and the output with outages, thefollowing adjustments have been made to the current study energy estimates ofTable 4.1:

The energy output has been adjusted to reflect the increased efficiency ofmodern turbines and generation plant. Following assessment of current plantspecifications, it is concluded that a constant efficiency majoration of +1.5%can be safely applied to historic data to reflect what could be expected frommodern day design and manufacture techniques. Further, an efficiency of97.5% for the generators (electrical power out = 0.975 x power on turbineshaft) has been taken for all machines. All previous studies used a generatorefficiency of 95% so there is a further +2.5% gain compared with previouswork. All historic energy predictions have been increased by +4.0% to givethe design annual energy output column in Table 4.1.Annual energy yield estimates have been reduced to account for outage(typically 10% of turbines not available at any one time which). Studies bySTPG found that this outage rate corresponded to 95% of maximum energycapture for barrages but would correspond to 10% for tidal fence options.The energy yield figures have also been verified, where practicable, by 0-Dand 1-D modelling9. In particular, all lagoon options, where changes inenergy yield are highly sensitive to basin capacity , have been confirmedusing preliminary 1-D modelling undertaken towards the end of this

9 0-D modelling estimates energy yield from the head generated at the turbines and the volume offlow through the turbines. It does not model the tidal range along the estuary and is limited tomodelling a single basin. 1-D modelling estimates energy by modelling the tidal range and flowalong the estuary. It can be used to model combinations of options and multiple basins and modelsthe effects of schemes on the tidal range.


component of the study and using the latest available bathymetry for theSevern.

The energy output for short listed schemes will also be estimated in more detailbased on the application of 1-D modelling. During that stage, an assessment willbe made of the effect on energy yield of alternative operating systems, includingebb and flood generation, flood pumping and the use of a secondary basin. Thepossibilities of generating continuous power will also be investigated. Forexample, combinations such as 1) the Cardiff-Weston barrage and a BridgwaterBay lagoon and 2) the Shoots barrage and Welsh Grounds lagoon could beinvestigated. These variations are considered to be refinements to options(should they be short listed), intended to optimise their performance in terms ofenergy value, implications of grid connection and environmental effects. Thisrefinement is based on the premise that the more advantageous single basin ebbonly schemes will provide the more advantageous opportunities for suchoptimisation (as discussed in Section 3.2). Therefore, all energy outputs shown inTable 4.1 are for ebb-only generation, except the tidal reef and tidal fence options.

For options with no published energy yield estimates, impounded areas havebeen estimated from Admiralty Chart data to derive energy yields from theenergy yield and impounded area relationship. Following development of a 1-Dmodel during the study, these initial estimates have been subsequently reviewedusing the latest bathymetric data available.

Figure 4.2 – Comparison of Bathymetric Profiles at Inner and Beachley Barrages

It should be noted, however, that the Beachley Barrage site is in the upper, narrow,portion of the Severn estuary. The installed capacity is limited by the number ofturbines that can be fitted into deep water at this site and the reduced head of waterthat can be generated. This is illustrated by Figure 4.2 which show a comparison ofthe bathymetric profiles of the estuary channel. Within the width of the channel atBeachley, it would be possible to incorporate eight 25 MW Straflo turbines compared


to thirty 30 MW Straflo turbines in the Shoots barrage. Furthermore, the channeldepth at the Beachley Barrage would be 14m shallower than at the Inner Barrage.Taking both factors into account, a compromise solution has been adopted whichinvolves some 6m depth of dredging to accommodate 50 no. 5m diameter turbineseach rated at 12.5MW. Annual energy output from the Beachley Barrage hastherefore been reduced compared with the value suggested by Figure 4.1 and afigure of 1.59TWh annual yield has been determined using 1-D modelling with theturbine configuration described above. A summary of the preliminary 1-Dmodelling outputs for Beachley Barrage and tidal lagoon options (those optionswhere the modelled output differs from the statistical assessment) is shown in Table4.1:

Lagoon Installed

Capacity

NrTurbine

s

TurbineSize

(MW)

RotorDia(5m)

NrSluices

Sluice

Area(m2)

Annual

Energy(TWh)

AnnualEnergy

with 5%outages

B5BeachleyBarrage

625 50 12.5 5 26 150 1.67 1.59

L2/L3bWelshGrounds

1360 108 12.5 5 41 150 2.43 2.31

L3a EnglishGrounds

760 60 12.5 5 25 150 1.48 1.41

L3cPeterstoneFlats

1120 90 12.5 5 33 150 2.45 2.33

L3dBridgwaterBay

1360 108 12.5 5 41 150 2.78 2.64

L3e(i)91km2offshorelagoon

1360 108 12.5 5 41 150 2.74 2.60

L3e(ii)50km2offshorelagoon

760 60 12.5 5 25 150 1.39 1.32

Table 4.1 Preliminary 1-D modelling results

Table 4.2, overleaf, shows the estimated energy yields based on the analysesdescribed in this section for all options. This includes initial assessment, forinformation purposes, for option U1 although it has been screened out.


Option Source Annual energyoutput from

previous work(TWh)

Number ofturbines and

diameter(m)

Totalcapacity

(MW)

Annualenergyoutput (TWh)

Impoundedarea (km2)

Notes

B1 Outer Barrage Current studyBondi (1981)

25.619.7

370 x 9m300 x 9m

1480012000

25.3 1060 EP 46 uprated due to increase ofinstalled capacity

B2 Lavernock toHinkley Point

Current Study 19.5 - - 19.3 595 Energy output estimated fromPower/Area correlation (sum ofB3 and L3 Bridgwater Bay)

B3 Lavernock toBrean Down

Current studySTPG (1989–90)Bondi (1981)

1717

12.9

216 x 9m216 x 9m

160 x 9m

86408640

7200

16.8 504

480

Based on STPG work

B4 Inner Current studyPB (2006)STPG (1986)

2.772.75

2.7 – 2.8

30 x 7.6m30 x 7.6m

36

10501050972

2.77 85 Based on STPG work andverified using 0-D modelling

B5 Beachley Current study 1.67 50 x 5m 625 1.59 57 Energy output estimated using1-D modelling as number ofturbines limited

F1a Tidal Fence Current studySTFG (2008)

0.73.5 256nr

- 0.7 N/A Based on independentassessment of energy yield forCardiff Weston using tidalstream technologies

F1b Tidal Fence Current studySTFG (2008)

3.33.5 800nr

- 3.3 N/A Based on STFG’s revisedproposals for Minehead toAberthaw



previous work(TWh)


diameter(m)

Totalcapacity

(MW)


Impoundedarea (km2)

Notes

L2 FlemingLagoon & L3bWelsh Grounds(Russell Lagoon)

1-DStatisticalProposer:

2.63.2

- 13601500

2.31 8280

Energy output estimated fromPower/Area correlation andamended using 1-D modelling.Additional output may beachieved if existing basin isexcavated to provide wall fill.

L3a EnglishGrounds (RussellLagoon)

1-DStatistical 1.48

60 x 5m 760 1.41 50 Energy output estimated fromPower/Area correlation andamended using 1D modelling

L3c PeterstoneFlats (RussellLagoon)

1-DStatistical 2.12

108 x 5m 1120 2.33 76 Energy output estimated fromPower/Area correlation andamended using 1-D modelling

L3d BridgwaterBay (landconnected)

1-DStatistical 2.44


L3e1 BridgwaterBay 91sq kmOffshore Lagoon

1-DStatisticalTidal ElectricLimited

2.459.15

108 x 5m 13601900

2.6 91 Energy output estimated fromPower/Area correlation andamended using 1-D modelling

L3e2 BridgwaterBay 50 sq kmOffshore Lagoon

1-DStatistical 1.35




previous work(TWh)


diameter(m)

Totalcapacity

(MW)


Impoundedarea (km2)

Notes

R1 Tidal Reef Current StudyArmstrongEvans (2008)

1311 - 14

- 5000 13 N/A independent assessment usingdata from Armstrong Evanssubmission

U1 Severn Lakes Current study 15.4 - - 15.0 464 Energy output estimated fromPower/Area correlation

Table 4.2 Estimated Energy Yields


4.2 Comparison with Call for Proposal Submissions

The comparison in Tables 4.2 and 4.3 below shows the differences between annualenergy yields based on the power/area relationship and the energy yields quoted inthe Call for Proposals submissions.

Call for Proposalssubmissions

Option

No

Option Name Annual outputestimated by currentstudy (TWh) Annual

output(TWh)

Source

B1 Outer Barragefrom Minehead toAberthaw

25.3 24 Burnham &SomersetLevels

B2 Middle Barragefrom Hinkley toLavernock Point(Severn Barrageto Hinkley andBrean)

19.32 22 Shawater

B3 Middle Barragefrom Brean Downto LavernockPoint (Cardiff toWeston Barrage)

16.80 Not submitted

B4 Inner Barrage(Shoots Barrage)

2.77 Not submitted

B5 Beachley Barrage 1.59 Not submitted

Table 4.2 – Comparison of Energy Yields Estimated and Quoted in Submissions(Barrages)


Call for Proposalssubmissions

Option

No

Option Name Annual outputestimated bypower/arearelationship (TWh)

Annualoutput(TWh)

Source

L2 Lagoon Enclosure onthe Welsh Grounds(Fleming Lagoon)

2.31 3.2 Fleming

L3a English Grounds(Russell Lagoon)

1.41 - Notsubmitted

L3b Welsh Grounds(Russell Lagoon)

2.31 - Notsubmitted

L3c Peterstone Flats(Cardiff-NewportRussell Lagoon)

2.33 - Notsubmitted

L3d Bridgwater Bay (landconnected lagoon)

2.64 - Notsubmitted

L3e(i) Bridgwater Bay(offshore lagoon)

2.6 9.15 TEL

Table 4.3 – Comparison of Energy Yields Estimated and Quoted in Submissions(Lagoons)

The analysis shows that the preliminary 1-D modelling gives a smaller energy yield tothat quoted by the Fleming Group for the Welsh Grounds lagoon.

The TEL estimate for the L3e Bridgwater Bay (offshore) lagoon is higher than thatestimated for this study. Preliminary 1-D modelling has been used to develop theenergy estimate based on an assumed location and alignment for an offshore lagoonwith an impoundment area of 90sq km. Details of TEL’s alignment of a 91km2

Bridgwater Bay offshore lagoon was made available at a late stage in the studyperiod, and the configuration and operation of a Bridgwater Bay offshore lagoon,including the use of multiple cells within the lagoons, were not available during thestudy period. The alignment of the TEL lagoon is different to the alignment of the91km2 L3e(i) lagoon shown in Figure L3e. However, the impounded area and the tidalrange are equivalent and therefore the energy estimated for the L3e(i) lagoon isexpected to be equivalent to the energy yield of the TEL Bridgwater Bay lagoon. Atthe time of writing, dialogue is ongoing with TEL with the aim of reconciling the


difference between the two estimates. Energy calculations in support of TEL’sBridgewater Bay estimated have not been made available and this study adopts the2.6TWh/year output which has been estimated using the fair basis principles to enablecomparison between schemes.

It is understood that the turbine and generator configuration of the L2 lagoon ispreliminary and subject to ongoing design development by the Fleming Group.Analysis of the turbine and generator configuration assumed in the Bondi studieshave also been found to require further design development (refer to section 6.3).Updated details of the configuration and operation of these lagoons are required toinform more refined modelling work.

Pending the availability of more refined energy modelling results, energy estimatesfrom the power/area relationship (verified by the earlier EP57 studies and/orpreliminary 1-D models) have been used for the options screening. However, theseestimates will be enhanced for short-listed options through the subsequent 1-D and 2-D modelling which takes greater account of the ‘live’ storage volume in theimpounded basin and related hydrodynamic effects.

4.3 Tidal Fence

The tidal fence option (which is recognised as an indicative option but for thepurposes of this report has been studied for the Cardiff to Weston and Minehead toAberthaw alignments proposed by STFG) does not lend itself to direct comparisonagainst energy estimates previously prepared for barrage schemes. This is because ituses tidal stream technology to capture the kinetic energy of the flow through thefence resulting from the effect it would have as a barrier to the tidal flow on thelandward side.

The formula used for conventional tidal stream energy schemes is as follows:35.0 VA

Assuming:

Density = 1025kg/m3Area = 147 turbines of diameter 18m (deep water) plus 109 turbines ofdiameter 12m (shallow water).A velocity variation through the year based on the maximum spring tidevelocity of 8 knots (4m/s) in tidal fence report and during neap tide 4 knots(2m/s).No outage is considered in this calculation, as it is often not included in tidalstream calculations.


Table 4.4 below uses the velocity distribution and power distribution developed fromSevern tidal curves to calculate the likely power output for 18m and 12 m rotordiameters for the Cardiff Weston Tidal Fence alignment.

Table 4.4 Energy from Tidal Stream Turbines

Output Data12m Value UnitsRotor diameter 12 mNumber ofrotors 109 /Rated PowerOutput 458 kWLoad factor 41% %

TOTAL Annualenergy per rotor

(12m) 1636 MWh/yTOTAL energy109 turbines of12m 178 GWh/y

Output Data18m Value UnitsRotor diameter 18 mNumber ofrotors 147 /Rated PowerOutput 1031 kWLoad factor 41% %

TOTAL Annualenergy per rotor

(18m) 3680 MWh/yTOTAL energy147 turbines of18m 541 GWh/y


A total annual energy of 719 GWh/year for the Cardiff Weston Fence alignment istherefore achieved. This is well below the 3.5TWh/year quoted by the proposer. Theimmediate reason for this is that the rated power of the turbines are around 1MW,rather than the 5MW originally quoted

If the same site conditions are taken (i.e. Vmsp=4m/s), and the calculations arerepeated with 256 turbines rated at 5MW, the annual energy production wouldeffectively be around 4.5TWh/y, as shown in Table 4.5 below.

Output Data 5MW Value UnitsRotor diameter x MNumber of rotors 256 /Rated Power Output 5000 kWLoad factor 41% %Mean power extracted perfarm 525 GWTOTAL Annual energy perdevice 17958 MWh/yTOTAL energy 256 turbinesof 5MW 4597 GWh/y

Table 4.5 – 5MW Turbine Calculations

However, a device of 5MW could not be built at this location, using conventional tidalstream turbines. To reach a 5MW rated power at the given location (assumingVmsp=4m/s, i.e. Vrated=65%*Vmsp=2.6m/s), the capture area of the device needs tobe 1234m2. This could mean that the device has an equivalent diameter of 40m.Ignoring the engineering feasibility of this, the proposed devices are already, at 18mand 12m, at their maximum size for this location.

Conclusions for the Cardiff Weston alignment are therefore that:

The final answer is very sensitive to a number of parameters, particularly:o Turbine diameter ando Rated rotor efficiency.

Care must be taken not to be overly optimistic about the improving efficiencyof stream turbines.The rated power output required in each turbine is only 1 MW, rather than thelarger 5 MW suggested by the fence promoters.

The above calculations do not invalidate the proposer’s approach, as they state thatthe technology used will need to be an advance on current turbine designs. It does,however, suggest that the turbines to be used will not be like a low-density tidalstream designs, but will somewhere between a tidal stream turbine and a moreconventional tidal barrage turbine. A more conventional turbine arrangement wouldnot, however, have the claimed environmental advantages of the tidal fence.


The proposal also included an estimate of the aggregate energy generated by acombination of the tidal fence and the Inner (Shoots) Barrage. This estimate showshow this combination would deliver power to the grid more consistently than eithersolution alone. This would occur because the fence generates maximum energy ataround mid-tide whilst a barrage (operating in ebb generation mode) generates themajority of its power between mid tide and low water.

If the tidal fence is to be used with a barrage or other scheme, the energy extracted bythe fence must be relatively small, or else the kinetic energy removed by the turbineswill be converted to loss in potential energy upstream. STFG have estimated that thetidal range for a Cardiff Weston alignment would be reduced by 13% although withthe revised energy outputs computed above, this is more likely to be 5%.

The proposer has also submitted proposals for a tidal fence located betweenMinehead and Aberthaw. This utilises 1.6MW turbines and produces a minimum of3.3TWh per annum. It also has a relativly small effect on tidal range with a reductionof possibly only 5% or a reduction in high water level of between 2.5% if the 5%reduction in tidal range is verified in subsequent hydrodynamic modelling. This isbecause the tidal fence is taking out a much lower proportion of energy at this estuarylocation.

4.4 Optimisation of EnergyAs stated above, a number of options can be operated in combination and/or usedifferent operational modes to enhance the value of energy generated. Duringsubsequent stages of this study, an assessment will be made of the effect on energyyield of alternative operating systems, including ebb and flood generation, floodpumping and the use of additional basins. This is based on the premise that the moreadvantageous single basin ebb only schemes will provide the more advantageousopportunities for such optimisation (As discussed in Section 3.2). Therefore, allenergy outputs shown in Table 4.1 are for ebb-only generation whilst Table 4.6overleaf summarises the main opportunities for enhancing energy value.


OptionRef.

Option Name “Core”OperatingMode

OperatingModePotential

Compatibilitywith SecondBasin

Compatibilitywith OtherProposals

B1 Minehead toAberthaw Barrage

Ebb Pump +Ebb &Flood

No No

B2 Hinckley Point toLavernock PointBarrage


Yes No

B3 Brean Down toLavernock PointBarrage


Yes Yes – L3d, L3e

B4 Shoots Barrage Ebb Yes Yes – F1, L2,L3

B5 Beachley Barrage Ebb Yes Yes – F1, L2,L3

F1a Tidal Fence - BreanDown to LavernockPoint

Ebb andFlood

No Yes –B4, B5,L2, L3

F1b Tidal Fence –Minehead toAberthaw

Ebb andFlood

No Yes –B3, B4,B5, L2, L3

L2 Russell Lagoon -Fleming Energy

Ebb Pump Yes Yes – F1, B4,B5, L3

L3 Tidal Lagoons(Generic)


Yes Yes – F1, B4,B5, L2

R1 Tidal Reef Ebb andFlood

No No

U1 Severn Lakes Ebb Pump +Ebb &Flood

Yes Yes – L3d, L3e

Table 4.6 Energy Value Enhancement Opportunities


SECTION 5

ENVIRONMENTAL, SOCIAL, ECONOMIC ANDREGIONAL CONSIDERATIONS


5 ENVIRONMENTAL, SOCIAL, ECONOMIC AND REGIONAL CONSIDERATIONS

Environmental, Social, Economic and Regional Considerations have been assessedfor a range of topics including:

Climatic FactorsHydrodynamics and GeomorphologyHabitats, biodiversity, flora and faunaMarine Water QualitySoils, groundwater and freshwaterHistoric EnvironmentLandscape/ SeascapeResource Efficiency and WasteMaterial AssetsPopulation and Health.

All options present a wide range of potential issues that require significant resourceand time (given the long life cycles of certain species) to understand adequately;and any qualitative review of options at this stage (prior to the detailed SEA) canonly provide a preliminary assessment. This section of the report has thereforebeen prepared using a precautionary approach.

The effect of many of the options would be to reduce the tidal range within theestuary, resulting in some loss of inter-tidal area, although this may be reducedthrough mode of operation and/or lagoon configuration. The effects of all optionson the morphology of the Severn Estuary are uncertain and subject to divergenthypotheses, but until further investigation it must be assumed that many of thesechanges are likely to be to the significant detriment of inter-tidal habitats. Alloptions are likely to adversely affect fish passage and survival within the estuary,but current understanding is that the impacts would be generally more significantfor barrage options.

All options therefore pose potentially high levels of risk to designated habitats andspecies, particularly, but not only, migratory fish and waterbirds. These risksrequire careful consideration having regard to the Habitats and Birds Directives andthe requirements for effective mitigation and compensation packages.

There is also a need for greater understanding of other potential risks such as forland and seascape, and the historic environment. Options also have the potential toaffect the water quality status of the Severn Estuary and need consideration havingregard to the objectives of the Water Framework Directive, and the issue ofdischarge licences under Review of Consents currently underway.

A wide range of other effects to the natural and human environment are also likely,regardless of the option pursued.


5.1 IntroductionThis section provides an initial qualitative environmental review of the long-listoptions identified in Section 3 of this Report. Generally, it has been prepared withthe precautionary principle in mind, in common with normal practice for consideringenvironmental effects. If a risk has been identified that tidal power options mightcause severe or irreversible harm to society or to the environment, and in the absenceof a scientific consensus that harm would not ensue, the assumption has been madethat such a risk exists. Application of the precautionary principle is not necessarily anindication of the severity or likelihood of effects. The precautionary approach has, ofitself, to identify the worst scenario that could reasonably be identified. Such anapproach provides assurance that potential environmental impacts are clearlyidentified enabling them to be studied in more detail and, as appropriate,suitable mitigation and compensation measures to be considered. However, furtherstudy may well show that some concerns are less severe than envisaged and also that,in some cases, mitigation measures can be identified that will reduce the scale of theeffects of a scheme.

This section is included to highlight specific environmental, socio-economic andregional issues in relation to the options on the long-list. It is not intended to bedefinitive or absolute and its data are drawn from the initial work being undertakento scope the Strategic Environmental Assessment. However, it does serve to set into anon-engineering context the effects that may arise from each of the options andsummarises the basis of the qualitative analysis used in the assessment framework.

This review concentrates on key qualitative criteria identified within the long-listoption assessment process, i.e. effects on:

Climatic FactorsHydrodynamics and GeomorphologyHabitats, biodiversity, flora and faunaMarine Water QualitySoils, groundwater and freshwaterLandscape/ SeascapeHistoric EnvironmentResource Efficiency and WasteMaterial AssetsPopulation and Health (including recreation and amenities).

Environmental legislation applies to many of these categories, and risks of failure incompliance with such legislation will be drawn-out in the relevant sections below.

Any major project of this nature will be likely to have a wide range of potentialenvironmental effects, and these are not all extensively described here. Anenvironmental assessment of options will be conducted within the SEA process. Thiswill follow from selection of the short-list of options. The intent of this review of thelong-list options is to focus on the relative risks of options in the key areas listedabove, to inform the identification of a short-list of options for more detailed


assessment. However, it must be noted that for some areas of study, e.g. fish, there isnot yet a sound evidence base. By focussing on these key areas, some topic areas willbe covered in much greater detail than others.

Coming at an early stage of options appraisal, inevitably this review uses an expert-based, but nonetheless incomplete, understanding of the potential issues. The optionswill be considered collectively (as a group) where the impacts are similar in scale andtype. The effects will therefore be considered under the following headings:

Relevant for All Options;Minehead to Aberthaw Barrage (B1), Hinkley Point to Lavernock PointBarrage (B2), and Brean Down to Lavernock Point Barrage (B3);Shoots Barrage (B4) and Beachley Barrage (B5);Russell (Fleming) Lagoon (L2) and Generic Tidal Lagoons (L3);Tidal Fence (F1);Tidal Reef (R1); andSevern Lakes (U1).

As explained elsewhere in this document, it has been assumed for the purposes ofthis review that the options would operate under an ebb-generation only mode ofoperation (with the exception of the F1 Tidal Fence and R1 Tidal Reef). Althoughoption U1 has been screened out (see Section 3), information is provided in thissection on those options for information purposes.


5.2 Qualitative environmental review of long-list optionsIntroduction

This review has been informed by the ongoing scoping phase of the SEA. Scopingactivities include literature and data review, and a programme of technicalconsultations. Space here does not permit a summary of the baseline environment ofthe Severn Estuary, but full descriptions can be found in the Sustainable DevelopmentCommission’s ‘Turning the Tide’ reports (2007). In particular, these reports includeextensive reviews of previous studies of the potential effects in relation to two of theoptions currently under consideration (approximating to barrage options B3 and B4).The relevant discussion therein, including the identification of the many areas ofuncertainty, is not repeated here.

In the following sections, each group of options is reviewed and the mainenvironmental effects identified. The information contained in this review will beused to guide the population of the long-list assessment criteria matrices and used toinform the selection of the short-list. For the purposes of long-list evaluation, ebbonly generation modes have been used as the default (except for F1 Tidal Fence andR1 Tidal Reef which are designed to operate only in ebb and flood modes). Ebb onlygeneration produces the highest energy outputs and exhibits the largest variations ontidal range. Some of the consequent environmental effects may be mitigated througha less extreme operational mode of ebb and flood generation where less energy isgenerated but it is distributed over a longer time period with an associated change inenvironmental effects.

The issues common to all the options under consideration are presented below, aheadof the option-specific reviews.

5.3 Environmental Issues Relevant for All OptionsClimatic Factors

For the purposes of this report, climatic factors are principally taken to relate to thebalance of carbon (carbon emitted and carbon emissions avoided). This section doesnot include a wider consideration of other climatic factors, which if relevant will needto be addressed in later stages of option assessment.

Initial studies by the Sustainable Development Commission suggest that the carbonemitted during construction is equivalent to the carbon emissions saved during a 6month to 1 year period of subsequent generation. Operationally, dredging activitiesmay contribute to carbon dioxide emissions but these are likely to be small in relationto the savings achieved through generation. Other climatic effects (such as effects onthe ability of the Severn Estuary to sequester carbon) will be tested within the overallassessment of carbon footprint, if the project proceeds to phase 2.


If other developments supported by a tidal-power scheme are brought into theoverall cost-benefit analysis, then the impact of the consequential carbon emissionswould need to be set against any benefits in phase 2.

Hydrodynamics and geomorphology

Any large-scale tidal power development within the Severn Estuary which takes asignificant fraction of the energy out of the system will inevitably make significantchanges to the tidal regime. It will reduce tidal energy over a wide area (both up anddownstream), with consequential effects for human activities and the naturalenvironment. Barrages in particular will modify the resonant characteristics of theestuary, reducing peak water elevations. An understanding of hydraulics andgeomorphology is therefore fundamental to predicting the environmental effects ofsuch schemes, including the effects on navigation and flood risk. A reduction in peakwater level could be detrimental to shipping unless appropriately mitigated. Theeffect on flood risk may be positive, due to peak water level reduction, but may alsobe negative due to the increased durations of static water levels and any effects ofgeomorphological changes on flood defences. The larger barrages and the tidal reefwill have a greater beneficial effect than other schemes. The extent over which theeffects of peak water level reduction will be experienced will be greater than smallerschemes. The effect on peak water level of a tidal fence will extend over a similar areaas a barrage constructed on a similar alignment but will cause a smaller reduction inpeak water level. It is assumed that existing land drainage standards of service andnavigation clearances will be maintained through mitigation and the estimated costsfor this are included in the cost estimates for each of the options where relevant.

Changed tidal conditions will have a wide range of secondary effects on the physicalenvironment of the Severn Estuary, including effects on water levels, flows, waves,estuary sediment regime and morphology, and water quality. The discussion thatfollows for each group of options concentrates on: water levels, geomorphology andwater quality, because of their direct relevance to other interests. This does notexclude the paramount need to understand the effects on all key aspects of thephysical environment of the Severn Estuary. It is possible that these effects could haveimpacts beyond the Severn Estuary itself and its tributaries – so called far field effects,which could lead to impact along the coast into the Bristol Channel. The proposedrange of studies, which will be undertaken if the project proceeds to Phase 2, willinclude study of these potential far field impacts.

The presence of an impoundment to generate tidal energy within the Severn Estuarywill result in accretion of sediment within the impoundment because of the lowertidal velocities within the basin. There is considerable uncertainty whether this willoccur within the sub-tidal area or within the inter-tidal area. In an estuary with lowwave energy but higher tidal energy, accretion is more likely to occur in the inter-tidal area, resulting in a convex slope from the shoreline to low water. However, inan estuary dominated by wave energy, accretion is more likely in the sub-tidal zonewith a resultant concave inter-tidal profile. The Severn Estuary presently has high


tidal energy and relatively high wave energy. Introducing an impoundment into theestuary will reduce the tidal energy, and possibly also reduce the wave energy. Therelative change to these natural forces will determine whether accretion is more likelyto happen in the inter-tidal area or the sub-tidal zone. The effects will vary fromlocation to location and for each of the options depending upon their individualcharacteristics. It is proposed to assess this in more detail on short-listed optionsusing specific modelling. For the purposes of this report, it would be premature toassess which of the above scenarios will results for each option

Habitats, biodiversity, flora and fauna

Habitats

The high tidal range in the Severn Estuary creates unique physical conditions whichstrongly influence the composition, distribution and abundance of flora and fauna.The resulting ecological importance of the estuary is recognised throughinternational, national and local nature conservation designations. At a Europeanlevel, much of the estuary is designated as a candidate Special Area of Conservation(cSAC) under the Habitats Directive and the intertidal areas are designated as aSpecial Protection Area (SPA) for Birds under the Birds Directive, and as a RamsarSite under the Ramsar Convention on Wetlands of International Importanceespecially as Waterfowl Habitat.

The EC Habitats Directive (92/43/EC) requires the establishment of an ecologicalnetwork of important high quality conservation sites, known as Natura 2000, thatenables the habitats and species identified in Annexes I and II of the HabitatsDirective to be maintained or restored at a favourable conservation status in theirnatural range. The listed habitat types and species are usually those considered to berare or endangered at a European level, with the overall aim of the Directive being themaintenance of biodiversity.

The Severn Estuary candidate Special Area of Conservation (cSAC) was submitted bythe UK to the European Commission on 31 August 2007 because it contains thefollowing habitat types and species that are threatened within a European context:

EstuariesMudflats and sandflats not covered by seawater at low tideAtlantic salt meadowsSandbanks which are slightly covered by sea water all the timeReefsSea lamprey Petromyzon marinusRiver lamprey Lampetra fluviatilisTwaite shad Alosa fallax.

Rivers adjacent to the Severn also of importance comprise the River Tywi SAC, RiverWye SAC and River Usk SAC. These sites include protection of; inter alia, Allis and


Twaite Shad, Sea, River and Brook Lamprey, and Atlantic Salmon (with the exceptionof the River Tywi SAC, where Atlantic Salmon are not a feature).

There are a large number of national nature conservation designations that occurwithin and adjacent to the Severn Estuary – for example there are 30 Sites of SpecialScientific Interest (SSSIs) within or adjacent to the Estuary. The sites have beendesignated for a range of geological and biological interests. In addition to thestatutory designations, there are a host of non-statutory local designations that applyto sites around the estuary.

All tidal options would reduce the tidal range within at least part of the SevernEstuary under ebb-only operation. This will result in a smaller intertidal area and theincreased risk of sedimentation within impounded basins could result in bed slopereduction. This may take many years and may require specifically designed dredgingprogrammes in initial years. Initial calculations, using a fair-basis approach for alloptions, have been made of the change in intertidal area at Spring tide that wouldarise from this alteration to the tidal range using data sources that can be appliedequally to all options and without taking account of any off-setting effects such asincreased sedimentation.

The intertidal area as exists today is taken as the area above 0m (Admiralty chartdatum), i.e. the maximum area of the Severn Estuary that can be exposed by thelowest astronomical tide.

This approach gives an overestimate of the intertidal area compared to estimatesbased, for example, on mean low water; and this conservative approach has beenused because of the need to use a common data source across all options to preservethe fair-basis evaluation. At the time of these estimations only Admiralty chart datawas available for all option locations.

The intertidal area for each option is based on ebb only generation assuming asimplified horizontal water surface and an approximate tidal range upstream of abarrage or within an impounded lagoon. This is a simplification which mayunderestimate or overestimate the loss of intertidal area.

The estimates do not allow for the change in tidal range causing a change in intertidalarea downstream of a barrage or outside an impounded lagoon where inter-tidal arealosses could be a significant proportion of the overall inter-tidal area lost dependingon the size, shape and location of the scheme.

Virtually all the intertidal area upstream of Option B2 is designated cSAC and SPA.However, these preliminary estimates do not distinguish between designatedintertidal and undesignated intertidal habitat, and the method of estimation meansthat the data does not closely match habitat estimates for the cSAC designation.


These calculations are recognised to be simplistic because of the coarseness of theAdmiralty chart data and the necessity to adopt simplifying assumptions at this stageof the study. The inter-tidal loss areas calculated are only intended to enable arelative comparison of options and not an absolute assessment of the effects of anyoption. Subsequent stages of this study will utilise more accurate estuary bed dataand water level modelling to refine these estimates. The data used at this stage aresummarised in Table 5.1.

The effect of tidal fences on the tidal range stated in Table 5.1 has been based on anestimate of its impact on flow speeds and a corresponding reduction in tidal range.The accuracy of these estimates is uncertain as more detailed research is required intothe effects of the fence on high and low water levels in the vicinity of the fence andfurther upstream and downstream. This further research would also need to addressuncertainties in the effect of the fence on patterns of erosion and sediment depositionwhich will also impact on the inter-tidal habitat. In any future research, the estimatesof inter-tidal loss will remain theoretical as there are no analogues to draw uponwhere fence construction has been employed at a full scale. Therefore, the estimatesmust be considered precautionary. An upper bound estimate could be equivalent to abarrage of similar energy yield which for F1b could incur an inter-tidal loss of around5,000 to 6,000ha.

These preliminary estimates of changes in intertidal area are of importance toconsiderations of compliance with the requirements of the Habitats Directive, and ofthe attainment and maintenance of ‘good ecological status’ under the WaterFramework Directive.

Important ecosystem services are known to be associated with intertidal habitats.These include CO2 sequestration, nutrient stripping and PM10 absorption. Intertidalhabitat losses on the scale proposed by the tidal power options are likely to havenegative impacts on these estuary services, and will be considered alongside the SEAin the next phase of assessment.

Estimated upstream intertidal area (ha)*OptionWithout option With option Loss

B1 Minehead to AberthawBarrage

31,500 3,500 28,000

B2 Hinkley Point to LavernockPoint Barrage

29,400 3,400 26,000

B3 Brean Down to LavernockPoint Barrage

22,500 2,500 20,000

B4 Shoots Barrage 5,100 100 5,000B5 Beachley Barrage 3,560 60 3,500F1a Tidal Fence between Cardiff

and Minehead22,500 20,500 2,000

F1b Tidal Fence between 31,500 28,700 2,800


Estimated upstream intertidal area (ha)*OptionWithout option With option Loss

Minehead and AberthawL3 Bridgwater Bay Lagoon (land-

connected)6,400 900 5,500

L3 Peterstone Lagoon 3,000 300 2,700L2/3

Russell (Fleming) Lagoon(Welsh Grounds)

6,947 540 6,500

L3 Russell Lagoon (EnglishGrounds)

2,200 200 2,000

R1 Tidal Reef Unquantified due to insufficient dataU1 Severn Lakes Scheme Unquantified due to insufficient data –

possibly similar to B3Table 5.1 Preliminary and Precautionary Intertidal Loss Assessments*Note: All estimates are preliminary and precautionary.

This preliminary assessment focuses on the loss of upstream intertidal owing tochanges in tidal range. There are many other important effects on habitats that mayarise, for example through the direct footprint of schemes, effects on water quality,sedimentation and erosion of foreshores etc. These effects are not yet wellunderstood for each option. Hence, whilst there is good broad-scale information forthe distribution of many estuarine features, a meaningful assessment of the effectsupon these is not possible until better information on the physical effects of eachoption is available. These effects are therefore an uncertainty at this stage.

The complete range of impacts of options on the other habitats and features of theSevern Estuary cSAC/ SPA and other designated sites will need to be considered inthe full assessment of options. Effects may arise both up and downstream.

Fish

Fish species which are designated features of the relevant internationally designatedsites are outlined above (e.g. Allis and Twaite Shad, Sea, River and Brook Lamprey,and Atlantic Salmon). All of these species are classed as diadromous migratoryspecies, i.e. they live in freshwater and marine environments at different stages intheir lifecycles.

Key environmental changes resulting from the development of the range of proposedtidal power options that are most relevant to migratory fish, marine/estuarine fishand angling (estuarine and upstream freshwater) include:

Alterations to migratory cues


For fish which display natal homing behaviour, such as Atlantic salmon and shad,any changes in salinity in the estuary basin could delay migration by disruptingtheir ability to locate their natal rivers contained within freshwater discharge.Reduced mixing upstream however and increased surface freshwater may aidnatal river identification and decrease transit time and straying upstream.Reduced turbidity in the basin may be both beneficial and detrimental withmurkier water disrupting navigation and clearer water aiding predation;however impacts are uncertain.

Disruption to route of passage

One of the prime sources of impact for fish is the presence of a tidal power projectstructure and the operation of its turbines. There is the potential for significantimpacts on fish survival, particularly that of the migratory species, of turbinepassage, shear stress, mechanical injury, pressure, cavitation, sluice passage, andany indirect impacts. These factors may be enhanced or reduced by alterations inturbine operations and possibly design but could result in local species extinctionand/or loss of genetic diversity. Consideration of detailed evidence and potentialmitigation (including potential fish screening and acoustic fish guidance systems)will be pursued in Phase 2 of the studies. In addition, flatfish and roundfish fry(2-10cm in length) migrate through estuaries using selective tidal streamtransport. This migration is predicated on the presence of a continuous intertidalforeshore. Loss or interruption of intertidal habitat is likely to have implicationsfor this migration pattern.

Habitat Changes

All options, by reducing the tidal range within at least part of the estuary, willresult in a smaller intertidal area and will impact on fish. This may affect thehabitat for juvenile and adult fish both upstream (landward) and downstream(seaward) of the project. The Severn Estuary, as well as being a migratorypathway is also important in its own right as an important fish nursery ground.

Water Quality

There are a number of potential effects of a tidal power project on water qualityincluding potential changes to salinity, temperature, suspended sediments,dissolved oxygen and contaminants that could affect fish and their movements.

Angling


Potential impacts on fish as a resource will potentially affect the freshwaterfisheries of the rivers which flow into the Estuary; and sea angling and marinecommercial fisheries in the Severn Estuary.

All the options are likely to have a negative effect on migratory fish. The severity ofthe impact will be dependent on the specifics of the design, for example the type ofturbine deployed, operating regime and use of screening / baffles etc to deter fishfrom encountering turbines. These factors collectively are likely to be as relevant asthe geographical location of the option, to the overall impacts upon fish.

There is currently low confidence in the effectiveness of measures available tomitigate these effects.

Birds

The EC Birds Directive (79/409/EEC) requires all member states to identify areas to begiven special protection for the rare or vulnerable species listed in Annex 1 of theDirective (Article 4.1), for regularly occurring migratory species (Article 4.2) and forthe protection of wetlands, especially wetlands of international importance. Theseareas are known as Special Protection Areas (SPAs).

The Severn Estuary SPA qualifies under Article 4.1 of the EU Birds Directive bysupporting internationally important populations of regularly occurring Annex Ispecies. It also qualifies under Article 4.2 of the EU Birds Directive in that it supports:

Internationally important populations of 18 regularly occurring migratoryspecies; andan internationally important assemblage of waterfowl (over 20,000 birds).

Sub-features of the SPA, which support these bird species, include:Intertidal mudflats and sandflats;Saltmarsh; andShingle and rocky shore.

Under the 1972 Ramsar Convention on Wetlands of International Importance, it is arequirement of signatory states to protect wetland sites of international importance,including those that are important waterfowl habitats. The Severn Estuary qualifies asa Ramsar Site through meeting a number of the qualifying criteria, as outlined below:

Criterion 1 - due to its immense tidal rangeCriterion 3 - due to its unusual estuarine communities, reduced diversity andhigh productivityCriterion 4 - as it is particularly important for the run of migratory fishbetween the sea and rivers via the estuaryCriterion 5 - bird assemblages of international importanceCriterion 6 - bird species/ populations occurring at levels of internationalimportance


Criterion 8 – the fish population of the whole estuarine and river system is oneof the most diverse in Britain with over 110 species recorded.

There are also a large number of national and non-statutory designations applicableto birds species, for example BAP and species listed under section 42 of the NaturalEnvironment and Rural Communities Act 2006. The list includes herring gull whichuse the estuary both in winter and summer, and wintering passerines which feed onthe salt marsh, such as twite, skylark and linnet and breeding lapwing.

In most cases, the physical changes of relevance to birds are broadly generic to thebarrage and lagoon options being considered. However, the magnitude of thechanges associated with each option will vary depending on their scale and theoption’s location relative to the distribution of key species. Most of the changes willprimarily affect estuarine wintering waterbirds, although predominantly freshwaterspecies and other groups such as gulls that are also included among the designatedfeatures may additionally be affected by some of the issues identified.

Other marine ecology

Planktonic communities reflect the prevailing physical conditions in the SevernEstuary. Phytoplankton growth within the estuary is limited by the high turbidity inthe water column and significant growth only occurs towards the outer BristolChannel. Zooplankton within the estuary is dominated by detrital grazers,supplemented by meroplanktonic species entering the estuary by larval transport.

