Strategic Sewer: Site Selection Methodology - Thames Water...1.2.2 This former river, its catchment...

Protecting residents from flooding

Strategic Sewer: Site Selection Methodology

Document Number C680-AH-00504-RP March 2014

Counters Creek Strategic Flood Alleviation Scheme

Counters Creek Strategic Storm Relief Sewer/ Site Selection Methodology Report: March 2014 Document Number: C680-AH-00504-RP

COUNTERS CREEK STRATEGIC FLOOD ALLEVIATION SCHEME

STRATEGIC SEWER SITE SELECTION METHODOLOGY REPORT:

Document Ref C680-AH-00504-RP Status Issued Document Type Report Title/Subject Strategic Sewer Site Selection Methodology Project Counters Creek Strategic Flood Alleviation Scheme Authors TWUL / Adams Hendry / Bruton Knowles / London Bridge

Associates / Mott MacDonald / URS Keywords Site Selection Methodology

REQUIRED APPROVALS

Co-ordinator Reviewer Approver (for publication)

Chris Colloff Associate, Savills

Mark Mathews

Town Planning Manager, TWUL

Martin Bennett

Project Lead, TWUL

Date 31.3.14 Date 31.3.14 Date 7.11.14


COUNTERS CREEK STRATEGIC FLOOD ALLEVIATION SCHEME

STRATEGIC SEWER SITE SELECTION METHODOLOGY REPORT:

LIST OF CONTENTS

PAGE

0 EXECUTIVE SUMMARY 1 1 INTRODUCTION 2 1.1 PURPOSE OF THIS REPORT 2

1.2 BACKGROUND TO THE PROJECT 2

1.3 DEVELOPING A STRATEGIC SOLUTION TO THE PROBLEM 4

1.4 SUMMARY OF THE SITE SELECTION PROCESS 5

1.5 APPROACH TO CONSULTATION AND STAKEHOLDER MANAGEMENT 7

1.6 PROJECT PROGRAMME 7

2 SITE SELECTION METHODOLOGY 8 2.1 INTRODUCTION 8

2.2 STAGE 1 – STRATEGIC OPTIONS REVIEW 8

2.3 STAGE 2A – SITE ASSESSMENT 8

2.4 IDENTIFYING SITES 13

2.5 ASSESSMENT OF LONGLIST TO CREATE A SHORTLIST OF SITES 14

2.6 STAGE 2B – ROUTE OPTIONS ASSESSMENT 15

2.7 STAGE 3 – IDENTIFICATION OF PREFERRED SITES 16

2.8 PREFERRED SITE SELECTION WORKSHOP 20

2.9 BACKCHECKING 21

3 CONSULTATION 22 3.1 STAGE 4A – PUBLIC CONSULTATION 22

4 SCHEME DEVELOPMENT AND SELECTION 25 4.1 STAGE 4B – ON-GOING SCHEME DESIGN DEVELOPMENT 25

4.2 STAGE 5 SELECTION OF SCHEME FOR APPLICATION 25

APPENDIX 1 INITIAL DATA AND INFORMATION SOURCES

Strategic Sewer Site Selection Methodology


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0 EXECUTIVE SUMMARY 0.1.1 The Counters Creek Strategic Flood Alleviation Scheme is required to reduce the

risk of flooding to basement properties within the Counters Creek catchment in the London Borough of Hammersmith and Fulham and the Royal Borough of Kensington and Chelsea. The present Counters Creek Flooding Register shows that over 1,700 properties are subject to flooding.

0.1.2 A number of solutions are being pursued, each of which plays a role in providing the relief necessary to guard against basement flooding. The strategic solutions comprise the provision of flooding local improvement projects (FLIPS), the introduction of pilot Sustainable Drainage Systems (SuDS) schemes, the implementation of sewer upgrade works and the construction of a strategic storm relief sewer (the ‘strategic sewer’ or ‘the scheme’).

0.1.3 This report sets out the site selection methodology to be employed when

identifying sites and assessing their suitability to assist in the delivery of the strategic sewer. It also highlights the parallel relationship of this process with that to be undertaken to identify the route alignments that might serve the delivery of the strategic sewer.

0.1.4 The report provides a brief background to the need for the project and the

solutions that will be provided, including the delivery of the strategic sewer before setting out in detail the multi stage sequential assessment process that will be employed to identify, assess, reject, retain and reserve sites that may assist in the delivery of the strategic sewer.

0.1.5 This report also identifies the consultation arrangements that will be put in place to

engage the public and stakeholders on the emerging sites and options for the development and the process by which consultation outcomes will be taken on board as the project is further defined ahead of submission for planning permission.



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1 INTRODUCTION 1.1 Purpose of this report 1.1.1 The Counters Creek Strategic Flood Alleviation Scheme is required to reduce the

risk of flooding to basement properties within the Counters Creek catchment in the London Borough of Hammersmith and Fulham and the Royal Borough of Kensington and Chelsea. The present Counters Creek Flooding Register shows that over 1,700 properties are subject to flooding.

1.1.2 In addition, it is believed that there are unreported basement flooding incidents in

the area not currently recorded on the register, and new reports of flooding continue to be received.

1.1.3 Consideration of this problem has identified that a key measure to tackle the

flooding will be to provide a strategic storm relief sewer in the Counters Creek catchment. This report sets out the methodology used to identify sites that will facilitate the delivery of that strategic sewer and is structured as follows:

• Section 1 provides an overall background to the strategic sewer, a

summary of the site selection process, the approach to consultation and the project programme;

• Section 2 describes in detail the site and options selection methodology and the process for identifying the preferred option and sites;

• Section 3 describes the approach to be taken to public consultation on the preferred scheme for the strategic sewer, and

• Section 4 explains the steps that will follow public consultation through to submission of a planning application fort he preferred scheme for the strategic sewer

1.2 Background to the project

The Counters Creek Catchment

1.2.1 Counters Creek is one of the ‘lost rivers’ of London. It was culverted over in the mid 19th Century and connected into the interceptor sewerage network then being developed for London by Sir Joseph Bazelgette. The Counters Creek sewer catchment encompasses parts of Hammersmith and Fulham and Kensington and Chelsea and extends as far north as Westminster, Camden, Brent and Ealing.

