Hampshire Groundwater Management Plan

Final Draft for Consultation October 2013

Hampshire County Council Economy, Transport and Environment Department The Castle Winchester

Hampshire SO23 8UD

Tel: 0845 603 5638 Fax: 01962 847055 www.hants.gov.uk

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Document Control Information

Document Information

Document Reference First Draft Hampshire Groundwater Management Plan for consultation

Document Revision -

Report Status FINAL DRAFT

Date 17 October 2013

Author M Barker

Checker A McConkey

Approver

Date of Next Review

Contents

1 Introduction 1 1.1 Background 1 1.2 Why have a Groundwater Management Plan? 2 1.3 Why a GWMP is different to a normal SWMP and why it is needed 2 1.4 Policy Setting, Roles and Responsibilities 2

2 Background to GWMP 5 2.1 How this GWMP is structured 5 2.2 How it relates to the PFRA and LFRMS 5 2.3 How this GWMP relates to other SWMP 5 2.4 Identifying the Level of Assessment 6 2.5 Scoping and Aims & Objectives 7

3 Establishing Partnerships 9 3.1 General Principles and Governance 9 3.2 Partnership for the GWMP 10 3.3 Roles and responsibilities for Groundwater Flooding in Hampshire 10

4 Study Area Characterisation 11 4.1 Regional Characteristics 11 4.2 Groundwater Flooding in Hampshire 11 4.2.1 Groundwater flooding from the Chalk 11 4.2.2 Groundwater Flooding from Permeable Superficial Deposits 12 4.3 Ecology & Environmental Designations 13 4.4 Infrastructure 13 4.4.1 Critical Infrastructure 13

5 Groundwater flooding initial risk assessment 15 5.1 Existing and Historic Flooding Incidents 15 5.2 Initial site selection and intermediate level assessment 15 5.3 Detailed assessment and identifying a short list for actions 17 5.4 Summary of at Risk Areas 19 5.4.2 Hambledon 19 5.4.3 Rowlands Castle 20 5.4.4 Kings Worthy 21 5.4.5 Finchdean and Deanlane End 22 5.4.6 Hursley 22 5.4.7 Bishops Sutton 23 5.4.8 Appleshaw 23 5.4.9 Bourne Rivulet Villages 24 5.4.10 West Meon 24 5.4.11 Preston Candover 25

5.5 Future / Potential Groundwater Flood Risk 25 5.5.1 Indicators based on historic events 25 5.5.2 Understanding of future groundwater flood risk 26 5.5.3 Potential impacts from climate change 26

6 Settlement risk assessment and measures assessment 28

6.1 Introduction 28 6.2 Overall Approach – Generic Measures 28 6.3 Planning for groundwater flooding 29 6.3.1 Development (Planning) Management 29 6.3.2 Local planning 30 6.3.3 Infiltration Drainage and Soakaways 30 6.3.4 Emergency Planning 31 6.4 Drainage Infrastructure Maintenance 31 6.4.1 Conveyance 31 6.4.2 Flood Resistance and Resilience 32 6.4.3 Dewatering 34 6.4.4 Management of sewage flooding 35 6.4.5 Road Traffic Management 35 6.5 Introduction - settlement risk assessment and action plans 36 6.5.1 Approach 36

7 Managing residual risk 37 7.1 Introduction 37 7.2 Environment Agency Flood Warnings 37 7.2.1 Overall Approach 37 7.2.2 Groundwater Flood Information and Warnings 37 7.2.3 The Flood Forecasting Centre and Flood Guidance Statement 39 7.3 Forming Flood Action Groups 39 7.3.1 Promotion of Flood Action Groups 39 7.3.2 The Parish Lengthsmen Scheme Pilots 40

8 Environmental Assessment 41 8.1 Introduction 41 8.2 Strategic Environmental Assessment 41 8.3 Habitats and Birds Directives 42 8.4 Water Framework Directive (WFD) 42