Macroalgal assemblages within the estuary exhibit the reduced diversity associatedwith estuarine environments. Zonation is truncated with no macroalgae occurringsubtidally because of the high turbidity of the overlying water.

A variety of epibenthic species occur in the estuary. In particular, there are seasonallylarge populations of the brown shrimp Crangon crangon in the estuary and mysidssuch as Schistomysis spiritus in the inner estuary.

There is little information on the distribution and abundance of cephalopods in theestuary and Bristol Channel although most of the commonly occurring species areknown to occur.

The highly turbid waters of the estuary are not significantly used by marinemammals. While significant numbers of harbour porpoise are seasonally present tothe west of Worms Head, there are few records for marine mammal in the estuary.

All the likely tidal power development options are likely to cause significant changesto the prevailing physical regime in the estuary once constructed. These changes arelikely to affect the distribution and abundance of marine ecological receptors. Inparticular, predicted reductions in tidal range upstream of tidal power developmentswould reduce the extent of intertidal areas and reduce inundation of saltmarsh.


Changes in erosion and deposition patterns within the estuary could also significantlyaffect the quality of existing habitat features. Reductions in salinity upstream of atidal power development would affect the distribution and abundance of species.Changes in turbidity and flushing rate could affect primary productivity in theestuary and change the composition of zooplankton.

Given the high sensitivity of many of the marine ecological receptors and thepotentially large environmental changes that could be introduced by tidal powerdevelopment, potentially significant risks are likely for most of the receptors for allthe tidal power development options considered.

Water quality

The EC Water Framework Directive (WFD) (2000/60/EC) establishes a framework forthe management and protection of Europe’s water resources. The WFD has two keyobjectives for all water bodies:

To prevent deterioration of the status of all surface water and groundwaterbodies; andTo protect, enhance and restore all bodies of surface and groundwater withthe aim of achieving good status in all surface water and good ground waterstatus by 2015.

The Severn Estuary is naturally a highly turbid estuary due to its physical shape, tidalregime and flow rates and the availability of fine sediment for resuspension. Thereare a wide range of direct and indirect discharges into the Severn Estuary, but it iscurrently classified as being of good quality in the upper estuary and fair quality inthe middle and lower estuary. Sediment concentrations of contaminants such asmetals, PAHs and PCBs are relatively uniform around the Severn Estuary and theBristol Channel. This reflects the strong tidal mixing and fluid mud transport whichdisperse contaminants from their source.

The potential water quality impacts are, to some extent, generic for all of the tidalpower options. This is because all of the options are likely to affect the prevailinghydrodynamic regime, which, in turn significantly influences the main physical,chemical and biological processes influencing water quality. Changes to thehydrodynamic regime have the potential to:

Change initial dilution and dispersion characteristics around outfalls anddischarges resulting in local changes in the concentrations of contaminantsand pathogens in the water column;Modify the salinity regime resulting in changes in the behaviour of adsorbedcontaminants;Increase the potential for salinity (density driven) stratification resulting inchanges in the behaviour of adsorbed contaminants and biological availabilityand influencing dissolved oxygen concentrations and nutrient cycling;


Modify flushing characteristics in the main estuary and tributary estuariesresulting in changes in residence times of contaminants and pathogens;Modify suspended sediment concentrations, sediment transport patterns andprocesses with consequences for dissolved oxygen concentrations and thetransport, fate and behaviour of sediment-associated contaminants;Change flushing time and light attenuation, affecting primary productivityand thus alter nutrient cycling within and export from the main estuary andtributary estuaries and export from the Severn Estuary;Changes in light attenuation may have consequential effects on bacterialconcentrations;Change physical processes and nutrient cycling, altering carbon cycling withinthe main estuary and tributary estuaries and export from the Severn Estuary;Change sediment properties and dynamics, affecting the potential forcolonization and sediment water interchanges.

Soils, groundwater and freshwater

The Severn Estuary is bordered by a complex sequence of geologically recentdeposits, most of which are water-bearing and in hydraulic continuity with thesurface water system, particularly on the low-lying land of the Somerset and GwentLevels. These deposits contain a large number of services, including drains, culvertsand sewers. They form the foundation for an extensive system of tidal defenceembankments, and contain building foundations and basements. They also containareas of landfill and historic waste disposal.

The recent deposits are underlain by folded and fractured bedrock which emerges atground surface on both sides of the coast, forms two islands in the estuary (Flat Holmand Steep Holm, both of which are designated as SSSIs) and is exposed extensivelysub-tidally. The Severn railway tunnel runs within these bedrock deposits. Severalgroundwater sources used for the Public Water Supply emerge from theCarboniferous Limestone and have Source Protection Zones that abut the coastline.

Because of the complexity of the geology, the Severn Estuary contains many sites ofgeological and geomorphological interest, several of which are designated as SSSIs.Several regionally important geological sites (RIGS) are also present.

Land drainage is dominated by the Severn Estuary itself, seven main sub-tributariesand a network of multiple drains on the lower levels, many of which are tide-lockedfor part of the tidal cycle. The low-lying land supports important habitats, some ofwhich are designated. Terrestrial surface water quality is complicated by thehydrodynamics and geomorphology of the Severn Estuary.

At this early stage of assessment, the potentially significant effects are considered tobe similar for each option:


Altered water quality (including sediment and salinity) caused by altered flowand sedimentation regimes within the impoundment, and the consequentialeffects on freshwater fisheries, shellfisheries , and biodiversity;Altered terrestrial groundwater regimes, with increased groundwaterelevations adjacent to impounded water and the consequential effects onadjacent land drainage (less capacity), soils (fertility, quality, diversity andaccess to agricultural machinery), trees and sites of water-dependent natureconservation importance;Reduced groundwater quality as a result of increased saline or brackishintrusion or the mobilisation of contaminants from natural or anthropogenicsources (such as landfills or other contaminated sites) affecting groundwateror freshwater sources used for the Public Water Supply;Increased groundwater elevations affecting the integrity of buildings(foundations, dampness in basements etc.) and subterranean infrastructure,including the Severn railway tunnel and other culverts, pipes etc. as wellpossibly affecting the stability of sea defences due to increased pore fluidpressure; andAn increased rate of decay or reduced access to designated sites of geologicaland geomorphological importance as a result of altered tidal regimes withinthe impounded basin.

Historic Environment

The historic environment of the Severn Estuary consists of both natural and builtcomponents and is one of the most significant in the UK. It consists of internationally,nationally, regionally and locally important sites. The Severn Estuary’s features arelocated along its coast-line (including prehistoric and Roman features); its waters holdfeatures reflecting its maritime heritage dating from the Bronze Age, and itsassociated levels and hills offers a rich and varied archaeological landscape. Thepotential of the Severn Estuary is not however limited to, or even fully representedby, the number of nationally designated sites, but also includes a vast number of non-designated sites and finds, and has a high potential for the discovery of new finds.

At this early stage, the significance of effects to the historic environment varies littlebetween the options; the historic environment is irreplaceable, and it is sensitive tochange. As many of the effects of the development will be irreversible and themagnitude could affect the entire estuary, changes are potentially significant.

On the Welsh side of the Severn Estuary, the Gwent Levels have been designated anArea of Special Interest, and are included in the Register of landscapes of historicinterest in Wales. In the draft Heritage Protection Bill which is likely to become law in2010, it will be a statutory duty for developers and consenting bodies to considerhistoric landscapes.


Within each of the options there are a number of other designated sites on both sidesof the estuary. However, future assessment should not be confined to designatedsites, as the potential for discoveries outside these areas may be high.

The potentially significant issues regarding the effects of development include direct,indirect and secondary effects. Direct effects include direct damage to structures,features, deposits, artefacts, and the disturbance of relationships between these andtheir wider surroundings. Indirect effects reach beyond the footprint of thedevelopment, including changes to hydrodynamics, coastline, tidal movement,sedimentation, erosion, water level and water quality. Secondary effects result fromdevelopment activities such as access roads and anchorages for construction vessels.Impact on the historic landscape and access to the historic environment are alsosignificant.

Landscape and Seascape

Landscape is deemed to include townscape and can be considered to be an area ortract of land, which can be of any extent or scale. Landscape results from theinteraction of both natural processes and human influences. These determine theform and appearance of the landscape and affect the way we experience it. Seascapecan be defined as the coastal landscape and adjoining areas of open water, includingviews from land to sea, from sea to land and along the coastline, and the effect onlandscape at the confluence of sea and land.

Large developments within the Severn Estuary will be visible over long distances dueto the open, flat character of the estuary and the raised, undulating topography of thecoastline. The necessary transmission infrastructure such as additional power lineswill also have implications for the landscape and need assessment. However muchdepends on public perceptions and the zone of visual influence in relation toreceptors. These aspects therefore require further investigation to be able todistinguish between options on the basis of risk to the sea and landscape.

Effects on the ‘marine landscape’; i.e. the dominant seabed, coastal and water columnfeatures are not directly considered at this stage, although its components areconsidered in the relevant sections of this assessment.

Resource Efficiency and Waste

Tidal range technologies require considerable use of natural resources duringconstruction although there are some minor mitigation opportunities such as use ofre-cycled materials during construction (for example aggregates and fuel ash inconcrete). However, during operation, tidal range technologies are a significantproducer of energy without consuming significant natural resources or producingwaste. Further information relating to the impact of resource efficiency and waste willbe undertaken as part of the Phase 2 study.


Material assets

Flood risk

As all options under consideration would change the tidal regime, particularlyupstream of a structure, they may consequently affect flood risk and land drainage.Whilst large barrage options (and to a lesser extent smaller barrages) have benefits inproviding protection from storm surges and sea level rise, there are also a number ofimpacts that require mitigation as well as some uncertainties. These are itemisedbelow:

Changes in the tidal regime may have flood risk implications for themaintenance of some flood defences, resulting in greater expendituremodifying or maintaining assets. This is partly dependent on the nature of theestuary’s geomorphological response, that is currently uncertain;All options will cause a reduction in the tidal range, including a reduction inpeak water level, and the extent and magnitude of the reduction will dependon the structure and the mode of operation. The more significant reduction intidal range will occur within the impounded basin of barrages and lagoonswhere there will be an increase in low water levels and a potential reductionin the peak water levels;Whilst the reduction in peak water levels will be beneficial in flood risk termsthere may also be some detrimental effects caused by increased erosion at thebase of tidal defences and saltmarsh;There is likely to be a change in the wave climate upstream of a tidal powerstructure. The reduced fetch resulting from a barrage will reduce waveheights but the amount of reduction and the potential beneficial effects areuncertain and require further research.A larger barrage may prevent waves generated in the south west approachesfrom propagating upstream. This would be a flood risk benefit;Barrage options, by providing a structure across the Severn that can be readilyadapted to protect against future sea level rise, provide a means of protectingupstream communities from the impacts of storm surges and sea level rise.DEFRA's current estimate of sea level rise for the South West and South Walesis approximately 1m by 2100 and continuing to rise thereafter. Thiswill increase flood risk severely for infrastructure and populated areas at riskfrom tidal flooding and to protect the upstream communities would requiresignificant expenditure. Such expenditure would need to be consideredagainst other flood defence priorities.The increased low water levels will restrict the free drainage of some outfallsand levels that discharge / drain into the tidal estuary and will thus requiremodification to enable pumped discharge (currently included within optioncost estimates);


Navigation

The Severn Estuary is home to a number of commercial ports including significantfacilities at Bristol, Cardiff, Newport and Sharpness/Gloucester. The largest port, thePort of Bristol comprises both Avonmouth and Royal Portbury docks. The ports andthe services they support are an important part of the local and regional economy,and are responsible for handling around 5% of Great Britain’s trade.

All of the major ports within the Severn Estuary currently rely on locking into theirrespective docks and each carefully plan ship movements according to availabledraughts as a direct consequence of the extremely large tidal range and advertisedhigh waters. The operation of the ports requires regular survey and dredging ofnavigation channels.

All of the options are considered likely to affect navigation within the Severn Estuaryin terms of where and when the activity takes place. The issues considered to bepotentially significant to the ports are:

The direct and immediate effect of any barrage option proposed is to providea direct barrier to navigation. This will require the addition of locks, withsufficient redundancy, to allow vessels to traverse the two different waterlevels;Reduction of spring tide levels which will decrease the access window thatvessels with large draughts will have to access the ports, unless mitigated byassociated reduction in the lock cill levels;Increase in low tide level which will increase the access windows that vesselshave to access the ports and provide flexibility to ports in managing vesselmovements. Some marine structures will however be permanently immersed;Reduction in salinity will increase the draft requirements for vessels (ships sitlower in fresh water than sea water because it is less dense), although this isnot considered significant to Sharpness/Gloucester;Long term effects on seabed geomorphology and sediment distribution areuncertain, potentially affecting dredging requirements;Any physical works on the Severn Estuary near navigation routes will affectcurrents and will also represent a potential navigation hazard.Reduced tidal currents and wave climate coupled with the higher low waterlevel will change sailing and leisure conditions in the estuary upstream of anybarrage.

Society and Economy

Many of the potential changes to the community and socio-economic environmentresulting from tidal power options are broadly similar in nature, but would vary inmagnitude according to the scale of the proposed scheme.


Such generic changes that are considered likely to occur arise from the substantialconstruction phase for most tidal power schemes. These include:

Employment opportunities during the construction and operation phase andcompetition for labour and loss of skilled labour in local businesses;Population migration in response to the construction phase, resulting socio-cultural changes and pressure on existing housing stock and services;Health effects through changes in noise and air quality emissions, principallyduring construction; post construction minor odour changes may be noticedfrom the changed tidal regime;Effect of such substantial proposals on existing, proposed and committeddevelopments and the future use of land;Regional economic effects including the opportunity for regeneration and newdevelopment.

Tourism is an important economic activity in the region with over 7.5m tourist visitsgenerating an income of over £1bn p.a. A wide range of recreational activities occuron or near the Severn Estuary, including: sailing, boating, windsurfing, canoeing,surfing, bore surfing, sand surfing, bathing, diving, wildfowling, bird watching andfishing. The presence of tidal power structures could benefit some of these activities(eg sailing, boating and windsurfing) whilst pose significant issues for others, forexample by creating visual impact issues, altering bird distributions and affectingrecreational angling opportunities. These latter issues are discussed in other relevantsections.

Amenity and recreational changes will also take place. The construction of a tidalpower project will provide opportunities for enhancement of some recreational uses.These range from interest during the construction phase, through to managedactivities resulting from the less aggressive tidal range upstream of a barrage, such assailing and other water sports. Opportunities arising from tidal lagoons include use ofthe lagoons for sailing and other water sports although these would require specificaccess arrangements which may have to be provided at additional cost. These may inturn result in environmental impacts that would need to be considered and managed.

Barrages may reduce or eliminate the Severn Bore phenomenon. It is unclear at thisstage whether a bore could be preserved by not generating from the barrage andallowing water levels to recover to their natural levels and flows at the time of apredicted Bore. Depending on the measures required, this may entail a significantcost in terms of lost energy yield.

Effects on certain other issues with a socio-economic bearing, namely fishing, floodrisk and navigation, are discussed in the relevant sections.

Minehead to Aberthaw Barrage (B1), Hinkley Point to Lavernock Point Barrage(B2), and Brean Down to Lavernock Point Barrage (B3)


Hydrodynamics and Geomorphology

Hydrodynamics

Hydrodynamic modelling undertaken as part of the EP57 studies confirm that thetidal regime upstream will be modified, quoting the top water level being suppressedby approximately 10% both upstream and immediately downstream of the barrageand the total tidal range being reduced by approximately 50%.

These studies also suggest that downstream of a large barrage there would be areduction in high water and raising of low water, resulting in a net reduction in tidalrange. Model studies for EP46 calculated a reduction in mean tidal range of 20% forthe B1 alignment and 14% for the B3 alignment. The modelling for EP57 calculated aslightly smaller reduction in mean tidal range just seaward of the B3 barrage. Thiseffect diminishes with distance, but the modelling for EP46 predicted a reduction inmean tidal range of 15cm for the B1 barrage and 5cm for the B3 barrage at MortePoint.

Geomorphology

The nature of potential geomorphological responses (both up and downstream) toenclosure by a barrage is uncertain and needs further assessment.

It has been postulated in discussions with statutory nature conservation agencies that,upstream, erosion of the upper foreshore by wind-generated waves, and the ongoingerosion of the upper-intertidal may be exacerbated. This is because, with a barrage inplace, there remains the potential for south-westerly wind-driven waves; and theexposure-time of the upper foreshore to such waves would be increased. Overall thiswould lead to a further reduction in intertidal habitat through erosion of softsediments. This hypothesis could also have significant consequences for flood riskmanagement and for other coastal habitats. It is widely recognised that intertidalhabitat fronting sea defences absorbs wave energy and protects built structures.

Conversely, studies of the Cardiff-Weston scheme in the 1980s have concluded thatthe upper intertidal / saltmarsh would stabilise and possibly increase in extent owingto a reduction in these erosive processes. This converse hypothesis is also supportedby conventional engineering assumptions which would recognise the wind fetch inthe basin as a different entity to the fetch downstream of the barrage (with the barrageabsorbing energy from the downstream fetch).

Other geomorphological responses that may arise include the risk of reduced sandtransport rates and possible ingress of fines impacting on a large proportion of theSabellaria spp. reefs that are a feature of the Severn Estuary cSAC. The enclosedestuary would be likely to undergo morphological change, with accumulation of finesin the deepest areas: Bristol Deep, Newport Deep etc., which are presently scouredafter neap tides.


The geomorphological response of the Severn Estuary to a tidal power scheme isfundamental to understanding its wider effects on the natural and humanenvironment, including many designated features. There are currently divergentschools of thought on the likely nature of the geomorphological response. As animportant area of uncertainty, it must be investigated further before the impacts ofsuch schemes can be understood.

Sedimentation

The Severn Estuary’s sediment budget, in comparison to the size of the enclosed basinfor these barrages, is not believed to be adequate for the estuary to establish a state ofdynamic equilibrium for centuries. The risk of sedimentation significantly affectingthe operation of these barrages is therefore generally considered to be low if there isno major requirement to maintain new channels to facilitate navigation (duringconstruction or operation). If there is such a need then sedimentation may be asignificant issue, albeit one which is likely to be manageable at a cost and associatedenvironmental impact.


Habitats

These options may result in a substantial reduction in intertidal area upstream of thebarrages. Without mitigation, which itself has a low confidence of being evenpartially effective, the majority of existing saltmarsh habitat would be lost (because ofthe reduction in high water levels). A smaller extent of new saltmarsh may beexpected to develop seaward of the existing marshes but previous studies haveshown that the net loss is likely to be significant. The extent of intertidal mudflat andsandflat habitat would also significantly reduce as a result of the reduction in tidalrange. The majority of these habitats are within the Severn Estuary cSAC/SPA andRamsar site, and the River Usk and River Wye SACs. Additional areas ofundesignated intertidal habitat would also fall within the enclosed basin of the B1and B2 barrages and be similarly adversely affected.

Intertidal habitat loss would primarily be caused by the reduced tidal range, leadingto lower-intertidal areas becoming sub-tidal, and upper intertidal areas no longerbeing exposed to inundation. The intertidal that remains within the barrage basinwill also have a reduced duration of exposure due to the holding of standing water inthe basin.

In absolute terms these options have the greatest impact on the designated area ofintertidal habitat through the change in tidal range, and are therefore likely to havethe greatest risks in this regard. The direct loss of existing habitat due to thefootprint of these barrages, may also be the greatest for any of the options currentlyproposed.


There are two contrasting schools of thought about the biological productivity of theremaining intertidal areas. One, that draws upon the tidal power scheme at La Rance(Brittany, France), a rocky estuary with a different morphology to the Severn,suggests that mudflats will increase in stability and their productivity will thereby beenhanced. The other draws upon the tidal barrage on the Eastern Schelde(southwestern Netherlands), which has more of a similar morphology to the Severn(although a very different tidal range), and suggests that foreshores will continue toerode and will become less biologically productive. It should be noted, when citinganalogues, that conditions in estuaries vary, particularly in terms of tidal range,sediment sources and configurations of structures. However, these contradictoryhypotheses are fundamental to any final conclusion about habitat changes in the longterm and require further investigation before any firm conclusions can be reached.

Further it is important to note that even if there were an increase in productivity itshould not be concluded that this would necessarily be a nature conservation benefit.The Severn Estuary is designated for its very particular habitats and communities,which have developed due to the unique physical conditions and as a representativeof an extreme of estuarine habitat within the United Kingdom.

For the purpose of this stage of option assessment, it is assumed that the relativeimpact of habitat loss will be in proportion to the area loss due to tidal range change.These options therefore have the greatest risks in this regard.

Birds

It has been noted above that these options present a very large reduction in the areaand exposure period of the intertidal habitat. Certain areas of the estuary are usedintensively for waterbird feeding and roosting, although information is needed tobetter understand their distributions. There is, therefore, potential for significantimpacts upon water birds. Those birds feeding or breeding in the saltmarsh areas,which may be subject to erosion, are especially vulnerable to the expected changes intidal range.

Previous studies in the 1980s for the Cardiff-Weston scheme suggested that, inrelation to bird interests, the reduction in intertidal area and exposure would be offsetby an improvement in the biological productivity of the remaining intertidal. Thiswas considered to be driven by an improvement in foreshore stability and reductionin water turbidity. This finding is under question given the contradictory hypothesesrelating to foreshore response described above. Conclusions on the biologicalproductivity of the remaining habitat and its ability to support birds cannot thereforebe drawn at this stage. Until this question is investigated and resolved, it is assumedat this stage that the scale of loss of waterbird habitat is in proportion to the intertidalarea lost through the change in tidal range.


A particular feature of the B1 option is that, being located furthest seaward; it offerslittle opportunity for birds displaced by the barrage to exploit other local intertidalareas for feeding.

By the scale of effect upon tidal range and habitats, these options and B1 in particular,are currently considered to have the greatest risks with regard to impacts on birds.However, much will depend on further investigations of the effects on the quality (aswell as quantity) of remaining habitat.

Fish

The protection of several fish species within the Severn, Usk, Wye and Tywi underthe Habitats Directive has been discussed above. Other rivers that may be adverselyaffected include the Rivers Ely, Taff (both already impounded by the Cardiff BayBarrage), Rhymney, Ebbw and Avon.

For the reasons described above, there are therefore risks of potentially significanteffects from a large barrage on important fish such as shad species, lamprey, salmon,eel, sea trout, sturgeon and estuarine fish species due to factors such as changes tomigration cues, water quality, habitat, disruption to route of passage includingturbine passage. This will have an associated effect upon the angling/ fish activitiesthese support.

Marine Water Quality

By enclosing much, if not all, of the Severn Estuary these barrages will have an effecton water quality: reduced currents may for example lead to reduced turbidity andincreased light penetration. There may however also be adverse effects on waterquality parameters. Impact on the attainment of WFD objectives will thereforerequire assessment.

The differences between options are likely to be reflected in the spatial extent andmagnitude of the changes in water quality factors. Being the largest schemes, thesehold the greatest risks of an adverse effect or the largest benefit if water qualityimproves..


The main effects will arise from construction, although geomorphological responsemay also lead to exposure or loss of features. Archaeological assessment is likely to belimited to the dryland margin. In these areas archaeological sites are quite visible andcan be protected by modifications in design or mitigated through comprehensivearchaeological excavation. On the Welsh side, the intertidal areas are quite short andare understood to have less archaeological potential.


Any assessment of the marine archaeological potential is very difficult andundertaking any mitigation almost impossible.

Landscape and seascape

A large barrage could have the following effect on the receiving landscape andseascape:

Changes to the character of the shoreline associated with changes in land useand infrastructure including link roads, power lines and on-shore builtdevelopment;Visual effect on views of the Severn Estuary from parts of the Glamorgan andExmoor Heritage Coasts, Exmoor National Park, the Wye Valley, QuantockHills and Mendip Hills AONBs and the Gwent Levels Historic Landscape (thedifferent options will have different impacts from different locations);Indirect effect of reduction in tidal range, loss of salt marshes and changes towater clarity due to reduced turbidity;The extent of the intertidal zone visible at low water level would be muchreduced;Indirect effect arising from a reduction in the dynamic character of the Estuaryincluding the loss of the Severn Bore phenomenon;Loss of tranquillity during the construction phase; andRequirement for significant grid reinforcement through additionaltransmission lines.

Material Assets

Flood Management

The effects of a large barrage on flood risk are uncertain but more likely to be positiveif the required mitigation works to offset any flood defence impacts are satisfactorilyundertaken. Predictions are wholly dependent upon the model of geomorphologicalresponse that is determined to be most applicable. If, as has been postulated inprevious studies, foreshores will accrete, then the stability of defences should beunaffected. If as an alternative hypothesis suggests, the foreshore will erode, then theprotection this provides to the defences will be reduced and the stability andeffectiveness of existing flood defences will be potentially compromised. This maytrigger the need for additional investment to secure flood defences are in a stableposition. Increased sedimentation and reduction in wave energy upstream of abarrage appear to suggest upstream flood defences should benefit but reflected waveenergy may not benefit downstream defences.

Flood risk benefits could arise if adverse impacts (such as required changes to tidaloutfalls to maintain existing standards of protection) are satisfactorily mitigated.


However, hydrodynamic and geomorphological changes may also have negativeimplications.

A large barrage may have flood defence benefits in protecting communities andagricultural land within the tidal flood plain upstream of the barrage from the effectsof sea level rise and storm surges. Barrages landing at Minehead (B1) and HinkleyPoint (B2) may protect the low lying areas of Somerset from tidal flooding as well asthe Wentlooge and Caldicot Levels (collectively known as the Gwent Levels) andAvonmouth, which would also be protected by B3.

Any attenuation of surge tides would have a direct benefit by both a reduction ofdamages on tidal events that overtop defences and also due to avoiding or delayingexpenditure to keep pace with sea level rise. This could be a significant benefit for thebarrage options, but is not expected to be significant for lagoon options.

The wave climate would be changed upstream of a power generating structure, withbarrage options having the bigger effect. The changes have the potential to bring bothflood risk benefits and increase risks, depending on the location, type of structure andoperating mode. This applies both to the risk of wave overtopping and erosive effects.

The reduced tidal range, particularly affecting the level of low tides, will impact onsome land drainage and surface water outfalls into the estuary. The effect will bedependent on the type of power generating structure, the mode of operation as wellas the location and characteristics of the outfalls. Some will suffer from a reducedperiod of free discharge and ‘tide lock’ with a corresponding increase in flood riskunless mitigating measures are introduced. These mitigation requirements have beenincluded in the cost assessments for options within this report on the basis that thestandard of service offered by existing flood defence assets should not becompromised.

The changed tidal regime could result in a reduction in the exposure of some outfalls,which may reduce the time available to undertake maintenance work. This may alsolead to siltation in some channels and pipework.

The changed tidal regime and wave climate may be a benefit in some locations, butcreate risks in others.

Navigation

These barrages will affect the operation of the Ports of Cardiff and Newport, the Portof Bristol and Sharpness Docks. Effects will include increased time to navigatethrough locks required to enable the passage of vessels through the barrage.


Navigation will be affected by changes in water levels. The reduction in water levelat high spring tide will affect those vessels which can only gain access to ports inthese high tides. There will be a reduction in tidal range which will increase theaccess window for all shallower draught vessels into all of the ports within theestuary. Changes in salinity will increase the available draught required by vessels asthey will sit lower in water with lower levels of salinity although this is less likely tobe an issue for ports in the upper part of the Severn Estuary. Depending on themorphological response to a scheme, channels and other navigational areas mightbecome more prone to siltation. Morphological changes may therefore changeexisting dredging and maintenance regimes.

The increase in low water levels will result in the permanent immersion of marinestructures in the whole of the Severn Estuary which were previously uncovered atlow water and could be maintained during these times. However, it will also allowgreater flexibility in marshalling vessels within the estuary.

Further consideration of navigation issues is included in section 6.2, includingproposed mitigation of the above effects.


Shoots Barrage (B4) and Beachley Barrage (B5)


Hydrodynamics

The hydrodynamic effects of barrages located this far upstream show a relativelysmall reduction in top water level upstream of the barrage and the total tidal rangebeing reduced by approximately 50%. The downstream tidal regime will be slightlyinfluenced with the tidal range reduced (high water slightly lower and low waterhigher by up to 1m) over a seaward distance of some 20km.

Geomorphology

The nature of potential geomorphological responses (both up and downstream) toenclosure by a small barrage is uncertain and needs further assessment.

These options are smaller but they are located in a more dynamic part of the estuary.Construction impacts have the potential to be significant and far reaching, withsubsequent requirements for long term maintenance dredging activities to facilitatenavigation.

Sedimentation

The estuary’s sediment budget, in comparison to the size of the enclosed basin forthese barrages, is relatively large, and therefore there is a potential risk ofsedimentation affecting their operation. Maintenance dredging to maintain the tidalprism and navigation may be required during construction and operation, withassociated environmental impact. The design of these options uses a large number ofhigh level sluices to manage this risk, but nonetheless the risks are greater for theseoptions relative to the larger impoundments of barrages further downstream. Inaddition, the fluvial sediment load is a larger proportion relative to the impoundedbasin volume.


Habitat

These options would risk a substantial reduction in area and tidal exposure, ofsaltmarsh and other intertidal habitats within the Severn Estuary cSAC/SPA andRamsar, and the Wye SAC, for much the same reasons as have been described above.The great majority of intertidal upstream of the barrages will be lost, includingreedbed, saltmarsh and intertidal mud.

These options result in a smaller absolute reduction in the designated area ofintertidal through the change in tidal range, and are therefore considered to poselesser risks than larger barrages in this regard.


Birds

It has been noted above that these options are likely to lead to a reduction in the areaand exposure period of the intertidal. Certain areas of the estuary are of more valuethan others for water birds; the area upstream of options B4 and B5 being lessimportant for some species although there are exceptions. There is, therefore,potential for impacts upon waterbirds although the area affected is much less thanthat for the larger barrages.

Fish

These options create a physical impediment to migratory fish movements betweenthe Outer Bristol Channel and the River Wye and Severn. Option B5 is upstream ofthe Wye but there is still some risk of impact (both to Wye and Usk populations)because shad, salmon and possibly lamprey may travel upstream in the Severn beforeentering the Wye and Usk.

There are likely to be potentially significant effects from a small barrage on shadspecies, lamprey, salmon, eel, sea trout, and sturgeon (but possibly less so than forlarge barrages in relation to estuarine fish species). This is due to factors such aschanges to migration cues, water quality, habitat, and disruption to route of passageincluding turbine passage. This will have an associated effect upon the angling/ fishactivities these support.

Although these barrages enclose fewer tributary rivers than the larger barrages theynonetheless pose the significant risk of major reductions in population of importantmigratory fish within several rivers, including salmon and shad in the Wye and Usk.Risks relative to lagoons are not readily discerned.


These options will have an effect on water quality, and their impact on the attainmentof WFD objectives will require assessment.

The positions of these barrages in relation to point source discharges to the estuaryimply that both benefits and disadvantages for water quality could arise. Forexample, concentrations of cadmium might reduce landward of a barrage, becausethe main sources are seaward of B4. In contrast, concentrations of nickel, copper andother substances at the head of the estuary could increase, partly because there is lessscope for their dispersion. There may also be less potential for a major reduction inwater turbidity.

The other effects on water quality have been previously discussed. Being smaller inscale these barrages may be expected to hold a smaller risk of water qualitydeterioration, that is still significant. Equally, any potential improvements in waterquality such as those caused by reduced tidal currents, reduced turbidity and


increased light penetration, will also be less significant. The smaller impoundment ofthe Beachley Barrage may result in increased risk of eutrophication effects caused bynutrient inputs from rivers.


For these barrages the main risks come from construction across the intertidal areas.There is experience from the building of the Second Severn Crossing, wherecomprehensive archaeological surveys and subsequent excavations were undertakenon both the English and Welsh sides of the estuary.

The risks of impact on the dryland margins is likely to be less than for the largerbarrages, but the need for new large drydocks in the intertidal area is a significantfactor.

Any assessment of the marine archaeological potential within the deepwater channelsis very difficult and undertaking any mitigation almost impossible.


The potential consequences of the small barrages in terms of landscape and seascapeare:

Changes to the character of the shoreline associated with changes in land useand infrastructure including link roads, power lines and on-shore builtdevelopment;Reduced intertidal visible at low tide;Indirect effect of reduction in tidal range and changes to water clarity due toreduced turbidity;Effect on views of the estuary from the Wye Valley, Cotswolds and MendipHills AONB and the Gwent Levels Historic Landscape; andRequirement for significant grid reinforcement but not on the scale of largebarrages.

Other than at close proximity to land falls, as these options are smaller they may beexpected to pose less risk than the larger barrages.

Material Assets

Flood Management

The flood management issues associated with a barrage have been previouslydiscussed. A barrage at English Stones or Beachley may have flood defence benefitsin protecting communities and agricultural land within the tidal flood plain upstream– primarily the tidal flood plain of the Gloucestershire banks on the Severn.


In keeping with larger barrage options, the implications for flood defences have short-term and longer-term scenarios, with considerable uncertainty about the long-termmorphological evolution both upstream and downstream of a barrage. Thesedifferences have more significant implications for management of the tidal basin, asan erosive regime could lead to proportionately more subtidal in-filling over the lifeof the barrage.

Navigation

These barrages will affect the operation of the Ports within Gloucester HarbourTrustee’s jurisdiction, the largest of which is Sharpness Docks. Effects will includeincreased time to navigate through locks required to enable the passage of vesselsthrough the barrage.

Navigation will be affected by changes in water levels. The reduction in water levelat high spring tide will affect those vessels which can only gain access to ports inthese high tides. There will be a reduction in tidal range which will increase theaccess window for all shallower draught vessels into all of the ports within theestuary. Changes in salinity will increase the available draught required by vessels asthey will sit lower in water with lower levels of salinity. Morphological changes willchange existing dredging and maintenance regimes.

Further consideration of navigation issues is included in section 6.2 includingpotential mitigation works.

Russell (Fleming) Lagoon (L2) and Generic Tidal Lagoons (L3)


Hydrodynamics

The hydrodynamic effects will depend greatly on the design of the lagoon andwhether it will drain down completely at low tide. The effects are nonethelessexpected to be similar to the smaller barrages in that the main effects (a potentialreduction in top water level) and reduction in tidal range are contained within theimpounded basin.

Due to a reduced estuary width, there may also be a reduction in tidal range andforeshore exposure outside the lagoon impoundments. The scale of change isuncertain and needs to be explored further, but is likely to be smaller than for largebarrages.

Geomorphology

The nature of potential geomorphological responses to the narrowing of the estuaryas a result of lagoon structures is not well-explored. It is nonetheless likely that a


series of major lagoons would alter the estuary regime: by leading to increasedcurrent velocities they could cause extensive erosion and transportation of sedimentsinto the inner estuary. Construction impacts will also be important with potentiallysignificant impacts on adjacent subtidal channels.

Whilst the spatial extent of impact from lagoons may be less compared to the largerbarrages, the lagoons are not obviously sited in areas which minimise their overallgeomorphological impact. Only following detailed study would it be possible tooptimise their effects on mobile features.

Sedimentation

The estuary’s sediment budget, in comparison to the size of the enclosed basin foreach lagoon, is substantial and there is likely to be a considerable cost entailed withthe management (probably through dredging) of sedimentation within the basin.Maintenance dredging might also be required to maintain navigation throughout theestuary. This would in itself have ecological and water quality impacts that wouldneed to be assessed along with the implications for the structure’s carbon footprintand wider sustainability.


Habitats

The effects of these options on tidal range are not as readily predicted as for thebarrages, but are assumed to risk a reduction (in the impoundments) in the extent ofsaltmarsh and other intertidal habitats within the Severn Estuary cSAC/SPA andRamsar, and the River Usk and River Wye SACs. The area enclosed and thereforepotentially affected is much smaller than for a large barrage.

Under lagoon options the tide is not likely to be truncated and the reduction in tidalprism is modest compared to the overall system. Tide propagation past the lagoonsmay be impacted but to a lesser degree than by construction of a barrage. The effectson tide levels and hence intertidal habitats outside the lagoons are therefore likely tobe relatively minor.

The degree to which the lagoon footprint would directly enclose intertidal area, variesbetween land-connected lagoon options. An offshore lagoon would mainly affectsub-tidal habitats, that are nonetheless protected in some locations. Conversely, aland-connected lagoon would mainly enclose intertidal habitat. The direct loss ofhabitat due to the footprint of the lagoon schemes, or sedimentation managementactivities such as dredging, will therefore vary. Indeed, there are potentialopportunities to create areas of intertidal habitat within lagoons, although this wouldbe at the expense of reduced power generation.


Birds

The principal effects on waterbirds from these options would relate to the effects of aland-connected lagoon on the intertidal. As has been stated above, the area affectedwill be smaller than for the larger barrages. However any effect would also beinfluenced by the relative importance of the impounded area as intertidal foraginghabitat for waterbirds. The Welsh Grounds, Bridgwater Bay and Peterstone Flats, i.e.the locations for some of the lagoons, are noted for their importance to several speciesof waterbirds. An offshore lagoon would have a much reduced effect on bird feedingareas. Effects of the lagoon structures on geomorphological processes such assediment erosion and redistribution could also potentially affect the quantity andquality of remaining habitat.

Nonetheless, in comparison to the large barrage options these options may presentless risk with regard to impacts on birds. Relative risks compared to smaller barragescannot be assigned at this stage.

Fish

These optionsare likely to pose an obstruction to migratory fish movements betweenthe Outer Bristol Channel and the Avon, Parrett, Usk, Wye and Severn.

There are therefore risks of potentially significant effects from lagoons on shadspecies, lamprey, salmon, eel, sea trout, and sturgeon. Land-connected lagoons inparticular may interrupt the continuity of the intertidal and thereby affect movementand survival of estuarine and migratory fish species. This will have an associatedeffect upon the angling/ fish activities these support.

It is uncertain as to what the risks are to migratory fish in comparison to the largerbarrage options, although they are still regarded as being significant. There is a poorunderstanding of fish movements in the estuary and the effect of the lagoons on tidalcurrents and geomorphological process. This makes it difficult to ascribe anassessment of impact of lagoons on fish movements per se.


Marine water quality issues have been previously described. It is likely that thelagoons would be designed to retain a minimum amount of water compared to thetidal exchange. The majority of the water retained within each lagoon wouldtherefore be flushed out on each tide. There is therefore unlikely to be a significantissue in relation to water quality retained within the lagoon, although this will bedependant on the nature of sediment interactions.

The lagoons would be likely to alter the tidal current regime within the estuary.Depending on the scale of lagoon development, the effect upon the estuary’s currentregime and water quality status is likely to be less than in comparison to the larger


barrage options. As lagoons are unlikely to affect estuary currents to the same extentas large barrages, they are therefore less likely to result in reduced turbidity andincreased light penetration. Nonetheless, these options may pose less risk in relationto compliance with the Water Framework Directive’s objectives, compared to barrageoptions.


Land-connected lagoons impound the large areas of tidal mudflats in the SevernEstuary. These mudflats have produced most of the best archaeological sites of allperiods with the Severn Estuary and Levels as a whole.

Given that the lagoons require embankments built with excavated foundations andwill introduce turbines and sluices which will create a whole array of new channels,these types of structure may well present the greatest threat to the historicenvironment.

These options are capable of full archaeological assessment, though working at thelimit of the tidal range is very challenging. Dryland and marine archaeological siteswill probably remain largely unaffected.


The potential consequences of land connected lagoons on the Welsh and English sidesof the Severn Estuary to the landscape and seascape are:

The lagoons would generally be located in the upper estuary adjacent to lowlying areas where they would be visible from elevated vantage pointsincluding Penarth and Brean Down. The visual effect would be mostprominent at low tide when the embankment would be fully exposed, and

There may be a visual effect on the Wye Valley, Quantock hills and MendipHills AONBs, the Glamorgan and Exmoor Heritage Coasts, Exmoor NationalPark and the Gwent Levels Historic Landscape.

There is likely to be the requirement for significant grid reinforcement through newtransmission lines, although on a smaller scale than for the larger barrages.

Material Assets

Flood Management


The flood management issues have been previously described. A tidal lagoon doesnot provide the same level of flood defence as a barrage, but equally impacts on landdrainage systems are less (for a land connected lagoon such as L2) or non existent foroffshore impoundments. Land-connected lagoons offer protection to the containedshoreline. However, there may be negative impacts in terms of changinggeomorphology which may in turn affect existing flood defences within the lagoon.Offshore lagoons provide no additional flood defence benefit and the increasedcurrents between the lagoon and the foreshore may result in increased coastalerosion.