1.2.2 This former river, its catchment and the sewer system form part of Thames Water’s sewerage network, drains all surface water from buildings and roads, as well as wastewater.

1.2.3 The sewerage system was constructed to take flows to Beckton Sewage Treatment Works. In early 20th Century, as London grew and the amount of land lying under impermeable surfaces increased, the volumes of flows in times of storms increased significantly.

1.2.4 Since then an extensive and complex sewer system comprising a series of storm

relief sewers (as shown on Figure 1) has been constructed to transfer excess storm flows to the River Thames when the sewers become full. This system has evolved to protect the low-lying land from an increasing risk of flooding caused by urban development.



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1.2.5 As Hammersmith and Fulham and part of Kensington and Chelsea are low lying areas in relation to the tidal river levels, it was not possible for the storm relief sewers to discharge into the river by gravity (without pumping). Hammersmith, Lots Road and the Western pumping stations were subsequently constructed to serve the storm relief sewers within the two boroughs (as shown on Figure 1).

Figure 1 The development of the interceptor and storm relief

sewerage systems in the Counters Creek Catchment.

Key and timeline for Figure 1

1850 Counters Creek

1930s Walham Green Hammersmith Brook Green

1860s Low Level Nos. 1& 2 Interceptors (dashed green line) – Kings Scholars Pond.

1940s Hammersmith Brook Green

1880s – Ranelagh

1950s Walham Parsons Green

1900s Mid Level 1 & 2 Interceptors (dashed purple line)

1960s Hammersmith, Counters Creek Duplicate

1920s Hammersmith Main Line – North Western

1980s North Western

1.2.6 The continuing growth of outer London resulted in the extension of the sewer

system northward and hence additional flows from the upper catchment entering the sewer system serving the low lying Counters Creek areas.

1.2.7 The additional flows have led to overloading and water levels within the existing sewers and manholes to rise. The increase in the water levels has in turn led to flows backing up the connection pipework into basements that were built at almost the same level as the sewer. The ever-increasing redevelopment of basements from storage areas into habitable properties in recent years has now brought this problem to the fore.

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The basement flooding problem

1.2.8 Thames Water began investigating the flooding problem following the storms of 2004 and 2007, when the majority of the basement flooding complaints were received. Information was recorded in the Counters Creek flood register, a register of all the properties in the Counters Creek Catchment that have been recorded as being flooded at some point in the past.

1.2.9 This register is in turn taken from the Thames Water Sewer Flooding History Database (SFHD). Properties are added to the register based on reported flooding incidents. Incidents are assessed to confirm whether or not the flood event was caused by an operational problem (i.e. a blockage), an extreme rainfall occurrence (greater than the current design criteria), or by a lack of capacity in the sewer.

1.2.10 The Counters Creek Flooding Register currently shows that over 1,700 properties

are subject to flooding within the London Borough of Hammersmith and Fulham and the Royal Borough of Kensington and Chelsea.

1.2.11 Sophisticated hydraulic models were used to simulate and verify the extent of basement flooding in the area and the results confirmed the existence of a widespread problem. Thames Water has examined the cause of flooding and determined that whilst there was no single cause, the flooding is generally caused by two main factors:

i. When sewers become inundated by storm water runoff, local sewer water

levels rise and back up the connection pipework into basements properties. ii. For many other properties, the hydraulic analysis indicated that flooding

was not solely caused by local surface water inundating the local sewerage network. Under certain storm conditions, storm relief sewers in the area run at full capacity (generally from the flows entering the system from the upper parts of the catchments), leaving inadequate capacity to provide relief for storm flows in the lower parts of the catchment. Therefore, flows build and back up into the connection pipework and then into basement properties.

1.3 Developing a strategic solution to the problem 1.3.1 Figure 2 below shows the locations of properties that have reported basement

flooding (the coloured dots), illustrating that the locations at which flooding occurs are widespread throughout the two boroughs.

1.3.2 The different coloured dots shown in Figure 2 indicate the type of solution proposed for a specific location. The Strategic Options Report (C680-TW-00503-RP) describes how each solution works, how they have been identified, the role they can play, and which solutions have been progressed.

1.3.3 The solutions comprise a strategic storm relief sewer (the strategic sewer) and

associated sewer upgrade works (properties protected by these are represented by purple dots), local package pumping systems known as ‘flooding local improvement projects’ (FLIPs – blue and red dots), local sewer upgrade works (green dots) and Sustainable Drainage Systems (SuDS – yellow dots).



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Figure 2 Proposed solutions to reported basement flooding

1.3.4 The widespread nature of the basement flooding problem coupled with the fact

that there is no single cause of flooding, means that there can be no single solution. For this reason a “bottom up” approach to addressing the problem has been adopted whereby each local flooding area (cluster) has been analysed to identify a viable solution and to establish the role that might be played in each area by flow storage, sewer upsizing, FLIPs, and SuDS.

1.3.5 Consideration was then given to the opportunities for combining and rationalising

these solutions as part of the process of establishing a strategy for managing flooding in the two boroughs and flows within the catchment.

1.3.6 Whilst this approach would provide protection for some properties through the use

flow storage, sewer upsizing, FLIPs, and SuDS, it cannot do so for all properties affected by the basement flooding problem. This is because the incoming flows into an area via sewers from the adjoining areas are so significant that those incoming flows need to be intercepted, cut off, or otherwise substantially reduced.

1.3.7 It was therefore concluded that, to robustly provide for the fullest possible coverage of the flooding problem a strategic sewer is required to intercept and store the major flows that are causing sewer overloading. This strategic sewer will, when provided alongside FLIPS, SuDS and the sewer upgrade works lower the top water levels in the sewer over the whole catchment to levels that are below the level of most of the basements thereby providing flooding protection.

1.4 Summary of the site selection process 1.4.1 A site selection process has been developed to assess and identify the most

suitable locations for the range of construction sites required to deliver the



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strategic sewer, namely drive shaft site(s), reception shaft site(s), interception shaft site(s), sewer outfall connections or new sewer outfalls, a pumping station and construction compounds.