9 Options Evaluation, Implementation and Recommendations 44

9.1 Generic Measures 44 9.1.1 Planning 44 9.1.2 Other generic Measures 44 9.1.3 Promotion of generic measures 44

9.2 Site Specific Measures 45

10 Review and Monitoring 46 10.1 On going review and updates of the GWMP 46 10.2 Collection and Maintenance of Groundwater flooding records 46 10.2.1 Monitoring and Recording Groundwater Levels 46 10.3 Collection and recording groundwater flood data during a flood

event 46

11 Conclusions 48

12 References 49

13 Abbreviations and Acronyms 50

Annexes Annex A Data Collection Annex B Maps and Figures Annex C Regional Site Characteristics Annex D Environmental Report Annex E Flood Data and Risk Assessment Annex F Settlement Action Plans Annex G Flood Warning Information Annex H Flood Action Groups Annex I Defra Proposed Flood Incident Recording Pro

Forma

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1 Introduction 1.1 Background

1.1.1.1 Hampshire has a known history of groundwater flooding. During winter 2000/2001, over 100 towns and villages across the county suffered significant flooding with over 400 properties flooded with significant disruption and damage to infrastructure.

1.1.1.2 At that time and in response to these events, Hampshire County Council (together with Winchester City Council) funded research into the impacts of long term flooding (Ref 1) and the Environment Agency (Southern Region) commissioned Halcrow to investigate the causes and extents of flooding, identify actions and undertake a risk assessment for all 105 villages that were affected by the flooding of the winter 2000/2001 (Ref 2). The action plans for these villages were agreed by all parties and mitigation works identified, although at that time, there was no specific duty on Hampshire County Council to carry out these actions.

1.1.1.3 Since these investigations were undertaken, Hampshire County Council, in its role as a Lead Local Flood Authority under the Flood and Water Management Act 2010, has a responsibility for the management of flood risk (including that from groundwater, surface water and ordinary watercourses) and to set out plans to address that risk. This GWMP is the first step in this process.

1.1.1.4 Other than winter 2000/2001, there have also been other less extensive and severe groundwater flooding events recorded in the county (e.g. in 1994/95 and 2002/2003).

1.1.1.5 Rainfall during 2012 reached a record high for England. From November 2012 onward groundwater levels in Hampshire rose leading to the issue of groundwater flood alerts by the Environment Agency (refer section 7.1). Despite this, the number of incidents of groundwater flooding reported to Hampshire County Council during this period were relatively limited and certainly less significant than in 2000/2001.

1.1.1.6 The worst affected areas appear to have been in the eastern part of the County in the Wallington and Lavant catchments (see section 4.2.1.4).

1.1.1.7 In Finchdean and Rowlands Castle, actions by the local community (including the Parish Flood Action Group and local flood wardens) encouraged riparian landowners to clear ditches and issued warnings to those who may be affected. Network Rail and the Environment Agency cleared the river bed and Hampshire Highways undertook works to clear ditches and pipes. These actions appeared to address the worst of the flooding, although some properties still had to install sump pumps to reduce the impact of flooding. There was also a lot of flooding of the roads, which were closed for some time until the groundwater levels dropped.

1.1.1.8 More prevalent were problems related to the ingress of groundwater into the mains sewage systems. These problems were more widespread, occurring to the East of the county (Hambledon) and to the North (St. Mary Bourne, Penton Mewsey).

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1.2 Why have a Groundwater Management Plan?

1.2.1.1 Groundwater flooding may be simply described as flooding caused by raised groundwater levels, typically following prolonged rain, although there are a number possible mechanisms of groundwater flooding with different characteristics (refer Annex C).

1.2.1.2 Past events in Hampshire have shown that there is significant flooding directly attributable to groundwater and groundwater emergence

1.2.1.3 On the basis that there is an established risk from groundwater flooding, Defra recognised in its ‘early outcomes’ programme for Surface Water Management Plans that a “SWMP” should be developed to specifically address groundwater flood risk.

1.2.1.4 The background to the GWMP and its relationship with other flood risk management plans and strategies is described further in Section 2.

1.3 Why a GWMP is different to a normal SWMP and why it is needed

1.3.1.1 The fundamental difference between the GWMP and SWMP is that SWMPs are carried at a District/ Borough council level whereas the GWMP specifically addresses groundwater flooding across the entire county, with a focus in groundwater flooding in the central Hampshire chalk catchments.

1.3.1.2 A further difference relates to the unique mechanisms behind groundwater flooding (explained in section 4) and how these influence the impact of that flooding, in particular the duration of flood events and impacts occasionally remote from areas normally affected by fluvial or surface water flooding.

1.3.1.3 These unique characteristics of groundwater flooding are such that a more targeted GWMP is needed to specifically address groundwater flood risk and its management.