Navigation

Tidal lagoons do not impede the passage of shipping and do not require ship locks.However, changes in currents and consideration of ship impacts on marine structuresdo require consideration. Effects may also include changes to the existing dredgingand maintenance regimes for Ports within the Estuary if tidal lagoons influencenearby navigation channels. It is assumed for the purposes of comparativeassessment that the above impacts can be satisfactorily mitigated.

Tidal Fence (F1a and F1b)

In broad terms the Tidal Fence options presents similar risks to the barrage options onsimilar alignments (F1b and B1, F1a and B3). The issues are therefore not repeatedhere. Areas of potential difference are summarised below:

The accelerated currents through and around the Tidal Fence are likely toexert geomorphological changes, the nature of which is not yet explored butcould be adverse for intertidal habitats locally;The greater ease of water passage through the structure suggests that risks ofchanges to water quality should be reduced, but the variations in velocityacross the fence suggest turbidity levels could be increased;The area of intertidal lost owing to the altered tidal regime is likely to besmaller than for a barrage on a similar alignment. This reflects the lesseramount of energy converted, therefore having lesser impacts on habitat forbirds (setting quality considerations aside);Issues arising from the divergent hypotheses over the long-termgeomorphological evolution of the Severn Estuary would apply here;The structure has more open passages and therefore may not hinder fishpassage to the same degree as barrage structures in the same location. Theaccelerated currents through these passages are not expected to prejudice fishmovements passively on the tide. The relative risks of fish damage from theturbines adopted under this option requires further study;The accelerated water currents through the structure requires carefulconsideration in relation to navigation, both in terms of safety of passagethrough the structure and potential for ship impact;


Connections with the land and the scale of the construction infrastructure maypose less risk to the historic environment, and may mean that somearchaeological assessment and mitigation is possible;The accelerated water currents through the shipping channel will also greatlyincrease the potential for scour along the channel. Structures to either side ofthe channel will require heavy protection against erosion. Similarly, the opensections at either end of the structure will likely experience accelerated watercurrents which will likely lead to erosion of the intertidal areas adjacent to theTidal Fence which would require heavy scour protection.

Although there are some possible advantages in terms of impact in comparison to thelarger barrages, there is uncertainty over the Tidal Fence’s effects owing to the limitedunderstanding and experience in the application of this type of project.

Tidal Reef (R1)

In broad terms the Tidal Reef presents similar risks to barrage option B1, adopting asimilar alignment. The issues are therefore not repeated here. Areas of potentialdifference are summarised below:

The accelerated currents through the Tidal Reef are likely to exertgeomorphological changes, the nature of which is not yet explored but couldbe adverse for intertidal habitats locally;The greater ease of water passage through the structure suggests that risks ofmajor water quality impacts should be minimal;The area of intertidal lost owing to the altered tidal regime is likely to besmaller than for a barrage on a similar alignment., therefore having lesserimpacts on habitat for birds (setting quality considerations aside);Issues arising from the divergent hypotheses over the long-termgeomorphological evolution of the Severn Estuary would apply here.

Although there are some potential advantages in terms of impact in comparison tothe larger barrages, there is uncertainty over the Tidal Reef’s effects owing to thelimited understanding and experience in the application of this type of project.

Severn Lakes (U1)

Severn Lakes adopts a sinuous alignment near to the barrage option B3. It is also amuch wider structure, being 1km wide to accommodate the other non-tidal powerrelated infrastructure. Whilst impacts on tidal range and geomorphology areassumed to be similar to a more typical tidal power project, it would also appear topose greater environmental risks. Many of the issues are similar to option B3 and aretherefore not repeated here. Some of the points of potential difference to option B3are summarised below:


The wider structure will result in greater footprint and consequential loss ofhabitat;The introduction of multiple uses onto the structure poses risks of additionaldisturbance to protected bird and fish species using nearby areas (e.g. noiseand lighting);The multiple uses of the structure poses additional risks in terms of impactsupon water quality;The much larger scale of structure suggests that impacts on the land andseascape will be greater.

This assessment does not take into account the scope for wider economic benefits (e.g.associated economic development) under this option.

5.4 Modes of Operation

For the purposes of differentiating each option, the quantitative analysis used withinthe Assessment Framework has focused on a “base case” for each option in terms of itsoperational mode. This is based on the premise that many of the options have similaropportunities for optimising energy through the use of ebb and flood generation,pump-assisted operation and/or the use of multiple basins and/or operating differentoptions in combination. The logic used is that those options that perform best in their“base-case” mode will also offer relatively better opportunities for optimisation bycomparison with options that have a higher cost of generation. The “base-case” modeis the operational mode which offers the best unit cost of electricity. Previous studieshave indicated this is ebb-only generation for the tidal range technologies used inbarrages and lagoons. More permeable options using the kinetic energy of the tides aremore constrained in their operational modes and operate only in ebb and floodgeneration mode.

In environmental terms, different modes of operation have different effects and theseare briefly considered below for each of the options:

Small Tidal Barrages B4 and B5

These utilise Straflo type turbines because of the physical restrictions of their locations.Straflo turbines have the benefit of requiring smaller caissons than their Bulb turbinecounterparts but have the disadvantage that they are not designed to operate in reversemode to either pump or generate on the flood tide. Because of the highersedimentation risks associated with the smaller barrage sites, low level inflows into thebasin by generating on the flood tide need to be avoided so the fact that the Strafloturbine is only able to operate one way is not necessarily disadvantageous, particularlywhen consideration is given to the energy outputs which are much more easilyabsorbed by the grid in comparison with the larger installations.

Larger Tidal Barrages and Tidal Lagoons B1, B2, B3, L2 and L3


These utilise Bulb turbines that can operate in flood and ebb mode and can also be usedfor pumping, albeit at some loss of overall efficiency. Increases in energy yield fromflood pumping have been estimated in previous studies (EP57) to improve energyyields by less than 5% Flood pumping would start at high water levels and mitigatesome of the loss in high water levels upstream of the barrage. Generation during bothebb and flood tides results in lower overall energy yields but a more distributed energyprofile over the tidal cycle. However, ebb and flood generation results in a furtherreduction in total tidal range with the high water level being lower than the equivalentebb only generation mode.

Tidal Fences F1

A tidal fence operates in both ebb and flood tide modes. The timing of generation isalso different and thus operation of a tidal fence with a barrage or lagoon locatedfurther upstream is in theory possible. However, the reduction in tidal range, and inparticular the reduction in high water level resulting from tidal fence generation,compromises the tidal range available from the barrage with the consequential impacton cost per unit energy.

5.5 Mitigation and compensation issues

As should be evident from the previous sections, all options present risks tointernationally designated bird and fish populations and their habitats. Certain ofthese risks may lead to effects that cannot be fully mitigated – for example habitat lossfor birds, and barriers to fish passage. To comply with the requirements of theHabitats Directive, there will therefore be a need to provide ‘compensatory measures’under the Directive to ensure ‘coherence of the Natura 2000 network’, subject to theother tests under the Habitats Directive being satisfactorily addressed.

A high-level review of the potential for mitigation and compensation under theHabitats Directive is currently underway. This review is likely to conclude that thescale and nature of the impacts presented by schemes of this sort pose unprecedentedchallenges, and that based on European Habitats Directive guidance there arecurrently few (if any) measures available with a high degree of confidence in theireffectiveness. It will therefore identify a number of requirements for additionalstudies to establish whether credible mitigation and compensation packages can bedeveloped. The options having the largest quantitative impacts on intertidal areas,and presenting the greatest obstruction to fish survival and passage, are seen to posethe most risk in this area.

Guidance on providing compensatory habitat, existing practice and precedent hasestablished that provision should be at a ratio that exceeds parity with the area ofhabitat lost to recognise the uncertainty and risks of establishing a habitat thatmaintains the ecological functions of the habitat that is lost.


The scale of potential compensation and its potential effect on a European site isunprecedented. This creates an additional element of uncertainty aroundquantifying and managing the risk.

Furthermore, it may be necessary to take measures in addition to those required bythe Habitats Directive, for example in relation to other nature conservation policy andlegislation, water quality, recreation, historic environment, and visual impact. Thesewill need to be considered in more detail under Phase 2 of the Study.

5.6 Ecosystem goods and services

Estuaries and coastal habitats provide a wide variety of ‘ecosystem goods andservices’ including carbon sequestration, nature conservation, flood defence,transport, treatment of water pollution, and recreational opportunities – indeed manyof the issues discussed in previous sections. Work on ecosystem goods and services isnot being undertaken as part of the SEA but the SEA will be able to provide data to,and be informed by, analysis of this sort that is being undertaken within a separatecomponent of the feasibility study.

5.7 Conclusion

Predictions about the possible ecological and socio-economic impacts hinge upon anunderstanding of possible geomorphological response both to barrages and tolagoons. There are currently divergent schools of thought in relation to suchresponses, and this means that all considerations must be subject to considerableuncertainty.

All options present a wide range of potential issues that require significant research,but clearly the central focus of the investigations must concentrate upongeomorphological responses and the risks associated with the two principal theories.

Any qualitative review of options at this stage (prior to detailed SEA) is thereforemade on the basis of information currently available. The extent of environmentalimpacts will continue to raise uncertainties until more detailed assessment is possibleduring the SEA scoping and assessment phases.


SECTION 6

CIVIL, MECHANICAL AND ELECTRICAL ENGINEERINGCONSIDERATIONS


6 CIVIL, MECHANICAL AND ELECTRICAL ENGINEERING CONSIDERATIONS

High level reviews of the primary engineering considerations have been undertakenfor each of the options. The purpose of this review is to identify any technical issueswith the scheme designs which may affect their technical feasibility. Many of theschemes use similar methods and technologies, albeit applied in different locationsand to different scales. Some use more novel technologies which are beingdemonstrated at relatively small scales but not in tidal range applications. Sometechnologies are at conceptual stage and have not been demonstrated at full scale.

The form of the civil, mechanical and electrical engineering technologiesincorporated in each scheme is appraised and key technical risks and issuesidentified. These include susceptibility to varying ground conditions, adaptabilityfor rising sea level and durability by design.

Navigation issues have focused primarily on the provision of appropriately sizedlocks within the barrage options.

Turbine and generating equipment proposals are also discussed. Most are largelybased on conventional hydropower equipment, the exception being the tidalcurrent turbines utilised in the Tidal Fence and the novel proposals for the TidalReef.

Electric grid connection and requirements for the reinforcement of the grid havebeen examined and grid reinforcement costs assessed at a high level.

6.1 Civil Engineering

6.1.1 Barrage Construction

Embankment Construction

B1, B2 and B3 Barrages

Available designs for barrage schemes include embankment sections based on thetraditional use of materials in a marine environment. For the B3 barrage alignment,the STPG Report 1989 proposed a single embankment formed of a tipped rock controlstructure on the seaward side and an hydraulically placed sand fill on the impoundedside contained by a series of rock mounds (“Christmas tree” construction). Theexposed faces would be protected with concrete armour units (dolos) on the seawardside and armourstone on the impounded side. Dolos units are no longer widely usedbut alternative Accropode units would be suitable. Granular filter layers of stonewould be used throughout.


The crest level adopted by STPG was conservatively set to protect against waveaction. Sea level rise as a consequence of climate change was not allowed for in theSTPG design and the crest height would need to be reviewed in line with current sealevel rise predictions. It would also be reasonably straightforward to design in thefacility to increase the height of the embankment in the future if sea level rise exceedsthe design levels.

The design would be a robust, possibly conservative, form of embankment for B3which could also be applied to B1 and B2. Nevertheless, some issues with theembankment design should be addressed to improve its durability. These include:

a review of the filter layers between the sand and rock control structureswhich should be generously proportioned;a review of the stability of slopes to confirm that temporary factors of safetyare no lower than 1.3 for appropriate soil parameters;a review of crest levels to provide tolerance for climate change.

There would be the potential to rationalise the embankment form for each barrage atdetailed design stage where ground conditions are less challenging. Theembankments for barrage B1 would be founded on more competent rock and gravelthan the embankments for B3.

Being further seaward, the B1 embankments would be more exposed and couldtherefore require higher crest levels and heavier armouring on both the eastward andwestward faces.

The ground conditions along the B2 and B3 embankments are more challenging onthe English side and would likely require significant dredging of at least 2 metres.Along challenging ground conditions, ongoing consolidation and differentialsettlement could lead to operation and maintenance difficulties. There would also bethe risk of scour at the toe of the embankment requiring scour blankets.

B4 and B5 Barrages

The original reports for B4 (MRM Partnership in association with AV Hooker – TheHooker Barrage1990) proposed an embankment built in three metre lifts, with ahydraulically placed sand fill core contained by a series of rock mounds on both sides.Both faces would be protected by rock armour. A scour blanket is provided in thesection.

This is a reasonably simple embankment form which could be applied to barrages B4and B5. Embankment construction for B4 and B5 would be less challenging than forthe more seaward barrages as the inter-tidal rock outcrops and sandy sediments atB4, and the sands at B5, provide reasonably good foundations for the embankments.Also, the embankment construction would be substantially above mean low waterspring tide and therefore could be constructed in the dry.


Some issues with this embankment design should be addressed to improve itsdurability. This would include:

a review of the protection against wave action;a review of protection against wave and current action during construction;a review of crest levels to provide tolerance for climate change.

Key delivery risks for embankments of all barrages is the availability of large volumesof rock which could impact on the market and may require a dedicated source. Sandfill would also be dependent on the availability of dredging plant which is currentlyvery limited in the UK. Dredging costs are sensitive to fuel costs. The larger B1, B2and B3 barrages are more susceptible to these risks.

Caisson Construction

B1, B2 and B3 Barrages

The 1989 STPG Report "Severn Barrage Project - Volumes III A and III B - CivilEngineering" provides a comprehensive review of the Civil Engineering andGeotechnical requirements of the B3 Cardiff to Weston barrage. Although the reportwas written nearly 20 years ago, and construction techniques have advanced in thoseyears, it is considered that most of the issues raised and conclusions reached are stillvalid today, and the report can be used as a basis for determining the viability of theB3 Cardiff to Weston barrage scheme and applying these to the B1 and B2 barrages.Similar principals could also be applied to the F1 tidal fence proposal subject to amore thorough understanding of the fence configuration. There are however someaspects of the proposals which need to be reviewed due to the passage of time, or forother reasons.

The B3 barrage would consist of a continuous line of reinforced concrete caissonsstretching across the estuary and three lengths of rock-armoured embankment.There would be 175 massive caissons up to 80m square in plan and up to 45m inheight. 54 of the caissons would contain turbines and 46 would contain sluice gates.The B1 and B2 barrages would require caissons of relatively similar scale butcorrespondingly larger numbers relative to their longer lengths.

Rock exists along the length of the B1, B2 and B3 barrages at, or close to the surface ofthe bed of the estuary. The surface rock is usually weathered but sound rock exists atlower levels, varying between about -20m AOD and -35m AOD along the B3alignment. The proposal would be to expose the sound rock by dredging a trench inthe weaker overlying layers of rock along the length of the barrage, and to overlaythis with a mattress of crushed rock on which the caissons would be founded. Therock mattress under each caisson would grouted up immediately after that caissonhas been installed.


The barrage structure would consist of a series of abutting cellular reinforced concretecaissons. The caissons could be constructed in dry dock, floated out to their locationon the barrage, lowered onto the pre-prepared foundations and ballasted with sandfor stability.

Following a high level review of the STPG caisson proposals, the following key issueshave been identified which require more detailed study:

The STPG report proposed seven dry docks to accommodate the simultaneousconstruction of several caissons for the B3 barrage and it is reasonable toassume similar infrastructure requirements for B1 and B2. The construction ofthese dry docks would be a major component of the whole barrage schemewhich would depend on the viability of their construction. Furtherconsideration of the form and location of the dry docks will be required if anyof these schemes are shortlisted. This should include consideration of issuesof draught required for caisson stability which will affect the size of the drydocks. Consideration should also be given to the particular requirements fordeep caissons;Several different measures are available for preventing deterioration of thecaissons with varying effects on maintenance requirements and initialconstruction costs. Some refinement of these options should be carried out toimprove certainty of caisson cost;Consideration should be given to simplification of the caisson design withoutincreasing caisson weight or incurring loss of facility. Recent developments incomputer aided design should facilitate such refinement;Updated consideration should be given to shipping impact forces and theopportunity to link caissons to improve resistance to impact;Consideration is required to the effects of climate change on caisson height,including how measures might be designed in for the future adaptation ofcaissons to deal with sea level rise and associated increase in wave heights andstorm surges.

B4 and B5 Barrages

The 1990 Report on B4 provides an overview of the caisson requirements for the B4inner barrage. Although the report was written nearly 20 years ago, and constructiontechniques have advanced in those years, it is considered that most of the issuesraised and conclusions reached are still valid today, and the report can be used as abasis for determining the viability of the B4 inner barrage scheme and applying theseto the B5 Beachley Barrage. There are however some aspects of the proposals whichneed to be reviewed due to the passage of time, or for other reasons.

The main structural components of the B4 barrage are as follows:

In-situ sluice caissons located on the Welsh rock platform founded onbedrock;


Four sluice caissons placed on excavated rock foundations where the bed levelis too deep for insitu construction;13 turbine and sluice caisson, and 2 turbine only caissons; sluices whereprovided are located at high level (which helps to prevents heavier sedimentsfrom being carried into the basin on the incoming tide) and the turbines arelocated at low level;Two plain caissons.

Following a high level review of the original caisson proposals, the following keyissues have been identified which should be the focus of more detailed studies forshort listed options:

The original report suggests that the dry dock for the caisson constructioncould be located in the Northwick deep anchorage upstream of the barrage.This recommendation was made before the Second Severn Crossing was built.It is considered that floating the caissons through the navigation span of thenew bridge would be ill-advised. The Second Severn Crossing is designed forimpact from ships up to 10,000 dwt (or 6000 dwt Class 1 ice- strengthen). Theproposed caissons are likely to have 10 times the mass of 10,000 dwt vesseland as they are far more rigid than a steel ship the impact force would be of ahigher order of magnitude than the impact force for which the piers of theSecond Severn Crossing have been designed. An impact between a caissonand the main pier of the Second Severn Crossing would almost certainly resultin the collapse of the main spans of the bridge, and, however carefully thecaissons are moved, the risk of an impact is unacceptably high. The dry dockor docks for caisson construction therefore need to be located downstream ofthe bridge for the B4 Inner Barrage where a deep water channel exists (or canbe dredged) out into the main navigation channel.Several different measures are available for preventing deterioration of thecaissons with varying effects on maintenance requirements and initialconstruction costs. Some refinement of these options should be carried out toimprove certainty of caisson cost;Updated consideration should be given to shipping impact forces, takingaccount of the shipping sizes that are permitted to pass beneath the SecondSevern Crossing;A review of the relative merits of steel and concrete caisson construction,together with a cost comparison at an appropriately high level;Consideration is required to the effects of climate change on caisson height,including how measures might be designed in for the future adaptation ofcaissons to deal with sea level rise and associated increase in wave heights andstorm surges and associated increase in wave heights and storm surges.


6.2 Lagoon Construction

L2 Fleming Lagoon Wall Construction

The wall enclosing the Fleming Lagoon consists of a typically 11 metre high by 13metre thick double- leaf gravity wall. The core of the wall consists of "dredgedmaterial and possibly imported material such as clean construction and demolitionwaste products". The core is retained by two 500mm thick vertical reinforcedconcrete slabs. The slabs which are 6m wide are precast and monolithic over the fullheight of the wall (14m). The slabs on opposite sides of the core are joined bydifferent methods depending on the ground conditions encountered. These optionsare described in the Table 6.1 below:

FlemingWallOption

Description Example Areas of Use

1A Twin 11m high panelsecured together with tierods (no anchors)

Good ground conditionssuch as exposed shallowrock, fill must remain

1B Single 11m and 14m highpanels secured togetherwith tie rod and 3m anchoron one side (ie 14m)

Good to Moderate groundconditions such as weakerexposed rock, fill mustremain dry unless anchorsare designed to providesuitable stability which mayrequire prestressing orsubstitution with piles

1C Twin 14m high panelssecured together with tierods and 3m anchors' onboth sides

Moderate groundconditions such as exposedweak rock, fill must remaindry unless anchors aredesigned to provide suitablestability which may requireprestressing or substitutionwith piles

2A Twin 11m high panelsecured together with PCbraces (no anchors)

Moderate groundconditions

2B Single 11m and 14m highpanels secured togetherwith PC braces and 3manchor on one side (ie 14m)

Moderate to poor groundconditions


FlemingWallOption

Description Example Areas of Use

2C Twin 14m high panelssecured together with PCbraces and 3m anchors onboth sides

Poor Ground Conditions

3A 11m high box caisson withno anchors

Poor Ground Conditions inexposed areas

3B 11m high box caisson withsingle row of anchors

Poor Ground Conditions inexposed areas

Each of these proposed wall constructions has their own structural viability and costs.Their use would vary, dependant on the ground conditions encountered within theWelsh Grounds. Although in general the proposals are all viable, stability for the tierod solutions are dependent on whether the fill within the wall can be kept dry orwhether it will become saturated by water ingress between the precast wall units andfill. Saturation of the fill causes buoyancy uplift within the fill which reduces thestability of the structure. If it can not be guaranteed that the fill will remain dry,which in practice is implausible, the anchors would need to be designed to providesuitable stability which may require pre-stressing or substitution with piles.

Given the diversity of the methods of construction of the wall the proposed range ofsolutions are likely to be able to meet the requirements of the varying groundconditions within the Welsh Grounds.

Further consideration should be given to the level of sea level rise and associatedincrease in wave heights and storm surges which the wall construction shouldaccommodate. As a minimum, the wall should be designed for current predicted sealevel rise over the design life. However, it is also noted that unlike traditionalembankment and caisson construction as proposed for the barrages, it would not bestraightforward to design in the facility to increase the wall height in the futureshould sea level rise exceed the design level.

Further consideration is also required on how to achieve closure of the lagoon withthe proposed wall panel construction. High velocities will occur through the gaps asthe lagoon approaches closure and it is questionable whether the partially filled wallpanels at the gaps will remain stable under these conditions. Erosion caused by thevelocities through the gaps will increase the risk of instability. Therefore, at theposition of closure the wall units may need to be replaced with rockfill embankments,constructed on extensive bed protection if the embankments are to be constructed onsand.


Other areas of concern that need to be addressed during further development of thiswall concept are:

The wall height may have to be higher than currently proposed to allow forvarying ground levels and varying ground conditionsPotential failure of large section of structure if a single panel failsRisk of damage and failure should the structure be hit by shipping vessel

Consideration will also need to given to the durability of the structure in order tomeet the 120 year design life requirement, in particular the potential failure of joints.

Embankment Construction for Lagoons

Section 3 listed the submissions in response to the Call for Evidence which related tolagoons within which were a variety of forms of construction which could be appliedto the L3 land connected lagoon concept. In addition, lagoons could also beconstructed of traditional marine embankment or wall construction such as has beenapplied in the designs available for the B3 and B4 barrages. These various forms areconsidered below.

Traditional marine embankment construction

A traditional form of embankment, based on the barrage proposals describedabove, could be applied to lagoon construction. The embankment form wouldvary along a lagoon embankment with the varying level of exposure andvarying ground conditions. Development of such a design would need to takeaccount of similar issues to those described for the barrages. Lagoons requirelonger lengths of embankment per volume impounded than barrages and it isconsidered that the application of this form of wall would be economicallyunfeasible.

Halcyon Pile Supported/Modular Barrier Construction

The proposed Halcyon construction consists of a line of "mini-caissons" spanningbetween "support columns" at 20m centres. The concrete panels are seated onvertical piles. The support columns consist of a combination of vertical andraked piles and a fabricated structure of steel tubes through which the piles aredrilled and grouted, and to which the mini-caissons are attached. The mini-caissons are elliptical in plan, 20m long and 4m wide at the thickest point. Thewalls of each unit are 300mm thick with a reinforced concrete base. Each 5mdeep caisson would be floated out to its required location, guided into positionby the support column, and sunk on top of the previous segment, ensuring thateach joint is sealed. The support column structure would be also fabricated onshore and floated out to site where it would be accurately positioned. Prior topile drilling, the tubes act as "legs" for the structure.


The application of this form of construction to lagoons requires furtherconsideration of the following potential issues:

It is anticipated that the life of the structure is only 60 years with anextension to 120 only by significant replacement of major components ofthe structure including a significant quantity of new structural steelwork.

As a minimum, the wall should be designed for current predicted sealevel rise and associated increase in wave heights and storm surgesover the design life. However, it is also noted that unlike traditionalembankment and caisson construction as proposed for the barrages, itwould not be straightforward to design in the facility to increase thewall height in the future should sea level rise exceed the design level.

Further consideration is also required of the wall detail at the positionsof lagoon closure where high velocities through the gaps as the lagoonapproaches closure are likely to increase pressures on the wall andcould lead to erosion of the bed.

Raked piles will prove to be a hazard to vessels and will be vulnerableto damage from shipping impact and therefore require navigationroutes with sufficient clearance from the structure.

Any failure to seal any joint within the structure could lead to internalstresses, in particular it will be important to seal the joint between theunderside of the bottom caisson and the seabed in order that erosionbeneath the structure does not occur. Halcyon's current proposalincludes the use of geotextiles and rock fill to ensure this, but statesthat "seepage need not be entirely eliminated", this would need to beresolved, possibly including testing.

There is no vehicular access along the top of the wall and no provisionfor inspection, maintenance or the replacement of turbines or sluices.Therefore, all access for inspection and maintenance would be from thesea. The maintenance regime would therefore need to be appraisedand allowed for in the whole life costing.

Application of the construction technology in deeper water wouldrequire piles of up to 100m length, projecting 25m in front of the wall.The feasibility of installing the large number of piles of this type needsfurther review. Given the engineering and maintenance difficulties withthe deeper proposal, significant changes would be required in order toconsider the use of this technology in these deeper areas. Subject to theoutcome of such a review, the proposals are only considered suitable forshallower wall construction provided there is suitable resolution of theabove issues.


Consideration is required on how the concept is fitted onto the sea bedwhen the bed is of varying depth.

Consideration is required to the effects of downwash from large waveswhich could require extensive erosion protection.

Rubicon Marine Scheme

The Rubicon Marine submission proposes a structural solution to theconstruction of lagoons which comprises box structures fabricated using acomposite of glass fibre reinforced panelling reinforced with a mesh constructedof recycled rubber coated bead hoops sourced from disused tyres. The boxeswould be filled with dredged material seated on a level dredge-filled geotextilebase. The boxes could be constructed from the seabed or founded on anembankment placed below water. This is an embryonic technology which wouldneed to be subject to further research and development, including prototypingwithin a marine environment, prior to application in tidal energy context.

Tidal Electric Limited Geotextile Reinforced Embankment

The TEL submission is based on an embankment structure comprising of looserock, sand and gravel with a core of fines (contained in geotextile bags) andclad with appropriately sized armourstone on the seaward side and turfreinforced matting on the basin side. It is a lower cost form of embankmentthan proposed for barrages and is likely to incur a different level ofmaintenance liability. The principal features of the TEL embankment whichdifferentiates it from barrage embankments are its more steeply sided slope onthe lagoon side, its narrow 3m crest width and lower crest height which wouldbe low enough for the embankment inner core to be overtopped at times.There are a number of issues with the design which would need to beaddressed in further development of the embankment design:

The design is susceptible to varying ground conditions and suitedonly to founding on rockhead. Where less competent foundingconditions exist, the side slopes would need to be slacker and theembankment founded on a granular scour blanket. In the absence ofsite investigation data, the proportion of the embankment that wouldbe founded on rockhead is difficult to estimate;Adequacy of the narrow crest width for anchoring of geosyntheticerosion control;Durability of the turf reinforced matting on the basin side, giving dueconsideration to the potential for vegetation only to becomeestablished over a narrow fringe around high tide level, which wouldbe vulnerable to wave induced erosion; hard erosion control should beconsidered as a more feasible alternative;


Type and availability of fill for geotextile filled tube construction;Sealing of gaps between the filled geotextile tubes to provide for waterretention;Anticipated design life and maintenance requirements; health andsafety implications would prohibit inspection and maintenance workfrom the surface of the embankment and all access would be from thewater;Durability during construction to prevent loss of material during hightides;The effects of climate change on embankment height, including howmeasures might be designed in for the future adaptation ofembankments to deal with sea level rise and associated increase inwave heights and storm surges.

Taking account of the above issues, an updated version of the TEL design hasbeen developed for the purpose of this study which could be applied to thelagoon schemes on sandy or rocky founding conditions. It is not consideredappropriate to apply a reinforced embankment on a soft foundation as theembankment would be susceptible to instability. The updated version of theembankment includes a 5m wide crest width sufficient to anchor the geotextilereinforcement at the crest and suitable for access, employs slacker side slopes(1: 2.5 on the basin side and 1:2.5 on the sea side) to ensure sufficient factors ofsafety against instability, employs hard erosion control on the basin side, andan unreinforced scour blanket on a sandy foundation.

It is understood that the TEL lagoon concept is not intended for constructionin water deeper than 5 metres below chart datum and a reinforcedembankment does not tend to be suited to deeper water applications. Deeperapplications have been considered for the purpose of estimating the cost aslagoons of the sizes included in the long list are located in deeper water oversome lengths. If an offshore lagoon concept is shortlisted, it will be necessaryto review the lagoon alignment to optimise the performance of the lagoon interms of embankment construction cost and energy yield. This optimisationcan also include a further review of crest widths and side slope gradients.

Further consideration is required on how to achieve closure of the lagoon witha reinforced embankment. High velocities will occur through the gaps as thelagoon approaches closure and it is questionable whether the integrity of theexposed ends of the reinforced embankment at the gaps can be preservedunder these conditions. Erosion caused by the velocities through the gaps willincrease the risk of instability and loss of material. Therefore, at the positionof closure the reinforced embankment may need to be replaced with rockfillembankments, constructed on extensive bed protection if the embankmentsare to be constructed on sand.

Further understanding of the alternatives to traditional marine embankmentconstruction, and resolution of issues arising from reviews of the alternatives,


is required to inform estimates of the cost of lagoon construction of theseforms.

L3e(i) and L3e(ii) Bridgwater Bay Offshore Lagoons

Alignment details have been made available by TEL for offshore lagoons just prior tothe conclusion of the options analysis. Prior to its receipt, a review was carried out ofthe potential for an offshore lagoon at various locations including those listed in theTEL submission. To enable a fair comparison against other schemes and in responseto the plan objective to deliver a strategically significant supply of renewable energy,the smallest lagoon considered in the review was 50km2. A limiting factor in thefeasibility of each location is the principle that an offshore lagoon should avoid as faras physically possible any impact on the inter-tidal zone whilst keeping clear of thenavigation routes to the commercial ports. Lagoons constructed close to the shorewould effect hydrodynamic induced changes between the lagoon and the shorelinewhich would be likely to adversely impact habitats and coastal defences. Theconclusion of the review was that Bridgwater Bay offers the optimum location for areasonably sized offshore lagoon. For the purpose of this study, two Bridgwater Baylagoons have been considered of 91km2 (reflecting the largest of the TEL submissions)and 50km2 (similar to the smaller land connected lagoons). A review of the TELlagoon alignments has not changed this conclusion.

Any of the forms of construction described above for the L3 land connected lagoonscould be applied to the L3 offshore lagoon subject to resolution of the issues identifiedabove.

6.3 Tidal Fence Construction

The proposed tidal stream systems would be surrounded by a duct and the ductedturbine mounted between two gravity base foundation structures. If deployed at theCardiff to Weston location, the channel above the turbines would be blocked bymodular concrete or steel flow barriers. Due to the limited design informationavailable for the Fence, it is not possible to further appraise the civil engineeringconstruction proposals.

6.4 Tidal Reef Construction

The main civil engineering elements of the Reef are the foundations for the modularturbine units. These would be founded on the sea bed. In comparison to barragecaissons, they would be smaller as they would be subject to a smaller two metredifferential head. The foundations will house service tunnels and cable ducting.Information from Evans Engineering suggests that the foundations might be piled butgravity structures are likely to be less expensive. Due to the limited design


information available for the Tidal Reef, it is not possible to further appraise the civilengineering construction proposals.

6.5 Navigation Issues

Overview

The ports in the estuary and the services they support are an important part of thelocal and regional economy, and are responsible for handling around 3% of the UKtrade. It is estimated that the Bristol and South Wales ports generate over 15,000 jobsbetween them. Navigation effects have the potential to hinder the commercialviability of the ports within the Severn Estuary.

It is recognised therefore that one key objective of the Strategic EnvironmentalAssessment will be to avoid significant impact on the ports and on the vesselstransiting the estuary. This section considers the issues in terms of the likely effect onthe construction and operation of the long listed schemes.

Structures Requiring Locks Downstream of the Ports of Bristol and CardiffMinehead to Aberthaw Barrage (B1), Hinkley Point to Lavernock Point Barrage (B2),Brean Down to Lavernock Point Barrage (B3), Severn Lakes Scheme (U1) and TidalReef (R1)

Proposed Shipping Transportation in the EstuaryThese options are downstream of many of the large ports within the Severn Estuaryincluding Bristol, Cardiff and Newport. The construction of such a structure wouldchange the way shipping travels both within the Estuary itself and through thebarrage. The previously published proposals for the B3 barrage incorporate two locksystems. One on the northern side, close to Cardiff, would become the main shippinglane, and a smaller lock would be provided on the southern side of the barrage,designed for smaller craft. The twin locks as originally published would only havesufficient capacity to allow large ships of around 275 metres in length.

Ship Sizes and LimitationsLarge ships of the type visiting the port facilities within the Estuary also transportgoods around the world. One of the main limitations on the size of these ships is thecurrent limitation through the Panama Canal. This bottleneck has led to the size ofship passing through here being limited to “Panamax” size. However the widening ofthis canal will enable a larger class ship known as the “Panamax II” to pass throughand therefore will become more prominent in ship transportation. It is proposed thatany barrage or similar barrier placed across the estuary includes a lock suitable tocarry a Panamax II class ship. The internal measurement for this lock would need tobe at least 427m long, 55 metres wide and have an available draught at all times of18.3 metres. This compares with the available lock size at Portbury dock of 366m longand 43m wide. It is also known that Port of Bristol wish to develop a deep water portfacility at Avonmouth and cater for Ultra Large Container Ships (ULCS) which have amaximum size of 381m long, 57m width and a draught of 14.5m. Port of Bristol have


requested that the locks are able to cater for ships up to 500m in length and 75m inwidth with an available draught of 18.3 metres and this has been reflected in therevised configuration and proposed costings for these potential barrage options.

Tidal Range and Depth of Water

The impoundment of the estuary would also alter the tidal range, speed of waterflows, and as a result effective depth of water within the estuaries shipping lanes. Areduced tidal range will increase the available depth of water the majority of the time.An exception to this is the reduction in the available depth of water at high tide. Thereduction is currently envisaged to be up to 1m for spring tides. Other risks to thelong-term use of the estuary for shipping could come from the deposition of sand andsilt within the channel due to the lower velocities of water within the main channel.Sufficient modelling work would have to be carried out to ensure that any barrageproposals ensure sediment build-up was within acceptable limits.

Navigation Summary

In order to minimise the negative effects and maximise the positive effects of thebarrage a number of issues should be incorporated in future stages of this study.

Specification of sufficiently large locksStudy of the sediment deposition and water velocity within the EstuaryStudy of the effect on the tidal range and the available water depth for the mainchannels and ports.

Further consultation will be undertaken with the development of the proposedshortlist schemes to further study these and other impacts of the change in regime onnavigation within the Estuary.

Structures Requiring Locks Upstream of the Ports of Bristol and Cardiff ShootsBarrage (B4) and Beachley Barrage (B5)

Proposed Shipping Transportation with the Estuary

These barrages are just downstream of the Second Severn Crossing and are upstreamof the main Estuary ports of Bristol, Cardiff and Newport. The ships travellingthrough this barrage will be travelling to/from ports in the areas such as Gloucester,Sharpness and Chepstow. It is envisaged in this barrage that a single twin lockfacility would operate within the “Shoots” channel as this is the only part of theestuary with sufficient depth of water at all parts in the tide cycle to ensure that shipsare able to pass through the locks. The current proposal within the Shoots Barrageenvisages a large lock to allow ships of up to 200m in length, a width of 37.5m and adraught of 10.5m.


Ship Sizes and Limitations

Since the conception of the Shoots proposal the Second Severn Crossing (SSC) hasbeen undertaken and this has placed limitations of the type and size of shippingpassing through and upstream of this bridge. The SSC was constructed with arestriction that a braced ship of no larger than 6,500dwt (Ice Class 1AS) would passunder it. These restrictions are set out in detail within the New Severn Bridge(Restriction of Navigation) Regulations 1993 (S.I. 1993 No 190). Any collision betweenthe bridge and a ship larger than this could cause serious damage to the bridge. Assuch the size of the lock facilities within the Shoots Barrage should be sized to caterfor this maximum size. It is therefore recommended that the lock size be reducedfrom the 200m by 37.5m by 10.5m to a smaller 175m by 20m with adequate depth toallow a vessel to navigate through Sharpness Dock lock with 6.5m draft at high water.

Tidal Range and Depth of Water

The impoundment of the estuary at this point would also alter the tidal range, speedof water flows, and, as a result, effective depth of water upstream of the barrage, andhave a minor effect downstream. The reduced tidal range will increase the availabledepth of water the majority of the time. An exception to this is the reduction in theavailable depth of water at high tide. Other risks to the long-term use of the estuaryfor shipping could come from the deposition of sand and silt within the channel dueto the lower velocities of water within the main channel. Sufficient modelling workwould have to be carried out to ensure that sediment build-up was within acceptablelimits.

Navigation Summary

In order to minimise the negative effects and maximise the positive effects of thebarrage a number of issues should be incorporated in future stages of this study.

Specification of correctly sized locksStudy of the sediment deposition and water velocity within the Estuary

Further consultation will be undertaken with the development of the proposedshortlist schemes to further study these and other impacts of the change in regime onnavigation within the Estuary.

Non Barrage Options (L2 and L3 Lagoons, R1 Reef and F1 Fence Options)

F1 Fence

Tidal fence options would not block the transit of vessels. Therefore, they would notaffect the tidal regime as significantly as a barrage and would be unlikely to causesignificant issues from changes in salinity. However, they may still introduce issues


relating to current velocity and estuary morphology. These would require furtherdetailed consideration and modelling before the severity of impact can be judged.

In relation to the F1 fences, the size of the opening for the shipping channel andmeasures necessary for safe navigation through the opening require detailedconsideration and an assessment of the risk of collision with the fence structures.Other issues vary in scale depending upon location but it is anticipated that tidalfences would be likely to have the following effects:

Reduction in tidal range and flow speeds of around 5%. This would result inreductions in the extreme tidal levels of 2.5% of the tidal range. Reductions inhigh tide levels have an impact on the upstream ports unless mitigated throughreduction of lock sills

Accelerated flow speed through the shipping channel would have an effect onshipping movements in the estuary. Between Cardiff and Weston, the meanspring peak flows in the shipping channels are naturally of the order of 6kts, sothe predicted effects would be an increase of 2kts over the existing currents. Theproposed channel in the fence, at 400m wide would represent a constriction forthe largest ships to use the estuary and would probably mean that shippingmovements would be exclusively upstream on the flood tide, and downstreamon the ebb. In particular there may be increased travel times and constraints onscheduling for shipping to the ports of Bristol and Cardiff.

R1 Reef

The Reef incorporates rotating modular turbine units that siphon the flow of wateracross the turbines. These rotating modules can be opened and closed to allowpassage of vessels without the need for locks. Also, the Reef would not affect the tidalregime as significantly as a barrage and would be unlikely to cause significant issuesfrom changes in salinity. However, it may still introduce issues relating to currentvelocity and estuary morphology especially in the region of the openings for vesselpassage where accelerated flows should be expected. These would require furtherdetailed consideration and modelling before the severity of impact can be judged.