1.4.2 The process takes account of engineering, environment (including noise and

transport), planning, property, socio-economic and community issues relevant to the selection of the most suitable combination of sites.

1.4.3 It draws upon other methodologies utilised for the Deephams Sewage Works Upgrade and for the Thames Tideway Tunnel to ensure that the approach and issues covered reflect best practice. Regard has also been had to the National Planning Policy Framework and the Development Plan for the area, along with key considerations affecting engineering decision-making and property assessment, when the assessment criteria in the methodology were identified. Initial data sources are listed in Appendix 1. The methodology is shown diagrammatically in Figure 3 below.

Figure 3 Site Selection Methodology

1.4.4 The methodology follows a sequential multi-stage process, with some stages

undertaken in parallel. There is an iterative relationship between site selection, route alignment and engineering design whereby as the engineering team refines the route options for the storm relief sewer associated restrictions on or requirements for sites are fed into the concurrent site selection process.

1.4.5 An essential part of the methodology is the use of an ongoing review process to revisit and check the validity of previous assessments. This is undertaken as each key stage of the assessment process is completed through document review and stage workshops and enables the assessment of sites (and concurrent assessment of options reported separately) to remain valid as information changes and new information is obtained.



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1.4.6 Where, for example, route alignment parameters change or available sites become restricted over time, stages in the process may be repeated (or back-checked) in order to take account of new information or other changes in circumstance.

1.5 Approach to consultation and stakeholder engagement 1.5.1 Community engagement is a key part of the strategic sewer scheme and the public

will be fully engaged with once the assessment work in Stage 3 is completed and sufficient information is available to begin public consultation under Stage 4a.

1.6 Project Programme 1.6.1 The current provisional project programme for the strategic sewer is:

• Evidence gathering / scheme development and testing: Jan – Oct 2014 • Phase 1 consultation on options: Nov 2014 – Jan 2015 • Environmental and planning assessments: July 2014 – May 2015 • Confirmation of the preferred option: May / June 2015 • Phase 2 pre-application consultation: May / June – July / Aug 2015 • Final design, planning and environmental work: July – Oct 2015 • Submission of application(s) for Planning Permission: Nov 2015 • Target for planning permission: July 2016 • Planning Conditions / Obligations discharged / procurement complete: Dec

2016 • Anticipated start on site: Jan 2017



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2 SITE SELECTION METHODOLOGY 2.1 Introduction

2.1.1 This section provides a detailed explanation of the site selection methodology

which will be used to identify, assess, retain and reject sites considered suitable for use as part of the provision of the Counters Creek strategic sewer, and as summarised by Figure 3 in Section 1 of this report.

2.2 Stage 1 - Strategic options review

2.2.1 The strategic options available to help address the issue of sewer flooding in the

Counters Creek catchment that have been considered as part of this project are documented in the Strategic Options Report (C680-TW-00503-RP), and summarised above in section 1.3 of this report.

2.2.2 The outcome of that review process concluded that whilst a range of measures will need to be implemented, the problem of basement flooding in the Counters Creek catchment can only be alleviated to the fullest extent if a strategic storm relief sewer is implemented. This would need to run either from Lots Road Pumping Station in Chelsea northward towards the Shepherds Bush area, or from Hammersmith Pumping Station eastwards and northwards to Shepherds Bush. In both cases a new pumping station at Lots Road would be provided.

2.2.3 The new strategic storm relief sewer will intercept the large over loaded sewers and store the flows until storms subside, after which the flows can be returned back into the system and passed forward for treatment. The new pumping station at Lots Road would discharge excess storm flows captured during very intense storms (when the volumes of rain are so substantial that can no longer be stored) into the tidal River Thames.

2.3 Stage 2a – Site assessment

Context

2.3.1 The purpose of Stage 2a of the assessment methodology is to identify and assess sites initially identified as having the potential to be used for the construction and operation of the strategic sewer.

2.3.2 In parallel to the site selection process, route alignment options will be explored by the engineering team (see Stage 2b below), which will ultimately affect the number and type of sites required.

2.3.3 In order to remain flexible to accommodate the most appropriate route option, it is assumed that sites may be needed for all or any of the following forms of development:

• Drive Shafts / Interception Shafts / Reception Shafts: to be used to facilitate

construction of the sewer and to be retained permanently for access and maintenance during operation.

• Construction of permanent ancillary infrastructure at or alongside the shaft sites listed above, where required, and to potentially include: § Motor Control Centres (MCCs); § power supply units;



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§ odour control units or vents, and § access provisions.

• Establishing temporary above ground main work areas serving multiple functions including: § offices; § employee parking; § delivery area for all plant and equipment; § laydown area for materials; § storage or excavated materials; § segment storage; § tunnelling equipment handling and storage, and § space for mechanical, electrical, instrumentation, control and

automation equipment (meica) to be accommodated at the main drive shaft site.

• Construction of new or provision of upgrades to existing pumping stations • Construction of new or provision of upgrades to existing outfalls • Construction compounds where required to provide additional space to

supplement the main work areas

Site characteristics

2.3.4 Full details regarding the anticipated site size for each of the site types listed in paragraph 2.3.3 above will be provided in the ‘Background Technical Report’ (Ref: C680-MMT-20029-RP). That report will include the site areas required for the following activities:

• Drive shaft site • Reception shaft site • Interception shaft site • Pumping Station site

2.3.5 The duration of use for each site will also be critical. Certain sites will only be

needed during the construction period, others also during operation.

2.3.6 Professional judgment will be used to determine whether a site should be included on the longlist based on whether it is potentially large enough to accommodate the development activities intended. There may be sites that may be too small to accommodate drive, interception or reception shaft construction sites and the associated work area required during the construction of the strategic sewer, but it may be recommended that they are retained to be used in combination with other sites as they could be suitable to accommodate all or part of the work area.

2.3.7 Consideration will also be given to any potential river, rail or strategic highway linkages for transport of materials.

2.3.8 The strategic sewer requires a pumped discharge at its most downstream location to allow the storm flows to discharge into the river in the event of the capacity of the sewer being exceeded. If the pumping station is located away from the river, then significant engineering works will be required to construct a large diameter rising main (around 2.5m diameter) to take the flows from the inland pumping location to an outfall location on the River Thames. It has therefore been assumed that where possible a pumping station will be co-located with a suitable riverside drive, interception or / and reception site.