1.3.1.4 On the basis of the above, the boundaries within which the GWMP is applied are therefore defined primarily by the outcrop of the Chalk (see Annex B Fig1 and Fig 6). Although other types of groundwater flooding are defined and described within this document, these may occur outside this boundary, are largely associated with fluvial and surface water flooding and should be addressed by the District level SWMPs.

1.3.1.5 The characteristics of groundwater flooding are such that many of the solutions identified in the settlement specific action plans are broadly similar as they essentially comprise the local application of generic solutions (see Section 6). Further, where there are no significant gains that may be identified from making (for example) specific local drainage conveyance improvements, or where these have already been undertaken, a large number of the actions identified in the settlement action plans, are those required to address the residual risk. These actions are described further in Section 7.

1.4 Policy Setting, Roles and Responsibilities

1.4.1.1 The key pieces of legislation, policy and guidance for flood risk management (FRM) in England and Wales are as follows:

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The Flood and Water Management Act 2010 (FWMA);

The Flood Risk Regulations 2009 (FRR);

Civil Contingencies Act 2004;

Land Drainage Act 1991;

Environment Act 1995;

Water Resources Act 1991

EU Water Framework Directive 2000 (WFD);

The Conservation of Habitats and Species Regulations 2010;

The National Planning Policy Framework (NPPF);

Surface Water Management Plan Technical Guidance;

Strategic Flood Risk Assessments (SFRM);

Catchment Flood Management Plans (CFMP);

River Basin Management Plans (RBMP);

1.4.1.2 Hampshire County Council has published the Hampshire Surface Water Management Plan (SWMP) Strategic Assessment and Background Information April 2012 (Ref 3). This “overarching SWMP” document provides more details and sets out the how key documents for development planning and flood risk management relate to each other and legislation, policy and guidance. This is summarised on Figure 1.1 below.

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Figure 1.1 : Existing Development and Flood Management Planning Policy and Guidance Framework

1.4.1.3 The overarching SWMP also sets out and describes more fully, roles and responsibilities within SWMPs, specifically for:

Hampshire County Council (and other LLFAs);

District and Borough Councils;

The Environment Agency (EA);

Water Companies;

Riparian Owners;

Others.

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2 Background to GWMP 2.1 How this GWMP is structured

2.1.1.1 This GWMP essentially combines elements of the strategic (i.e. equivalent to the overarching SWMP), intermediate level, and detailed SWMPs. It has been broadly set out in accordance with the technical guidance provided by Defra (Department for Environment, Food and Rural Affairs) in 2010 (Ref 4) although this is also set in the context of the SWMPs already produced or planned by Hampshire County Council. For example, it is not the intention to reproduce information already available in the overarching SWMP (see section 2.3), rather to add information specific to groundwater flood risk management.

2.2 How it relates to the PFRA and LFRMS

2.2.1.1 In 2010 Hampshire County Council produced a Preliminary Flood Risk Assessment (PFRA) (Ref 5), in order to satisfy the legal requirements of the Flood Risk Regulations (2009) and the EU Floods Directive. The PFRA is a strategic document which identifies, collates and assesses information on flood risk as well as identifying areas where additional investigation may be necessary. The PFRA provides a high level overview of flood risk from a variety and combination of sources including surface water, groundwater and ordinary watercourses together with their interactions with river, the sea and reservoir flooding.

2.2.1.2 Although the PFRA did not specifically identify the need for a GWMP, it did identify that there were established risks from groundwater flooding in the county and a history of such events, notably in the winter of 2000/2001.

2.2.1.3 The information gathered for the PFRA was used to identify areas of local flood risk and set priorities for further, more detailed investigation and analysis. In turn, this information has been used to inform the Local Flood Risk Management Strategy (LFRMS) (Ref 6 - now adopted), required under the Flood and Water Management Act (2010) and identified areas where Surface Water Management Plans (SWMP) are required.

2.3 How this GWMP relates to other SWMP

2.3.1.1 The “overarching” document (Ref 3) provides a single, concise and consolidated reference on matters relating to surface water flooding and flood risk across Hampshire. It provides a review of relevant guidance documents and legislation to be considered as part of any SWMP. It identifies and sets out the responsibilities of the various different organisations with a role in the management of flood risk and the provision and maintenance of flood water infrastructure. The document also sets out, in line with Defra guidance, the four stage process ( preparation, risk assessment, mitigation options, implementation) to be followed in the preparation of Surface Water Management Plans for different areas at different scales (Strategic, Intermediate, Detailed).