In a similar manner to the F1 fences, the size of the opening for the shipping channeland measures necessary for safe navigation through the opening require detailedconsideration and an assessment of the risk of collision with the reef structures. TheReef would also be likely to have the following effects:

Reduction in tidal range and flow speeds with a possible decrease in high waterlevel of around one metre and a similar increase in low water level. Reductionsin high tide levels have an impact on the upstream ports unless mitigatedthrough reduction of lock sills

Accelerated flow speed through the shipping channel would have an effect onshipping movements in the estuary. The proposed opening in the Reef would


represent a constriction for the largest ships to use the estuary and wouldprobably mean that shipping movements would be exclusively upstream on theflood tide, and downstream on the ebb. In particular there may be increasedtravel times and constraints on scheduling for shipping to the ports of Bristoland Cardiff.

Lagoons

A land connected lagoon enclosing Bridgwater Bay would require a small ship lock toenable navigation on the River Parrett.

Other land connected lagoons and the offshore lagoons have the potential to affectcurrents and water levels within the estuary though these effects will be much smallerthan the effects of barrages, fences and the reef. Detailed modelling is required toquantify these effects.

6.6 Adaptability for Sea Level Rise

Any tidal power development scheme should be designed to tolerate sea level rise atleast in line with the current guidance existing at the time of the design development.Current guidance predicts sea level rise up to one metre in the next one hundred yearsbut predictions of much more significant sea level rise of several metres have also beenput forward. For reasons of economy, it is not anticipated that a scheme would bedesigned to tolerate estimates of sea level rise above current guidance within thedesign life nor the potential for future sea level rise beyond the intended design life asthe benefits may either not be realised or would not be expected to be realised for sometime. Therefore, a consideration in the design of a tidal power development is how thescheme can be designed to be adaptable in the event sea level rise exceeds the levelallowed for in the design.

Designs submitted for the L2 lagoon wall and the design adopted for the L3embankment for the purpose of the cost estimates could not be adapted withoutmodifying the entire length of wall or embankment structures so that a suitable factorof safety is maintained against instability under the increased water pressures thatwould occur in the event of sea level rise. Embankment structures required forbarrages and assumed to be required for the tidal reef would require similarmodification. In contrast, turbine caissons would be determined by the space requiredto accommodate the turbines, gates and ducting and can be designed to be adaptablefor sea level rise without needing as onerous modifications as would be required forembankments. Sluice caissons could be designed to be adaptable for sea level rise butwould require a greater level of initial structural redundancy than turbine caissons.

The tidal reef could be designed to be adaptable for sea level rise but is likely to requiremore onerous modifications and a greater level of initial structural redundancy than


other tidal schemes. This is because the turbine modules would need to be raised andthe foundations would need to be designed and constructed from the outset toaccommodate the increased water pressures which would occur with sea level rise.Similar but probably less onerous issues would be faced with the tidal fences.

In conclusion, barrages would be the most adaptable of all schemes in the event thatsea level rise exceeds the tolerance built into the design as they have the largestproportion of turbine caissons. The larger barrages are also the schemes which providethe greater degree of flood risk benefits due to the protection they would provideagainst surge tides and the greater extent of the reduction in high water level whichthey would cause.

6.7 Turbines and Generating Equipment

Barrage Proposals

A summary of the turbine configurations anticipated for each barrage option isprovided in Table 6.2. It should be noted that these configurations are not necessarilyoptimal for maximum energy yield as no optimisation has been carried out for thepurpose of this study.

OptionNo

Option Name Anticipatedturbineconfiguration

Commentary

B1 Outer Barragefrom Mineheadto Aberthaw

370 x 40 MW 9mdia. bulbturbines

Configuration from theBondi studies (1981)expected to remainappropriate althoughturbine numbers andoutput has been increasedin line with EP57 studyconclusions for CardiffWeston.

Large number of turbinescould over-stretchEuropean and possiblyworldwide manufacturingresources, withconsequential constraintson delivery period and costof supply.

B2 Middle Barragefrom Hinkley to

Total capacity9000MW

Similar to B3 but withadditional turbines along


OptionNo


Commentary

Lavernock Point(Severn Barrageto Hinkley andBrean)

possiblycomprising 225x 40 MW 9mdia. bulbturbines

Steepholm to Hinkley line.

B3 Middle Barragefrom BreanDown toLavernock Point(Cardiff toWeston Barrage)

216 x 40 MW 9mdia. bulbturbines

Configuration from the1989-90 STPG studiesexpected to remainappropriate although use ofdouble regulated bulb unitsrather than single regulatedunits (as previouslyproposed) may providemore overall efficiency andat least 2.5% additionalenergy. Good experiencehas been gained of doubleregulated bulb units at LaRance.


OptionNo


Commentary


30 x 35MW,7.6m dia Strafloturbines

Configuration from 1990MRM report expected toremain appropriate. Offersadvantages over bulbturbines being morecompact and providingconstruction cost savings.A single 20MW 7.6m diaturbine exists at AnnapolisRoyal which has beenreported to operate welland a number of smallerunits have been installed inEurope. However, use ontidal schemes is limited.

B5 BeachleyBarrage

50 x 12.5MW,5.0m dia Strafloturbines

Configuration based on B4in the absence of previouslypublished information

Table 6.2 Barrage Turbine Configurations

Bulb turbines are proposed for the larger barrages because, although more costly thanStraflo turbines, provide the opportunity for flood pumping. Also, only one knownmanufacurer of Straflo turbines is in existence which could constrain availability andaffect cost of supply where larger numbers are required.


Lagoon Options

L2 Russell Lagoon Option

Information submitted by the Fleming Group indicates a nominal capacity of 1250 to1700 MW. Turbine selection by the Fleming Group is the subject of ongoing workand it is understood that between 25 and 34 no 50MW turbines are being considered.0-D and 1-D modelling for the purpose of this study has verified that the requiredcapacity is likely to be towards the lower end of this range. This capacity issignificantly larger than the nominal generation capacity of 945 MW originally statedat the time of the Bondi studies for the same lagoon, which had a slightly longerembankment length. This lesser capacity was based on 21 x 45 MW, 9m units perlagoon. .

It should be noted however that the turbine size is constrained by available depth.Work of the STPG after the original Bondi study resulted in the use of slightly smallerunits, later modified to 40MW for technical and other reasons. An alternativearrangement of 12.5 to 25 MW units may prove to be more viable in this case. Unitsof this size would require a dredged channel to provide sufficient submergence toprotect against cavitation effects with an average dredged depth below existing bedlevel of 5 to 7.5 metres depending on turbine size.

It should be noted that configurations described above are not necessarily optimal forfor maximum energy yield as no optimisation has been carried out for the purpose ofthis study. Energy yields have been determined by 1-D modelling using the latestbathymetric model for the Severn Estuary. Additional energy output could beachieved from the Welsh Grounds if the materials used in construction wereexcavated from within the basin to achieve greater live storage. This is more feasibleat the Welsh Grounds site than other lagoon sites because of the relatively highformation level of the impounding basin compared with the turbine axis level. Thiswould marginally increase energy yield by up to 5%.

The configuration includes 35 to 45 sluice gates at various locations around thestructure. Operation is proposed using only ebb generation because of the 0.6mreduction in head on the flood tide.

L3 Tidal Lagoon Concept

The turbine sizes for land connected lagoons will be constrained by available depth.Turbine sizes may therefore need to be reduced to between 12.5 and 25MW. Asummary of L3 lagoon turbine configurations, based on energy modelling undertakenfor this study is provided in table 6.3 below. Dredged depths of up to 7.5 metresbelow existing bed level will be required to provide sufficient submergencedepending on the turbine size selected.


Lagoon Configuration

L3a Russell Lagoon (English Grounds) 60 x 12.5MW 5.0 m dia bulbunits

L3b Russell Lagoon (Welsh Grounds) 108 x 12.5MW 5.0 m dia bulbunits

L3c Russell Lagoon (Peterstone Flats) 90 x 12.5MW 5.0 m dia bulbunits

L3d Russell Lagoon (Bridwater Bay) 108 x 12.5MW 5.0 m dia bulbunits

L3e(i) 90km2 offshore lagoon off BridgwaterBay

108 x 12.5MW 5.0 m dia bulbunits

L3e(ii) 50km2 offshore lagoon off BridgwaterBay

60 x 12.5MW 5.0 m dia bulbunits

Table 6.3 Lagoon Turbine Configurations

It should be noted that configurations described above are not necessarily optimal forfor maximum energy yield as no optimisation has been carried out for the purpose ofthis study.

Bulb turbines are proposed for the lagoons because, although more costly than Strafloturbines, provide the opportunity for flood pumping. Also, only one knownmanufacurer of Straflo turbines is in existence which could constrain availability andaffect cost of supply where larger numbers are required.

Tidal Fence

The original tidal fence submission (F1a) proposed some 256 no 5 MW ducted tidalstream turbines of 18 metres diameter to deliver a power output of 3.5TWh/yr. Thiswould represent a significant advancement in turbine output capability as currentexperience demonstrates that much lower power outputs are likely to be capable fromthese units.

For example, a similar size prototype turbine recently installed at Strangford Narrowsin Northern Ireland (Seagen) is reported to produce 1.2 MW output, with the use oftwin 16m diameter rotors. Further research would therefore be required to provideevidence to show that by installing a ducting arrangement, the turbine output can beincreased by such large magnitudes. Although ducting may be expected to increasethe specific flowrates somewhat, in practice the operation of the machine is going tobe limited by blade velocity and other factors. Further analysis has been undertaken


(see section 4) and it is concluded that turbines of 1MW are appropriate for theCardiff Weston alignment giving an annual energy yield of some 0.7TWh,significantly lower than the original 3.5TWh.

The proposer has also reviewed the concept and has submitted an alternate proposal(F1b) for the Minehead to Aberthaw alignment comprising 800 1.6MW units with aphased construction programme installing 100 units a year over 8 years followinginitial construction advance works. This proposal is more likely to achieve theclaimed output of 3.5TWh although there are risks, particularly related to currentvelocity distributions within the channel and at different tidal states.

Further detailed work is required to establish the technical feasibility of this optionand the optimum turbine ratings and resulting energy yields. There are also potentialconstruction issues associated with housing the turbines. In particular the ductingarrangement is considered to be vulnerable to hydraulically induced fatigue and dailydistortions associated with the tidal flows and pressure differentials involved,particularly affecting any welded joints. Constructionally, the ducting would mostprobably require to be embedded in concrete, as is done in conventional hydropowerpractice. In addition there are numerous construction issues for the configuration ofthe generators and turbines taking account of the size of the generators which wouldneed to be considered.

The durability of the structures proposed is also a concern and full replacement costsare included in the economic assessment with an asset life of 20 years being used forthe turbines, generators and all electrical equipment..

Other concerns are for the potential of scour:

In the open, coastal, margin.In the shipping channel.

If shortlisted, these issues will need to be considered in more detail with the fullestuary 2-D model, but they are considered briefly below for the Cardiff Westonalignment (F1a).

The tidal fence assumes that velocities in the shipping channel for a spring tide willincrease from 4 knots to 8 knots (2m/s to 4m/s). Neap tide velocities have also beenassumed to increase from 2 knots to 4 knots (1m/s to 2m/s).

Using the July 1981 report, Severn Tidal Power – Two-dimensional water movementmodel study (Hydraulics Research Station, Wallingford report EX 985), to obtainobserved velocities in the estuary, pre-barrage velocites, close to the line of the tidalfence, are approximately 2m/s for a spring tide and 1m/s for a neap tide. .


The following velocities are thus calculated through the channel for heads across thefence:

Head across fence (m) Velocity (m/s)0.5 2.41.0 3.41.5 4.12.0 4.7

From the information received, it is assumed that the tidal fence proposers have, atthis stage, assumed the same velocities through the turbines as through the shippingchannel. This is an optimistic assumption as it is probable that velocities in theshipping channel will be higher, and the velocities in the turbines lower, due to:

Higher velocities occurring in the deeper water areas;The channel providing less resistance to flow on size alone; andThe turbines providing additional resistance to flow.

Navigation issues will therefore need careful review to ensure that shipping will beable to safely pass through the fence.

The other engineering issue with the fence is that of scour. Increasing the tidalvelocity to 4m/s at the shipping channel will greatly increase the potential for scouralong the channel. The structures to either side of the channel will have to be heavilyprotected by rip-rap or similar protection, that will be both large and costly.

‘Open’ areas are proposed at either end of the tidal fence structures, where flow willbe able to pass between the fence and the shore. However, it is likely that the currentvelocity of flow parallel to the shore will be small, and the concentration of the flowwill increase velocities and cause major erosion of the intertidal areas adjacent to thefence.

Tidal Reef

The tidal reef comprises 1000 x 5MW 10m diameter turbines oriented on a verticalaxis and housed within a siphon module which conveys the flow across the reef viathe turbines. The modules are able to be rotated 90 degrees to open the reef andincrease its permeability at times when it is desired to increase the tidal range topreserve habitat and allow passage of vessels. The reef can also be closed to protectagainst surge tides.

The reef turbines are at concept stage and design information is very limited.Prototyping of this turbine technology is required to prove the concept before the reefcould feasibly proceed to full scale deployment. A pilot scheme on a smaller scalewould also help develop the concept and significantly reduce the technology riskassociated with a reef at the outer estuary location.


Procurement and Manufacturing Issues

Installation of a relatively large number of units on one site poses particularprocurement issues. Sourcing options for the bulb units proposed on the variousbarrage and lagoon schemes is likely to be from one of the four major internationalturbine manufacturers capable of producing units of the required size, havingsuitable track record with reference of installed plants elsewhere. Very fewmanufacturers have produced bulb units near 9m diameter, which is considered to beat the limit of current experience. For Straflo units, likewise these would be probablysourced in a number of European locations, with final assembly at the supplier’sworks in Austria and/or Germany.

Design life and maintenance issues

For the fair basis comparison, a design life of 40 years has been assumed forconventional hydropower turbines and generators, after which major refurbishmentwill be required. Routine maintenance of some 4-6 weeks per unit per two years canbe expected, plus 1 weeks forced outage per year. Maintenance would normally becarried out on a rolling ongoing basis in an annual cycle. Maintenance costs would berelatively high at approximately 1.5 x the cost for a conventional hydro plant. Asignificant degree of maintenance would be necessary to carry out long-termmonitoring and replacement of cathodic protection and other corrosion protection ofthe units. Removal and decommissioning aspects will be relatively complex,involving the removal of the main bulb units in situ and significant excavation ofembedded parts.

Electrical and mechanical plant used in projects based on tidal stream technology areanticipated to have shorter asset lives and will require replacement sooner than the 40years for conventional hydropower technology. A life of 20 years has been adoptedfor tidal stream technology.

6.8 Grid Connection and Reinforcement

Overview

High-level estimates for the likely level of network reinforcement required to connectthe generation are included in this section. The network reinforcement works arethose works undertaken by and owned by National Grid, and include all the works toestablish a local connection point to the transmission system, as well as widertransmission reinforcements remote from the local connection point. These works donot include the electrical systems between the generators and the connection point tothe transmission system. The cost of these works is included in Section 8.

For a standard large generator National Grid would build and own a substation in thevicinity of the generating site, and would build the connection from this substation to


the rest of the transmission system. The generator would build and own the electricalsystem connecting their generators into National Grid’s substation.

It has been estimated that the peak power output of the proposed Severn Estuarytidal generation schemes lies between 0.2GW and 14.8GW. Given the magnitude ofthe generation capacity, a connection to the 275kV or 400kV networks, owned andoperated by National Grid, is required.

400kV Network Capacity

The National Grid network in the vicinity of the Severn Estuary is below.

2008/09 Transmission System as at 31st December 2007

National Grid publishes network capacity studies in their Seven Year Statement inorder to indicate the level of spare transmission capacity within each of the 17 zonesthat comprise their network. This information can be used to generally ascertain thelevel of generation that can be connected to the network before major reinforcement isrequired. The proposed generation would be connected into zones 13 and 17, asshown below. ”

400kV Network275kV Network


2008 Generation Connection Opportunities

The studies show that the combined generation capacity available in zones 13 and 17is up to 0.25GW. Further analysis has shown that there have been significantincreases in the capacity of planned generation connections onto the National Gridnetworks in recent years and it is understood that two new reactors are planned atHinkley Point for commissioning around 2017. The effect of other generatingschemes on overall demand will affect the severity of the issue of grid capacity.

From the information published in the 2008 Seven Year Statement, it can beconcluded that significant 400/275kV network reinforcement will be required beforethe Severn Estuary generation can be connected. The degree and cost of the requirednetwork reinforcement will be dependent on a number of factors, but primarily theproposed peak generation capacity.

Grid Connection and Reinforcement Requirements

400kV grid substations would be instated on the Welsh or English shore close to thegeneration. In the case of the barrage schemes with a peak generation capacity inexcess of approximately 5GW, 275kV or 400kV substations are likely to be required onboth shores to facilitate connection into both Zone 13 and Zone 17 of the NationalGrid network.

The detailed grid connection studies from the 1989 Department of Energy reportentitled “Severn Barrage Project, Volume II” stated that for the Cardiff – Westernbarrage:“Approximately 370km of new 400kV line route would be required, plus 75km of line


rebuilt over existing 400kV routes, 150km of reconductoring to increase line capacities and55km of uprating to 400kV of existing 275kV routes. A new 400kV substation would be builtat Seven Springs and reactor coupling would be necessary at eight National Gridsubstations.”

A high level estimate of the grid reinforcement required by each proposal has beenprepared by scaling the reinforcement detailed within the 1989 studies by the peakgenerating capacity of each of the long-listed schemes. National Grid would typicallypay for these works, and charge the regulated cost reflective tariff to the generatingcompany. National Grid would own the assets and earn a regulated rate of return onthe investment, normally over 40 years. Although National Grid would pay for andown the transmission assets, an estimate of overall costs has been factored into theassessment process so that the various options can be compared. The gridreinforcement required is therefore estimated to be as shown in Table 6.5. The highlevel estimate for these works is shown in Table 6.4.

Typical 2008 equipment prices were then used when calculating the total cost.Advances in technology since 1989, such as the use of high capacity GAP conductorsor HVDC systems, have not been considered at this stage. In addition, changes ingenerator capacity will result in step changes to the reinforcement requirement asadditional new plant and circuits are required. Such step changes are not accountedfor in this sliding scale approach.

Option Installed Capacity(GW)

High Level Grid ReinforcementEstimate (£m)

B1 14.8 3,950B2 9 2,400B3 8.64 2,300B4 1.05 280B5 0.625 167F1a 0.256 68F1b 1.280 189L2 1.36 363L3a 0.76 203L3b 1.36 363L3c 1.12 299L3d 1.36 363L3e(i) 1.36 363L3e(ii) 0.76 203R1 5.0 1,300

Table 6.4 High-Level Grid Reinforcement Cost Estimates (Note: Figures for alloptions are provisional and estimates only)


Table 6.5 Grid Reinforcement Works (Note: Figures for all options are provisional and estimates only)

Option B1 B2 B3/U1 B4 B5 F1 F1b L2 L3a L3b L3c L3d L3e(i) L3e(ii)Peak GenerationCapacity (GW)

14.8 9 8.64 1.05 0.625 0.256 1.28 1.36 0.76 1.36 1.12 1.36 1.36 0.76

400kV doublebusbarsubstations:

2 1 1 0 0 0 0 0 0 0 0 0 0 0

New 400kV lineroute (km):

630 390 370 40 30 11 50 60 30 60 50 60 60 30

New 400kV cableroute (km):

17 10 10 1 1 0 1 2 1 2 1 2 2 1

400kV linesrebuilt (km):

130 80 75 10 10 2 10 10 10 10 10 10 10 10

400kV linesreconductored(km):

260 160 150 20 10 4 20 20 10 20 20 20 20 10

275kV linesuprated to 400kV(km):

90 60 55 10 0 2 10 10 0 10 10 10 10 0

Reactor couplinginstallations:

14 8 8 1 1 0 1 1 1 1 1 1 1 1


System studies have not been undertaken at this stage to assess the likely NationalGrid reinforcement requirements. The above estimate should therefore only be usedas a high-level guideline, as the actual amount of grid reinforcement required mayvary considerably, and the grid costs would be recovered through revenues. Itshould also be noted that no land acquisition or consenting costs have been includedin the estimates above.

Equipment lifespan

The electrical equipment required for the generator connection arrangements and forgrid connection has a typical life-span of 40 years although some ancillary plantequipment would likely need to be refurbished or replaced at around 20 years.Control systems are likely to require replacement after 10 to 15 years. Some cablesmay last an additional 20 years before replacement is required.

Further Considerations for Connection to the Transmission System

The proposed generation would impose a significant fault infeed contribution to theNational Grid network. Fault level studies are essential to ensure that fault levels donot exceed switchgear ratings at existing substations.

Transient stability studies detailed in the 1989 Department of Energy report entitled“Severn Barrage Project, Volume II” indicate that for an 8GW barrage, at 60% ofmaximum demand and above, the system would be stable for three phase doublecircuit faults. For demand conditions below 60% it was necessary to restrict thebarrage output. System studies are recommended to verify that the 1989 resultsremain valid.

The GB Security and Quality of Supply regulations state the maximum capacity ofgeneration that can be connected via a single or double circuit. This restriction isimposed in order to maintain system frequency to within a range of 49.5Hz and50.5Hz following a fault that results in a disconnection of generation. Therequirements are entitled ‘Normal infeed loss risk’ and ‘Infrequent infeed loss risk’.These are currently under review, but are presently defined as follows:-

Normal Infeed Loss Risk: This is the level of risk of the loss of power which is coveredover for the loss of a single transmission circuit or busbar. This is set at 1000MW andis to avoid a frequency deviation of greater than 0.5Hz in the long term due to apermanent outage such as a cable failure. In reference to the proposed generation thiswould mean that no more than 1000MW could be connected on a single generationcircuit.

Infrequent Infeed Loss Risk: This is the level of risk of the loss of power which iscovered over the loss of up to two circuits, both on the same double circuit line, innormal operation or the loss of one circuit at the same time as a planned outagewithin the transmission system. This is set at 1320MW and is to avoid a frequency


deviation of greater than ±0.5Hz for more than 60 seconds. In reference to theproposed generation this would mean that generation above 1320MW would need tobe connected by at least 3 transmission circuits to account for an N-2 event.

If the 1000MW/1320MW limits are changed, this would have a significant impact onthe design of the local grid connection works, including those between the generatorsand the point of connection to the transmission system.

For the large tidal generators, there may be restrictions on how quickly the output canbe changed up or down. For example, National Grid normally accommodates rates ofchange of 40-50MW per minute.


SECTION 7

ESTIMATED FIRST YEAR OF OPERATION


7 ESTIMATED FIRST YEAR OF OPERATION

Construction programmes and the estimated first year of operation have been basedon a common preconstruction programme but with varying construction times.Since the publication of Energy Paper 57, shortened construction programmes havebeen proposed for the Cardiff Weston Barrage and the Shoots barrage althoughdetailed work substantiating these reductions in programme is not available. Forthis reason, all options have been compared on a similar basis using the workundertaken in EP57 as a baseline. However, it should be noted that achievement offaster construction programmes may be feasible and this will be reviewed in moredetail during the work being undertaken to optimise the short-listed options. Theopportunity for schemes to deliver energy in phases leading up to full scale poweroutput has been taken into account.

7.1 Overview

For a fair basis comparison, a common pre-construction programme has beenassumed for all schemes on the basis that they are all of a scale and complexity torequire the length of periods for design, environmental studies, EnvironmentalImpact Assessment, consents and permitting as would be required for any very largescale infrastructure project. Schemes of different scales could be prepared for withinsimilar timescales but would require different levels of resource.

The common pre-construction programme is as follows:

SEA Complete April 2010Consultation Complete Dec 2010Environmental Studies and EIA Complete Mid 2012Consents, approvals, agreement and financing in place Dec 2013

Given the detailed studies behind the programme set out in the DOE Report 1989 VolIIIA for the Cardiff to Weston Barrage, this programme is taken as a benchmark forconstruction timeframes. The 2002 reappraisal of the B3 Barrage (ETSU Report NoT/09/00212/00/REP) concluded that the accelerated 6 year programme for the Cardiffto Weston Barrage should be adopted. Subsequent studies reported by SDC in theirreport “Turning the Tide” indicate a shorter construction period of 5 years for OptionB3 but, for the purposes of the fair basis evaluation, the 6 year programme has beenused. Overall construction programmes have been estimated at a high level based ona comparison of the principal quantities of turbines, embankments and caissonsstructures.


7.2 Innovation Risks

The programme set out in 7.1 above does not take account of specific programmerisks relating to innovations in the individual proposals. With the exception of F1, R1,L2 and L3, all proposals are based around relatively traditional civil engineeringdesign and construction. The engineering innovations included in F1, L2, L3 and R1are discussed in section 6.

Traditional methods of construction and operation for a barrage (which can equallybe applied to a lagoon) have been proven by prototypes at La Rance and AnnapolisRoyal. Innovative solutions without such prototypes carry a higher degree of risk toinvestors because of higher uncertainty over such issues as construction methods andprogramme, suitability of materials, durability and maintenance cost, and lost energyoutput. It seems likely that investors will have less appetite for innovative solutionsapplied to a full scale development in the Severn Estuary than more traditionalproven methods, particularly if the financial viability of the proposal is dependent onthe effectiveness of the innovation. Therefore the Tidal Fence (F1) may require asmaller scale prototype development to enhance the conceptual evidence base andconfirm likely energy yields to reduce financial and technology risk which coulddelay the estimated first year of production by several years. In addition,the proposed size and form of ducted turbine requires its own form of validationusing a single prototype before large scale implementation such as envisaged byOption F1. It is therefore unlikely that the fence will be sufficiently developed inreadiness for a 2014 construction start.

As discussed in section 3.7, the embryonic status of the reef concept is such that 10 to15 years may be required for the development of the technology prior to full scaleconstruction in the estuary.

The SDC Report "Turning the Tide" proposed construction of a pilot for tidal lagoons(Options L2 and L3) although the technologies involved in lagoons are similar tothose in barrages, particularly in respect of turbine types and calculation of energyyield. For this reason, comprehensive trials through pilots or prototypes are notenvisaged for lagoons. However, because of the longer embankment lengthsrequired of lagoons compared with barrages, innovative embankment / wallconstruction techniques have been proposed for tidal lagoons to bring the unit costof creating the impoundment structure down. The application of innovativeembankment/wall construction techniques will in themselves require further researchwhich may involve construction of small pilots. There is also the issue ofsedimentation risks associated with lagoons (and smaller barrages) which are morelikely to be determined by mathematical modelling than field trials. The impact ofsuch research on timescales is difficult to estimate accurately but would be lessthan more fundamental proof of concept prototyping


7.3 Construction Programmes and Estimated First Year of Operation

Construction programmes and the phasing of power generation are set out in thissection subject to the innovation risks which are discussed in 7.2 above.

Lagoon options L2 and L3 and the smaller B4 and B5 barrages would deliver full scalepower in the first year of operation.

The larger barrages would deliver power in a phased manner as the installation ofturbines after barrage closure is critical to the programme for delivery of full scalepower.

The 6 year programme for the B3 Barrage provided for approximately 50% outputshortly after barrage closure, increasing to 75% one year after closure and to 100% twoyears after closure. The same phasing has been assumed for barrages B1 and B2.

The full power output of the F1a fence would be achieved in two phases.Approximately one third capacity would be installed after four years fromconstruction start with the remainder installed in the following year.

The full power output of the F1b fence would be achieved progressively over an eightyear period. Based on information submitted by STFG, 100 turbines per year wouldbe installed per year commencing three years after construction starts. An additional100 turbines would be installed per year until the full capacity is installed.

Little design information is available on which to base a construction programme forthe R1 reef. However, it seems reasonable to assume that a reef constructed over asimilar alignment to the B1 barrage would take a similar length of time and an overallconstruction programme of 10 years has therefore been selected. The method ofoperation of the reef would not require its full completion prior to first energygeneration although it would not be able to develop the intended 2 metre differentialhead over the full length of the reef until it is completed. It is assumed that turbineswould be installed progressively along the reef as the structure is constructed and inthe initial phases the reef would capture the energy from the tidal stream passingthrough the reef. It is therefore assumed that until completion of the reef structure,which could occur after 7.5 years construction, the reef delivers energy progressivelyat the same rate as the F1b fence. Thereafter, the reef would ramp up to fullproduction.

Potential construction programmes and estimated first years of operation areprovided in Table 7.1 below.


OptionNo

Option Name Period fromconstructionstart to firstenergyproduction(years)

Estimated Yearof FirstOperation and %of Full Capacity

SubsequentPhasing ofPower Output

B1 Outer Barragefrom Minehead toAberthaw

7.5 years 2022 (50% ) 2023 (75%)

2024 (100%)

B2 Middle Barragefrom Hinkley toLavernock Point(Severn Barrage toHinkley andBrean)

7 2021 (50%) 2022 (75%)

2023 (100%)

B3 Middle Barragefrom Brean Downto LavernockPoint (Cardiff toWeston Barrage)

6 2020 (50%) 2021 (75%)

2022 (100%)


5 2019 (100%) None

B5 Beachley Barrage 4 2018 (100%) None

F1a Tidal FenceProposal(Lavernock toBrean Downalignment)

4 2018 at earliestbut embryonicnature of fencelikely to require

trial (33%)

2019 (100%)

F1b Tidal FenceProposal (outeralignment)

3 2017 at earliestbut embryonicnature of fencelikely to require

trial (12.5%)

12.5% addedyear on yearfrom 2018 to

2024

L2 Lagoon Enclosureon the WelshGrounds (FlemingLagoon)

5 2019 None


OptionNo

Option Name Period fromconstructionstart to firstenergyproduction(years)

Estimated Yearof FirstOperation and %of Full Capacity

SubsequentPhasing ofPower Output

L3a Russell Lagoon(English Grounds)

4 2018 None

L3b Russell Lagoon(Welsh Grounds)

5 2019 None

L3c Russell Lagoon(Peterstone Flats)

5 2019 None

L3d Russell Lagoon(Bridwater Bay)

5 2019 None

L3e(i) 90km2 offshorelagoon offBridgwater Bay

6 2020 None

L3e(ii) 50km2 offshorelagoon offBridgwater Bay

5 2019 None

R1 Tidal Reef 4 2018 at earliestbut embryonicnature of fencelikely to require

trial

0.41TWh addedper year from2018 to 2021when reef‘closure’ is

achieved. Fullpower then

ramped up from50% to 100%

over four years.

Table 7.1 Construction Programmes


SECTION 8

SCHEME COST AND COST OF ENERGY


8 SCHEME COST AND COST OF ENERGY

The estimation of cost per unit energy generated has been undertaken using a fairbasis approach applied equally to all options where sufficient evidence / data exists.This entails the application of a consistent set of unit rates applied to the principalquantities for all options with additional costs covering other elements such asdesign, overheads, ancillary works, grid transmission costs and habitatcompensation, for example.

Reasonably detailed estimates have been prepared for the B3 and B4 barrages andthe unit costs for the main components of these barrages have been applied toproduce high level cost estimates of the other barrages. A high level estimate hasbeen made of the L2 lagoon proposed by Fleming Energy in their submission to theCall for Proposals. High level estimates have also been made of the costs of the L3lagoons based on an assessment of the several forms of construction which could beapplied to the impoundment with the lowest cost solution adopted for thederivation of the scheme costs. High level assessments have been prepared forOption F1 (Tidal Fence) at both the outer and Lavernock to Brean Down positionsand of the R1 Tidal Reef. Insufficient data are available to estimate the costs of theU1 Severn Lakes concept.

A discounted cash flow model has been used which incorporates schemeconstruction costs spread over the timeline of the construction phase (Section 7) andoperation, maintenance and asset replacement costs (derived from section 6) andenergy yields (Section 4) spread over a 120 year design life which has been assumedfor all schemes. Discount rates of 8% have been applied with sensitivity testsapplied at 3.5% and 15%, to bring all values to a net present day value per kWh ofenergy generated. Whilst the assumed 120 year design life would not account forthe potential for some schemes to remain serviceable for longer periods, in practicalterms energy yields and costs beyond 50 years have little impact on net presentvalue for the discount rates applied.

Appendix A contains a detailed breakdown of the scheme cost estimates andcontains the discounted cash flow model.

8.1 Pre-Construction Cost EstimatesCivil Engineering Cost Methodology

A common set of assumptions has been applied to the pre-construction cost estimatesof all schemes as set out in Table 8.1 below:


Item Cost AssumptionProject Management 0.25% of construction costDesign (up to procurement stage) 25% of total design cost (see 8.2)Site Investigation 1.25% of civil engineering construction costEnvironmental Impact Assessmentand Consents

0.3% of construction cost

Table 8.1 Pre-construction Cost Estimates (fair basis assumptions)

8.2 Barrage and Lagoon Civil Engineering Cost EstimatesCost Methodology

The main purpose of the civil engineering cost estimates is to provide a reasonablebasis for comparison between the various long list options. The estimates presentedin this section do not necessarily reflect the optimal cost assessments for specificoptions but are instead derived from the generalised and consistent application ofcost rates across all the options.

A reasonably detailed estimate has been prepared for the B3 Barrage based onapproximate quantities for the civil engineering work derived from informationprovided in Vols 3A and 3B of the DOE Report. Rates and prices have been assessedat 1st quarter 2008 price level. No allowance has been made for future inflationbeyond this date.

The same approach had been taken for the B4 Barrage estimate, however the designinformation is less well developed and the quantities are correspondingly moreuncertain. In order to achieve pricing consistency between B4 and B3, unit rates havebeen taken as those used for B3.

For these options, principal quantities have been estimated for the following items:

PreliminariesCaissons (including casting yards, construction, installation and fit-out works)Embankments (including preparatory works, construction, and fit-out works)Navigation locks (where required)Surface BuildingsAncillary works (for example, navigation modifications, land drainage pumpingstations)

Much less detailed information is available for other long list options and theestimates are therefore inherently less accurate. Estimates for other long list barrageoptions have therefore been based on a comparison between the overall dimensions


of the main civil engineering components and costs attributed in proportion to the B3and B4 estimates as appropriate.

A high level estimate has been made of the L2 Fleming lagoon wall constructionbased on the principal components of the design shown in the Call for Proposalssubmission and following detailed review and subsequent revision by proposers oftheir designs. The estimate assumes that the scheme can be designed to include thelower cost forms of the wall solution (ie. forms 1A and 1B described in Section 6.1).More robust forms of wall will incur an increase in construction cost. A discussion onsome issues over the technical feasibility of the lower cost wall forms is included inSection 6.1 and until these issues are resolved, the L2 cost estimate should beconsidered as a lower bound and treated with caution.

The cost of the L3 lagoons is highly dependent on the technology employed toconstruct the impoundment structure. Therefore, a high level estimate has been madeof the forms of construction considered in Section 6.1 to determine which formsreflect the potential lower bound construction cost of the impoundment structures.Detail of this comparison is included in Appendix A.

8.3 Barrage and Lagoon Mechanical and Electrical Cost Estimates

Turbines and Generators

For the Bulb and Straflo turbines, cost estimates for turbines and generators havebeen developed by both independent review of existing turbine contracts andconsultation with turbine manufacturers. These resulted in cost estimates that werewithin 2% of each other.

For multiple unit bulb turbines of 35 to 40 MW per unit capacity, a cost of £0.676m perMW has been applied consistently for the larger capacity barrages and lagoons.Straflo units, proposed for the B4 and B5 Barrages, are expected to be moreeconomical at £0.611m per MW. These unit costs include delivery, installation,commissioning and contingency.

The turbine and generator costs have been based on the installed capacities estimatedfor this study (as set out in section 6.3).

Turbine and Sluice Gates

Gate costs have been estimated in detail for the B3 and B4 Barrages based on theavailable design information. These estimates have provided a cost per turbine and acost per sluice for each different sluice gate size.

For the other barrages, an estimate has been made of the number and size of sluicegates taking account of the relative live storage volumes and, in the case of the OuterBarrage, taking account of the sluice gate sizes and numbers obtained from Bondi


(1981). The turbine costs have allowed for the number and size of turbines that havebeen estimated for each barrage. For turbines and sluices, the costs per gate derivedfor B3 have been applied to B1 and B2 barrages and those for B4 Barrage have beenapplied to B5 Barrage and the L2 and L3 lagoons.

Transmission and Grid Connection

An assessment has been made of the principal components required between thegenerator terminals and the connections to onshore substations. A full breakdown ofthese costs is contained in Appendix A.

8.4 Tidal Fence Civil, Mechanical and Electrical Cost Estimate

The same principles as apply to barrages have been used to estimate the civilengineering costs of the F1a and F1b tidal fences which have been broken down intodredging and bed preparation, flow barrier construction, turbine foundationmodules. An allowance has also been made for an access bridge. The detail isprovided in Appendix A.

For the tidal fence turbines, research was undertaken of existing on-shore and off-shore turbine/generator costs as well as reference to existing demonstration projectcosts. A figure of £2m per MW of installed capacity has been used in the analyses forthe turbine, gearbox and generator with additional costs on a per unit basis for thecowl and installation. Although not identical, offshore wind turbine equipmentoffers the closest comparator although accurate costs are difficult to predict asmaterial costs have been rising significantly since 2005. Costs of 2.23 million eurosper megawatt (BTM Consult APS 2008) which equates to approximately £1.8m perMW have been reported in 2008 for offshore turbine equipment whilst earlier studies(Sustainable Development Commission Research Report 5 - Tidal Energy CaseStudies, 2007) have used ranges of between £1m and £6m per MW of installedcapacity for equipment and all associated costs. The 1.2MW demonstration turbine atStrangford Lough in Northern Ireland has a reported cost of £12m (all inclusive)which equates to £10m per MW. For this study, the total project cost for the F1b TidalFence is approximately £4m per MW which is significantly less than the StrangfordLough costs (reflecting the large scale implementation) and is the middle range of thecosts bands used in the SDC Research Report.

8.5 Tidal Reef Civil, Mechanical and Electrical Cost EstimateVery little design information is available on which to estimate the cost of a tidal reef.Therefore, a very high level estimate has been prepared and the detail of this estimateis set out in Appendix A. The estimate makes a number of very broad high levelassumptions and approximations. None of these is considered precautionary and theoverall estimate should therefore be treated with caution as it is likely to represent anoptimistic estimate given the level of design information available and the absence of


any prototype or analogue on which to base the estimate. The assumptions are asfollows:

Embankment required as a barrier to flow in the shallower regions estuarynear each shoreline will be equivalent to B1;No navigation lock as such is proposed although the reef structure will requirerotating turbine modules with a longer span than elsewhere on the reef toprovide a navigable opening. There will be costs associated with theseelements but none is included as there is no information available todetermine the quantum;Surface building costs will be the same as B1;The structures which support the turbine and siphon modules and incorporateservice tunnels, cable ducts, access shafts etc and the siphon modulesthemselves which house the turbine generators have been broadly estimatedas 45% of the caisson cost of B1. This is on the basis that for stability thestructure will require 45% of the weight of the B1 structure due to the reducedhead differential. This assumes that the cost per tonne of barrage and reefstructural components, including precasting, transportation, positioning,placing and infilling, are the same. It also assumes that the reef structure is agravity structure and not piled (piled strucutres would be expected to be moreexpensive). This is not precautionary as it does not allow for special factorssuch as the complexity of the movable siphons modules;Turbine generators will be akin to tidal stream turbines and therefore the same£2m per MW rate has been used as applied to the tidal fence. This allows forfabrication, installation, commissioning and for elements required to fit theturbines into the structure. A further discussion on the cost of tidal streamturbines is included in Section 8.4;Grid connection cost will be 34% of the B1 cost pro-rata’d on the basis ofinstalled capacity;The gate cost estimate assumes 2000 gates (2 per turbine), each 10m by 4m tocontrol flow through the siphon and to act as stoplogs for turbine access.Costs have been based on £13,000 per sq. m which is equivalent to B1 and anadditional allowance of £300m for temporary bulkheads during construction.

On the above principles, the overall civil, mechanical and electrical construction costfor the tidal reef is estimated at £15.7m which equates to just over £3m per MWcompared to the £4m per MW estimated for the tidal fence. As stated above, thisestimate should be treated with caution due to the lack of design information and thevery broad assumptions stated above, many of which look favourably on the reef.The confidence behind this estimate is the least of all schemes. It must not beconcluded that the reef concept is more economical than the fence concept as agenerous optimism bias should be added to allow for uncertainty. With the currentlevel of available design information, the estimate could conceivably be at least twicethe £3m per MW estimate but without the application of optimism bias, which hasbeen omitted from the fair basis approach, there is no rationale for making such aglobal adjustment to the estimate.