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2.3.9 Recognising that there is the potential for the capacity of the sewer to be exceeded and for a pumped discharge into the River Thames to be required at the sewers’ most downstream location, it will be necessary for the strategic sewer to be gravity fed, whereby it is constructed with a constantly falling gradient to enable flows to travel to the point at which pumping must occur. In turn this requirement constrains the degree to which the depth of the sewer may fluctuate below ground. Defining the Site Search Area

2.3.10 To ensure that the process of identifying sites for assessment as part of the

longlist addresses only those sites which have the potential to be used for the development of the strategic sewer it will be necessary to establish the parameters that define the area in which the sewer is to be constructed.

2.3.11 This process will begin by utilising initial research into the feasibility of the project, as reported in the Strategic Options Report (C680-TW-00503-RP), along with any initial background technical information regarding the engineering requirements for the development. In particular, a key parameter within the search area will be the need to intercept flooding problems within the catchment that cannot be resolved by other strategic options being progressed as part of the Counters Creek Flood Alleviation Scheme.

2.3.12 Work was undertaken by Thames Water to establish the location of these interception points. Hydraulic investigations were undertaken in the Counters Creek catchment by the engineering team, which identified that the sewers listed in Table 1 below were heavily overloaded. It was identified that by cutting off (intercepting) the flows along certain sections of the sewer (also listed in Table 1), the downstream sewers would be relieved resulting in flood protection.

Table 1 Overloaded sewers and sections requiring interception

Overloaded Sewer Section required to be intercepted

Hammersmith Storm Relief Sewer Brook Green Branch

Area from Shepherds Bush Green to Brook Green.

Hammersmith Storm Relief Sewer Duplication Branch

Area near Swanscombe Road

Counters Creek Sewer Area near to Holland Gardens /Upper Addison Gardens

North End Sewer Area near Mund Street.

Walham Green Storm Relief Sewer and Low Level 1 Sewer

Various sections between Lots Road and New Kings Road.

2.3.13 The strategic sewer will therefore need to run from one interception point to the

next to collect the flows at the identified interception points. The flows will be stored in the strategic sewer before being pumped back into the existing sewer system to be passed forward for treatment through the network following storm subsidence.

2.3.14 To facilitate initial site search work the outcomes of the investigations undertaken to inform the consideration of strategic options will be used to define a search area that can be used to guide the Stage 2a Longlist site search and Stage 2b initial route options assessment work.



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2.3.15 This includes an initial route option identified and assessed by MWH as part of the base case to inform the likely provisions of a strategic sewer as part of that Strategic Options review, and has been labelled as the ‘MWH Base Case Alignment’ on Figure 4 below to differentiate it from the work being carried out as par of these current detailed assessments.

2.3.16 This initial potential route option ‘MWH Base Case Alignment’ (shown in purple on Figure 4) runs between the identified interception locations and carries all captured flows to a pumping station at Lots Road (at the most downstream interception location, namely at the Walham Green Storm Relief and Low Level 1 Sewers). This ‘MWH Base Case Alignment’ option seeks to make use of the existing outfall at Cremorne Wharf into the River Thames (for discharge of excess flows during intense storms).

2.3.17 As part of the process of identifying the search area for longlist sites the potential route option ‘MWH Base Case Alignment’ (shown in purple in Figure 4) was reviewed in respect of constructability. That review of the ‘MWH Base Case Alignment’ route option and of the investigations reported in the Strategic Options Report identified that certain strategic parameters needed to be taken into account with regards to the constructability of the that route option. It was identified that the area around the potential route option is heavily congested with existing underground assets including the TfL Underground network (Piccadilly and Central line). It was also identified that the route may require adjustment because of the potential for it to conflict with a number of underground assets such as the UK Power Network Tunnel, the National Grid London Power Tunnel as well the safeguarded Crossrail 2 route.

2.3.18 For example, the strategic sewer can only cross the National Grid London Power Tunnel from Brompton Cemetery northwards, where the cable tunnel dives down to a greater depth. This may mean that all of the areas to the west of the National Grid London Power Tunnel from Lots Road to just south of Earl’s Court might not be reachable by the strategic sewer without the need for crossing that tunnel, which may in turn require additional pumping. To ensure that the assessment process was able to accommodate these uncertainties whilst continuing to assess parameters and route options already identified through previous investigations, a further route alignment option (shown in turquoise in Figure 4) was therefore proposed.

2.3.19 As part of the Strategic Options investigations and the initial ‘MWH Base Case Alignment’ route options an option to connect to the Thames Water pumping station at Hammersmith (Chancellors Road) had been investigated. To ensure that the route options and site search process considered all potential options for the strategic sewer to avoid the constraints identified above a further route option to Hammersmith Pumping Station was added to the search area, as shown in light green on Figure 4.

2.3.20 Using the limitations explained above and shown on Figure 4 the following search area corridors were defined from the centre point of the potential route alignments in order to identify potential longlist sites:

• construction site search area (drive shaft, interception / reception shaft,

pumping station, outfall and construction compound) - 400m corridor: 200m either side of the route alignment options (shown in red in Figure 4).



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• construction compound site search area only (for example: materials storage, site offices) – 1,000m corridor: 500m corridor either side of the route alignment options (shown in dark green in Figure 4).

Figure 4 Proposed route alignments and site search areas

2.2.5 A 400m wide search corridor along the potential route alignment options was chosen as it was considered that: • a site located further than this distance would increase the length of the

strategic sewer as the interception points are generally fixed. • increasing the length of the strategic sewer and the need for additional

construction sites would substantially increase the costs associated with



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site acquisition and set-up in these parts of London, such that the project would be placed at risk of exceeding its funding budget.

• the increased tunnel length and the need for additional construction sites associated with a wider search area would also widen the construction influence of the project, increase the number of properties potentially being affected by construction and the duration of construction.

2.3.21 The least disruptive approach would be to keep all construction support facilities

within the construction site itself. However, due to the densely developed nature of the project area, this may not be possible and it may therefore be necessary to identify additional sites for use as construction compounds as close as practicable to the main construction site to which they relate. A 1,000m wide search corridor for construction support sites was therefore selected. Sites beyond this were not considered to be close enough to the interception sites to provide any value or benefit to construction activities or site workers.