2.3.1.2 Furthermore, the overarching document, through a high level risk assessment, identifies those areas thought to require preparation of an Intermediate Surface Water Management Plan and sets out the objectives for these, namely to:

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Map historic flood incident data;

Map flooding locations influenced by surface water;

Identify surface water flooding ‘hotspot’ areas;

Assess, compare and prioritise ‘hotspot’ areas for detailed assessment;

Identify measures where appropriate, assess options and confirm preferred mitigation options for identified ‘hotspots’;

Engage with partners and stakeholders;

Make recommendations for the next stages of assessment.

2.3.1.3 In addition to the overarching document and this GWMP, an intermediate level SWMP is being prepared for each of the 11 Districts of Hampshire. The order of undertaking these is in accordance with the nature and level of risk identified in each District. The publication status of these documents is identified in Table 2.1 below. Although presented as Annexes to the overarching document, these intermediate level plans form separate volumes that, using a common template, provide more local information on flood risk. Whilst Southampton City Council and Portsmouth City Council have completed SWMPs, this GWMP does not cover areas within these jurisdictions. Table 2.1 Intermediate (District/Borough) Surface Water Management Plans

2.4 Identifying the Level of Assessment

2.4.1.1 The Defra guidance sets out a hierarchy of strategic, intermediate and detailed stages of assessment.

2.4.1.2 The GWMP broadly fits alongside the intermediate level risk assessments represented by the 11 District and Borough assessments currently underway or planned (see above).

2.4.1.3 However, given the work already undertaken at a more detailed level by the Environment Agency (Ref 2), there is sufficient information available to allow a

District/ Borough Status Basingstoke and Deane Borough In progress East Hampshire District In progress Eastleigh Borough Issued for consultation (January 2013) Gosport Borough Proposed start 2015/2016 Fareham Borough Proposed start 2015/2016 Hart District In progress Havant Borough Proposed start 2014/2015 New Forest Proposed start 2015/2016 Rushmoor Issued for consultation (January 2013) Test Valley Proposed start 2013/2014 Winchester Proposed start 2014/2015

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more detailed level of assessment to be carried out, including the development of more locally targeted action plans.

2.4.1.4 Hence, it has been recognised that the GWMP should both:

Provide a “SWMP” document compatible with other SWMPs including the production of a joint action plan specific to groundwater flooding;

Develop more detailed action plans, targeted at those settlements most at risk.

2.4.1.5 On this basis, the GWMP becomes a “hybrid” between the intermediate level of assessment and the detailed level of assessment. This approach was approved and agreed by the stakeholder group (see section 3.1.1.2)

2.5 Scoping and Aims & Objectives

2.5.1.1 The scoping process for a GWMP should be no different from a more “conventional” SWMP. Under the Defra guidance, the scoping stage focuses on:

Establishing an engagement plan;

Identifying the level of assessment;

Setting aims and objectives;

Identifying the availability of information.

2.5.1.2 Following these initial steps, the brief issued by Hampshire County Council for the GWMP, set out specific aims and objectives, as agreed by the stakeholder group. These are as follows:

Develop a joint action plan to identify actions to be taken by relevant authorities in the partnership and other stakeholders;

Develop proposals to address outstanding groundwater risk locations based on the Halcrow report on 2000/2001 flooding and other identified high risk areas;

Identify and make recommendations for maintenance and management of winterbournes and other drainage systems that take groundwater flow and development of (or enhancement of existing) plans to manage groundwater flow that cannot be accommodated by these systems;

Make recommendations for areas where soakaway drainage should be avoided;

Make recommendations for improvement of Flood Warden schemes and other self-help programmes such as the development of local Flood Action Plans;

Develop action plans influenced by engagement with local communities local and development of a framework for ongoing awareness raising and engagement;

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Set out the warning signs for groundwater flooding, including clarification of the coverage offered by the groundwater flood warning service provided by the Environment Agency and work with them to enhance this service where possible;

Identify what generic measures may be adopted to mitigate the effects of groundwater flooding.