8.6 Grid Reinforcement

A high level estimate of the grid reinforcement is included in Section 6. These costshave not been included in the scheme cost estimates as National Grid would typicallypay for these works, and charge the regulated cost reflective tariff to the generatingcompany.

8.7 Compensatory Habitat

Guidance on providing compensatory habitat, existing practice and precedent hasestablished that provision should be at a ratio that may exceed 1 Ha of compensatoryhabitat for every 1 Ha of habitat lost (in some cases a ratio of 3:1 has been required).This recognises the uncertainty and risks of establishing a habitat that maintains theecological functions of the habitat that is lost.

This study provides estimates of the cost of providing compensatory habitat at ratiosof 3 Ha for every 1 Ha lost, and at 1Ha for every 1 Ha lost. This acts as a sensitivityanalysis by offering a range of values for each option. It should be noted that this doesnot make any assumptions about an appropriate ratio to apply to the Severn Estuaryand that some compensation ratios have exceeded a 3:1 ratio. At this stage of theassessment it should also be recognised that the basis of this estimating is simplisticbased on area of inter-tidal habitat lost and takes no account of the need and likelycost of other compensatory measures that might be required. The scale of any optionand its potential effect on a European site is unprecedented and could require anunprecedented level of compensation. This creates an additional element ofuncertainty around quantifying and managing the risk and effectiveness ofcompensatory measures which has not been considered at this stage.

The cost estimate for the offshore lagoon at Bridgwater Bay assumes that nocompensatory habitat is required although it should be noted that this is not aprecautionary assumption.

Compensation costs have been provisionally estimated, based on the replacement ofareas of intertidal areas lost under each option through 'managed realignment'. Thisis a simple approach, prior to more detailed investigation, to derive costs for thecompensation of the unmitigated loss of internationally designated habitats andspecies. In practice, managed realignment is very unlikely to be the only approachtaken to deliver compensation measures, but it would almost certainly represent thegreat majority of the cost. The costs have been estimated at £65k per Hectare basedon calculation of inter-tidal areas from the static models that are used in the fair basisassessment of proposals. This cost rate is derived from literature review of the costsof implementing managed realignment schemes to create new intertidal areas (Rupp-Armstrong et al, 2008, CIRIA, 2001) and consultation with Statutory ConsultationBodies. Whilst this rate is in the upper range for managed realignment schemes inthe UK, it reflects the higher cost associated with Natura 2000 compensatory schemesand / or those where a new counter wall of significant length is required. In addition


to the uncertainty of likely cost per hectare, it is also likely that the static models over-estimate the total area of inter-tidal areas lost and that subsequent hydrodynamicmodelling will achieve a more refined estimate of total areas lost through the changedtidal regime.

8.8 Ancillary Works Costs

All options require consideration of ancillary works - works that are necessary as aconsequence of the construction of a tidal power facility to mitigate the impact on dayto day operation of existing assets. These are in addition to any mitigation worksincorporated directly into an energy generation structure such as ship locks, fishpasses etc. Such assets include:

- Modification of port facilities as a consequence of reduced high water levelsand changes in vessel buoyancy

- Navigational aid requirements- Pumping systems at tidal outfalls to allow land drainage discharges that

would otherwise have been prevented from the reduced tidal range- Permanent works for dredging and sedimentation management- Additional flood defence protection from increased erosion due to changed

water levels

At present, these costs are included as a provisional sum for each option with the sizeof provision, for this stage, depending upon the assessed change in water levels foreach proposal. The sums are calculated on a linear scale between £400m for a largeeffect on the tidal range over the estuary upstream of the Outer barrage location to£10m for a small effect on the tidal range over a smaller region.

Client’s promotional costs

Client’s promotional costs, including the client’s project management, have beenincluded in the cost estimates at a rate of 2% of the capital cost.

Exclusions

The following items have been excluded from the construction cost estimates:

Environmental mitigation (except impacted land drainage – see 8.8 above)Historical costs incurred on projectLand and property acquisitionParliamentary costs and public relationsPublic road or rail link across barrage (or passive provision for them)VAT

Contingency and Optimism Bias


A 15% contingency has been applied to the combined net values of the civilengineering works, including gates. For the initial fair basis evaluation, optimismbias has not been applied as there has not yet been an assessment of appropriateoptimism bias specific to each scheme. A consistent application of the 66% optimismbias adjustment recommended in Treasury guidance10 for non-standard civilengineering projects would not affect the selection of options to study further inPhase 2. Cost estimates should therefore not be used as an assessment of the likelyout-turn project cost.

The contingency item should be regarded as a temporary provision subject to theresults of a quantitative risk assessment which should be carried out at a future stagein the study. Once completed, estimates can then be reconciled with Treasuryguidelines.

Construction Cost Estimates

Construction cost estimates (fair basis assumptions) are presented in Table 8.2 foreach long list option before habitat compensation costs.

10 HMT Green Book Supplementary Guidance on Optimism Bias, http://www.hm-treasury.gov.uk/d/5(3).pdf

http://www.hm-/


Option AssessedConstruction Cost

(excludingcompensatory

habitat cost) (£bn)B1 - Outer Barrage from Minehead to Aberthaw 29.0B2 - Middle Barrage from Hinckley Point to LavernockPoint

21.9

B3 – Middle Barrage from Brean Down to LavernockPoint (formerly Cardiff – Weston)

18.3

B4 – Inner Barrage (Shoots) 2.6B5 - Beachley Barrage 1.8F1a – Tidal Fence (Lavernock to Brean Down) 4.4F1b – Tidal Fence (Outer) 6.3L2 – 2008 Russell Lagoon Option (based on Flemingtied panel construction)

3.1

L3a – Russell Lagoons English Grounds 2.6L3b – Russell Lagoons Welsh Grounds 3.7L3c – Russell Lagoons Peterstone Flats 3.3L3d – Bridgwater Bay Land Connected Lagoon 3.0L3e(i) – 90km2 offshore lagoon off Bridgwater Bay 5.8L3e(ii) – 50km2 offshore lagoon off Bridgwater Bay 3.5R1 – Tidal Reef 18.1U1 – Severn Lakes Scheme Unquantified due to

insufficient data

Table 8.2 Construction Cost Estimates (fair basis assumptions)

It should be noted that the fair basis assumptions have resulted in cost estimateswhich are higher than those previously published. This includes the estimatedconstruction cost of the L2 2008 Russell Lagoon which differs markedly from the £2bncost estimated referenced in the Fleming Group submission. Further dialogue hasbeen held with Proposers to reconcile engineering issues that influence cost estimates.

A sensitivity test has been applied during the assessment of options to assess thedegree to which increased ratios of habitat compensation impact the relativedifferences between the options. This is shown in Table 8.3 for all options.


Construction Cost EstimateOptionBased on 1:1 ratioof compensatory

habitat provided tohabitat lost (£bn)

Based on 3:1 ratioof compensatory

habitat provided tohabitat lost (£bn)

B1 - Outer Barrage from Mineheadto Aberthaw

31.0 34.7

B2 - Middle Barrage from HinckleyPoint to Lavernock Point

23.5 26.9

B3 – Middle Barrage from BreanDown to Lavernock Point (formerlyCardiff – Weston)

19.6 22.2

B4 – Inner Barrage (Shoots) 2.9 3.5B5 - Beachley Barrage 2.1 2.5F1a – Tidal Fence (Lavernock toBrean Down)

4.5 4.8

F1b – Tidal Fence (Outer) 6.5 6.9L2 – 2008 Russell Lagoon Option(based on Fleming tied panelconstruction)

3.6 4.4

L3a – Russell Lagoons EnglishGrounds

2.7 3.0

L3b – Russell Lagoons WelshGrounds

4.1 4.9

L3c – Russell Lagoons PeterstoneFlats

3.5 3.8

L3d – Bridgwater Bay LandConnected Lagoon

3.4 4.1

L3e(i) – 90km2 offshore lagoon offBridgwater Bay

5.8 5.8

L3e(ii) – 50km2 offshore lagoon offBridgwater Bay

3.5 3.5

R1 – Reef 18.7 19.8U1 – Severn Lakes Concept Unquantified due to insufficient data

Table 8.3 Construction Cost Estimates for Alternative Amounts of CompensatoryHabitat

A summary breakdown of costs by option for all options (including habitatcompensation at the 3:1 ratio) is shown in Figures 8.1 (large barrage options) and 8.2(smaller options).


Summary of Construction Costs

-

5,000

10,000

15,000

20,000

25,000

30,000

35,000

40,000

B1 B2 B3 R1

Options

Cos

t £m

Habitat CompensationContingencyAncillary CostsM&ECaissonsGeneral Civil WorksPrelims and OverheadsSite InvestigationDesign and SupervsionPlanning and PM

Figure 8.1 Summary Breakdown of Costs for Large Barrages and Reef

Summary of Construction Costs

-1,0002,0003,0004,0005,0006,0007,000

B4 B5 F1a F1b L2 L3a L3b L3c L3d L3e(i) L3e(ii)

Option

Cos

t £m


Figure 8.2 Summary Breakdown of Costs for Smaller Options


Figure 8.3 Summary Breakdown of Costs for Large Barrages as % of Total

Summary of Construction costs as % of Total Cost

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

B4 B5 F1a F1b L2 L3a L3b L3c L3d L3e(i) L3e(ii)

Options

% o

f Tot

al C

ost


Figure 8.4 Summary Breakdown of Costs for Smaller Options as % of Total

8.9 Cost per Unit EnergyMethodology

The costs per unit energy, using a fair basis costing approach are detailed in Table 8.4.The fair basis costing approach includes a number of assumptions which are appliedequally to all options. As such, the costs per unit energy are intended as indicators ofenergy cost differences between options not a reflection of actual cost which will bedeveloped in more detail for short-listed options.


Construction costs are as detailed in section 8.1 and are inclusive of grid connection,and compensation works for land drainage and navigation. The costs are exclusive ofgrid reinforcement costs. The cost per unit energy in Table 8.4 are based onconstruction costs inclusive of high level indicative estimates for habitatcompensation (using a 3:1 ratio) whilst the costs per unit energy in Table 8.5 excludecosts of habitat compensation. Costs per unit energy have been calculated taking intoaccount construction programme (as set out in section 7.2), estimated energy outputand operation and maintenance costs. Costs have been discounted at a rate of 8% andat 3.5% and 15% to assess sensitivity to discount rate. The discounted costs have beencalculated over the full lifetime of the scheme up 2140. This period covers the fullassumed 120 year useful life although the more robust schemes would be expected tohave a useful life of at least 120 years with appropriate maintenance. The effect ofdiscounting causes costs beyond 2140 to have a negligible impact on the assessment.

The assessment assumes that construction costs are distributed evenly over theconstruction period. It also assumes that where there is opportunity to do so,generation is commenced earlier than completion of construction and that output isramped up as turbine and generating equipment is installed and comes on line, as setout in Section 7.

Operation and maintenance costs have been estimated in past studies for Cardiff toWeston and Shoots Barrages as 1.25% and 1.75% respectively. The differencerepresents an economy of scale and these percentages have been applied to otheroptions based on their comparable scale. The costs include staff costs, routine minorcivil mechanical and electrical maintenance, consumables, business rates, andinsurances.

These allowances do not include major maintenance liabilities. For the purpose ofcalculating the cost of energy, all barrage and lagoon options have been assumed tohave a major maintenance intervals of 40 years. The tidal fences have been assumedto have major maintenance intervals of 20 years as tidal stream technology is expectedto have a 20 year design life. 20 year intervals have also been assumed for the tidalreef as the turbine generator technology is expected to be more akin to tidal streamthan traditional hydropower technology. In the assessment, a major maintenance costhas been attributed to each scheme at these intervals to reflect the maintenanceliability which will vary between proposals.

The major maintenance common to all proposals is the refurbishment of on-barrage/lagoon mechanical and electrical equipment which has been included in thecomparison to take account of the different scales of equipment in each option. Forbarrages and lagoons, this has been estimated at a present day cost of 70% of thesupply, installation and commissioning costs of mechanical and electrical equipmentincurred every 40 years. For tidal fences, it has been estimated at a present day cost of100% every 20 years.


Sedimentation represents a potentially very significant cost item which could varysignificantly between options. However, the severity of sedimentation relating toeach option (and therefore the cost of dredging of sediment deposits) is difficult toquantify without further analysis of the effect each option will have on the sedimentregime. Sedimentation has therefore only been considered qualitatively as a keyenvironmental effect.

Mitigation of other environmental impacts will also have implications with respect toconstruction and operational costs, and could potentially have an impact on energyyield. The magnitude of the construction and operational costs, and energy yieldimplications, depends on the magnitude of the impact which has only beenconsidered qualitatively at this stage. Therefore, a quantitative assessment in terms ofconstruction cost and cost of energy has not been carried out.

Maintenance costs relating to the caisson and embankment structures have beenexcluded on the basis that they would be designed for a 120 year design life withoutmajor maintenance and routine maintenance of these components will notdifferentiate the energy costs of the different options. It has been assumed that thealternative lagoon wall proposals would be designed to be sufficiently robust so asnot to require major maintenance over a 120 year life. Whilst the components of thewall are not themselves innovative, the application of these components in the formproposed in a marine environment is. There are inherent risks in such an innovationwhich could lead to the wall carrying a greater liability than an equivalentembankment as discussed in section 6.2.

Unit Costs of Energy

The costs per unit energy for each scheme is presented in Table 8.4. The capital cost,maintenance, replacement costs and energy yields on a year by year basis are set outin Appendix A.

Cost of energy (p/kWh) for different discountrates (based on 3:1 habitat compensationratios)

OptionNo

Option Name

8% 3.5% 15%


16.24 7.30 37.51

B2 Middle Barrage fromHinkley to LavernockPoint (Severn Barrage toHinkley and Brean)

16.67 7.82 36.82


Cost of energy (p/kWh) for different discountrates (based on 3:1 habitat compensationratios)

OptionNo

Option Name

8% 3.5% 15%

B3 Middle Barrage fromBrean Down to LavernockPoint (Cardiff to WestonBarrage)

15.29 7.39 32.35


13.68 6.69 27.55

B5 Beachley Barrage 16.48 8.21 31.98

F1a Tidal Fence (Lavernock toBrean Down)

75.00 40.47 135.24

F1b Tidal Fence (Outer) 24.20 14.33 42.75

L2 2008 Russell LagoonOption (based on Flemingtied panel construction)

20.43 9.99 41.20

L3a Russell Lagoons EnglishGrounds

22.22 11.35 42.71

L3b Russell Lagoons WelshGrounds

23.01 11.27 46.31

L3c Russell Lagoons PeterstoneFlats

18.06 9.03 36.03

L3dLagoon

Bridgwater Bay LandConnected Lagoon

16.85 8.29 33.88

L3e(i) 90km2 offshore lagoon offBridgwater Bay

25.90 12.86 53.29

L3e(ii) 50km2 offshore lagoon offBridgwater Bay

29.64 15.05 58.68

R1 Tidal Reef 21.671 12.161 43.571

Note:

1. These estimates should be read in conjunction with the comparison of unit energycosts in Section 8 which notes that the R1 reef cost estimates are highly uncertain andcould be at least twice the stated values

Table 8.4 Unit Costs of Energy


Table 8.5 shows the differences in energy cost between the options excluding theprovision of habitat compensation and the likely range in costs for provision ofhabitat compensation based on rations of 1:1 and 3:1.

Cost of energy (p/kWh) excluding and includinghabitat compensation

OptionNo

Option Name

8% 3.5% 15%

Habitat Compensation

Excl – excluded

Inc – Included (range)

Excl Inc Exc Inc Exc Inc


13.94 14.70-16.24

6.42 6.72 -7.30

31.92 33.78 -37.51

B2 Middle Barrage fromHinkley to LavernockPoint (Severn Barrage toHinkley and Brean)

13.96 14.87-16.67

6.78 7.13 -7.82

30.41 32.54 -36.82

B3 Middle Barrage fromBrean Down to LavernockPoint (Cardiff to WestonBarrage)

12.94 13.72-15.29

6.46 6.77 -7.39

27.00 28.79 -32.35


10.40 11.49-13.68

5.35 5.79 -6.69

20.51 22.86 -27.55

B5 Beachley Barrage 12.58 13.88-16.48

6.58 7.13 -8.21

23.91 26.60 -31.98

F1a Tidal Fence (Lavernock toBrean Down)

69.40 71.68-75.00

38.00 39.04-40.47

124.30 128.70-135.24

F1b Tidal Fence (Outer) 22.72 23.35-24.20

13.70 13.98-14.33

39.79 41.02 -42.75

L2 2008 Russell LagoonOption (based on Flemingtied panel construction)

15.46 17.18-20.43

7.98 8.68 -9.99

30.48 34.18 -41.20

L3a Russell Lagoons EnglishGrounds

19.72 20.55-22.22

10.30 10.65-11.35

37.52 39.25 -42.71


Cost of energy (p/kWh) excluding and includinghabitat compensation

OptionNo

Option Name

8% 3.5% 15%

L3b Russell Lagoons WelshGrounds

17.84 19.56-23.01

9.16 9.87 -11.27

35.21 38.91 -46.31

L3c Russell Lagoons PeterstoneFlats

15.93 16.64-18.06

8.16 8.45 -9.03

31.46 32.99 -36.03

L3dLagoon

Bridgwater Bay LandConnected Lagoon

13.02 14.30-16.85

6.73 7.25 -8.29

25.66 28.40 -33.88

L3e(i) 90km2 offshore lagoon offBridgwater Bay

25.90 25.90 12.86 12.86 53.29 53.29

L3e(ii) 50km2 offshore lagoon offBridgwater Bay

29.64 29.64 15.05 15.05 58.68 58.68

R1 Tidal Reef 20.301 20.77-21.671

11.631 11.82-12.161

40.351 41.43 -43.571

Note:

1. These estimates should be read in conjunction with the comparison of unit energy costsin Section 8 which notes that the R1 reef cost estimates are highly uncertain and could be atleast twice the stated values

Table 8.5 Unit Costs of Energy excluding and including habitat compensation

Comparison of Unit Energy Costs

The comparison of energy costs shows that cost of energy generally becomes moreeconomic between the Outer Barrage and the Inner Barrage which is consistent withthe finding of earlier studies. The Beachley Barrage has been found to be lesseconomic than the Shoots Barrage which would be a result of its lower outputpotential due to the limitations on turbine numbers that could be provided within thespace available. Barrage B4 is the most economical of all the schemes. Barrage B5 iscomparable to B3.

The comparison shows that the L3d Bridgwater Bay lagoon is the most economical ofthe L3 lagoons whilst L2 is more economical than all L3 lagoons except L3d in mostsensitivity tests. The comparison also shows that the more economical lagoons haverelatively similar costs per unit energy to the larger barrages, higher unit energy coststhan the smaller barrages but lower than the tidal fence options.


Offshore lagoons at Bridgwater Bay are less economic than land connected lagoons onaccount of the additional construction required to enclose the basin. The largeroffshore lagoon is the more economic of the two considered but both are the leasteconomic of all options with the exception of the F1a fence.

The Tidal Fence F1a option proves to be significantly less economic than F1b and theleast economic of all schemes. It is less economic than F1b because:

at the outer location a turbine size of 1.6MW is feasible compared to only1MW at the Lavernock to Brean Down location;the civil engineering infrastructure requirements at the outer location are lessonerous; and800 turbines can be accommodated at the outer location compared to 256 atthe Lavernock to Brean Down location.

The R1 Tidal Reef has a higher estimated cost per unit energy than the barrages and theland connected lagoons but a lower unit cost than the offshore lagoons and the tidalfences. However, the estimates for the tidal reef should be treated with caution as theconstruction cost is based on very limited design information and a high degree ofuncertainty is attached to these estimates due to the embryonic nature of the concept.Optimism bias has not been applied in the fair basis approach but it should be notedthat the estimated unit costs for the R1 reef could be at least twice the quoted values.

8.10 Risk Assessment

Each option has been assessed in terms of risk. Risk has been qualitatively assessed interms of probability (High, Medium, Low) and impact (High, Medium, Low). Thetechnical risk assessment is a development of work carried out across the feasibilitystudy workstreams which included risk workshops attended by the study team andinvited experts, and through informed technical work carried out as part of the optionsanalysis. The risks considered in this assessment are those technical risks thatdifferentiate between the schemes. Non-technical risks, such as political andreputational risks, have not been considered. Environmental risks, such as risk ofgeomorphological change and risk of sedimentation, have been considered in Section 5and are assessed qualitatively during the assessment screening process. Environmentalrisks are therefore not assessed in this section.

The risks assessment is set out in Table 8.6. An analysis of the risk assessment is setout in Table 8.7.


Description Mitigation Likelihood/Consequence

B1 B2 B3 B4 B5 F1a F1b L2 L3a - d

L3e(i)

L3e(ii)

R1

Likelihood M M M M M M M H H H H MDesigns based on groundinvestigation data may requiremodification if ground conditionsencountered during constructionprove more challenging than forecastintroducing construction delays andincreased costs

Conduct furtherdetailed groundcondition surveys

Consequence M M M M M M M H H H H M

Likelihood L L L L L M M M M M M MThe requirement to pay a royalty touse the technology employed in theconstruction of the scheme.

Scheme choice couldbe amended based onthe costs ofintellectual propertyapplicable to someschemes

Consequence L L L L L L L L L L L L

Likelihood M M M L L M M L L M L MMaterial availability can impact uponoverall project costs through bothdirect cost increases and timeoverruns. A lack of materials willstall the project and could also add apremium on to material price. This isespecially true for the larger schemedue to the vast quantities of materialsrequired.

Alerting the suppliermarket to materialrequirements inadvance ofconstruction. Consequence H H H H H H H H H H H H

Likelihood M M M L L M M L L M L MDifficulties in procuring marine plantequipment due to resourcecompetition from other projects.Competition for plant could increasecosts through the creation of a pricepremium as well as delay projectcompletion

The pre-procurementof plant equipment;and alerting themarket to the exactplant requirementswell in advance ofconstruction




B1 B2 B3 B4 B5 F1a F1b L2 L3a - d

L3e(i)

L3e(ii)

R1

Likelihood H H H H H H H H H H H HAdverse tides and weather conditionsmay have an impact on constructioncausing delays to delivery andpossible damage to electrical andmechanical equipment increasingcosts

Appointorganisations withexperience inoperating in similarconditions, who arelikely to price the riskinto the contract, thiswill ensure the projectis not delayed morethan necessary


Likelihood M M M L L H H L L L L HIt is questionable whether the marketwill be able to meet the project'sdemand for turbines. If the market isunable to provide the number ofturbines required within thetimeframe available it will cause timedelays to completion and potentiallyprice premiums on the turbines.

The testing of themarkets capability tomeet the demandlevel required wouldbe a good indicator -this would also givethem market time toreact to the forecastdemand. It could alsobe possible tocommission theturbine contract early.

Consequence H H H L L H H L L L L H

Likelihood M M M L L M M L L M L MThere will be other large scaleconstruction projects commencing atthe same time as a Severn TidalPower project which will lead tocompetition for labour. This couldresult in labour shortages causingproject delays; there is also thepotential for cost escalation due topremium wages demanded byspecific manpower.

Forward planning ofresourcerequirements

Consequence M M M L L M M L L M L M



B1 B2 B3 B4 B5 F1a F1b L2 L3a - d

L3e(i)

L3e(ii)

R1

Likelihood L L L L L L L L L L L LThere is a chance that a rise in sealevels could limit the effectiveness ofany of the schemes. The lagoonschemes are more susceptible to sealevel rise.

Build the potential forsea level rise into thedesign of each of theschemes. Consequence L L L L L L L M M M M L

Likelihood L L L L L H L L L L L HOnce operational there is anincreased risk of shipping accidents

Navigation measuresprovided in estuary

Consequence H H H M M H H L L L L H

Likelihood L L L L L M M L L L L HDelays in development of technologycause longer than planned pre-construction development periodwith delay to generation or possiblecancellation

Use of establishedtechnologyprototyping oftechnology and pilottesting at smallerscale

Consequence L L L L L H H L L L L H

Key

H = High

M = Medium

L = Low

Table 8.6 Technical Risk Assessment of Long Listed Options


Option Summary of Higher Risks OverallAssessment

B1 - Outer Barrage fromMinehead to AberthawB2 - Middle Barrage fromHinckley Point toLavernock PointB3 – Middle Barrage fromBrean Down to LavernockPoint (formerly Cardiff –Weston)

Higher risks compared to otherschemes relate to:

Material, labour and plantavailabilityRisk of shipping accidents

Mediumrisk schemes

B4 – Inner Barrage (Shoots)B5 - Beachley Barrage

The only higher risks compared toother schemes is the increased risk ofshipping accident

Low riskschemes

F1a – Tidal Fence(Lavernock to Brean Down)F1b – Tidal Fence (Outer)

Higher risks compared to otherschemes are in:

Intellectual property costsMaterial, plant and labouravailabilityTurbine availabilityRisks of shipping accidentsDelay in development oftechnology

High riskschemes

L2 – 2008 Russell LagoonOption (based on Flemingtied panel construction)

Higher risks compared to otherschemes are in:

The suitability of the wallsolution to prevailing groundconditions and vulnerability tovariable ground conditionsIntellectual property costsPotential to adapt for sea levelrise not easily built into schemedesign

Mediumrisk scheme

L3a – Russell LagoonsEnglish GroundsL3b – Russell LagoonsWelsh GroundsL3c – Russell LagoonsPeterstone FlatsL3d – Bridgwater Bay LandConnected Lagoon

The risk profile is similar to L2 Mediumrisk schemes


Option Summary of Higher Risks OverallAssessment

L3e(i) – 90km2 offshorelagoon off Bridgwater Bay

The risk profile is similar to L2 andL3(a to d) but with the additional riskof material, plant and labouravailability

Mediumrisk schemes

L3e(ii) – 50km2 offshorelagoon off Bridgwater Bay

The risk profile is similar to L2 andL3(a to d)

Mediumrisk scheme

R1 – Reef Higher risks compared to otherschemes are in:

Intellectual property costsMaterial, plant and labouravailabilityTurbine availabilityRisks of shipping accidentsDelay in development oftechnology

High RiskScheme

U1 – Severn Lakes Concept Insufficient data on which to evaluate risk

Table 8.7 Risk Analysis


SECTION 9

ASSESSMENT SCREENING


9 ASSESSMENT SCREENING

The assessment of each option has been undertaken by issue areaexperts and subject to peer review. The quantitative input to theassessment is based on the consistent application of assumptionsand principles which are aimed at achieving a fair comparisonbetween options. The input is not provided in absolute terms butinstead reflects the merits of each option relative to each other withthe aim of establishing whether the individual proposal could betaken forward and be developed to meet the plan objectives.

The assessment is summarised in the assessment screening sheetscontained within this section which should be read in conjunctionwith the remainder of this options analysis report. The fullassessment model is reproduced in Appendix B.

9.1 Application of the Assessment Framework

Quantitative ScreeningThe assessment worksheet provides the data on which the options will be assessedquantitatively to determine those options which are significantly more favourable interms of the cost and amount of energy they are likely to produce, their financialfeasibility, timescales for power generation, degree of technical risk and theirpotential contribution to the UK’s commitments under the forthcoming RenewableEnergy Directive and Climate Change Act and goal to deliver a secure supply of low-carbon electricity. The analysis of this data is summarised in Section 10 and themodel outputs are contained within Appendix B.

Qualitative ScreeningAll options have been assessed qualitatively in terms of their environmental, social,economic and regional effects in the assessment worksheets. Those options whichhave less favourable assessments from the quantitative screening but may bemarginal in terms of the energy criterion have been subject to a qualitative screeningto determine whether, on the information currently available, they appear to beattractive when environmental, grid compatibility, and regional economic andconstruction impact are considered. The analysis of this data is summarised in belowand the model outputs are contained within Appendix B.


9.2 Summary of Analysis

To assist in the presentation of the conclusions, the options have been categorised intothree groups so that options with similar characteristics are presented together. Thethree groups are:

Tidal Barrages

Tidal Lagoons

Embryonic Options

The options are considered under three headings:

Initial Screen

Quantitative Assessment

Qualitative Assessment


Initial Screen

Severn Lakes (U1)

The Severn Lakes concept was originally included because one of its objectives is toproduce power using the tidal range of the Severn. Tidal power is part of thebusiness plan which also relies on many other economic drivers to substantiate thecost of building a 1km wide causeway across the Severn, including developmentland, marinas, landfill and other renewable energy technologies. This isacknowledged by the proposer. The information relating to this option comes fromthe proposer’s web site and provides details of the general conceptual details. It isunderstood that specific design elements are being worked on but are not availablefor consideration by this study.

The construction of a wide causeway could not result in a lower cost of energycompared to an equivalent barrage because of the increased civil engineering worksrequired. Therefore, for the scheme to be justifiable on commercial grounds, thevalue of the mixed development would need to offset the opportunity cost of theincrease in energy cost.

As this study is only examining potential options from an energy perspective thisoption will not considered specifically by the Study. However, should tidal powerdevelopment from the Severn form part of Government’s future energy policy, aprivately proposed option such as Severn Lakes could be considered in the future.For this reason, this report will reference information relevant to Severn Lakes forinformation.

Quantitative Assessment Summary

The Quantitative Assessment focuses on energy (including contribution towards theUK’s climate change goals), time and costs. The key metrics that capture the variousquantitative measures are the levelised costs and annual energy output (and thus thepotential reduction in carbon dioxide emissions) for each option. The levelised costsare calculated by discounting the stream of generation costs over the lifetime of theasset (120 years) and dividing this value by the amount of electricity generated overthis period to calculate the price at which the generator would have to sell theelectricity generated in order to break even over the period.

The tables below tabulate the annual energy yield and total carbon dioxide emissionssavings over the assumed lifetime of each option. Carbon costs during construction,decommissioning and major refurbishment have been accounted for and 1MWh ofenergy production has been equated with 0.43t CO2 to be consistent with theRenewable Energy Strategy. Capital Cost excluding compensatory habitats and gridreinforcement costs are also given. The tables are presented for the three categoriesreferenced above, namely tidal barrages, tidal lagoons and tidal fences.


The second and third tables within each category present the levelised costs for eachoption. These cover a period of 120 years for all options and where individual assetlives are less than this, the cost of refurbishment and/or replacement as appropriatehas been included. These figures are presented excluding habitat compensation costsand including an estimate of compensatory habitat using a 3:1 replacement ration ofnew habitat to inter-tidal habitats lost.

Levelised costs here are calculated by discounting the stream of generation costs overthe lifetime of the asset (120 years) and dividing this value by the amount ofelectricity generated over this period to calculate the cost per MWh of electricitygenerated such that the generator would break even. Calculating levelised costs overthe lifetime of the asset illustrates the cost of generation if the lifetime of the asset isthe same as the financial lifetime of the project. If the financial lifetime of the projectis shorter than this, the levelised costs would be higher than those shown here butwould exclude the residual value of the asset beyond the financing period of theproject.

Tidal Barrage Options

OPTION B1 B2 B3 B4 B5Annual Energy

Yield (TWh) 25.3 19.3 16.8 2.8 1.6

Lifetime CO2emission savings

(mt)1,270 970 845 140 80

Capital Cost (£bn)excluding habitats 29 22 18 2.6 1.8

Capital Cost (£bn)with 3:1 habitatcompensation

35 27 22 3.5 2.5

Table 9.1 Energy Yield, Lifetime CO2 savings and Capital Costs forTidal Barrage Options

OPTION B1 B2 B3 B4 B5Discount Rate(%)

Excluding Habitat Compensation

3.5 6.42 6.78 6.46 5.35 6.588 13.94 13.96 12.94 10.40 12.58

15 31.92 30.41 27.00 20.51 23.91

Table 9.2 Levelised Costs excluding habitat compensation costs forTidal Barrage Options


OPTION B1 B2 B3 B4 B5Discount Rate(%)

3:1 Habitat Compensation Ratio

3.5 7.30 7.82 7.39 6.69 8.218 16.24 16.67 15.29 13.68 16.48

15 37.51 36.82 32.35 27.55 31.98

Table 9.3 Levelised Costs including habitat compensation costs at 3:1ratio for Tidal Barrage Options

The key conclusions from these tables are summarised below. For ease ofcomparison, capital costs quoted exclude compensatory habitats and levelised costsare presented using an 8% discount rate:

Barrage B1 (Minehead to Aberthaw) makes the greatest contributionto climate change targets (~1270mt reduced CO2 emissions over 120years or 10mt per year) but at the greatest capital cost (£29bn);

Of the larger barrages, B3 (Cardiff to Weston) contributes significantlyto climate change targets (7mt reduced CO2 emissions per year) andwith the least unit cost (12.94p/kWh).

Of all tidal barrages, B4 (Shoots) has the lowest cost per kWh(10.40p/kWh)and whilst its contribution to climate change targets isstill significant (1.2mt reduced CO2 emissions per year) it issignificantly less than for larger barrages.

B5 (Beachley Barrage) has the lowest capital cost (£1.8bn) and wouldsave 0.67mt CO2 emissions per year.

Subject to the time taken to achieve planning consents, all large barrage optionscould be initiated in the next decade and be contributing to the UK’s Climate Changetargets in the subsequent decade (2020 to 2030)

It will be seen that, for the lower discount rate, the variation between options arerelatively small. The Outer Barrage, with its greater energy output, emergesrelatively strongly from this analysis, although it is likely to be subject toconsiderations from other work within the Feasibility Study, particularlyconsiderations of affordability and the ability for the grid to absorb relatively largeintermittent inputs of energy, particularly the low demand period at night when 50%of the energy will be produced. These are highlighted as risks for Option B3 so thescale of risk is greater for the larger B1 option.

At all discount rates, B4 (Shoots) has the lowest cost per energy of all optionsconsidered by this study, including non barrage options.


Tidal Lagoon Options

OPTION L2 L3a L3b L3c L3d L3eAnnual Energy

Yield (TWh) 2.31 1.41 2.31 2.33 2.64 2.6


(mt)116 71 116 117 132 131

Capital Cost (£bn) 3.2 2.6 3.7 3.3 3.0 5.8Capital Cost (£bn)

with 3:1 habitatcompensation

4.4 3.0 4.9 3.8 4.1 5.8

Table 9.4 Energy Yield, Lifetime CO2 savings and Capital Costs forTidal Lagoon Options

OPTION L2 L3a L3b L3c L3d L3e

Discount Rate (%)Excluding Habitat Compensation

3.5 7.98 10.30 9.16 8.16 6.73 12.868 15.46 19.72 17.84 15.93 13.02 25.90

15 30.48 37.52 35.21 31.46 25.66 53.29

Table 9.5 Levelised Costs excluding habitat compensation costs forTidal Lagoon Options

OPTION L2 L3a L3b L3c L3d L3eDiscount Rate(%)


3.5 9.99 11.35 11.27 9.03 8.29 12.868 20.43 22.22 23.01 18.06 16.85 25.90

15 41.20 42.71 46.31 36.03 33.88 53.29

Table 9.6 Levelised Costs including habitat compensation costs at 3:1ratio for Tidal Lagoon Options

The key conclusions from these tables are:

Tidal lagoon options are similar in scale to the smaller barrage options(B4 and B5);

Lagoons located at Welsh Grounds (L2 and L3b) and (or off)Bridgwater Bay (L3d and L3e) plus Peterstone Flats (L3c) make thebest contribution to climate change targets of all lagoons (>1mtreduced CO2 emissions per year). Although significant andcomparable with the smaller barrages it is significantly less than forlarger barrages.


The design of lagoon proposed by the Fleming Group for WelshGrounds (L2) and the land-connected Bridgwater Bay lagoon (L3d)using a variant of the geotextile construction proposed by TidalElectric Limited (TEL) offer the least cost per kWh (13.0 to 15.5p/kWh)for lagoons as well as the best contribution to carbon targets. The costper kWh is higher than the smallest barrages but of a similar order tothe larger barrages.

The most expensive lagoon option is the offshore proposal (L3e). Thishas been modelled as a generic example of an offshore lagoon, locatedsuch that its foundations do not encroach on the inter-tidal zone. Thishas the benefit of having zero inter-tidal loss as a consequence ofgenerating tidal energy. However, the depth of wall construction (bydefinition it has to exceed the tidal range if it is not to encroach on theinter-tidal zone) increases the cost of construction significantly, nomatter what innovative forms of wall construction are used, bycomparison with land connected lagoons of similar storage capacityby virtue of their shallower and therefore less expensive constructioncosts, albeit that wall lengths are longer.

Subject to the time taken to achieve planning consents, all tidal lagoon options couldbe initiated in the next decade and be contributing to the UK’s Climate Changetargets in the subsequent decade (2020 to 2030)


Embryonic Options

OPTION F1a F1b R1Annual Energy

Yield (TWh) 0.7 3.3 13


(mt)35 165 654

Capital Cost (£bn) 4.4 6.3 18

Table 9.7 Energy Yield, Lifetime CO2 savings and Capital Costs forTidal Fence Options

OPTION F1a F1b R1Discount Rate(%)

Excluding Habitat Compensation

3.5 38.00 13.7 11.638 69.4 22.72 20.30

15 124.3 39.79 40.35

Table 9.8 Levelised Costs excluding habitat compensation costs forTidal Fence Options

OPTION F1a F1b R1Discount Rate(%)


3.5 40.47 14.33 12.168 75.00 24.20 21.67

15 135.24 42.75 43.57

Table 9.9 Levelised Costs including habitat compensation costs at 3:1ratio for Tidal Fence Options

The key conclusions from these tables are:

The alignment for Fence Option F1a between Cardiff and Weston isnot viable and that if tidal fence technology is to be deployed in theSevern, an alignment between Minehead and Aberthaw (F1b) ispreferable both in terms of contribution to carbon reduction targetsand cost per kWh.

The energy output and the savings in carbon dioxide emissions fromOption F1b are slightly greater than small barrages and lagoons butless than large tidal barrages.


The Tidal Reef delivers significantly greater energy yields and lifetimecarbon savings than tidal fences.

The cost per unit energy for all embryonic options is greater than forlarge barrages and significantly higher than the lowest cost option(B4).

It should be noted that the tidal fence uses tidal stream technology. At present this isstill in demonstration stage with a single 1.2MW twin rotor unit commissionedwithin Strangford Lough within the past year. It is therefore likely that significantlymore development time will be required to achieve sufficient confidence in theimplementation costs and associated turbine performance before large scaledeployment on the Severn could be realised. This implies that full scale generationof tidal fence technology on the Severn would lag tidal barrage and tidal lagoonoptions.

Tidal Reef technology has not yet been developed and proposals are at concept stageonly. Development of tidal reefs is therefore likely to lag behind tidal fences by asmuch as ten years if similar development cycles are anticipated.

Construction and Technology Risks

All options involve risks. Tidal barrages represent the least risk but neverthelessweather related risks during construction increase the further downstream an optionis located. Weather related risks can increase both construction timeframes andcosts.

Tidal lagoons, if selected as the preferred option, are likely to be constructed using arelatively innovate form of wall construction to create the tidal impoundmentrequired. Analysis of these wall designs during this stage of the study has indicatedthat these designs have higher degrees of risk associated with them than moreconventional (but more expensive) forms of construction. Such risks presentthemselves in terms of ground conditions and structural stability duringconstruction, ability to withstand extreme surge events, ship impact and durability.

More embryonic options have the additional risks of new product developmentcycles and the time required to attract sufficient confidence for large scaledeployment.

Qualitative Assessment Summary

A key component of the assessment is the review of all options from a qualitativeperspective in terms of environmental, social, economic or regional effects to


determine whether there are any significant issues that should either a) prevent anyof the above options proceeding to the short list or b) allow other options which haveless advantageous economic characteristics to proceed to the short list.

A review of this indicates that all options have both positive and negative effectsand that the scale of these effects differs across options.

Impacts on HabitatsAll options would impact inter-tidal habitats including offshore lagoons. Althoughan offshore lagoon does not directly lead to loss of inter-tidal habitats, resultantchanges in tidal currents and geomorphology will effect adjacent habitats. Followingappropriate assessment which involves consideration of alternatives, and subject tothe requirements of the Habitat regulations, should a decision to proceed on the basisof the over-riding public interest, compensatory measures would be requiredincluding habitat compensation for lost intertidal habitat. Not all compensationwould necessarily be located in the Severn. For this report, these costs have beenassessed in headline terms only using a range of possible replacement ratios and anindicative cost per ha.