2.3.22 Further details on the assessment of the range of options associated with these proposed route options are provided in the Stage 2b Report– Emerging Route Options Report. As additional knowledge regarding the above and below ground land use constraints is gathered, and further details regarding the requirements of the strategic sewer are established, it will be possible to more clearly identify the route option limitations that exist and which define the most practicable area within which to search for sites capable of accommodating the uses listed in paragraph 2.3.4 above.

2.4 Identifying Sites

2.4.1 For the purpose of the methodology, ‘a site’ is generally defined as an area for which boundaries can be readily distinguished.

2.4.2 Limited exclusionary criteria are applied when seeking to identify potential sites, so

as to ensure that an appropriately wide list of potential sites is available for assessment at the longlist assessment stage.

2.4.3 Land occupied by existing housing, including associated private gardens and lands (e.g. garages), will be excluded on the basis of London Plan Policy 3.14 – Existing Housing. This policy protects existing residential stock unless there is a planned replacement. In addition, this policy is supported in adopted Core Strategies, saved policies in Unitary Development Plans (UDPs) and emerging Local Plans across London Local authorities. The aim across London is to prevent the loss of existing housing stock unless replaced as part of the proposed development.

2.4.4 As exceptions to this general rule, where derelict or vacant housing sites are identified, or if particular sites are put forward by local authority stakeholders as being potentially suitable, they will be considered.

2.4.5 Other land uses that will be excluded from assessment comprise cemeteries, schools and hospitals.

2.4.6 Sites for inclusion can potentially include informal and designated open spaces, undeveloped land or brownfield sites, car parks and open areas of hardstanding, current and allocated employment uses, major opportunity and regeneration areas identified in the relevant development plan.



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2.4.7 The process of searching for sites within the identified boundary areas and for the available types of land will be carried out using mapping information, aerial photography and mapping and site visits. Sites found to be suitable for inclusion on the longlist by virtue of land type will then be mapped onto a Geographical Information System and their key characteristics will be documented.

2.4.8 Each site will then be allocated a reference number and recorded in a matrix, along with key details relating to its location, size and potential use.

2.5 Assessment of longlist to create a shortlist of sites

2.5.1 The identified longlisted sites will then be assessed against a defined range of engineering, planning and environmental and property criteria. The criteria used will ensure that a sufficiently broad base of information on the longlisted sites will be collected and assessed to enable a shortlist of sites to be robustly formed. Key issues that can constrain the use of a site for functions identified in paragraph 2.3.4 above will then be recorded.

2.5.2 A red, amber, green classification will be used to highlight the sites performance against each of the different assessment criteria. It is important to note that none of these classifications automatically exclude a site, indicating instead the potential presence or absence of important constraints and / or project risks if a site is retained.

2.5.3 At the longlist stage the criteria will reflect key hierarchical designations associated with planning and environmental criteria, or the practical considerations of acquisition and use associated with property and engineering issues. The criteria and their indicative values are set out in Table 2.

Table 2 Longlist assessment criteria and indicative values

CRITERION INDICATIVE VALUES

Red Amber Green

Engineering – To be completed by the Engineering and Design Teams

Site Size (to include consideration of using adjacent roads for construction)

Size or shape below the minimum technically feasible for site type

Size of shape below preferred sites dimensions for site type, but above technically feasible minimum / has potential as a linked site

At or above preferred site size for site type.

Site Features Site features have potential to prohibit development of site.

Will require compromise/ mitigation in order to be workable

No or limited constraints.

Location Site is adjoined by other land uses or features making engineering / construction difficult to achieve

Site is adjoined by other land uses or features but engineering / construction can be achieved with mitigation

Site is not adjoined by other land uses or features that would impede making engineering / construction

Means of access Significant difficulties achieving road, rail or river access

Road, rail or river access can be achieved but compromise/ mitigation

Good road, rail or river access



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CRITERION INDICATIVE VALUES

Red Amber Green required

Planning and Environment – To be completed by the Planning and Environment Teams

Heritage designation National Regional/Local None or positive.

Landscape/Townscape National Regional/ Local None or positive

Open Space National Regional/local None or positive

Ecological designation National Regional/local None or positive

Neighbouring land uses Nature of surrounding land use likely to preclude development

Nature of surrounding land use not ideal, but mitigation measures would ensure acceptability

Neighbouring land uses do not conflict with use of site

Existing or designated use of site

Existing/designated use of site likely to preclude development

Existing/ designated use of site not ideal but mitigation measures would ensure acceptability

Existing/ designated use of site does not conflict with use of site

Property – to be completed by the Property Team

Special Land and Crown Land

Land comprises special land for the purposes of the Acquisition of Land Act 1981 or Crown Land

Land includes some special land for the purposes of the Acquisition of Land Act 1981 or Crown Land

Land does not include any ‘special land’ for the purposes of the Acquisition of Land Act 1981 or Crown Land

Acquisition Costs Acquisition costs likely to be relatively high

Acquisition costs likely to be moderate

Acquisition costs likely to be relatively low

2.5.4 Professional engineering, property, planning and environment advisors within the

project team will then evaluate each site through desk top surveys applying professional judgement to the data and information collected on the site in relation to the criteria in Table 2.1. The outcomes of this analysis will then be discussed at project workshops to establish the overall performance of each site against all criteria.

2.5.5 The results will be recorded in site proformas, which will identify the outcomes from the application of the criteria and values to each site, provide a commentary on that assessment and provide a summary judgment as to whether or not the site should be retained and moved on to a shortlist, or rejected from further consideration. These will be appended to a report detailing the approach taken and the outcomes from the longlist assessment process (document reference C680-AH-00505-RP).

2.6 Stage 2b - Route options assessment

2.6.1 In parallel to the Stage 2a assessment of long list sites the engineering team shall continue to investigate routing options for the storm relief sewer tunnel.