Environmental EffectsClimate change is already affecting the Severn Estuary and any environmental effectshave to be seen in the light of this changing baseline. The most significantenvironmental effects of a scheme will be those relating to the geomorphologicalresponse of the estuary to any tidal power structure, loss of inter-tidal habitat,changes to habitats including feeding grounds available to birds, salt marsh andsedimentation, effects on fish and changes in water quality. For some of the smalleroptions, whilst the effects will continue to be significant, the scale of impact may besmaller (for example availability of feeding grounds for birds). Other effects includechanges to water quality and turbidity. Fish behaviour will be changed by alloptions and where fish navigate upstream or downstream through turbines,increased mortality rates will be experienced, although mitigation measures will seekto reduce this.

Social, Economic and Regional Effects

The construction of any tidal power project in the Severn will result in significantemployment opportunities both during and after construction. Impacts duringconstruction will require careful management but will result in benefits for localservice industries.

Transportation links have not been considered by this study as there is no policy atpresent to increase the number of transportation links across the Severn. Theactivities of commercial ports will be affected by tidal barrages in particular and willentail navigation through an additional set of ship locks (increasing transit times)and modification of existing facilities to accommodate changed water levels. A


potential benefit for impacted ports will be increased high water standing times anda significant increase in low water level. Non barrage options will impact ports indifferent ways – tidal reefs and tidal fences will present challenges in time of entry /exit through their navigation provision because of the increased tidal currents thatwill prevail. Tidal lagoons may have less impact on ports although changes todredging regimes may result from all options. The numbers of ports impacteddiffers depending upon the location of options

Flood defence is potentially enhanced upstream of any option which prevents sealevels being transferred upstream. This includes any option that barrages the Severnand also the Bridgwater Bay land connected lagoon, providing mitigation of adverseeffects (for example submerged tide locked land drainage outfalls) is achieved so thatexisting standards of flood protection are maintained. These options may thereforeoffer improved protection from storm surges and sea level rise to communitieslocated upstream compared with the other options.

Embryonic Technologies

Tidal fence and tidal reef technology is still embryonic and there is less data availableto assess environmental performance as none have yet been built. It is likely that, asthese technologies present some impediment to flows though the Severn, both willhave some effect on fish as they are attracted through the turbines. Geomorphologyof the estuary will also change as a consequence of constructing these structures. Fora tidal fence, associated benefits such as providing protection from sea level rise arenot as significant as barrage options whilst the reduction in top water level impactsport operations located upstream – more ports are likely to be impacted than anequivalent output barrage options located further upstream, although the scale ofimpact will be less.

Tidal fences have different characteristics than tidal barrages and lagoons as theyutilise the kinetic energy of the tidal currents with some limited augmentation fromthe tidal range through the resistance to flow provided by the tidal fence. Theincrease in velocity profile across the fence may lead to negative effects in terms ofwater quality and potential erosion of the existing shoreline due to the acceleratedestuary currents.

On current information, for both tidal fence and tidal reef options, the loss of inter-tidal habitats is less than equivalent barrage structures but is likely to extend overgreater lengths of the estuary shoreline (a consequence of locating tidal fencestructures further downstream in the Estuary than an equivalent tidal barrage). Theestimated loss of inter-tidal habitat should be considered with caution because it isbased on limited information due to the absence of any precedent and the embryonicstatus of the concept. There is therefore a significant degree of uncertainty attachedto these options.


SECTION 10

CONCLUSIONS


10 CONCLUSIONS

This section presents the overall conclusions from the analysis ofoptions and the application of the assessment framework. This,alongside other work being undertaken as part of the FeasibilityStudy will be used by Government to recommend a draft short-listof options that have the technical potential to form the reasonablealternatives for the Strategic Environmental Assessment (SEA). Thedraft short-list will be finalised following examination byGovernment of non-technical issues which could impact on theoverall feasibility of an option, and public consultation.

Following finalisation of a short-list, options will be worked up inmore detail in order to develop a more detailed assessment of costand energy yield, including modifying option configurations toachieve the optimal results having regard to construction/operatingcosts, value of energy produced and environmental/regionalimpacts.


10.1 Conclusions

The conclusions from this study have been developed following a logical process ofdata collection, analysis, evaluation and application of the assessment framework.The main conclusions are:

There are many options for generating tidal power from the Severn Estuary.These include both different locations and different technologies;

Contribution to reduction in carbon emissions is driven mainly by the annualenergy yield and the earliest date by which energy production can be achieved.Those options that can contribute more to the Government’s Climate Changereduction targets will be the larger (energy yield) options and those that aremature in technology development terms.

The energy yields range from 0.7TWh per year to over 25TWh (7% of the UK’selectricity demand) per year depending upon the option under consideration.Construction costs range from over £1bn to circa £30bn or more if compensatoryhabitat costs are included;

All options, by virtue of capturing significant energy from the tidal regime, willeffect, to some degree, the existing environment. In particular, thegeomorphological response of the estuary and the effects of changes to the tidalrange will need careful consideration as well as additional works to beundertaken to mitigate or compensate for these effects;

Other significant environmental effects include:

Rate of sedimentation for tidal lagoons and the smaller tidal barrages.

The impact on fish of changing currents and flow passages and thedifferent mortality rates depending upon location, operational mode andtype of turbines used.

The impact on birds, particularly for those options where inter-tidalhabitats that are lost account for a significant proportion of the estuary.

Not all environmental effects are necessarily negative. For example, reducedcurrents within impounded basins could lead to a reduction in suspended siltwith the consequent improvement in turbidity and biological productivity.

Regional and social effects also comprise impacts and benefits. Negative impactsinclude effects on ports and fisheries. However, positive effects includeemployment during and after construction, and, particularly for tidal barragesand the tidal reef, enhanced protection from storm surges and sea level rise (onthe basis that mitigation costs are included to modify tidal outfalls upstream ofbarrages and lagoons to deliver the same land drainage performance).

All schemes should be designed to accommodate predicted sea level rise in linewith guidance current at the time of design development and all would be


adaptable if actual sea level rise exceeds predictions. Barrages would be the mostadaptable of all schemes in the event that sea level rise exceeds the tolerance builtinto the design, as they have the largest proportion of turbine caissons. The largerbarrages are also the schemes which provide the greater degree of flood riskbenefits, due to the protection they would provide against surge tides and thegreater extent of the reduction in high water level which they would cause. Tidallagoons, the tidal reef and tidal fences would require onerous modificationsand/or a greater degree of initial structural redundancy to adapt for sea level rise.

Costs of tidal power generation, on a per kWh basis, vary significantly dependingupon the discount rate used because of the initial high capital cost. At lowerdiscount rates, the benefit of the effectively zero fuel cost has greater significance.

Cost per unit energy for barrages and lagoons reduce as the natural tidal rangeincreases, but increase with barrage / lagoon length and depth or if the site isphysically constrained in terms of feasible turbine capacity.

Land-connected tidal lagoons are constructed in shallower waters than offshoretidal lagoons (by definition, if an offshore lagoon is not to impact inter-tidal areas,wall depths have to exceed the maximum tidal range). Although land connectedlagoons generally require longer wall lengths to impound the same live storagevolume, the cost per metre length of wall is significantly less than for an off-shorelagoon of the same volume because of the reduced wall depth.

It has been recognised by the SDC Report “Turning the Tide” as well as othersources, that there are more promising locations for tidal stream technology (asused in the Tidal Fence options) than the Severn. Although outside the scope forthis report, nevertheless, it is relevant to note that development of a tidal fencemay have a better return on investment in higher tidal current locations such asthe Pentland Firth.

Tidal Fence costs are influenced by water depth and their ability to efficientlycapture the kinetic energy within the constraints of the Severn. Because most ofthe tidal fence costs are made up of manufacturing and installation costs andinvolve a large number (800 for Option F1b) of individual turbines, the rate andcost of manufacture and installation is subject to change.

The Tidal Reef concept is not yet sufficiently advanced to permit reasonableassessment of energy yields / costs although an indicative analysis of the usingfair basis assumptions gives a maximum 13TWh annual yield and £18bnconstruction costs. At an 8% discount rate, these figures produce a cost per kWhof approximately 20.3p.

Both tidal fence and tidal reef options are embryonic and require furtherdevelopment before large scale implementation. Tidal stream technology is atdemonstration project status, with 1.2MW being tested currently. No tidal fenceas proposed using this technology exists as yet. The tidal reef is at pre-designstage and exists as a concept only. If it follows a similar development path totidal stream technology, it is likely that it will take at least ten years to pilot thetechnology followed by smaller scale implementation than that envisaged for theSevern. Although the programme assumptions for a tidal fence have been


modelled using the same start date as the more conventional tidal range projects(to enable fair comparison), the likely start date for first generation would bebeyond this. Although this does not change the volume of carbon emissionsavings over the lifetime of the project, it will impact on the contribution thisoption could make to the Government’s 2050 carbon reduction target.

Costs of tidal power generation are also influenced by the constructionprogramme and in particular the ability to generate power before the project as awhole is complete. This benefits the larger tidal barrage options where the civilengineering and grid connection works can be completed to allow generationfrom installed turbines ahead of all turbines being delivered and commissioned.It also benefits the modular tidal fence concept. This does not apply to thesmaller barrage and tidal lagoon options, because of the smaller number ofturbines which would be connected prior to first generation.

The costs involved in satisfying the requirements of the Habitats Directive aresubject to detailed consideration in themselves and may be expected to increasethe unit cost of energy by between 0 and 35%, depending upon the optionselected and the assumptions made.

Different options have different effects, depending upon the technologies used, theirlocation and the amount of energy abstracted from the estuary. In general, the more“permeable” (the greater the unimpeded flow) options have less impact than the leastpermeable (such as a barrage) for any given location. However, the more “efficient”options (the greater the energy yield at a specific location) affect a smaller area of estuarycompared with the less efficient but more permeable options.

10.2 Overall Summary

The conclusions from the Interim Options Analysis Report will form one of the inputsinto the Government’s Feasibility Study. Outside of this report, wider questions willbe asked as to whether there are issues beyond technical capability which maynegatively impact on a proposal’s overall feasibility. For example a low confidence onthe technology will attract greater levels of risks in terms of deliverability, costs andfinancing. The draft short-list will be finalised following examination byGovernment of non-technical issues which could impact on the overall feasibility ofan option.

The key conclusions from the analysis of options are presented in Table 10.1 overleaf.


Table 10.1- Summary for Each of the Options



Largest producer of energy (25TWh/a) but with highest capital cost (£29bn);Cost of energy is 13.94p/kWh excluding compensatory habitat costs ;Largest environmental impact footprint, and will result in reduction of water levels and tidalrange, loss of inter-tidal habitats and impacts on bird and fish populations in the Severn;Benefits include protection from effects of storm surges, sea level rise and reduced turbidity;

Severn Ports upstream will be affected, primarily Barry, Bristol, Cardiff, Newport andSharpness.

B2 Middle Barrage fromHinkley to LavernockPoint (Shawater concept)

Longest barrage option - based on the B3 option but with additional embankment extending thebarrage to Hinkley Point - Energy output of 19TWh/a;Although the capital cost is less (£22bn), the cost of energy is similar to Option B1 at 13.96p/kWh;Environmental effects are similar to those for B1 as this option seeks to provide similar flooddefence benefits by crossing Bridgwater Bay;


B3 Middle Barrage fromBrean Down toLavernock Point(commonly known asthe Cardiff to WestonBarrage)

Most studied of any of the options and reported on in Energy Paper 57;Annual energy output of 17TWh and a capital cost of £18bn;The cost of energy is the best of all the “large” options at 12.94p/kWh excluding compensatoryhabitat costs ;Environmental impacts are potentially significant, as with other large barrage options, and willresult in reduction of water levels and tidal range, loss of inter-tidal habitats and impacts on birdand fish populations in the Severn; Benefits include protection from effects of storm surges, sealevel rise and reduced turbidity.





Significantly smaller than the large barrage options, this option is located just downstream of theSecond Severn Crossing co-incident with the highest tidal range in the Severn;Generates 2.77TWh per year at a capital cost of £2.6bn and achieves the lowest cost per unitenergy at 10.4p/kWh;Environmental impacts are similar in type (although not necessarily scale) to other barrageoptions although there is an increased risk of sedimentation;

This option does not impact the Ports of Bristol or the ABP Ports on the Welsh coast.

B5 Beachley Barrage Located upstream of the Wye, smallest barrage option studied (£1.8bn) and has similarcharacteristics to Option B4;Annual energy output is 1.59TWh/a, 57% of Option B4 whilst the cost per energy is 12.58p/kWh;Similar environmental effects as Option B4 except that the Wye is not impounded andsedimentation risk is higher;

This option affects ports in the Gloucester Harbour Trustees administered waters.

F1 Tidal Fence Proposalssubmitted by STFG Tidal

Initially, proposed between Cardiff and Weston but a more feasible alignment was subsequentlyconsidered between Minehead and Aberthaw;Annual energy output of 3.3TWh is achievable at a cost of £6.3bn. Cost of energy is more thandouble the lowest cost option at 22.72p/kWh;Assumes future development costs will reduce significantly from the current demonstrationproject costs for tidal stream technology. This implies a significant period of furtherdevelopment and experience before large scale implementation could be achieved. Unlikely thata decision to proceed with a tidal fence could be made in the short-term;

It does offer the possibility of less significant environmental effects than barrage options



although the area affected is as large as the biggest barrage option.

L2 Tidal Enclosure on theWelsh Groundsproposed by FlemingEnergy

Land connected lagoon located on the relatively high Welsh Grounds just downstream of theShoots Barrage (B4);It has an annual energy output (2.3TWh/a) achieved at a cost of £3.1bn. Cost per unit energy is15.46p/kWh and is thus more expensive than the larger barrage options, although developmentalongside B4 would reduce energy cost. Additional energy output could be achieved from theWelsh Grounds if the materials used in construction were excavated from within the basin toachieve greater live storage. This would marginally increase energy yield and thus reduce thecost of energy;

Land connected lagoons, like barrages, result in loss of inter-tidal habitats because of thesignificant reduction in tidal range within the impounded area. Other environmental effects aresimilar to smaller barrages except that impacts on fish and navigation are expected to be lessbecause they do not form a barrier across the estuary.

L3 Tidal Lagoon Concept(which has beensubsequently modelledas four land-connectedlagoons and threeoffshore lagoons basedon various generalsubmissions receivedfrom the Call forEvidence)

Various land connected and offshore lagoon configurations have been studied using differentforms of lagoon wall construction;As lagoon costs are influenced by the length and depth of wall forming the impounded basin,innovative methods of wall construction are required and the lowest cost option, (apart from thewall design proposed by Fleming Group for Option L2) comprises a geotextile solution usingmaterial dredged from the estuary and protected by rock armour (externally) and revetment(internally);Aside from the L2 Welsh Grounds proposal, Bridgwater Bay offers the most cost effective lagoonoption with a higher energy yield (2.64TWh/a) and slightly reduced capital costs than L2 givinga cost per kWh of 13.02p/kWh.

An offshore lagoon, located below the low water contour (and reduced impact on habitats), hasbeen modelled to produce a similar energy output using the same forms of construction.



Because of the much deeper wall construction required, it is more expensive with a capital costof £5.8bn for the same energy output of 2.6TWh/a as the £3bn Bridgwater Bay land connectedoption. This is also reflected in the cost of energy which is more than double the land connectedlagoon alternative.

R1 Tidal Reef proposed byEvans Engineering.

Entirely new concept that has continued to evolve during the study period.Studied and reported on to a level commensurate with the information available but theassessment has not been able to provide as definitive estimates as other options on which todevelop reliable cost base and energy yields. Outline estimates provide a capital cost of £18.1bnwith an energy yield of 13TWh/a with a preliminary estimated cost of energy of 20.30p/kWh.

Development period would be greater than other options and require demonstration projects totest the concept – this would take between 10 and 15 years if tidal stream technology is taken asa benchmark.

U1 Severn Lakes (promotedby Gareth Woodham)

Originally included because one of its objectives is to produce power using the tidal range of theSevern.The cost of constructing a 1km wide causeway 16km in length would be significantly more thana conventional tidal barrage and clearly requires additional investment streams to justify its cost.On the basis of the information within the public domain, this is also recognised by the proposerwho envisages other revenue streams from land, recreational and other energy developments aspart of this scheme.This study is only examining potential options from an energy perspective. For this reason thisoption is not considered specifically by the Study.

Should tidal power development from the Severn form part of Government’s future energypolicy, a privately proposed option such as Severn Lakes could be considered in the future.

FinalDecember 2008

APPENDIX A

FINANCIAL ANALYSIS DATA

APPENDIX A

FINANCIAL ANALYSIS DATA

APPENDIX A1 EXPLANATORY OVERVIEW OF COSTESTIMATES

DISCOUNTED CASH FLOW WORKSHEETS

SHEETS 1 TO 3 - NO HABITAT COMPENSATION

Sheet 1 Summary of Costs

Sheet 2 Annual Cost Flows

Sheet 3 Annual Energy Outputs

SHEETS 5 TO 8 - HABITAT COMPENSATION RATIO OF 1:1




SHEETS 7 TO 9 - HABITAT COMPENSATION RATIO OF 3:1




Appendix A1 - Explanatory Overview of Cost Estimates

A1.1 OVERVIEWThis appendix provides further information on the scheme cost estimates presentedin Section 8. Pre-construction costs are set out in A1.2. The cost build up of thebarrages, lagoons and fences are set out A1.3 to A1.4. The cost estimate of the tidalreef is set out in A1.5. Additional costs and promotional costs are contained in A1.6and A1.7 respectively.

A1.2 PRE-CONSTRUCTION COSTSPre-construction costs have been applied on the same basis for all schemes as follows:

Planning 0.55% of construction costDesign to procurement 25% of total design costsSite investigation 1.25% of civils cost

A1.3 CIVIL ENGINEERING COST ESTIMATES

Preliminaries and Site Overheads

For all Options these costs have been assessed at 15% of the building and civilengineering value. This is deemed to include staff & supervision, offices, welfare &messing, stores, workshops, materials testing etc; temporary power; general serviceplant; site transport, personnel & materials hoists etc.

Barrage and Lagoon Caisson Costs

A reasonably detailed estimate has been prepared for the B3 Barrage caissons basedon approximate quantities for the civil engineering work derived from informationprovided in Vols 3A and 3B of the DOE Report. Temporary casting yard costs assume4 no purpose-built basins on the Severn plus one modified existing yard remote fromthe Severn Estuary – probably in Scotland.

Typical measured work rates used for the caissons items are:

Structural concrete £120 per m3

Formwork (avg of any size, orientation or profile) £40 per m2

Steel bar reinforcement £1050 per tonneBallast (sand) £15 per m3

Ballast (concrete) £110 per m3

The estimated costs include preparatory works, construction, installation and fit-outcosts for the barrage caissons, summarised as follows:

B3 Barrage Caisson EstimatesCasting Yards(Including establishment and removal) £ 96m

Construction(including preparations for tow and installation)

£ 3,868

Installation (including marine plant, dredging, temporary & permanentfoundations, scour protection etc)

£ 1,037m

Fit-Out Works(including extra cost of fitting out deeper caissons at wet dock,gantry cranes, attendance on and civil engineering work inconnection with installation of turbines and sluice gates)

£ 313

Total for Caissons £ 5,315

The same approach had been taken for the B4 Barrage estimate, however the designinformation is less well developed and the quantities are correspondingly moreuncertain. In order to achieve pricing consistency between B4 and B3, unit rates havebeen taken as those used for Cardiff-Weston. Temporary casting yard costs assume 1no purpose-built basin on the Severn. Equivalent figures for B4 Barrage (includingin-situ open sluices) are:

B4 Barrage Caisson EstimatesCasting Yards(Including establishment and removal)

£ 27m

Construction(including preparations for tow and installation)

£ 445

Installation (including marine plant, dredging, temporary & permanentfoundations, scour protection etc)

£ 99

Fit-Out Works(including extra cost of fitting out deeper caissons at wet dock,gantry cranes, attendance on and civil engineering work inconnection with installation of turbines and sluice gates)

£ 37

Total for Caissons £ 608

The average “all-up” cost of the caisson work for B3 and B4 (excluding open sluices)can be expressed as follows:

B3 Barrage B4 BarrageAverage CostQuantity Unit Cost Quantity Unit Cost

Average cost per m3

of caisson structuralconcrete (i.e.excluding concreteused as ballast or incaisson foundations)

7,512,879 m3 £ 707 / m3 665,561 m3 £ 725 m3

Average cost percaisson (all types)

145 no £ 36.7m / unit 21 no £23.0 m / unit

Average cost per m3

of caisson volume24,684,090 m3 £ 215 / m3 1,499,400 m3 £ 322 / m3

Rough assessments have been made of the overall volumes of each type of caisson(turbine / sluice / plain) for each option. Caisson estimates for each option are theproduct of the assessed volumes and the volumetric cost.

B5 barrage, L2 Fleming lagoon, L3b Welsh Grounds lagoon, L3c Peterstone Flatslagoon, and L3d Bridgwater Bay lagoon would require a dredged channel for theturbine caissons to provide sufficient submergence for the turbines. The cost of thisdredging is over and above the cost of dredging included in the “all-up” caisson costfor B3 and B4. Dredging costs have been calculated using a unit rate of £63/ m3

assuming an 80:20 split between hard and weathered rock. The dredging costs asfollows:

Scheme Dredged Volumem3 x 1000

Dredging Cost£ m

B5 - Beachley Barrage 1,264,000 80L2 – Fleming Lagoon on Welsh Grounds 928,800 59L3b – Russell Lagoons Welsh Grounds 928,800 59L3c – Russell Lagoons Peterstone Flats 160,000 10L3d – Bridgewater Bay Lagoon 726,000 46

Caisson costs for barrage and lagoon schemes are as follows:

SchemeCaissonVolumem3 x 1000

O/A CaissonCost£ m

Cost Basis

B1 - Outer Barrage from Minehead toAberthaw

40,872 8,708 Based on B3analysis

B2 –Barrage from Hinkley to LavernockPoint

25,728 5,646 Based on B3analysis

B3 –Barrage from Brean Down toLavernock Point

24,684 5,315 B3 analysis

B4 – Inner Barrage 1,499 608 B4 analysis

B5 - Beachley Barrage 1,608 601 Based on B4analysis

L2 – Fleming Lagoon on WelshGrounds 819 319 Based on B4

analysis

L3a – Russell Lagoons English Grounds 630 200 Based on B4analysis

L3b – Russell Lagoons Welsh Grounds 819 319 Based on B4analysis

L3c – Russell Lagoons Peterstone Flats 1,103 360 Based on B4analysis

L3d – Bridgewater Bay Lagoon 1,044 377 Based on B4analysis

L3e(i) - 90km2 offshore lagoon offBridgwater Bay

1,662 535 Based on B4analysis

L3e(ii) - 50km2 offshore lagoon offBridgwater Bay

913 294 Based on B4analysis

Barrage Embankment Costs

A reasonably detailed estimate has been prepared for the B3 Barrage embankmentsbased on approximate quantities for the civil engineering work derived frominformation provided in Vols 3A and 3B of the DOE Report and a number of crosssections.

Rates used for supply and deposition of embankment materials are as follows:

Placed above –2mOD (per m3)

Placed below –2m OD(per m3)

Control structure rockfill £48 £51Derrick stone £68 £71Containment mounds £20 £22Rip rap £72 £76Filter material Type 1 £31 £33Filter material Type 2 £43 £45Filter material Type 3 £43 £45Sand core Note 1 £7 £7Armour stone (1-3 tonne) £70 £73Rock (0.3 – 1 tonne) Note 2 £43 £46Precast concrete armour units £580 each £610 each1 Assumed to be sourced from dredging arisings2 Applicable to Shoots and other options

The B3 Barrage embankment cost estimate is as follows:

B3 Barrage Embankment Cost Estimate

Preparatory Works(Including rail heads, rock handling harbour, moorings and materialshandling facilities on embankments, casting yard for PC armour unitsand provision of barge fleet)

£ 95m

Welsh Embankment(including filling and armouring)

£42m

Steep Holm Embankment(including dredging and disposal of underlying sediment asnecessary, filling and armouring)

£116m

English Embankment(including dredging and disposal of underlying sediment asnecessary, filling and armouring)

£199m

Fit Out Works(including service road, concrete service ducts between substations 1& 2, connections to public roads each side of embankment)

£53m

Total for Embankments £505m

The overall B3 embankment volume is 11,700,200 m3. This includes the volumeoccupied by pre-cast concrete armour units and the replacement of underlyingsediment removed by dredging where required. No specific allowance has beenincluded for filling materials punched into the seabed and it is suggested that thisshould be regarded as a risk item until a reliable assessment is made. The overalllength of embankment works is 3,475m and the average cost is approximately£145,000 per m.

Equivalent figures for B4 Barrage have been determined as follows using the samerates for supply and deposition of embankment materials as B3:.

B4 Barrage Embankment Cost EstimatePreparatory Works(Including rail heads, rock handling harbour, moorings and materialshandling facilities on embankments and provision of barge fleet –reduced provision as compared with Cardiff Weston)

£ 36m

Welsh Embankment(including filling and armouring)

£ 47m

English Embankment(including filling and armouring)

£ 46m

Fit Out Works(including service road, concrete service ducts between substationsonly, connections to public roads each side of embankment)

£ 30m

Total for Embankments £ 159m

The overall embankment volume is 4,433,500 m3. No specific allowance has beenincluded for filling materials punched into the seabed and it is suggested that thisshould be regarded as a risk item until a reliable assessment is made. The overall

length of embankment works is 4,100m and the average cost is approximately £39,000per m.

Embankment costs for barrage options B1, B2 and B5 were estimated by calculatingan average cost per metre, using the same rates as B3 and B4 applied to a number ofcross sections, and applied to the embankment length. Allowances are included forPreparatory Works (rail heads, rock handling harbour etc) and Fit-Out Works(serviceroads, service ducts, public road connections etc). Overall lengths and average costsper metre run of embankments are as follows:

o/a EmbankmentLength (CSAvaries)

Avg cost permetre run Embankment cost

B1 - Outer Barrage from Mineheadto Aberthaw Note 1

2,380 m £131,000 £ 311m

B2 –Barrage from Hinkley toLavernock Point Note 1

12,450 m £185,000 £2,303m


3,475 m £ 145,000 £ 505m

B4 – Inner Barrage 4,100 m £ 39,000 £ 159mB5 - Beachley Barrage Note 1 710 m £27,000 £ 19mNote:1. Embankment quantities calculated from cross-sections at selected locations. Roughly similar

estimating accuracy to Options B3 (Cardiff Weston) and B4 (Shoots)

Lagoon Embankment and Wall Costs

Average construction costs per metre have been estimated for each of theembankment and wall solutions submitted in response to the Call for Proposals.These rates include plant, labour and material costs but exclude VAT, contingency,optimism bias, design and supervision, and ground investigation costs.

Construction Technology MaximumHeight (m)

Average cost permetre run (£/m)

Applicability

12.5 28,49222.5 52,717

Geosynthetic reinforcedembankment

32.5 79,398

All L3 lagoons

Halcyon piled wall(applicable only to

11 60,000 Shallowerlengths of L3bWelsh Groundslagoon andL3dBridgwaterBay lagoon Note 1

11 21,705L2 tied wall panels13.5 32,558

L2 WelshGrounds lagoon

Note:1. The Halcyon wall has not been applied to deeper applications. Refer in

Section 6.1.

The comparison of unit rates shows that the geosynthetic reinforced embankmentsare lower cost compared to the Halcyon wall and this solution has therefore beenapplied for the cost estimate of all L3 lagoons.

The estimated embankment and wall costs of the L2 and L3 lagoons are as follows:

o/aEmbankment/Wall

Length (CSAvaries)

Avg costper metre

run

Embankment cost

L2 – Fleming Lagoon on Welsh Grounds 29,992 m £26,507 £795m

L3a – Russell Lagoons English Grounds 17,916 m £50,458 £904m

L3b – Russell Lagoons Welsh Grounds 29,992 m £37,443 £1,123m

L3c – Russell Lagoons Peterstone Flats 21,338 m £47,427 £1,012m

L3d – Bridgewater Bay Lagoon 14,590 m £43,729 £638m

L3e(i) - 90km2 offshore lagoon offBridgwater Bay

39,000 m £ 60,923 £2,376m

L3e(ii) - 50km2 offshore lagoon offBridgwater Bay

26,000 m £ 56,231 £1,462m

Tidal Fence Civil Engineering Costs

Tidal fence civil engineering costs have been developed using the same principles asapply to the barrage. However, the two fence options have different configurationsand therefore different cost build ups as follows:

Component F1a F1b

Dredging and Bed Preparation for Tidal Fences £493m £616m

Dredging and Bed Preparation for the Non-GeneratingBarriers

£164m n /a

Flow Barriers in Areas Too Shallow for GeneratorModules

£299m n/a

Axial Flow Turbine Foundation Modules £535m £1,672m

Shallow Water Generator Foundation Modules Included in Item 4 above

Access bridge £335m n/a

Totals £1,826m £2,288m

Navigation Locks

A reasonably detailed estimate has been prepared for the B3 Barrage navigation locksbased on approximate quantities for the civil engineering work derived frominformation provided in Vols 3A and 3B of the DOE Report and a number of crosssections.

Costs for navigation locks (excluding the lock gates which are included in the M&E sectionof estimate) are as follows:

B3 BarrageMain Navigation and Small Craft Lock Complex (towards Welsh Shore):

£m

Rubble Mound Breakwater (west)(Including dredging and disposal of underlying sediment as necessary, rock filland armouring, concrete capping, service road and wave wall)

140

Rubble Mound Breakwater (east)(Including dredging and disposal of underlying sediment as necessary, rock filland armouring, concrete capping, service road and wave wall)

70

Breakwater Caissons(Including preparation, construction, installation and fit-out of 16 no plainbreakwater caissons)

213

Channel Caissons(Including preparation, construction, installation and fit-out of lock channelcaissons)

174

Gate Caissons(Including preparation, construction, installation and fit-out of 5 no lock gatecaissons)

149

Small Craft Lock Caisson(Including preparation, construction, installation and fit-out of 1 no small craftlock caisson)

21

Landing Area(including approx 1.3m m3 of fill, 30,000 m2 of apron slab, allowances forfendering and dock furniture, lock control and other buildings, flood & berthlighting, floating landing stages for small craft)

66

Civil Engineering Work and Attendance in connection with Lock Gates(for 5 no main lock gates and 2 pairs of sector gates for small craft lock)

3

Approach Works(Including lead-in structures (approx 3000m length), waiting berths, allowancesfor navigation aids and remote navigation lights)

25

Bascule Bridges(Including 2 no x 70m span & 1 no x 15m span bridges)

25

Total for Main Navigation Lock Complex 886

B3 BarrageSmall Boat Lock (towards English Shore):

£m

Rubble Mound Breakwater(Including dredging and disposal of underlying sediment as necessary, rock filland armouring, concrete capping, service road and wave wall)

73

Small Craft Lock Caisson(Including preparation, construction, installation and fit-out of 1 no small craftlock caissons)

21

Landing Area(including apron slab, allowances for fendering and dock furniture, lockcontrol building, flood & berth lighting, floating landing stages for small craft)

1

Civil Engineering Work and Attendance in connection with Lock Gates(for 2 pairs of sector gates for small craft lock)

Less than 1

Approach Works(Including vertical screen breakwater and suspended quay structures,allowances for navigation aids and remote navigation lights)

17

Bascule Bridges(Including 1 no x 15m span bridge)

4

Total for Small Boat Lock Complex 116

Equivalent figures for the single Navigation Lock for B4 Barrage are:

B4 Navigation Lock Complex £ m

Rubble Mound Breakwater(not required for Shoots)

-

Small Craft Lock Caissons(Including preparation, construction, installation and fit-out of 1 no small craftlock caisson)

29

Landing Area(including allowances for fendering and dock furniture, lock control, flood &berth lighting, floating landing stages for small craft)

2

Civil Engineering Work and Attendance in connection with Lock Gates(for 2 pairs of sector gates for small craft lock)

Less than 1

Approach Works(Including waiting berths, allowances for navigation aids and lights)

17

Bascule Bridges(Including 1 no x 20m span bridge)

5

Total for Main Navigation Lock Complex 53

There is little available information on the construction of the B4 navigation lock. Forthe purposes of pricing consistency, it has been priced as a concrete caisson similar tothe Small Craft Locks in the Cardiff Weston option.

B1 and B2 Barrages are assumed to have the same lock requirements as B3 and theyhave been priced the same.

B5 Beachley Barrage is assumed to have the same lock requirements as B4 and hasbeen priced the same.

An allowance of £20m has been included for a small boat lock in Lagoon L3d toprovide navigable access to the River Parrett. The same has been allowed forLagoons L3e(i) and (ii) to provide access into the basin for maintenance anddredging.

No other options require navigation locks.

In summary, the navigation lock (excluding gate) costs are as follows:

Scheme Navigation Lock Cost(£m)

B1 - Outer Barrage from Minehead to Aberthaw 1,002B2 –Barrage from Hinkley to Lavernock Point 1,002B3 –Barrage from Brean Down to Lavernock Point 1,002B4 – Inner Barrage 53B5 - Beachley Barrage 53L2 – Fleming Lagoon on Welsh Grounds 0L3a – Russell Lagoons English Grounds 0L3b – Russell Lagoons Welsh Grounds 0L3c – Russell Lagoons Peterstone Flats 0L3d – Bridgewater Bay Lagoon 20L3e(i) - 90km2 offshore lagoon off Bridgwater Bay 20L3e(ii) - 50km2 offshore lagoon off Bridgwater Bay 20

Surface Buildings

For B3 barrage, 3 no substations are included in the proposals detailed in DOE Vols3A / B. A notional allowance has been made for these together with other buildingswhich might be expected as follows. Costs are based on historical analyses of similarfunction buildings. These costs include architectural fit-out and normal buildingservices:

B3 Barrage Surface Building Cost Estimate

400 kV electrical substation #1 (centre embankment)say 1500 m2 @ £9,000

£ 13m

400 kV electrical substation #2 (centre embankment)say 1500 m2 @ £9,000

£13m

400 kV electrical substation #3 (built on caisson in construction yard -permanent location above turbine caisson towards Welsh shore)say 1500 m2 @ £8,000

£ 12m

Control Centre - assume 2 storey (centre embankment)say 600 m2 @ £15,000

£ 9m

Storessay 3600 m2 @ £3,000

£ 11m

Workshopsay 1800 m2 @ £4,000

£ 7m

Sundry other buildingssay 2250 m2 @ £6,000

£ 14m

Tourist centresay 600 m2 @ £6,000

£ 4m

Total for Surface Buildings £ 83m

Equivalent figures for the single powerhouse building indicated for B4 Barrage are asfollows, equating to £40,000 per MW installed capacity:

B3 Barrage Surface Building Cost Estimate

Main power house over the turbine damsay 6000 m2 @ £7,000(assumed that control facilities, stores , workshops, visitor centre etcwill be accommodated within this building or area allowance)

£ 42m

Options B1 and B2 are assumed to have the same requirements as B3 (Cardiff-Weston) and have been priced the same.

The surface building requirements for schemes of similar installed capacity to B4 (ie.F1b, L2, L3b, L3c, L3d and L3e(i)) has been taken as the same as B4. Requirements forsmaller schemes have been estimated at £40,000 per MW of installed capacity as forB4.

A1. 4 MECHANICAL AND ELECTRICAL COSTS

Generating Equipment

Turbine and generator costs have been based on the traditional use of scaling ofknown plant costs using parameters of power and head, speed and machinediameter, escalated to a 2008 price level. For multiple unit bulb turbines of 35 to 40MW per unit capacity, a cost of £0.676m per MW has been applied consistently forthe larger capacity barrages and lagoons. Straflo units, proposed for the Inner andBeachley Barrages, are expected to be more economical at £0.611m per MW. Theseunit costs include turbines and generators, turbine control gates, contingency,delivery, installation, commissioning and contractor’s oncosts and profit. For the F1fences, a figure of £2m per MW of installed capacity has been used in the analyses forthe turbine, gearbox and generator (refer to section 8.4) .

The turbine and generator costs have been based on the installed capacities estimatedfor this study (as set out in section 6.3). The generating costs are therefore as follows:

Scheme Installed Capacity(MW)

Turbine andGenerator Cost

(£m/MW)

Turbine andGenerator Cost

(£m)B1 - Outer Barrage from Mineheadto Aberthaw

14,800 0.676 10,005

B2 –Barrage from Hinkley toLavernock Point

9,000 0.676 6,084


8,640 0.676 5,841

B4 – Inner Barrage 1050 0.611 642B5 - Beachley Barrage 625 0.611 382F1a – Cardiff to Weston TidalFence

256 2.75 704

F1b – Aberthaw to Minehead TidalFence

1280 2.25 2,880

L2 – Fleming Lagoon on WelshGrounds

1360 0.676 919

L3a – Russell Lagoons EnglishGrounds

760 0.676 514

L3b – Russell Lagoons WelshGrounds

1360 0.676 919

L3c – Russell Lagoons PeterstoneFlats

1120 0.676 757

L3d – Bridgewater Bay Lagoon 1360 0.676 919L3e(i) - 90km2 offshore lagoonoff Bridgwater Bay

1360 0.676 919

L3e(ii) - 50km2 offshore lagoonoff Bridgwater Bay

760 0.676 514

Gates

Turbine control gate costs are included in the unit rates applied for the turbine andgenerator costs.

Sluice gate and associated stoplog panel costs have been estimated for B3 and B4barrages based on available design information. The gates for B1 and B2 barragesare assumed to be similar to B3. Sluice gates for B5 and lagoons are assumed to besimilar to B4. The number of gates has been estimated for each scheme and the totalcost based on the relevant cost per gate. These estimates include fabrication, delivery,installation and commissioning but exclude design fees and contingency. Gantrycranes for stoplog handling have also been included.

Temporary bulkheads for caisson floating have been estimated for B3 barrage andapplied to B1 and B2.

Lock gates have similarly been estimated for B3 and B4 based on available designs.Lock gates for B1 and B2 are assumed to be similar to B3. Lock gates for B5 areassumed to be similar to the smaller lock gates required for B4. Lock gates for L3dBridgwater Bay and L3e offshore lagoons are assumed to be similar to the small craftlock gates required for B3. Other lagoons do not include navigation locks.

A summary gate costs is as follows:

Barrage Gate Cost Estimates B1 B2 B3 B4 B5

Gate Items UnitCosts(£k)

No Cost (£k) No Cost (£k) No Cost (£k) No Cost (£k) No Cost (£k)

22m span Radial Sluice gate,hoist and elec controls 4,661 213 992,750 128 596,582 117 545,314 0 0 0 014m span Radial Sluice gate,hoist and elec controls 2,166 213 461,358 54 116,964 49 106,134 0 0 0 0Set of 22m stoplog panels(U/S orD/S) 1,793 24 43,032 13 23,309 12 21,516 0 0 0 0Set of 14m stoplog panels(U/S orD/S) 796 24 19,114 7 5,575 6 4,778 0 0 0 0Set of 22m stoplog BIPs (U/S orD/S) 564 426 240,264 256 144,384 234 131,976 0 0 0 0Set of 14m stoplog BIPs (U/S orD/S) 294 426 125,244 108 31,752 98 28,812 0 0 0 0

Gantry crane 180te capacity 1,000 12 12,000 4 4,000 3 3,000 0 0 0 0

Gantry crane 320te capacity 1,500 12 18,000 6 9,000 6 9,000 0 0 0 0Temporary bulkheads forcaisson floating 1,293 142 183,691 88 113,837 80 103,488 0 0 0 0

B3 E

quiv

alen

ts

Temporary bulkheads 808 142 114,807 44 35,574 40 32,340 0 0 0 030m span Radial Sluice gate,hoist and elec controls 5,776 0 0 0 0 0 0 42 242,626 26 150,197Set of 14m stoplog panels(U/S orD/S) 1,215 0 0 0 0 0 0 8 9,724 8 9,724Set of 14m stoplog BIPs (U/S orD/S) 336 0 0 0 0 0 0 168 56,448 104 34,944

B4 E

quiv

alen

ts

Gantry crane 180te capacity 1,000 0 0 0 0 0 0 2 2,000 2 2,000Main Lock Gates - 170,000 - 170,000 - 170,000 - 45,000 - 45,000Small Lock Gates - 4,000 - 4,000 - 4,000 - 0 - 0

Totals 2,384,260 - 1,254,977 - 1,160,358 - 355,798 - 241,865

Land Connected Lagoon Gate Cost Estimates L3a L2/L3b L3c L3d

Gate Items UnitCosts(£k)

No Cost (£k) No Cost (£k) No Cost (£k) No Cost (£k)

30m span Radial Sluice gate, hoist and elec controls 5,776 25 144,420 41 236,849 33 190,634 41 236,816Set of 14m stoplog panels(U/S or D/S) 1,215 8 9,724 16 19,448 12 14,586 16 19,448Set of 14m stoplog BIPs (U/S or D/S) 336 100 33,600 164 55,104 132 44,352 160 53,760Gantry crane 180te capacity 1,000 2 2,000 4 4,000 4 4,000 4 4,000Main Lock Gates - 0 - 0 - 0 - 7,000

Totals 189,744 - 315,401 - 253,572 - 321,024

Offshore Lagoon Gate Cost Estimates L3e(i) L3e(ii)

Gate Items Unit Costs(£k)

No Cost(£k)

No Cost(£k)

30m span Radial Sluice gate, hoist and eleccontrols 5,776 40 236,816 22 127,072Set of 14m stoplog panels(U/S or D/S) 1,215 16 19,448 9 10,935Set of 14m stoplog BIPs (U/S or D/S) 336 160 53,760 88 29,568Gantry crane 180te capacity 1,000 4 4,000 2 8,000Main Lock Gates - 7,000 - 7,000

Totals 321,024 182,575

Grid ConnectionAn assessment has been made of the principal components required between thegenerator terminals and the connections to onshore substations. A 15% contingencyhas been applied to the cost estimate for each scheme. The grid connection costestimates are as follows:

SchemeGrid Connection Cost

(£m)B1 - Outer Barrage from Minehead to Aberthaw 868B2 –Barrage from Hinkley to Lavernock Point 557B3 –Barrage from Brean Down to Lavernock Point 500B4 – Inner Barrage 96B5 - Beachley Barrage 47F1a – Cardiff to Weston Tidal Fence 217F1b – Aberthaw to Minehead Tidal Fence 334L2 – Fleming Lagoon on Welsh Grounds 113L3a – Russell Lagoons English Grounds 91L3b – Russell Lagoons Welsh Grounds 113L3c – Russell Lagoons Peterstone Flats 95L3d – Bridgewater Bay Lagoon 90L3e(i) - 90km2 offshore lagoon off Bridgwater Bay 98L3e(ii) - 50km2 offshore lagoon off Bridgwater Bay 84

A breakdown of the grid connection costs are provided below:

Large Barrage Grid Connection CostBreakdown B1 Barrage B2 Barrage B3 Barrage

ItemVoltage(kV)

Unit Cost(£k) Quantity

Total Cost(£k) Quantity


Total Cost(£k)

Offshore installation All 5000 4 20000 4 20000 4 20000Standard Generator Disconnectors 8.6 10 1110 11100 675 6750 648 6480Incoming SF6 Generator Breakers 8.6 200 188 37600 116 23200 108 21600Fault Current Limiters 8.6 25 0 0 0 0 0 0Earthing Transformer + Resistor 8.6 750 93 69750 57 42750 54 40500Variable Frequency Starting Drives 8.6 1500 0 0 0 0 0 0Series Reactor 8.6 500 0 0 0 0 0 0Connection (180MW) per LV TXwinding 8.6 2000 94 188000 58 116000 54 108000Cable (35MW) per block of four 8.6 20 93 1860 57 1140 54 1080Protection / 8 machine group 8.6 500 47 23500 29 14500 27 135003-Winding Transformer (360MVA) 400 / 8.6 4000 47 188000 29 116000 27 108000350mm^2 cable (km) 400 300 36 10800 22 6600 21 6300Disconnectors 400 35 114 3990 70 2450 66 23105-Switch Meshed Substation 400 10000 5 50000 3 30000 3 300003 x 2000mm^2 single core cable (km) 400 600 150 90000 108 64800 72 43200Cable Joints 400 60 900 54000 600 36000 500 30000Cable Sealing Ends 400 150 40 6000 24 3600 24 3600

Sub-totals - 754,600 - 483,790 - 434,570Contingency at 15% 113,190 - 72,569 - 65,006

Totals - 867,790 - 556,359 - 499,756

B4 Barrage Grid Connection cost Breakdown

Item Voltage (kV)Unit Cost(£k) Quantity

Total Cost(£k)

Offshore installation All 5000 4 20000Standard Generator Disconnectors 8.6 10 90 900Incoming SF6 Generator Breakers 8.6 200 16 3200Fault Current Limiters 8.6 25 0 0Earthing Transformer + Resistor 8.6 750 8 6000Variable Frequency Starting Drives 8.6 1500 0 0Series Reactor 8.6 500 0 0Connection (360MW) per LV TXwinding 8.6 2000 8 16000Cable (40MW) per block of four 8.6 20 8 160Protection / 8 machine group 8.6 500 4 20003-Winding Transformer (320MVA) 400 / 8.6 4000 4 16000350mm^2 cable (km) 400 300 3 900Disconnectors 400 35 12 4204-Switch Meshed Substation 400 8000 1 80003 x 2000mm^2 single core cable (km) 400 600 4.1 2460Cable Joints 400 60 100 6000Cable Sealing Ends 400 150 8 1200

Sub-total 83,240Contingency at 15% 12,486

Total 95,726

B5 Barrage Grid Connection Cost Breakdown

ItemVoltage(kV)


Total Cost(£k)

Offshore installation All 5000 1 50000.69/33kV Transformer(2.5MVA) 33/0.69 70 50 3500SF6 Breakers 33 40 100 4000Cable (35MVA) 33 200 3 600400/33kV transformer(120MVA) 400/33 1000 2 20003-switch offshoresubstation 400 7500 2 15000Cable (150MW) 400 300 4 1200Cable Joints 400 10 20 200Cable Sealing Ends 400 150 4 600Protection / 4 machinegroup 33 500 2 10004-switch mesh (onshore) 400 8000 1 8000


Total 47,265

F1a Tidal Fence Grid Connection Cost Breakdown

Item Voltage (kV)UnitCost (£k) Quantity

TotalCost(£k)

Offshore installation All 5000 4 200000.69/33kV Transformer(5MVA) 33/0.69 70 256 17920SF6 Breakers 33 40 24 960Cable (35MVA) 33 200 15 3000132/33kV transformer(120MVA) 132/33 1000 12 120004-switch meshedsubstation 132 2000 12 24000Cable (35MVA) 132 900 6.72 6048400/132kV transformer(360MVA) 400/132 2000 4 80004-switch meshedsubstation 400 10000 4 40000Cable (360MW) 400 600 4 2400Cable Joints 400 25 60 1500Cable Sealing Ends 11 150 8 1200Protection / 7 machinegroup 33 438 37 16187.56-switch mesh 400 12000 3 36000


Total 217,598

Option F1a is based on F1b costs but pro-rata’d in terms of installed capacity and structure length and estimated at £334m.

Land Connected Lagoon Grid Connection CostBreakdown L2 and L3b L3a L3c L3d

ItemVoltage(kV)




Total Cost(£k) Quantity Total Cost (£k)

Offshore installation All 5000 4 20000 4 20000 4 20000 4 20000Standard GeneratorDisconnectors 8.6 10 72 720 57 570 72 720 72 720Incoming SF6 GeneratorBreakers 8.6 200 12 2400 12 2400 12 2400 12 2400Fault Current Limiters 8.6 25 0 0 0 0 0 0 0 0Earthing Transformer + Resistor 8.6 750 6 4500 5 3750 6 4500 6 4500Variable Frequency StartingDrives 8.6 1500 0 0 0 0 0 0 0 0Series Reactor 8.6 500 0 0 0 0 0 0 0 0Connection (180MW) per LV TXwinding 8.6 2000 6 12000 6 12000 6 12000 6 12000Cable (35MW) per block of four 8.6 20 6 120 5 100 6 120 6 120Protection / 8 machine group 8.6 500 3 1500 3 1500 3 1500 3 15003-Winding Transformer(360MVA) 400 / 8.6 4000 3 12000 3 12000 3 12000 3 12000350mm^2 cable (km) 400 300 3 900 3 900 3 900 3 900Disconnectors 400 35 10 350 10 350 10 350 10 3505-Switch Meshed Substation 400 10000 1 10000 0 0 0 0 0 04-Switch Meshed Substation 400 8000 0 0 1 8000 1 8000 1 80003 x 2000mm^2 single core cable(km) 400 600 44.55 26730 17.9 10740 21 12600 14.5 8700Cable Joints 400 60 100 6000 100 6000 100 6000 100 6000

Cable Sealing Ends 400 150 8 1200 8 1200 8 1200 8 1200Sub-totals - 98,420 - 79,510 - 82,290 - 78,390

Contingency at 15% - 14,763 - 11,927 - 12,344 - 11,759Totals - 113,183 - 91,437 - 94,634 - 90,149

OffshoreLagoon Grid Connection Cost Breakdown L3e(i) L3e(ii)

ItemVoltage(kV)


TotalCost (£k) Quantity

Total Cost(£k)

Offshore installation All 5000 4 20000 4 20000Standard GeneratorDisconnectors 8.6 10 72 720 42 420Incoming SF6 GeneratorBreakers 8.6 200 12 2400 8 1600Fault Current Limiters 8.6 25 0 0 0 0Earthing Transformer + Resistor 8.6 750 6 4500 4 3000Variable Frequency StartingDrives 8.6 1500 0 0 0 0Series Reactor 8.6 500 0 0 0 0Connection (180MW) per LV TXwinding 8.6 2000 6 12000 4 8000Cable (35MW) per block of four 8.6 20 6 120 4 80Protection / 8 machine group 8.6 500 3 1500 2 10003-Winding Transformer(360MVA) 400 / 8.6 4000 3 12000 2 8000350mm^2 cable (km) 400 300 3 900 2 600Disconnectors 400 35 10 350 8 2805-Switch Meshed Substation 400 10000 1 10000 1 100003 x 2000mm^2 single core cable(km) 400 600 21.75 13050 21.75 13050Cable Joints 400 60 100 6000 100 6000Cable Sealing Ends 400 150 8 1200 8 1200

Sub-totals - 84,740 - 73,230Contingency at 15% - 12,711 - 10,985

Totals - 97,451 - 84,215

A1.5 TIDAL REEF

Very little design information is available on which to estimate the cost of a tidal reef. Therefore, a very high level estimate has beenprepared and the basis for this estimate is set out in the table below. The estimate makes a number of very broad high level assumptionsand approximations. None of these is considered precautionary and the overall estimate should therefore be treated with caution as it islikely to represent an optimistic estimate given the level of design information available and the absence of any prototype or analogueon which to base the estimate.

Item Cost Estimate (£m) Estimate BasisPreliminaries andSite Overheads

647 15% of civil engineering construction cost

Embankments 311 Same as B1 on the assumption that these are required as a barrier to flow in order to achieve a head differential across thereef

Navigation Locks 0 No navigation lock as such is proposed although the reef structure will require rotating siphons with a longer span thanelsewhere on the reef to provide a navigable opening. There will be costs associated with these elements that are notincluded in this estimate but there is no information available to determine the quantum.

Surface Buildings 83 Same as B1Caissons 3,919 This includes the structures which support the turbine and siphon units and incorporate service tunnels, cable ducts, access

shafts etc. This also includes the cost of the siphon units themselves which house the turbine generators. It is broadlyestimated that for stability the structure will require 45% of the weight of the B1 structure due to the reduced headdifferential. Therefore, the overall structure cost is taken as 45% of the cost of the B1 caissons. This assumes that the costper tonne of barrage and reef structural components, including precasting, transportation, positioning, placing and infilling,are the same. It also assumes that the reef structure is a gravity structure and not piled (piled strucutres would be expectedto be more expensive). This is not precautionary as it does not allow for special factors such as the complexity of themovable siphons.

Generating Plant 13,750 5000MW at £2.75m per MW. Turbine generators will be akin to tidal stream turbines. The upper bound cost per MW asapplied to the tidal fence has been adopted to allow for fabrication, installation, commissioning and to allow for elementsrequired to fit the turbines into the structure. A furhter discussion on the cost of tidal stream turbines is included in Section6.4.

Grid Connection 300 34% of the B1 cost pro-rata’d on the basis of installed capacityGates 1,080 Allows for 2000 gates (2 per turbine), each 10m by 4m to control flow through the siphon and to act as stoplogs for turbine

access. Cost based on £13,000 per sq. m which is equivalent to B1. Also allows £300m for temporary bulkheads duringconstruction.

Total ConstructionCost

£20,050

A1.6 ADDITIONAL ITEMS

The following costs have been applied on the same basis for all schemes:

Item Cost BasisDesign and supervision (includes outlineand detailed design and constructionsupervision)

4% of overall civil engineering and gatecost (except B1, B2, B3 and R1 which are3.5%) plus 1.5% on value of caissons

Site investigation (during outline anddetailed design and construction)

0.25% of overall civil engineering cost

Contingencies 15% of overall civil engineering and gatecost

Contractor’s Oncosts and Profit 9.25% of overall civil engineering andgate cost

Ancillary costs

Ancillary costs are intended to cover works which are a consequence of the schemeconstruction and operation but which do not form part of the scheme. Theyprimarily arise as a consequence of the effect of the scheme on the tidal range andestuary geomorphology. The costs therefore cover works required on land drainage,sea defences, permanent dredging installations, improvements to navigation andharbour works etc. The ancillary costs have been assessed in relation to the extentand severity of the potential consequences in order to inform a comparison of therelative ancillary costs between options. A detailed breakdown of these costs has notbeen prepared. Ancillary costs allocated to each scheme are as follows:

Scheme Ancillary Cost (£m)B1 - Outer Barrage from Minehead to Aberthaw 400B2 –Barrage from Hinkley to Lavernock Point 350B3 –Barrage from Brean Down to Lavernock Point 300B4 – Inner Barrage 100B5 - Beachley Barrage 80F1a – Cardiff to Weston Tidal Fence 10F1b – Aberthaw to Minehead Tidal Fence 10L2 – Fleming Lagoon on Welsh Grounds 50L3a – Russell Lagoons English Grounds 50L3b – Russell Lagoons Welsh Grounds 50L3c – Russell Lagoons Peterstone Flats 50L3d – Bridgewater Bay Lagoon 50L3e(i) - 90km2 offshore lagoon off Bridgwater Bay 10

L3e(ii) - 50km2 offshore lagoon off Bridgwater Bay 10R1 – Reef from Minehead to Aberthaw 50

A1.7 PROMOTIONAL COSTS

The project promotor’s project management costs have been included as 0.5% of theoverall construction cost for all schemes.

Severn Tidal Power - Options Analysis

CONSTRUCTION & OPERATIONAL COSTS Base Case - No Habitat Compensation

Option No B1 B2 B3 B4 B5Option Name Aberthaw - Minehead Barrage Cardiff - Hinkley Point

BarrageCardiff - Weston Barrage Shoots Barrage Beachley Barrage

Installed capacity (MW) 14800 9000 8640 1050 625Annual Energy Output (TWh) 25.3 19.3 16.8 2.77 1.59

Pre Construction Period (years) 4 4 4 4 4Construction Period (years) 10 8 7 5 4

First generation (years from start of const) 7 7 6 5 4

PRE-CONSTRUCTIONTOTAL PLANNING 317,414,634 271,637,173 209,225,373 29,967,394 21,656,261

CONSTRUCTIONPreliminaries & Site Overheads 1,515,593,727 1,355,003,993 1,035,722,544 129,272,441 104,057,312

GENERAL CIVILSEmbankments 311,066,774 2,303,000,000 505,365,908 159,038,723 19,358,340

Other CivilsNavigation Locks 1,001,840,886 1,001,840,886 1,001,840,886 52,733,413 52,733,413Surface Buildings 83,100,000 83,100,000 83,100,000 42,000,000 25,000,000

TOTAL GENERAL CIVILS 1,396,007,660 3,387,940,886 1,590,306,794 253,772,136 97,091,753

CAISSONSCaissons 8,707,950,519 5,645,419,070 5,314,510,167 608,044,136 600,623,659

TOTAL CAISSONS 8,707,950,519 5,645,419,070 5,314,510,167 608,044,136 600,623,659

M&EGenerating Plant 10,005,416,667 6,084,375,000 5,841,000,000 642,000,000 382,000,000Grid Connection 868,000,000 557,000,000 500,000,000 96,000,000 47,000,000

Gates 2,384,000,000 1,255,000,000 1,160,000,000 356,000,000 242,000,000TOTAL M&E 13,257,416,667 7,896,375,000 7,501,000,000 1,094,000,000 671,000,000

ADDITIONAL ITEMSDesign and Supervision 425,773,346 333,580,413 271,489,685 38,808,174 31,424,546

Outline + Detail Design and Supervision based on 4% on o/a civil works and gates only (exceptB1, B2 & B3 which are 3.5%) plus 1.5% on value of caissons

Site Investigation 3,490,019 8,469,852 3,975,767 634,430 242,729(eg site investigation during design & construction)

Ancilliaries 400,000,000 350,000,000 300,000,000 100,000,000 80,000,000(eg navigation and land drainage improvements)

Contingencies 1,873,193,727 1,543,253,993 1,209,722,544 182,672,441 140,957,312(15% on civil works and gates only)

Contractors Oncosts and Profit 1,155,136,132 951,673,296 745,995,569 112,648,005 86,923,6769.25% on civil works and gates only

TOTAL ADDITIONAL ITEMS 3,857,593,223 3,186,977,555 2,531,183,564 434,763,050 339,548,262TOTAL CONSTRUCTION COSTS 28,734,561,795 21,471,716,504 17,972,723,069 2,519,851,763 1,812,320,986

VAT - - - - -TOTAL CONSTRUCTION COSTS (inc VAT) 28,734,561,795 21,471,716,504 17,972,723,069 2,519,851,763 1,812,320,986

COMPENSATORY HABITATSLoss of Inter-tidal Areas: 27,949 25,697 20,240 4,946 3,514

Cost of Compensatory Habitats: - - - - -VAT - - - - -

PROMOTIONAL COSTSClient Project Management Costs 143,672,809 107,358,583 89,863,615 12,599,259 9,061,605

(Project promoter delivery costs)

VAT - - - - -

TOTAL PROJECT COST 29,195,649,239 21,850,712,259 18,271,812,058 2,562,418,416 1,843,038,852

BARRAGES



Option No L2 L3a L3b L3c L3d L3e(i) L3e(ii)Option Name Welsh Grounds Lagoon -

FlemingRussel Lagoon (English

Grounds)Russel Lagoon (Welsh

Grounds)Russel Lagoon

(Peterstone Flats)Bridgwater Bay (LandConnected Lagoon)

91sq.km OffshoreLagoon


Installed capacity (MW) 1360 760 1360 1120 1360 1360 760Annual Energy Output (TWh) 2.31 1.41 2.31 2.33 2.64 2.6 1.32

Pre Construction Period (years) 4 4 4 4 4 4 4Construction Period (years) 5 4 5 5 5 6 5

First generation (years from start of const) 5 4 5 5 5 6 5

PRE-CONSTRUCTIONTOTAL PLANNING 41,664,432 37,829,982 51,264,760 46,941,614 38,889,710 92,442,903 56,181,699

CONSTRUCTIONPreliminaries & Site Overheads 161,338,849 170,191,222 222,600,290 212,191,772 161,509,048 445,874,445 271,018,834

GENERAL CIVILSEmbankments 795,000,000 904,208,147 1,123,001,931 1,012,611,816 637,726,985 2,375,496,302 1,462,392,226

Other CivilsNavigation Locks 0 0 0 0 20,000,000 20,000,000 20,000,000Surface Buildings 42,000,000 30,400,000 42,000,000 42,000,000 42,000,000 42,000,000 30,400,000

TOTAL GENERAL CIVILS 837,000,000 934,608,147 1,165,001,931 1,054,611,816 699,726,985 2,437,496,302 1,512,792,226

CAISSONSCaissons 319,000,000 200,000,000 319,000,000 360,000,000 377,000,000 535,000,000 294,000,000

TOTAL CAISSONS 319,000,000 200,000,000 319,000,000 360,000,000 377,000,000 535,000,000 294,000,000

M&EGenerating Plant 919,000,000 514,000,000 919,000,000 757,000,000 919,000,000 919,000,000 514,000,000Grid Connection 113,000,000 91,000,000 113,000,000 95,000,000 90,000,000 98,000,000 84,000,000

Gates 315,000,000 190,000,000 315,000,000 254,000,000 321,000,000 321,000,000 183,000,000TOTAL M&E 1,347,000,000 795,000,000 1,347,000,000 1,106,000,000 1,330,000,000 1,338,000,000 781,000,000

ADDITIONAL ITEMSDesign and Supervision 42,202,500 37,020,964 50,812,551 47,851,060 40,931,583 92,473,028 55,539,546

Outline + Detail Design and Supervision based on 4% on o/a civil works and gates only(except B1, B2 & B3 which are 3.5%) plus 1.5% on value of caissons

Site Investigation 2,092,500 2,336,520 2,912,505 2,636,530 1,749,317 6,093,741 3,781,981(eg site investigation during design & construction)

Ancilliaries 50,000,000 50,000,000 50,000,000 50,000,000 50,000,000 10,000,000 10,000,000(eg navigation and land drainage improvements)

Contingencies 220,650,000 198,691,222 269,850,290 250,291,772 209,659,048 494,024,445 298,468,834(15% on civil works and gates only)

Contractors Oncosts and Profit 136,067,500 122,526,254 166,407,679 154,346,593 129,289,746 304,648,408 184,055,7819.25% on civil works and gates only

TOTAL ADDITIONAL ITEMS 451,012,500 410,574,960 539,983,024 505,125,955 431,629,695 907,239,622 551,846,141TOTAL CONSTRUCTION COSTS 3,115,351,349 2,510,374,329 3,593,585,244 3,237,929,543 2,999,865,727 5,663,610,369 3,410,657,201

VAT - - - - - - -TOTAL CONSTRUCTION COSTS (inc VAT) 3,115,351,349 2,510,374,329 3,593,585,244 3,237,929,543 2,999,865,727 5,663,610,369 3,410,657,201

COMPENSATORY HABITATSLoss of Inter-tidal Areas: 6,500 2,000 6,500 2,700 5,500 0 0

Cost of Compensatory Habitats: - - - - - - -VAT - - - - - - -

PROMOTIONAL COSTSClient Project Management Costs 15,576,757 12,551,872 17,967,926 16,189,648 14,999,329 28,318,052 17,053,286


VAT - - - - - - -

TOTAL PROJECT COST 3,172,592,538 2,560,756,183 3,662,817,931 3,301,060,805 3,053,754,766 5,784,371,325 3,483,892,187

LAGOONS



Option No F1a F1b R1Option Name Cardiff to Weston Tidal

fenceAberthaw to Minehead

Tidal fenceAberthaw to Minehead

Tidal Reef

Installed capacity (MW) 256 1280 5000Annual Energy Output (TWh) 0.7 3.30 13

Pre Construction Period (years) 4 4 4Construction Period (years) 5 10 10

First generation (years from start of const) 4 3 3

PRE-CONSTRUCTIONTOTAL PLANNING 71,245,729 83,701,452 165,177,258

CONSTRUCTIONPreliminaries & Site Overheads 377,136,000 349,518,750 647,000,000

GENERAL CIVILSEmbankments 0 0 311,000,000

Other Civils 1,826,000,000 2,288,125,000Navigation Locks 0 0 0Surface Buildings 10,240,000 42,000,000 83,100,000

TOTAL GENERAL CIVILS 1,836,240,000 2,330,125,000 394,100,000

CAISSONSCaissons 678,000,000 - 3,919,000,000

TOTAL CAISSONS 678,000,000 - 3,919,000,000

M&EGenerating Plant 512,000,000 2,560,000,000 10,000,000,000Grid Connection 217,000,000 334,000,000 300,000,000

Gates - - 1,080,000,000TOTAL M&E 729,000,000 2,894,000,000 11,380,000,000

ADDITIONAL ITEMSDesign and Supervision 73,626,300 61,165,781 185,657,625


Site Investigation 4,590,600 5,825,313 985,250(eg site investigation during design & construction)

Ancilliaries 10,000,000 10,000,000 50,000,000(eg navigation and land drainage improvements)

Contingencies 377,136,000 349,518,750 808,965,000(15% on civil works and gates only)

Contractors Oncosts and Profit 232,567,200 215,536,563 498,861,7509.25% on civil works and gates only

TOTAL ADDITIONAL ITEMS 697,920,100 642,046,406 1,544,469,625TOTAL CONSTRUCTION COSTS 4,318,296,100 6,215,690,156 17,884,569,625

VAT - - -TOTAL CONSTRUCTION COSTS (inc VAT) 4,318,296,100 6,215,690,156 17,884,569,625

COMPENSATORY HABITATSLoss of Inter-tidal Areas: 2,024 2,795 8,600

Cost of Compensatory Habitats: - - -VAT - - -

PROMOTIONAL COSTSClient Project Management Costs 21,591,481 31,078,451 89,422,848


VAT - - -

TOTAL PROJECT COST 4,411,133,309 6,330,470,059 18,139,169,731

TIDAL FENCE & TIDAL REEF


SUMMARY OF CASH FLOWS Base Case - No Habitat Compensation

Option No B1 B2 B3 B4 B5Option Name Aberthaw -

Minehead BarrageCardiff - Hinkley

Point BarrageCardiff - Weston

BarrageShoots Barrage Beachley Barrage

Installed capacity (MW) 14800 9000 8640 1050 625Pre Construction Period (years) 4 4 4 4 4

Construction Period (years) 10 8 7 5 4First generation (years from start of const) 7 7 6 5 4

Refurbishment Interval (years) 40 40 40 40 40Refurbishment Period (years) 5 5 5 2 2Pre-Construction Annual Cost 79,353,659 67,909,293 52,306,343 7,491,849 5,414,065

Annual Construction Costs 2,887,823,460 2,697,384,386 2,580,369,526 506,490,204 455,345,648Annual Operation Costs 359,182,022 375,755,039 314,522,654 44,097,406 31,715,617

Annual Refurbishment Costs(inc operation costs) 1,759,940,356 1,227,567,539 1,132,262,654 268,797,406 165,415,617

YEAR2010 79,353,659 67,909,293 52,306,343 7,491,849 5,414,0652011 79,353,659 67,909,293 52,306,343 7,491,849 5,414,0652012 79,353,659 67,909,293 52,306,343 7,491,849 5,414,0652013 79,353,659 67,909,293 52,306,343 7,491,849 5,414,0652014 2,887,823,460 2,697,384,386 2,580,369,526 506,490,204 455,345,6482015 2,887,823,460 2,697,384,386 2,580,369,526 506,490,204 455,345,6482016 2,887,823,460 2,697,384,386 2,580,369,526 506,490,204 455,345,6482017 2,887,823,460 2,697,384,386 2,580,369,526 506,490,204 455,345,6482018 2,887,823,460 2,697,384,386 2,580,369,526 506,490,204 31,715,6172019 2,887,823,460 2,697,384,386 2,580,369,526 44,097,406 31,715,6172020 2,887,823,460 2,697,384,386 2,737,630,853 44,097,406 31,715,6172021 2,887,823,460 2,885,261,905 314,522,654 44,097,406 31,715,6172022 3,067,414,472 375,755,039 314,522,654 44,097,406 31,715,6172023 3,157,209,977 375,755,039 314,522,654 44,097,406 31,715,6172024 359,182,022 375,755,039 314,522,654 44,097,406 31,715,6172025 359,182,022 375,755,039 314,522,654 44,097,406 31,715,6172026 359,182,022 375,755,039 314,522,654 44,097,406 31,715,6172027 359,182,022 375,755,039 314,522,654 44,097,406 31,715,6172028 359,182,022 375,755,039 314,522,654 44,097,406 31,715,6172029 359,182,022 375,755,039 314,522,654 44,097,406 31,715,6172030 359,182,022 375,755,039 314,522,654 44,097,406 31,715,6172031 359,182,022 375,755,039 314,522,654 44,097,406 31,715,6172032 359,182,022 375,755,039 314,522,654 44,097,406 31,715,6172033 359,182,022 375,755,039 314,522,654 44,097,406 31,715,6172034 359,182,022 375,755,039 314,522,654 44,097,406 31,715,6172035 359,182,022 375,755,039 314,522,654 44,097,406 31,715,617

2036 359,182,022 375,755,039 314,522,654 44,097,406 31,715,6172037 359,182,022 375,755,039 314,522,654 44,097,406 31,715,6172038 359,182,022 375,755,039 314,522,654 44,097,406 31,715,6172039 359,182,022 375,755,039 314,522,654 44,097,406 31,715,6172040 359,182,022 375,755,039 314,522,654 44,097,406 31,715,6172041 359,182,022 375,755,039 314,522,654 44,097,406 31,715,6172042 359,182,022 375,755,039 314,522,654 44,097,406 31,715,6172043 359,182,022 375,755,039 314,522,654 44,097,406 31,715,6172044 359,182,022 375,755,039 314,522,654 44,097,406 31,715,6172045 359,182,022 375,755,039 314,522,654 44,097,406 31,715,6172046 359,182,022 375,755,039 314,522,654 44,097,406 31,715,6172047 359,182,022 375,755,039 314,522,654 44,097,406 31,715,6172048 359,182,022 375,755,039 314,522,654 44,097,406 31,715,6172049 359,182,022 375,755,039 314,522,654 44,097,406 31,715,6172050 359,182,022 375,755,039 314,522,654 44,097,406 31,715,617

Continues to 120 years after operational start date

BARRAGES



Option No L2 L3a L3b L3c L3d L3e(i) L3e(ii)Option Name Welsh Grounds

Lagoon - FlemingRussel Lagoon

(English Grounds)Russel Lagoon

(Welsh Grounds)Russel Lagoon

(Peterstone Flats)Bridgwater Bay

(Land ConnectedLagoon)



Installed capacity (MW) 1360 760 1360 1120 1360 1360 760Pre Construction Period (years) 4 4 4 4 4 4 4

Construction Period (years) 5 4 5 5 5 6 5First generation (years from start of const) 5 4 5 5 5 6 5

Refurbishment Interval (years) 40 40 40 40 40 40 40Refurbishment Period (years) 2 2 2 2 2 2 2Pre-Construction Annual Cost 10,416,108 9,457,495 12,816,190 11,735,403 9,722,427 23,110,726 14,045,425

Annual Construction Costs 626,185,621 630,731,550 722,310,634 650,823,838 602,973,011 948,654,737 685,542,097Annual Operation Costs 54,518,649 43,931,551 62,887,742 56,663,767 52,497,650 99,113,181 59,686,501

Annual Refurbishment Costs(inc operation costs) 376,168,649 223,831,551 384,537,742 321,613,767 374,147,650 420,763,181 239,586,501

YEAR2010 10,416,108 9,457,495 12,816,190 11,735,403 9,722,427 23,110,726 14,045,4252011 10,416,108 9,457,495 12,816,190 11,735,403 9,722,427 23,110,726 14,045,4252012 10,416,108 9,457,495 12,816,190 11,735,403 9,722,427 23,110,726 14,045,4252013 10,416,108 9,457,495 12,816,190 11,735,403 9,722,427 23,110,726 14,045,4252014 626,185,621 630,731,550 722,310,634 650,823,838 602,973,011 948,654,737 685,542,0972015 626,185,621 630,731,550 722,310,634 650,823,838 602,973,011 948,654,737 685,542,0972016 626,185,621 630,731,550 722,310,634 650,823,838 602,973,011 948,654,737 685,542,0972017 626,185,621 630,731,550 722,310,634 650,823,838 602,973,011 948,654,737 685,542,0972018 626,185,621 43,931,551 722,310,634 650,823,838 602,973,011 948,654,737 685,542,0972019 54,518,649 43,931,551 62,887,742 56,663,767 52,497,650 948,654,737 59,686,5012020 54,518,649 43,931,551 62,887,742 56,663,767 52,497,650 99,113,181 59,686,5012021 54,518,649 43,931,551 62,887,742 56,663,767 52,497,650 99,113,181 59,686,5012022 54,518,649 43,931,551 62,887,742 56,663,767 52,497,650 99,113,181 59,686,5012023 54,518,649 43,931,551 62,887,742 56,663,767 52,497,650 99,113,181 59,686,5012024 54,518,649 43,931,551 62,887,742 56,663,767 52,497,650 99,113,181 59,686,5012025 54,518,649 43,931,551 62,887,742 56,663,767 52,497,650 99,113,181 59,686,5012026 54,518,649 43,931,551 62,887,742 56,663,767 52,497,650 99,113,181 59,686,5012027 54,518,649 43,931,551 62,887,742 56,663,767 52,497,650 99,113,181 59,686,5012028 54,518,649 43,931,551 62,887,742 56,663,767 52,497,650 99,113,181 59,686,5012029 54,518,649 43,931,551 62,887,742 56,663,767 52,497,650 99,113,181 59,686,5012030 54,518,649 43,931,551 62,887,742 56,663,767 52,497,650 99,113,181 59,686,5012031 54,518,649 43,931,551 62,887,742 56,663,767 52,497,650 99,113,181 59,686,5012032 54,518,649 43,931,551 62,887,742 56,663,767 52,497,650 99,113,181 59,686,5012033 54,518,649 43,931,551 62,887,742 56,663,767 52,497,650 99,113,181 59,686,5012034 54,518,649 43,931,551 62,887,742 56,663,767 52,497,650 99,113,181 59,686,5012035 54,518,649 43,931,551 62,887,742 56,663,767 52,497,650 99,113,181 59,686,501

2036 54,518,649 43,931,551 62,887,742 56,663,767 52,497,650 99,113,181 59,686,5012037 54,518,649 43,931,551 62,887,742 56,663,767 52,497,650 99,113,181 59,686,5012038 54,518,649 43,931,551 62,887,742 56,663,767 52,497,650 99,113,181 59,686,5012039 54,518,649 43,931,551 62,887,742 56,663,767 52,497,650 99,113,181 59,686,5012040 54,518,649 43,931,551 62,887,742 56,663,767 52,497,650 99,113,181 59,686,5012041 54,518,649 43,931,551 62,887,742 56,663,767 52,497,650 99,113,181 59,686,5012042 54,518,649 43,931,551 62,887,742 56,663,767 52,497,650 99,113,181 59,686,5012043 54,518,649 43,931,551 62,887,742 56,663,767 52,497,650 99,113,181 59,686,5012044 54,518,649 43,931,551 62,887,742 56,663,767 52,497,650 99,113,181 59,686,5012045 54,518,649 43,931,551 62,887,742 56,663,767 52,497,650 99,113,181 59,686,5012046 54,518,649 43,931,551 62,887,742 56,663,767 52,497,650 99,113,181 59,686,5012047 54,518,649 43,931,551 62,887,742 56,663,767 52,497,650 99,113,181 59,686,5012048 54,518,649 43,931,551 62,887,742 56,663,767 52,497,650 99,113,181 59,686,5012049 54,518,649 43,931,551 62,887,742 56,663,767 52,497,650 99,113,181 59,686,5012050 54,518,649 43,931,551 62,887,742 56,663,767 52,497,650 99,113,181 59,686,501


LAGOONS




fenceAberthaw to

Minehead Tidal fenceAberthaw to

Minehead Tidal Reef

Installed capacity (MW) 256 1280 5000Pre Construction Period (years) 4 4 4

Construction Period (years) 5 10 10First generation (years from start of const) 4 3 3

Refurbishment Interval (years) 20 20 20Refurbishment Period (years) 4 8 8Pre-Construction Annual Cost 17,811,432 20,925,363 41,294,314

Annual Construction Costs 867,977,516 624,676,861 1,797,399,247Annual Operation Costs 75,570,182 108,774,578 312,979,968

Annual Refurbishment Costs(inc operation costs) 128,000,000 320,000,000 1,250,000,000

YEAR2010 17,811,432 20,925,363 41,294,3142011 17,811,432 20,925,363 41,294,3142012 17,811,432 20,925,363 41,294,3142013 17,811,432 20,925,363 41,294,3142014 867,977,516 624,676,861 1,797,399,2472015 867,977,516 624,676,861 1,797,399,2472016 892,915,676 638,273,683 1,836,521,7432017 918,609,538 651,870,505 1,875,644,2392018 943,547,698 665,467,327 1,914,766,7352019 75,570,182 679,064,150 1,953,889,2322020 75,570,182 692,660,972 1,993,011,7282021 75,570,182 706,257,794 2,032,134,2242022 75,570,182 719,854,616 2,071,256,7202023 75,570,182 733,451,438 2,110,379,2162024 75,570,182 108,774,578 312,979,9682025 75,570,182 108,774,578 312,979,9682026 75,570,182 108,774,578 312,979,9682027 75,570,182 108,774,578 312,979,9682028 75,570,182 108,774,578 312,979,9682029 75,570,182 108,774,578 312,979,9682030 75,570,182 108,774,578 312,979,9682031 75,570,182 108,774,578 312,979,9682032 75,570,182 108,774,578 312,979,9682033 75,570,182 108,774,578 312,979,9682034 75,570,182 108,774,578 312,979,9682035 184,677,636 415,177,756 1,523,857,4722036 184,677,636 415,177,756 1,523,857,4722037 184,677,636 415,177,756 1,523,857,4722038 184,677,636 415,177,756 1,523,857,4722039 75,570,182 415,177,756 1,523,857,4722040 75,570,182 415,177,756 1,523,857,4722041 75,570,182 415,177,756 1,523,857,4722042 75,570,182 415,177,756 1,523,857,4722043 75,570,182 108,774,578 312,979,9682044 75,570,182 108,774,578 312,979,9682045 75,570,182 108,774,578 312,979,9682046 75,570,182 108,774,578 312,979,9682047 75,570,182 108,774,578 312,979,9682048 75,570,182 108,774,578 312,979,9682049 75,570,182 108,774,578 312,979,9682050 75,570,182 108,774,578 312,979,968




SUMMARY OF ENERGY YIELDS Base Case - No Habitat Compensation







First generation (years from start of const) 7 7 6 5 4Annual Energy Yield during refurbishment 20.24 15.44 13.44 1.385 0.795

Refurbishment Interval (years) 40 40 40 40 40Refurbishment Period (years) 5 5 5 2 2

Annual Energy yield during construction is: 6.325 4.825 4.2 0 0Note: Overwrirtten cells are in italics

YEAR2010 - - - - -2011 - - - - -2012 - - - - -2013 - - - - -2014 - - - - -2015 - - - - -2016 - - - - -2017 - - - - -2018 - - - - 1.592019 - - - 2.77 1.592020 - - 8.40 2.77 1.592021 - 9.65 12.60 2.77 1.592022 12.65 14.48 16.80 2.77 1.592023 17.39 19.30 16.80 2.77 1.592024 22.14 19.30 16.80 2.77 1.592025 25.30 19.30 16.80 2.77 1.592026 25.30 19.30 16.80 2.77 1.592027 25.30 19.30 16.80 2.77 1.592028 25.30 19.30 16.80 2.77 1.592029 25.30 19.30 16.80 2.77 1.592030 25.30 19.30 16.80 2.77 1.592031 25.30 19.30 16.80 2.77 1.592032 25.30 19.30 16.80 2.77 1.592033 25.30 19.30 16.80 2.77 1.592034 25.30 19.30 16.80 2.77 1.592035 25.30 19.30 16.80 2.77 1.59

2036 25.30 19.30 16.80 2.77 1.592037 25.30 19.30 16.80 2.77 1.592038 25.30 19.30 16.80 2.77 1.592039 25.30 19.30 16.80 2.77 1.592040 25.30 19.30 16.80 2.77 1.592041 25.30 19.30 16.80 2.77 1.592042 25.30 19.30 16.80 2.77 1.592043 25.30 19.30 16.80 2.77 1.592044 25.30 19.30 16.80 2.77 1.592045 25.30 19.30 16.80 2.77 1.592046 25.30 19.30 16.80 2.77 1.592047 25.30 19.30 16.80 2.77 1.592048 25.30 19.30 16.80 2.77 1.592049 25.30 19.30 16.80 2.77 1.592050 25.30 19.30 16.80 2.77 1.59


BARRAGES













First generation (years from start of const) 5 4 5 5 5 6 5Annual Energy Yield during refurbishment 1.155 0.705 1.155 1.165 1.32 1.3 0.66

Refurbishment Interval (years) 40 40 40 40 40 40 40Refurbishment Period (years) 2 2 2 2 2 2 2

Annual Energy yield during construction is: 0Note: Overwrirtten cells are in italics