2.6.2 The Emerging Route Options Report (document reference: C680-MMT-20074-RP)

will explain the hydraulic review that has been carried out of the interception points to ensure that the location of interception points has been optimised. It will detail the route options that are available, explaining their connections from one



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interception point to another and detailing the key constraints associated with each route option.

2.6.3 That assessment of each route option and its key constraints will include

consideration of the following:

• The number of drive sites and construction sites required; • The extent of mitigation measures required in respect of impacts upon

above and below ground structures; • The ease of access and spoil handling / transportation associated with

each option, and • The presence of sensitive land uses and constraints, for example Common

Land. 2.6.4 The report will then present an assessment of each of the route options identified

and provide recommendations as to how each route should continue to be considered within the project. The routing options that are assessed through Stage 2b and recommended for ongoing assessment will then be assessed in parallel to the process of identifying the preferred sites in Stage 3 of the process as set out below.

2.7 Stage 3 – Identification of preferred sites.

Assessment of the shortlist of sites

2.7.1 Utilising the outcomes of the longlist site assessment in Stage 2a, a more detailed assessment of the resulting shortlisted sites will be undertaken. The assessment criteria to be applied to the shortlisted sites are set out in Table 3 below.

Table 3 Shortlist assessment criteria and indicative values

Assessment Issue Assessment Criteria

ENGINEERING

Clean Water / Waste Water Assets

• Are important clean water or other water resources and assets affected?

Connection Feasibility • Distance from sewer interception • Infrastructure / structures between sewer and shaft

Means of Access • Availability of rail connection / practicability of accessing rail connection • Suitability of road links to site and river • Ability for site to handle Abnormally Indivisible Loads • Jetty / wharfage facilities available • Jetty / wharfage facilities can be created • Availability of any other means of access • Worker transport considerations

Odour Control • Assessment of potential operational odour generation and costs of mitigation

Site Efficiency • Ability to accommodate all requirements on one site and if not describe how facilities can be achieved via a combination of sites.

• Assessment of potential for effects from development upon existing site or adjacent services e.g. power supply/communications/other

Site Features • Above and below ground conditions (including 3rd party services, assets



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Assessment Issue Assessment Criteria and infrastructure)

• Geology • Site levels • Other considerations

Site Geometry • Does the site geometry lend itself for use intended?

Site Size • What is the site suitable for – drive shaft, intermediate or reception shaft, pump station, outfall or other e.g. welfare office

Tunnelling, Construction and System Engineering Requirements

• Ability to be compatible with likely system and tunnelling requirements in the vicinity of the site

ENVIRONMENT

Community & Amenity • Sensitivity to dust, odour and other construction effects • Visual impact during construction upon amenity • Visual impact during operation upon amenity

Ecology • Nature conservation / reserve designations

Flood Risk • Assessment of fluvial / tidal / surface water flood risk

Heritage • Archaeology priority areas • Scheduled Ancient Monuments • Historic Parks and Gardens • Conservation Areas • Listed Buildings

Landscape • Assessment of potential for Landscape, townscape, visual designations. • Assessment of potential for impacts on other landscape/open space

designations • Assessment of potential for impacts on informal/undesignated open

space

NOISE

Distance from centre of site to receptor

• Type of receptor

Height of Receptor • Type of receptor

PLANNING

Common Land • Nature of common land site • Size of common land site • Area required during construction • Area required during operation • Potential for use

Community & Amenity • Impact upon formal or informal community facilities • Neighbouring land uses and amenity considerations • Allotment land • Residential gardens / restricted open space

Employment • Are there potential impacts on local employment opportunities?

London Plan / Borough Policy Allocation or Special Policy Area

• Assessment of compliance or conflict with specific land use allocations or planning objectives

Metropolitan Open Land / Green Belt

• Assessment against Green Belt and Metropolitan Open Land



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Assessment Issue Assessment Criteria

Open Space • Assessment against Open Space policy

Planning Applications / Permissions

• Application expected • Awaiting determination • Unimplemented • Implemented

Public Access & Recreation • Impacts on informal / undesignated open space • Impacts on navigation and recreational water use • Impacts on recreational sites and assets • Impact upon leisure or sports facilities • Impact upon tourism • Permissive rights of access • Public Rights of Way

PROPERTY

Access and Material Transfer Rights

-

Common Land • Ownership status • Potential for acquisition or rights to develop • Operational access / status

Crown Land and Special Land -

Estimated Acquisition Cost -

Ownership of Site • Is the site owned by TWUL / in single 3rd Party ownership / multiple 3rd Party ownerships?

TRANSPORT

Connection to Rail Network During Construction

• Connection to railway siding and suitability of interconnecting access route

Water Freight Practicability During Construction

• Location of wharf and suitability of interconnecting access route to wharf

Suitability of Road / Interconnecting Road Access During Construction

• Road layout, width and junction geometry suitability for Heavy Goods Vehicles

Sensitivity of Access Route During Construction

• Residential streets, shopping streets, tourist areas, schools, play areas, hospitals, bus routes

Operational Transport and Access Requirements

-

2.7.2 As with the longlist assessment criteria set out in Table 2.1, the significance of the

issues recorded at each site will be determined as red, amber or green for each criterion.

2.7.3 As previously stated, none of these gradings are exclusionary – i.e. red does not

mean that a site should automatically be excluded from further consideration. However, unlike the Table 2.1 assessment process, the values associated with the shortlisted sites require a greater interpretation of data and use of professional judgement to establish the opportunities and limitations of each site.

2.7.4 The assessment process therefore requires the following judgments to be made:



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Mitigation can be achieved / policy or other land use / environmental issues can be overcome, but will be very challenging.

Mitigation can be achieved / policy or other land use / environmental issues can be overcome.

Criterion has no implications for site. 2.7.5 As part of this process each shortlisted site will be assessed in terms of its

suitability for each of the different types of use identified. These sites will then be compared with the outcomes of the engineering options assessment identified in Stage 2b to establish the best performing combination of sites within each shortlisted route alignment.

2.7.6 In particular, this part of the process will begin to clarify which sites would be used

as a drive shaft, reception shaft, interception shaft, storm outfall and a pumping station, and will enable the assessment team to begin the process of identifying the emerging preferred option for the strategic sewer in engineering, planning, environment and property terms.