YEAR2010 - - - - - - -2011 - - - - - - -2012 - - - - - - -2013 - - - - - - -2014 - - - - - - -2015 - - - - - - -2016 - - - - - - -2017 - - - - - - -2018 - 1.41 - - - - -2019 2.31 1.41 2.31 2.33 2.64 - 1.322020 2.31 1.41 2.31 2.33 2.64 2.60 1.322021 2.31 1.41 2.31 2.33 2.64 2.60 1.322022 2.31 1.41 2.31 2.33 2.64 2.60 1.322023 2.31 1.41 2.31 2.33 2.64 2.60 1.322024 2.31 1.41 2.31 2.33 2.64 2.60 1.322025 2.31 1.41 2.31 2.33 2.64 2.60 1.322026 2.31 1.41 2.31 2.33 2.64 2.60 1.322027 2.31 1.41 2.31 2.33 2.64 2.60 1.322028 2.31 1.41 2.31 2.33 2.64 2.60 1.322029 2.31 1.41 2.31 2.33 2.64 2.60 1.322030 2.31 1.41 2.31 2.33 2.64 2.60 1.322031 2.31 1.41 2.31 2.33 2.64 2.60 1.322032 2.31 1.41 2.31 2.33 2.64 2.60 1.322033 2.31 1.41 2.31 2.33 2.64 2.60 1.322034 2.31 1.41 2.31 2.33 2.64 2.60 1.322035 2.31 1.41 2.31 2.33 2.64 2.60 1.32

2036 2.31 1.41 2.31 2.33 2.64 2.60 1.322037 2.31 1.41 2.31 2.33 2.64 2.60 1.322038 2.31 1.41 2.31 2.33 2.64 2.60 1.322039 2.31 1.41 2.31 2.33 2.64 2.60 1.322040 2.31 1.41 2.31 2.33 2.64 2.60 1.322041 2.31 1.41 2.31 2.33 2.64 2.60 1.322042 2.31 1.41 2.31 2.33 2.64 2.60 1.322043 2.31 1.41 2.31 2.33 2.64 2.60 1.322044 2.31 1.41 2.31 2.33 2.64 2.60 1.322045 2.31 1.41 2.31 2.33 2.64 2.60 1.322046 2.31 1.41 2.31 2.33 2.64 2.60 1.322047 2.31 1.41 2.31 2.33 2.64 2.60 1.322048 2.31 1.41 2.31 2.33 2.64 2.60 1.322049 2.31 1.41 2.31 2.33 2.64 2.60 1.322050 2.31 1.41 2.31 2.33 2.64 2.60 1.32


LAGOONS



Option No F1a F1b L2 R1Option Name Cardiff to Weston Tidal

fenceAberthaw to

Minehead Tidal fenceWelsh Grounds

Lagoon - FlemingAberthaw to

Minehead Tidal Reef

Installed capacity (MW) 256 1280 1360 5000Annual Energy Output (TWh) 0.7 3.3 2.31 13

Pre Construction Period (years) 4 4 4 4Construction Period (years) 5 10 5 10

First generation (years from start of const) 4 3 5 3Annual Energy Yield during refurbishment 0.525 2.8875 1.155 11.375

Refurbishment Interval (years) 20 20 40 20Refurbishment Period (years) 4 8 2 8

Annual Energy yield during construction is: 0.233333333 0.4125 0 0.4125Note: Overwrirtten cells are in italics

YEAR2010 - - - -2011 - - - -2012 - - - -2013 - - - -2014 - - - -2015 - - - -2016 0.23 - - -2017 0.23 0.41 - -2018 0.23 0.83 - 0.412019 0.70 1.24 2.31 0.832020 0.70 1.65 2.31 1.242021 0.70 2.06 2.31 1.652022 0.70 2.48 2.31 6.502023 0.70 2.89 2.31 8.662024 0.70 3.30 2.31 10.832025 0.70 3.30 2.31 13.002026 0.70 3.30 2.31 13.002027 0.70 3.30 2.31 13.002028 0.70 3.30 2.31 13.002029 0.70 3.30 2.31 13.002030 0.70 3.30 2.31 13.002031 0.70 3.30 2.31 13.002032 0.70 3.30 2.31 13.002033 0.70 3.30 2.31 13.002034 0.70 3.30 2.31 13.002035 0.53 2.89 2.31 13.002036 0.53 2.89 2.31 11.382037 0.53 2.89 2.31 11.382038 0.53 2.89 2.31 11.382039 0.70 2.89 2.31 11.382040 0.70 2.89 2.31 11.382041 0.70 2.89 2.31 11.382042 0.70 2.89 2.31 11.382043 0.70 3.30 2.31 11.382044 0.70 3.30 2.31 13.002045 0.70 3.30 2.31 13.002046 0.70 3.30 2.31 13.002047 0.70 3.30 2.31 13.002048 0.70 3.30 2.31 13.002049 0.70 3.30 2.31 13.002050 0.70 3.30 2.31 13.00




CONSTRUCTION & OPERATIONAL COSTS Base Case - Ration of 1:1 Habitat Compensation












TOTAL CAISSONS 8,707,950,519 5,645,419,070 5,314,510,167 608,044,136 600,623,659


Gates 2,384,000,000 1,255,000,000 1,160,000,000 356,000,000 242,000,000TOTAL M&E 13,257,416,667 7,896,375,000 7,501,000,000 1,094,000,000 671,000,000










Cost of Compensatory Habitats: 1,816,685,000 1,670,305,000 1,315,600,000 321,490,000 228,410,000VAT - - - - -



VAT - - - - -


BARRAGES







(Peterstone Flats)Bridgwater Bay (Land

Connected Lagoon)91sq.km Offshore

Lagoon50sq.km Offshore

Lagoon










TOTAL CAISSONS 319,000,000 200,000,000 319,000,000 360,000,000 377,000,000 535,000,000 294,000,000


Gates 315,000,000 190,000,000 315,000,000 254,000,000 321,000,000 321,000,000 183,000,000TOTAL M&E 1,347,000,000 795,000,000 1,347,000,000 1,106,000,000 1,330,000,000 1,338,000,000 781,000,000










Cost of Compensatory Habitats: 422,500,000 130,000,000 422,500,000 175,500,000 357,500,000 - -VAT - - - - - - -



VAT - - - - - - -


LAGOONS






Tidal Reef










TOTAL CAISSONS 678,000,000 - 3,919,000,000


Gates - - 1,080,000,000TOTAL M&E 729,000,000 2,894,000,000 11,380,000,000










Cost of Compensatory Habitats: 131,560,000 181,668,500 559,000,000VAT - - -



VAT - - -




SUMMARY OF CASH FLOWS Base Case - Ration of 1:1 Habitat Compensation










YEAR2010 79,353,659 67,909,293 52,306,343 7,491,849 5,414,0652011 79,353,659 67,909,293 52,306,343 7,491,849 5,414,0652012 79,353,659 67,909,293 52,306,343 7,491,849 5,414,0652013 79,353,659 67,909,293 52,306,343 7,491,849 5,414,0652014 3,069,491,960 2,906,172,511 2,768,312,383 570,788,204 512,448,1482015 3,069,491,960 2,906,172,511 2,768,312,383 570,788,204 512,448,1482016 3,069,491,960 2,906,172,511 2,768,312,383 570,788,204 512,448,1482017 3,069,491,960 2,906,172,511 2,768,312,383 570,788,204 512,448,1482018 3,069,491,960 2,906,172,511 2,768,312,383 570,788,204 31,715,6172019 3,069,491,960 2,906,172,511 2,768,312,383 44,097,406 31,715,6172020 3,069,491,960 2,906,172,511 2,925,573,710 44,097,406 31,715,6172021 3,069,491,960 3,094,050,030 314,522,654 44,097,406 31,715,6172022 3,249,082,972 375,755,039 314,522,654 44,097,406 31,715,6172023 3,338,878,477 375,755,039 314,522,654 44,097,406 31,715,6172024 359,182,022 375,755,039 314,522,654 44,097,406 31,715,6172025 359,182,022 375,755,039 314,522,654 44,097,406 31,715,6172026 359,182,022 375,755,039 314,522,654 44,097,406 31,715,6172027 359,182,022 375,755,039 314,522,654 44,097,406 31,715,6172028 359,182,022 375,755,039 314,522,654 44,097,406 31,715,6172029 359,182,022 375,755,039 314,522,654 44,097,406 31,715,6172030 359,182,022 375,755,039 314,522,654 44,097,406 31,715,6172031 359,182,022 375,755,039 314,522,654 44,097,406 31,715,6172032 359,182,022 375,755,039 314,522,654 44,097,406 31,715,6172033 359,182,022 375,755,039 314,522,654 44,097,406 31,715,6172034 359,182,022 375,755,039 314,522,654 44,097,406 31,715,6172035 359,182,022 375,755,039 314,522,654 44,097,406 31,715,617

2036 359,182,022 375,755,039 314,522,654 44,097,406 31,715,6172037 359,182,022 375,755,039 314,522,654 44,097,406 31,715,6172038 359,182,022 375,755,039 314,522,654 44,097,406 31,715,6172039 359,182,022 375,755,039 314,522,654 44,097,406 31,715,6172040 359,182,022 375,755,039 314,522,654 44,097,406 31,715,6172041 359,182,022 375,755,039 314,522,654 44,097,406 31,715,6172042 359,182,022 375,755,039 314,522,654 44,097,406 31,715,6172043 359,182,022 375,755,039 314,522,654 44,097,406 31,715,6172044 359,182,022 375,755,039 314,522,654 44,097,406 31,715,6172045 359,182,022 375,755,039 314,522,654 44,097,406 31,715,6172046 359,182,022 375,755,039 314,522,654 44,097,406 31,715,6172047 359,182,022 375,755,039 314,522,654 44,097,406 31,715,6172048 359,182,022 375,755,039 314,522,654 44,097,406 31,715,6172049 359,182,022 375,755,039 314,522,654 44,097,406 31,715,6172050 359,182,022 375,755,039 314,522,654 44,097,406 31,715,617

Continues to 120 years after operational start date.

BARRAGES





(English Grounds)Russel Lagoon (Welsh










YEAR2010 10,416,108 9,457,495 12,816,190 11,735,403 9,722,427 23,110,726 14,045,4252011 10,416,108 9,457,495 12,816,190 11,735,403 9,722,427 23,110,726 14,045,4252012 10,416,108 9,457,495 12,816,190 11,735,403 9,722,427 23,110,726 14,045,4252013 10,416,108 9,457,495 12,816,190 11,735,403 9,722,427 23,110,726 14,045,4252014 710,685,621 663,231,550 806,810,634 685,923,838 674,473,011 948,654,737 685,542,0972015 710,685,621 663,231,550 806,810,634 685,923,838 674,473,011 948,654,737 685,542,0972016 710,685,621 663,231,550 806,810,634 685,923,838 674,473,011 948,654,737 685,542,0972017 710,685,621 663,231,550 806,810,634 685,923,838 674,473,011 948,654,737 685,542,0972018 710,685,621 43,931,551 806,810,634 685,923,838 674,473,011 948,654,737 685,542,0972019 54,518,649 43,931,551 62,887,742 56,663,767 52,497,650 948,654,737 59,686,5012020 54,518,649 43,931,551 62,887,742 56,663,767 52,497,650 99,113,181 59,686,5012021 54,518,649 43,931,551 62,887,742 56,663,767 52,497,650 99,113,181 59,686,5012022 54,518,649 43,931,551 62,887,742 56,663,767 52,497,650 99,113,181 59,686,5012023 54,518,649 43,931,551 62,887,742 56,663,767 52,497,650 99,113,181 59,686,5012024 54,518,649 43,931,551 62,887,742 56,663,767 52,497,650 99,113,181 59,686,5012025 54,518,649 43,931,551 62,887,742 56,663,767 52,497,650 99,113,181 59,686,5012026 54,518,649 43,931,551 62,887,742 56,663,767 52,497,650 99,113,181 59,686,5012027 54,518,649 43,931,551 62,887,742 56,663,767 52,497,650 99,113,181 59,686,5012028 54,518,649 43,931,551 62,887,742 56,663,767 52,497,650 99,113,181 59,686,5012029 54,518,649 43,931,551 62,887,742 56,663,767 52,497,650 99,113,181 59,686,5012030 54,518,649 43,931,551 62,887,742 56,663,767 52,497,650 99,113,181 59,686,5012031 54,518,649 43,931,551 62,887,742 56,663,767 52,497,650 99,113,181 59,686,5012032 54,518,649 43,931,551 62,887,742 56,663,767 52,497,650 99,113,181 59,686,5012033 54,518,649 43,931,551 62,887,742 56,663,767 52,497,650 99,113,181 59,686,5012034 54,518,649 43,931,551 62,887,742 56,663,767 52,497,650 99,113,181 59,686,5012035 54,518,649 43,931,551 62,887,742 56,663,767 52,497,650 99,113,181 59,686,501

2036 54,518,649 43,931,551 62,887,742 56,663,767 52,497,650 99,113,181 59,686,5012037 54,518,649 43,931,551 62,887,742 56,663,767 52,497,650 99,113,181 59,686,5012038 54,518,649 43,931,551 62,887,742 56,663,767 52,497,650 99,113,181 59,686,5012039 54,518,649 43,931,551 62,887,742 56,663,767 52,497,650 99,113,181 59,686,5012040 54,518,649 43,931,551 62,887,742 56,663,767 52,497,650 99,113,181 59,686,5012041 54,518,649 43,931,551 62,887,742 56,663,767 52,497,650 99,113,181 59,686,5012042 54,518,649 43,931,551 62,887,742 56,663,767 52,497,650 99,113,181 59,686,5012043 54,518,649 43,931,551 62,887,742 56,663,767 52,497,650 99,113,181 59,686,5012044 54,518,649 43,931,551 62,887,742 56,663,767 52,497,650 99,113,181 59,686,5012045 54,518,649 43,931,551 62,887,742 56,663,767 52,497,650 99,113,181 59,686,5012046 54,518,649 43,931,551 62,887,742 56,663,767 52,497,650 99,113,181 59,686,5012047 54,518,649 43,931,551 62,887,742 56,663,767 52,497,650 99,113,181 59,686,5012048 54,518,649 43,931,551 62,887,742 56,663,767 52,497,650 99,113,181 59,686,5012049 54,518,649 43,931,551 62,887,742 56,663,767 52,497,650 99,113,181 59,686,5012050 54,518,649 43,931,551 62,887,742 56,663,767 52,497,650 99,113,181 59,686,501


LAGOONS





Tidal fenceAberthaw to

Minehead Tidal Reef






YEAR2010 17,866,432 20,980,363 41,294,3142011 17,866,432 20,980,363 41,294,3142012 17,866,432 20,980,363 41,294,3142013 17,866,432 20,980,363 41,294,3142014 902,329,516 646,863,711 1,853,299,2472015 902,329,516 646,863,711 1,853,299,2472016 927,498,676 660,548,033 1,892,421,7432017 953,430,538 674,232,355 1,931,544,2392018 978,599,698 687,916,677 1,970,666,7352019 76,270,182 701,601,000 2,009,789,2322020 76,270,182 715,285,322 2,048,911,7282021 76,270,182 728,969,644 2,088,034,2242022 76,270,182 742,653,966 2,127,156,7202023 76,270,182 756,338,288 2,166,279,2162024 76,270,182 109,474,578 312,979,9682025 76,270,182 109,474,578 312,979,9682026 76,270,182 109,474,578 312,979,9682027 76,270,182 109,474,578 312,979,9682028 76,270,182 109,474,578 312,979,9682029 76,270,182 109,474,578 312,979,9682030 76,270,182 109,474,578 312,979,9682031 76,270,182 109,474,578 312,979,9682032 76,270,182 109,474,578 312,979,9682033 76,270,182 109,474,578 312,979,9682034 76,270,182 109,474,578 312,979,9682035 185,202,636 415,790,256 1,528,857,4722036 185,202,636 415,790,256 1,528,857,4722037 185,202,636 415,790,256 1,528,857,4722038 185,202,636 415,790,256 1,528,857,4722039 76,270,182 415,790,256 1,528,857,4722040 76,270,182 415,790,256 1,528,857,4722041 76,270,182 415,790,256 1,528,857,4722042 76,270,182 415,790,256 1,528,857,4722043 76,270,182 109,474,578 312,979,9682044 76,270,182 109,474,578 312,979,9682045 76,270,182 109,474,578 312,979,9682046 76,270,182 109,474,578 312,979,9682047 76,270,182 109,474,578 312,979,9682048 76,270,182 109,474,578 312,979,9682049 76,270,182 109,474,578 312,979,9682050 76,270,182 109,474,578 312,979,968




SUMMARY OF ENERGY YIELDS Base Case - Ration of 1:1 Habitat Compensation









, Annual Energy yield during construction is: 6.325 4.825 4.2 0 0Note: Overwrirtten cells are in italics

YEAR2010 - - - - -2011 - - - - -2012 - - - - -2013 - - - - -2014 - - - - -2015 - - - - -2016 - - - - -2017 - - - - -2018 - - - - 1.592019 - - - 2.77 1.592020 - - 8.40 2.77 1.592021 - 9.65 12.60 2.77 1.592022 12.65 14.48 16.80 2.77 1.592023 17.39 19.30 16.80 2.77 1.592024 22.14 19.30 16.80 2.77 1.592025 25.30 19.30 16.80 2.77 1.592026 25.30 19.30 16.80 2.77 1.592027 25.30 19.30 16.80 2.77 1.592028 25.30 19.30 16.80 2.77 1.592029 25.30 19.30 16.80 2.77 1.592030 25.30 19.30 16.80 2.77 1.592031 25.30 19.30 16.80 2.77 1.592032 25.30 19.30 16.80 2.77 1.592033 25.30 19.30 16.80 2.77 1.592034 25.30 19.30 16.80 2.77 1.592035 25.30 19.30 16.80 2.77 1.59

2036 25.30 19.30 16.80 2.77 1.592037 25.30 19.30 16.80 2.77 1.592038 25.30 19.30 16.80 2.77 1.592039 25.30 19.30 16.80 2.77 1.592040 25.30 19.30 16.80 2.77 1.592041 25.30 19.30 16.80 2.77 1.592042 25.30 19.30 16.80 2.77 1.592043 25.30 19.30 16.80 2.77 1.592044 25.30 19.30 16.80 2.77 1.592045 25.30 19.30 16.80 2.77 1.592046 25.30 19.30 16.80 2.77 1.592047 25.30 19.30 16.80 2.77 1.592048 25.30 19.30 16.80 2.77 1.592049 25.30 19.30 16.80 2.77 1.592050 25.30 19.30 16.80 2.77 1.59


BARRAGES





(English Grounds)Russel Lagoon (Welsh









, Annual Energy yield during construction is: 0Note: Overwrirtten cells are in italics

YEAR2010 - - - - - - -2011 - - - - - - -2012 - - - - - - -2013 - - - - - - -2014 - - - - - - -2015 - - - - - - -2016 - - - - - - -2017 - - - - - - -2018 - 1.41 - - - - -2019 2.31 1.41 2.31 2.33 2.64 - 1.322020 2.31 1.41 2.31 2.33 2.64 2.60 1.322021 2.31 1.41 2.31 2.33 2.64 2.60 1.322022 2.31 1.41 2.31 2.33 2.64 2.60 1.322023 2.31 1.41 2.31 2.33 2.64 2.60 1.322024 2.31 1.41 2.31 2.33 2.64 2.60 1.322025 2.31 1.41 2.31 2.33 2.64 2.60 1.322026 2.31 1.41 2.31 2.33 2.64 2.60 1.322027 2.31 1.41 2.31 2.33 2.64 2.60 1.322028 2.31 1.41 2.31 2.33 2.64 2.60 1.322029 2.31 1.41 2.31 2.33 2.64 2.60 1.322030 2.31 1.41 2.31 2.33 2.64 2.60 1.322031 2.31 1.41 2.31 2.33 2.64 2.60 1.322032 2.31 1.41 2.31 2.33 2.64 2.60 1.322033 2.31 1.41 2.31 2.33 2.64 2.60 1.322034 2.31 1.41 2.31 2.33 2.64 2.60 1.322035 2.31 1.41 2.31 2.33 2.64 2.60 1.322036 2.31 1.41 2.31 2.33 2.64 2.60 1.322037 2.31 1.41 2.31 2.33 2.64 2.60 1.322038 2.31 1.41 2.31 2.33 2.64 2.60 1.322039 2.31 1.41 2.31 2.33 2.64 2.60 1.322040 2.31 1.41 2.31 2.33 2.64 2.60 1.322041 2.31 1.41 2.31 2.33 2.64 2.60 1.322042 2.31 1.41 2.31 2.33 2.64 2.60 1.322043 2.31 1.41 2.31 2.33 2.64 2.60 1.322044 2.31 1.41 2.31 2.33 2.64 2.60 1.322045 2.31 1.41 2.31 2.33 2.64 2.60 1.322046 2.31 1.41 2.31 2.33 2.64 2.60 1.322047 2.31 1.41 2.31 2.33 2.64 2.60 1.322048 2.31 1.41 2.31 2.33 2.64 2.60 1.322049 2.31 1.41 2.31 2.33 2.64 2.60 1.322050 2.31 1.41 2.31 2.33 2.64 2.60 1.32


LAGOONS




fenceAberthaw to

Minehead Tidalfence

Aberthaw toMinehead Tidal Reef



First generation (years from start of const) 4 3 3Annual Energy Yield during refurbishment 0.525 2.8875 11.375

Refurbishment Interval (years) 20 20 20Refurbishment Period (years) 4 8 8

, Annual Energy yield during construction is: 0.233333333 0.4125 0.4125Note: Overwrirtten cells are in italics

YEAR2010 - - -2011 - - -2012 - - -2013 - - -2014 - - -2015 - - -2016 0.23 - -2017 0.23 0.41 -2018 0.23 0.83 0.412019 0.70 1.24 0.832020 0.70 1.65 1.242021 0.70 2.06 1.652022 0.70 2.48 6.502023 0.70 2.89 8.662024 0.70 3.30 10.832025 0.70 3.30 13.002026 0.70 3.30 13.002027 0.70 3.30 13.002028 0.70 3.30 13.002029 0.70 3.30 13.002030 0.70 3.30 13.002031 0.70 3.30 13.002032 0.70 3.30 13.002033 0.70 3.30 13.002034 0.70 3.30 13.002035 0.53 2.89 13.002036 0.53 2.89 11.382037 0.53 2.89 11.382038 0.53 2.89 11.382039 0.70 2.89 11.382040 0.70 2.89 11.382041 0.70 2.89 11.382042 0.70 2.89 11.382043 0.70 3.30 11.382044 0.70 3.30 13.002045 0.70 3.30 13.002046 0.70 3.30 13.002047 0.70 3.30 13.002048 0.70 3.30 13.002049 0.70 3.30 13.002050 0.70 3.30 13.00




CONSTRUCTION & OPERATIONAL COSTS Base Case - Ratio of 3:1 Habitat Compensation












TOTAL CAISSONS 8,707,950,519 5,645,419,070 5,314,510,167 608,044,136 600,623,659


Gates 2,384,000,000 1,255,000,000 1,160,000,000 356,000,000 242,000,000TOTAL M&E 13,257,416,667 7,896,375,000 7,501,000,000 1,094,000,000 671,000,000










Cost of Compensatory Habitats: 5,450,055,000 5,010,915,000 3,946,800,000 964,470,000 685,230,000VAT - - - - -



VAT - - - - -


BARRAGES







(Peterstone Flats)Bridgwater Bay (Land

Connected Lagoon)91sq.km Offshore

Lagoon50sq.km Offshore

Lagoon










TOTAL CAISSONS 319,000,000 200,000,000 319,000,000 360,000,000 377,000,000 535,000,000 294,000,000


Gates 315,000,000 190,000,000 315,000,000 254,000,000 321,000,000 321,000,000 183,000,000TOTAL M&E 1,347,000,000 795,000,000 1,347,000,000 1,106,000,000 1,330,000,000 1,338,000,000 781,000,000










Cost of Compensatory Habitats: 1,267,500,000 390,000,000 1,267,500,000 526,500,000 1,072,500,000 - -VAT - - - - - - -



VAT - - - - - - -


LAGOONS






Tidal Reef










TOTAL CAISSONS 678,000,000 - 3,919,000,000


Gates - - 1,080,000,000TOTAL M&E 729,000,000 2,894,000,000 11,380,000,000










Cost of Compensatory Habitats: 394,680,000 545,005,500 1,677,000,000VAT - - -



VAT - - -




SUMMARY OF CASH FLOWS Base Case - Ratio of 3:1 Habitat Compensation










YEAR2010 79,353,659 67,909,293 52,306,343 7,491,849 5,414,0652011 79,353,659 67,909,293 52,306,343 7,491,849 5,414,0652012 79,353,659 67,909,293 52,306,343 7,491,849 5,414,0652013 79,353,659 67,909,293 52,306,343 7,491,849 5,414,0652014 3,432,828,960 3,323,748,761 3,144,198,098 699,384,204 626,653,1482015 3,432,828,960 3,323,748,761 3,144,198,098 699,384,204 626,653,1482016 3,432,828,960 3,323,748,761 3,144,198,098 699,384,204 626,653,1482017 3,432,828,960 3,323,748,761 3,144,198,098 699,384,204 626,653,1482018 3,432,828,960 3,323,748,761 3,144,198,098 699,384,204 31,715,6172019 3,432,828,960 3,323,748,761 3,144,198,098 44,097,406 31,715,6172020 3,432,828,960 3,323,748,761 3,301,459,425 44,097,406 31,715,6172021 3,432,828,960 3,511,626,280 314,522,654 44,097,406 31,715,6172022 3,612,419,972 375,755,039 314,522,654 44,097,406 31,715,6172023 3,702,215,477 375,755,039 314,522,654 44,097,406 31,715,6172024 359,182,022 375,755,039 314,522,654 44,097,406 31,715,6172025 359,182,022 375,755,039 314,522,654 44,097,406 31,715,6172026 359,182,022 375,755,039 314,522,654 44,097,406 31,715,6172027 359,182,022 375,755,039 314,522,654 44,097,406 31,715,6172028 359,182,022 375,755,039 314,522,654 44,097,406 31,715,6172029 359,182,022 375,755,039 314,522,654 44,097,406 31,715,6172030 359,182,022 375,755,039 314,522,654 44,097,406 31,715,6172031 359,182,022 375,755,039 314,522,654 44,097,406 31,715,6172032 359,182,022 375,755,039 314,522,654 44,097,406 31,715,6172033 359,182,022 375,755,039 314,522,654 44,097,406 31,715,6172034 359,182,022 375,755,039 314,522,654 44,097,406 31,715,6172035 359,182,022 375,755,039 314,522,654 44,097,406 31,715,617

2036 359,182,022 375,755,039 314,522,654 44,097,406 31,715,6172037 359,182,022 375,755,039 314,522,654 44,097,406 31,715,6172038 359,182,022 375,755,039 314,522,654 44,097,406 31,715,6172039 359,182,022 375,755,039 314,522,654 44,097,406 31,715,6172040 359,182,022 375,755,039 314,522,654 44,097,406 31,715,6172041 359,182,022 375,755,039 314,522,654 44,097,406 31,715,6172042 359,182,022 375,755,039 314,522,654 44,097,406 31,715,6172043 359,182,022 375,755,039 314,522,654 44,097,406 31,715,6172044 359,182,022 375,755,039 314,522,654 44,097,406 31,715,6172045 359,182,022 375,755,039 314,522,654 44,097,406 31,715,6172046 359,182,022 375,755,039 314,522,654 44,097,406 31,715,6172047 359,182,022 375,755,039 314,522,654 44,097,406 31,715,6172048 359,182,022 375,755,039 314,522,654 44,097,406 31,715,6172049 359,182,022 375,755,039 314,522,654 44,097,406 31,715,6172050 359,182,022 375,755,039 314,522,654 44,097,406 31,715,617


BARRAGES
















YEAR2010 10,361,108 9,457,495 12,816,190 11,735,403 9,722,427 23,110,726 14,045,4252011 10,361,108 9,457,495 12,816,190 11,735,403 9,722,427 23,110,726 14,045,4252012 10,361,108 9,457,495 12,816,190 11,735,403 9,722,427 23,110,726 14,045,4252013 10,361,108 9,457,495 12,816,190 11,735,403 9,722,427 23,110,726 14,045,4252014 871,645,621 728,231,550 975,810,634 756,123,838 817,473,011 948,654,737 685,542,0972015 871,645,621 728,231,550 975,810,634 756,123,838 817,473,011 948,654,737 685,542,0972016 871,645,621 728,231,550 975,810,634 756,123,838 817,473,011 948,654,737 685,542,0972017 871,645,621 728,231,550 975,810,634 756,123,838 817,473,011 948,654,737 685,542,0972018 871,645,621 43,931,551 975,810,634 756,123,838 817,473,011 948,654,737 685,542,0972019 53,818,649 43,931,551 62,887,742 56,663,767 52,497,650 948,654,737 59,686,5012020 53,818,649 43,931,551 62,887,742 56,663,767 52,497,650 99,113,181 59,686,5012021 53,818,649 43,931,551 62,887,742 56,663,767 52,497,650 99,113,181 59,686,5012022 53,818,649 43,931,551 62,887,742 56,663,767 52,497,650 99,113,181 59,686,5012023 53,818,649 43,931,551 62,887,742 56,663,767 52,497,650 99,113,181 59,686,5012024 53,818,649 43,931,551 62,887,742 56,663,767 52,497,650 99,113,181 59,686,5012025 53,818,649 43,931,551 62,887,742 56,663,767 52,497,650 99,113,181 59,686,5012026 53,818,649 43,931,551 62,887,742 56,663,767 52,497,650 99,113,181 59,686,5012027 53,818,649 43,931,551 62,887,742 56,663,767 52,497,650 99,113,181 59,686,5012028 53,818,649 43,931,551 62,887,742 56,663,767 52,497,650 99,113,181 59,686,5012029 53,818,649 43,931,551 62,887,742 56,663,767 52,497,650 99,113,181 59,686,5012030 53,818,649 43,931,551 62,887,742 56,663,767 52,497,650 99,113,181 59,686,5012031 53,818,649 43,931,551 62,887,742 56,663,767 52,497,650 99,113,181 59,686,5012032 53,818,649 43,931,551 62,887,742 56,663,767 52,497,650 99,113,181 59,686,5012033 53,818,649 43,931,551 62,887,742 56,663,767 52,497,650 99,113,181 59,686,5012034 53,818,649 43,931,551 62,887,742 56,663,767 52,497,650 99,113,181 59,686,5012035 53,818,649 43,931,551 62,887,742 56,663,767 52,497,650 99,113,181 59,686,501

2036 53,818,649 43,931,551 62,887,742 56,663,767 52,497,650 99,113,181 59,686,5012037 53,818,649 43,931,551 62,887,742 56,663,767 52,497,650 99,113,181 59,686,5012038 53,818,649 43,931,551 62,887,742 56,663,767 52,497,650 99,113,181 59,686,5012039 53,818,649 43,931,551 62,887,742 56,663,767 52,497,650 99,113,181 59,686,5012040 53,818,649 43,931,551 62,887,742 56,663,767 52,497,650 99,113,181 59,686,5012041 53,818,649 43,931,551 62,887,742 56,663,767 52,497,650 99,113,181 59,686,5012042 53,818,649 43,931,551 62,887,742 56,663,767 52,497,650 99,113,181 59,686,5012043 53,818,649 43,931,551 62,887,742 56,663,767 52,497,650 99,113,181 59,686,5012044 53,818,649 43,931,551 62,887,742 56,663,767 52,497,650 99,113,181 59,686,5012045 53,818,649 43,931,551 62,887,742 56,663,767 52,497,650 99,113,181 59,686,5012046 53,818,649 43,931,551 62,887,742 56,663,767 52,497,650 99,113,181 59,686,5012047 53,818,649 43,931,551 62,887,742 56,663,767 52,497,650 99,113,181 59,686,5012048 53,818,649 43,931,551 62,887,742 56,663,767 52,497,650 99,113,181 59,686,5012049 53,818,649 43,931,551 62,887,742 56,663,767 52,497,650 99,113,181 59,686,5012050 53,818,649 43,931,551 62,887,742 56,663,767 52,497,650 99,113,181 59,686,501


LAGOONS






Minehead Tidal Reef






YEAR2010 17,866,432 20,925,363 41,294,3142011 17,866,432 20,925,363 41,294,3142012 17,866,432 20,925,363 41,294,3142013 17,866,432 20,925,363 41,294,3142014 954,953,516 679,177,411 1,965,099,2472015 954,953,516 679,177,411 1,965,099,2472016 980,122,676 692,774,233 2,004,221,7432017 1,006,054,538 706,371,055 2,043,344,2392018 1,031,223,698 719,967,877 2,082,466,7352019 76,270,182 733,564,700 2,121,589,2322020 76,270,182 747,161,522 2,160,711,7282021 76,270,182 760,758,344 2,199,834,2242022 76,270,182 774,355,166 2,238,956,7202023 76,270,182 787,951,988 2,278,079,2162024 76,270,182 108,774,578 312,979,9682025 76,270,182 108,774,578 312,979,9682026 76,270,182 108,774,578 312,979,9682027 76,270,182 108,774,578 312,979,9682028 76,270,182 108,774,578 312,979,9682029 76,270,182 108,774,578 312,979,9682030 76,270,182 108,774,578 312,979,9682031 76,270,182 108,774,578 312,979,9682032 76,270,182 108,774,578 312,979,9682033 76,270,182 108,774,578 312,979,9682034 76,270,182 108,774,578 312,979,9682035 185,202,636 415,177,756 1,523,857,4722036 185,202,636 415,177,756 1,523,857,4722037 185,202,636 415,177,756 1,523,857,4722038 185,202,636 415,177,756 1,523,857,4722039 76,270,182 415,177,756 1,523,857,4722040 76,270,182 415,177,756 1,523,857,4722041 76,270,182 415,177,756 1,523,857,4722042 76,270,182 415,177,756 1,523,857,4722043 76,270,182 108,774,578 312,979,9682044 76,270,182 108,774,578 312,979,9682045 76,270,182 108,774,578 312,979,9682046 76,270,182 108,774,578 312,979,9682047 76,270,182 108,774,578 312,979,9682048 76,270,182 108,774,578 312,979,9682049 76,270,182 108,774,578 312,979,9682050 76,270,182 108,774,578 312,979,968




SUMMARY OF ENERGY YIELDS Base Case - Ratio of 3:1 Habitat Compensation









Annual Energy yield during construction is: 6.325 4.825 4.2 0 0Note: Overwrirtten cells are in italics

YEAR2010 - - - - -2011 - - - - -2012 - - - - -2013 - - - - -2014 - - - - -2015 - - - - -2016 - - - - -2017 - - - - -2018 - - - - 1.592019 - - - 2.77 1.592020 - - 8.40 2.77 1.592021 - 9.65 12.60 2.77 1.592022 12.65 14.48 16.80 2.77 1.592023 17.39 19.30 16.80 2.77 1.592024 22.14 19.30 16.80 2.77 1.592025 25.30 19.30 16.80 2.77 1.592026 25.30 19.30 16.80 2.77 1.592027 25.30 19.30 16.80 2.77 1.592028 25.30 19.30 16.80 2.77 1.592029 25.30 19.30 16.80 2.77 1.592030 25.30 19.30 16.80 2.77 1.592031 25.30 19.30 16.80 2.77 1.592032 25.30 19.30 16.80 2.77 1.592033 25.30 19.30 16.80 2.77 1.592034 25.30 19.30 16.80 2.77 1.592035 25.30 19.30 16.80 2.77 1.59

2036 25.30 19.30 16.80 2.77 1.592037 25.30 19.30 16.80 2.77 1.592038 25.30 19.30 16.80 2.77 1.592039 25.30 19.30 16.80 2.77 1.592040 25.30 19.30 16.80 2.77 1.592041 25.30 19.30 16.80 2.77 1.592042 25.30 19.30 16.80 2.77 1.592043 25.30 19.30 16.80 2.77 1.592044 25.30 19.30 16.80 2.77 1.592045 25.30 19.30 16.80 2.77 1.592046 25.30 19.30 16.80 2.77 1.592047 25.30 19.30 16.80 2.77 1.592048 25.30 19.30 16.80 2.77 1.592049 25.30 19.30 16.80 2.77 1.592050 25.30 19.30 16.80 2.77 1.59


BARRAGES















Annual Energy yield during construction is: 0Note: Overwrirtten cells are in italics

YEAR2010 - - - - - - -2011 - - - - - - -2012 - - - - - - -2013 - - - - - - -2014 - - - - - - -2015 - - - - - - -2016 - - - - - - -2017 - - - - - - -2018 - 1.41 - - - - -2019 2.31 1.41 2.31 2.33 2.64 - 1.322020 2.31 1.41 2.31 2.33 2.64 2.60 1.322021 2.31 1.41 2.31 2.33 2.64 2.60 1.322022 2.31 1.41 2.31 2.33 2.64 2.60 1.322023 2.31 1.41 2.31 2.33 2.64 2.60 1.322024 2.31 1.41 2.31 2.33 2.64 2.60 1.322025 2.31 1.41 2.31 2.33 2.64 2.60 1.322026 2.31 1.41 2.31 2.33 2.64 2.60 1.322027 2.31 1.41 2.31 2.33 2.64 2.60 1.322028 2.31 1.41 2.31 2.33 2.64 2.60 1.322029 2.31 1.41 2.31 2.33 2.64 2.60 1.322030 2.31 1.41 2.31 2.33 2.64 2.60 1.322031 2.31 1.41 2.31 2.33 2.64 2.60 1.322032 2.31 1.41 2.31 2.33 2.64 2.60 1.322033 2.31 1.41 2.31 2.33 2.64 2.60 1.322034 2.31 1.41 2.31 2.33 2.64 2.60 1.322035 2.31 1.41 2.31 2.33 2.64 2.60 1.322036 2.31 1.41 2.31 2.33 2.64 2.60 1.322037 2.31 1.41 2.31 2.33 2.64 2.60 1.322038 2.31 1.41 2.31 2.33 2.64 2.60 1.322039 2.31 1.41 2.31 2.33 2.64 2.60 1.322040 2.31 1.41 2.31 2.33 2.64 2.60 1.322041 2.31 1.41 2.31 2.33 2.64 2.60 1.322042 2.31 1.41 2.31 2.33 2.64 2.60 1.322043 2.31 1.41 2.31 2.33 2.64 2.60 1.322044 2.31 1.41 2.31 2.33 2.64 2.60 1.322045 2.31 1.41 2.31 2.33 2.64 2.60 1.322046 2.31 1.41 2.31 2.33 2.64 2.60 1.322047 2.31 1.41 2.31 2.33 2.64 2.60 1.322048 2.31 1.41 2.31 2.33 2.64 2.60 1.322049 2.31 1.41 2.31 2.33 2.64 2.60 1.322050 2.31 1.41 2.31 2.33 2.64 2.60 1.32


LAGOONS






Minehead Tidal Reef



First generation (years from start of const) 4 3 3Annual Energy Yield during refurbishment 0.525 2.8875 11.375

Refurbishment Interval (years) 20 20 20Refurbishment Period (years) 4 8 8

Annual Energy yield during construction is: 0.233333333 0.4125 0.4125Note: Overwrirtten cells are in italics

YEAR2010 - - -2011 - - -2012 - - -2013 - - -2014 - - -2015 - - -2016 0.23 - -2017 0.23 0.41 -2018 0.23 0.83 0.412019 0.70 1.24 0.832020 0.70 1.65 1.242021 0.70 2.06 1.652022 0.70 2.48 6.502023 0.70 2.89 8.662024 0.70 3.30 10.832025 0.70 3.30 13.002026 0.70 3.30 13.002027 0.70 3.30 13.002028 0.70 3.30 13.002029 0.70 3.30 13.002030 0.70 3.30 13.002031 0.70 3.30 13.002032 0.70 3.30 13.002033 0.70 3.30 13.002034 0.70 3.30 13.002035 0.53 2.89 13.002036 0.53 2.89 11.382037 0.53 2.89 11.382038 0.53 2.89 11.382039 0.70 2.89 11.382040 0.70 2.89 11.382041 0.70 2.89 11.382042 0.70 2.89 11.382043 0.70 3.30 11.382044 0.70 3.30 13.002045 0.70 3.30 13.002046 0.70 3.30 13.002047 0.70 3.30 13.002048 0.70 3.30 13.002049 0.70 3.30 13.002050 0.70 3.30 13.00



ANALYSIS OF OPTIONS FOR TIDAL POWER DEVELOPMENT IN …e680/energy/pdf_files/... · ANALYSIS OF...

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