2.7.7 To facilitate the assessment process workshops shall be held to discuss the sites

and routing options. Shortlist site assessment matrices will be completed as the assessment progresses and the outcomes of the assessment process will be recorded in a Shortlist Report (document reference C680-AH-00506-RP), which will conclude by identifying the sites which are to be retained and which sites are to be rejected from further consideration.

2.7.8 Those retained sites will then be subjected to detailed testing through Site

Suitability Reports to enable decisions and recommendations to be made by the project team as to the preferred sites to support the emerging preferred strategic sewer route option.

2.7.9 Those recommendations will identify the preferred sites considered best able to

facilitate delivery of the emerging preferred route option and will be considered by Thames Water as project promoter. Thames Water will then take a decision whether to proceed with the subsequent stages of the site and route selection and consultation process.

Site Suitability Reports

2.7.10 A Site Suitability Report will be prepared for each of the retained sites identified

through the shortlist assessment. Each report will follow a set template that will generally reflect the following considerations: • Site information and an explanation of the proposed use of the site during

the construction and operational phase. • Engineering assessment - engineering, geotechnical, groundwater and

technical matters that impact on a site’s ability to host required on-site activities, ‘buildability’ and ‘operability’.

• Planning assessment - review of any planning applications and permissions that relate to the site and a review of relevant site specific national, London-wide and local planning policies, including impact on planning and environmental designations plus results of any site surveys.

• Environmental assessment - an appraisal from environmental specialists. Where a specialist’s discipline is relevant to the site, an appraisal would be



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made of potential impact along with potential mitigation measures that may overcome any identified impacts. In particular: § A summary of the conclusions from the desktop noise assessments

that shall be undertaken for each of the sites. A simple noise model, including assumptions about plant likely to be used at each location, will be prepared for each site. Conclusions will be drawn about the suitability of the site informed by the outputs of this noise model.

§ Transportation opportunities and constraints associated with access to and from sites and the ability to make use of the strategic road network, the rail network, and the blue ribbon network. A summary of the conclusions from the desktop transportation survey that shall be undertaken for each of the sites.

• Socio-economic and community assessment – an assessment of any socio-economic or community issues and impacts associated with the use of the site (and required mitigation measures) during construction and operation and potential restoration and after uses for the site.

• Property assessment – assessment of acquisition risks (including site acquisition, services and operational matters) and potential for compensation events.

• Site conclusions - conclusions from each discipline on the general level of suitability of the site based on relevant considerations and use of professional judgment.

2.7.11 Each report will be published separately and provided a separate reference

number to be assigned once the outcomes of the shortlisting process are known.

Ongoing options assessment

2.7.12 In parallel to the site shortlisting and suitability reporting processes the strategic sewer route alignment options assessment process will continue to progress. This will work through the interception and alignment parameters that control where flooding must be tackled and what other infrastructure must be avoided to establish the best selection of route options capable of helping to enable project delivery.

2.7.13 The outcome of this work will be for a reduced list of route options to be identified for testing as part of the process of making recommendations as to the preferred route option. Emerging Route Options Report (document reference: C680-MMT-20074-RP).

2.8 Preferred option and site selection workshop 2.8.1 A workshop or workshops as necessary will be held to consider and focus on the

detailed contents of the Site Suitability Report for each retained shortlist site. The emerging preferred route option will also be known at that stage and so will also be discussed as part of that workshop or series of workshops.

2.8.2 The outcomes of the workshop process will then be reported in the Preferred Option and Sites Report (document reference: C680-AH-00519-RP), which will recommend the preferred scheme for public consultation in Stage 4a (Set out in Section 3 below).



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2.8.3 Retained sites held in reserve (alternative sites), and sites that have been rejected, will also be presented during the consultation process, along with the records of all site identification, longlisting and shortlisting work described above.

2.9 Backchecking 2.9.1 Within and between each stage of the process from Stage 2a through to Stage 3,

and across all assessment work associated with the longlist and shortlist assessments, the subsequent SSRs and the parallel route options investigations the project team will when required undertake a process of backchecking.

2.9.2 This process is essential to the overall assessment and ensures that information gathered at subsequent stages of the process that might affect previous work and outcomes is fully considered and the implications of that information reflected as the assessment moves forwards.

2.9.3 Implementing this process of backchecking enables the assessments to retain

validity over what may be likely to be a lengthy site and route options analysis covering many months and within which external factors may change and project parameters may be adjusted.

2.9.4 For example, new developments by third parties, additional records of flooding

incidents, or improvements in the project teams knowledge about the requirements of the strategic sewer may all influence decisions made previously, or require adjustment to ensure that all sites and options are assessed consistently.

2.9.5 Where necessary, previous stages, or parts of stages, of assessment may be

repeated in order to take account of new information or changes in circumstances.



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3 CONSULTATION 3.1 Stage 4a – Public Consultation 3.1.1 Information on the preferred sites and options will be published for public

consultation. There are six parts to Stage 4a:

• Pre-consultation period liaison; • Phase 1 public consultation process; • Consultation activities: briefing sessions and technical fora; • Consultation activities: exhibitions; • Review and assessment of all consultation responses; and, • Consultation feedback report.

3.1.2 This stage applies to all of the preferred sites that will be identified and the

selected route option, which together make up the preferred scheme for the strategic sewer. It is important to stress that this methodology outlines consultation activities as they relate to the option and sites selection process.

3.1.3 Thames Water will engage regularly with both potentially affected London local authorities and other stakeholders in the period leading to submission of applications for consent for the strategic sewer and beyond. A Stakeholder and Community Engagement Strategy will be prepared that outlines Thames Water’s proposals for consulting on its proposals.

Pre-consultation period liaison

3.1.4 As investigations into the strategic sewer route and sites advances early pre consultation period liaison will be undertaken. This will include: • strategic briefings to the LBH&F, RBK&C and the GLA; • project and technical / engineering briefings to the EA, TfL and the PLA; • land ownership briefings to site owners affected by emerging proposed

development sites and strategic sewer route, and major landowners adjacent to the same;

• land ownership briefings to agencies responsible for managing Crown Land, if affected, and

• detailed pre consultation briefings to LBH&F and RBK&C planning and highways teams and elected members, and affected elected Members of Parliament

3.1.5 Where additional knowledge is obtained through these liaisons that benefits the

route option and site assessments it will be integrated into the ongoing assessment work and resulting recommendations.

Phase 1 public consultation process

3.1.6 The Phase 1 public consultation process on the preferred scheme will take place in Autumn / Winter 2014.

3.1.7 Widespread notification and publicity about the consultation period will be given to statutory consultees and local communities near to the preferred route or any preferred sites before and during the consultation period.



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Consultation activities: briefing sessions and technical fora

3.1.8 Once the preferred route and sites have been identified, an initial series of briefing sessions will be held with affected local stakeholders. These sessions will aim to begin the engagement process in these neighbourhoods. It is envisaged that local Ward Councillors, local MPs and community leaders and representatives will be invited to a briefing session on the scheme. Those to be invited will be agreed with the local planning authorities and other relevant statutory consultees.

3.1.9 A series of technical forum meetings will also be established to bring together professional stakeholders responsible for formally representing various planning, environmental, social and economic agencies through the planning system. These are intended to ensure that stakeholders too are fully briefed on the scheme, its route and its sites and to encourage debate and the identification of issues and, where possible, consensus over statutory, policy and technical interests inherent to the successful promotion of the scheme.

Consultation activities: exhibitions

3.1.10 Following these briefings, public exhibitions will be organised to engage directly with the local communities, groups and people living and working in the areas potentially affected. These exhibitions will be designed to provide information on the overall purpose of the scheme and use of the sites and allow the gathering of opinions and comments from local communities and interested stakeholders.

3.1.11 The exhibitions will take the form of events at which information is presented on a series of display boards. The events will be staffed by members of the Counters Creek project team and its consultants, so that questions can be answered and information on the display boards explained in more detail where required. The exhibitions will be publicised to the relevant local communities via the press and local sources.

3.1.12 The events will be located as close as possible to the selected sites, so as to make it as easy as possible for the communities likely to be most directly affected to attend. The events will be timed to allow people to fit in a visit around their other home and work commitments. A range of methods will be used to capture comments, such as traditional comment forms, graffiti wall, flip charts and acetate sheets on top of boards and plans.

3.1.13 It is likely that the display boards will cover the following elements:

• an introduction to the Counters Creek project; • history of the project’s evolution to date; • rationale, need and benefits of the project; • explanation of the types of sites and their features; • details of the site selection methodology and process which has been used

to generate the list of all the preferred sites – plan showing all sites; • details of the sites that have not been taken forward and the reasons for

their non-selection; • deadline to make comments and programme for the next steps with the

sites and the project; and, • details and timings of future opportunities to engage with local communities

and other stakeholders.



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Review and Analysis of Consultation Responses

3.1.14 All consultation responses received will be reviewed and analysed from all sources. A summary table will be created that will include: • a unique reference for each consultee; • how many people made each particular comment; • a summary of substantive comments; • a response to substantive comments; and • recommended changes to the list of preferred sites.

Consultation feedback report

3.1.15 A consultation feedback report will be prepared that analyses all consultation

responses received and identifies responses, recommendations and, where appropriate, may identify potential mitigation measures to address issues that have been raised. The report and the outcomes it reports will be fed into Stage 4b and will inform the ongoing process of refining the scheme and the route and sites that it will utilise.

3.1.16 Following the issue of the consultation feedback report a further round of backchecking will be undertaken to ensure the assessment process remains up to date and valid throughout. Further information on backchecking is provided in section 2.9 of this report.



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4 SCHEME DEVELOPMENT AND SELECTION 4.1 Stage 4b – on-going scheme design development 4.1.1 In Stage 4b the public consultation outcomes and on-going scheme development

will be assessed to confirm whether the preferred sites will be taken forward. The on-going scheme design development will take account of property, planning and environment, and engineering issues relating to the preferred sites for drive shaft, reception shaft, interception shafts, pumping stations and outfalls, taking account of consultation feedback and any potential changes of circumstance.

4.1.2 Detailed planning and environmental work will be undertaken during Stage 4b as part of the process of preparing a planning application for the strategic sewer. The studies undertaken to support the planning application will enable the design team to identify any potential impacts arising from the construction and operation of the preferred sites and incorporate mitigation measures into the design work to reduce any potential impacts of the development.

4.2 Stage 5 – Selection of scheme for application

4.2.1 The scheme proposed for the planning application will take account of public consultation and on-going scheme design development. The public and stakeholders will be consulted on the proposed scheme through a Phase 2 pre-application consultation process that is likely to take place in summer 2015. Comments will be taken into account in deciding on the final scheme to be the subject of the planning application. A planning application to construct the strategic sewer will then be submitted in November 2015.



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APPENDIX 1 INITIAL DATA AND INFORMATION SOURCES • The Town and Country Planning Act 1990 • The Listed Buildings and Conservation Areas Act 1991 • The Water Industry Act 1991 • Works on Common Land, etc. (Procedure) (England) Regulations 2007 • The National Planning Policy Framework • Communities and Local Government (2005). Planning Policy Statement 10:

Planning for Sustainable Waste Management • National Planning Practice Guidance • Office for National Statistics • The London Plan – relevant policies, specific designated areas, views and protected

areas • The Mayor’s Office adopted Supplementary Planning Documents/Guidance

(SPD/SPGs) and Action Area Plans (AAPs) • Relevant Local Development Documents (LDDs), saved sections of Unitary

Development Plans (UDPs), London Borough Supplementary Planning Documents/Guidance (SPD/SPGs) and Action Area Plans (AAPs) - relevant policies, specific designated areas, protected views and local areas

• Borough Council GIS layers • English Heritage records for Schedule Ancient Monuments and Listed Buildings plus

London Archaeological Archive and Research centre (LAARC) • Natural England records on international, national, local designations • Environment Agency maps on flooding and watercourses • National Land Use Database (NLUD) • Aerial photographs (Counters Creek Project, 2008) • 1:25,000 and 1:10,000 Ordnance Survey Sheets • Greater London Street Atlas • Site selection methodology for the Deephams Sewage Works Upgrade • Site selection methodology for the Thames Tideway Tunnel

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