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3 Establishing Partnerships 3.1 General Principles and Governance

3.1.1.1 In Hampshire, the Overarching SWMP (Ref 3) sets out the Principles for Governance and Partnership to be adopted with SWMPs (see Figure 3.1). At a strategic level key stakeholders are represented at the Hampshire Strategic Flood and Water Management Group. This multi agency group aims to ensure stakeholders are kept up to date on the different aspects of flood risk legislation as well as working together to ensure a holistic and joint approach in discharging responsibilities under the Flood and Water Management Act and Flood Risk Regulations across the Hampshire County Council administrative area and beyond.

3.1.1.2 A Flood Risk Management officer group has been set up to provide the technical input for the development of SWMPs, the PFRA and other technical aspects of the FWMA. It enables the key stakeholders to meet and discuss any issues within the relative organisations and to support the Hampshire Strategic Flood and Water Management group.

Figure 3.1 Governance arrangements within Hampshire

Regional Flood and Coastal Committees

Reg

iona

l H

amps

hire

Si

te/lo

catio

n Sp

ecifi

c

Regional Resilience Forum

Hampshire Wide Strategic Flood and Water Management Group

Hampshire Flood Risk Management Officer

Surface Water Management Plan Groups

Shoreline Management Plan

Local Resilience

Flooding and Environment

LRF Sub

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3.2 Partnership for the GWMP

3.2.1.1 Given partnering arrangements for the surface water management plan groups are already in place, these have been adopted for the GWMP, although a more targeted specific engagement plan will need to be developed with these partners. At a more local level, engagement will initially be undertaken through the Hampshire Association of Local Councils (HALC), although further engagement at a more local level may be required as individual risk assessments and action plans are progressed. The documents will also be available for public comment on the County Council’s website. This will be publicised through the usual media actions (press releases etc.).

3.3 Roles and responsibilities for Groundwater Flooding in Hampshire

3.3.1.1 Roles and responsibilities within Surface Water Management Plans, including for groundwater flooding, are set out in Section 4 of the “overarching SWMP” (the Hampshire Surface Water Management Plan (SWMP) Strategic Assessment and Background Information April 2012). (Ref 3).

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4 Study Area Characterisation 4.1 Regional Characteristics

4.1.1.1 As well as rainfall events, the occurrence, extent and impact of groundwater flooding is dictated by the regional setting of topography, soils, geology and hydrogeology. This regional setting is described in more detail in Annex C along with generic descriptions of the causes and mechanisms of groundwater flooding. An understanding of these processes is essential to evaluating groundwater flood risk.

4.2 Groundwater Flooding in Hampshire

4.2.1 Groundwater flooding from the Chalk

4.2.1.1 Groundwater flooding in Hampshire is primarily due to flooding mechanisms in the Chalk, as described in Annex C. Typically groundwater flooding may be defined as the emergence of groundwater at the ground surface away from perennial river channels, under conditions where the 'normal' ranges of groundwater level and groundwater flow are exceeded.

4.2.1.2 Exceptionally large flows from perennial springs or large flows from intermittent or dormant springs, may also be defined as groundwater flooding, and can cause both localised flooding in the vicinity of the springs and down gradient where surface water drainage channels may not be adequate.

4.2.1.3 High groundwater levels can have a large effect on many rivers within the catchment causing higher than normal baseflow, increasing the risk of fluvial flooding – although impacts from this increase in fluvial flow are not considered as groundwater flooding.

4.2.1.4 The Chalk aquifer can take several months to become saturated and does not react quickly to intense rainfall, however once the groundwater level has reached the surface, flooding can last several months.

4.2.1.5 The faulted nature of the Chalk and it’s division into a number of regional and semi- regional “blocks” (bounded by faults) with different properties (which may include permeability, the degree of fracturing and the geological structure) is such that there is different behaviour (and flooding response to extreme rainfall) across the county. Additional factors that may contribute to these regional differences include topography, catchment shape, land use, soil and superficial deposits cover.

4.2.1.6 As a result, even given similar conditions of rainfall and antecedent groundwater levels, there will be different timing to both the onset and duration of groundwater flooding.

4.2.1.7 This regional variation in groundwater flooding behaviour is illustrated by a comparison between the eastern catchments (Meon, Wallington) and the more central catchments (Itchen, Test).

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4.2.1.8 In the eastern catchments, the response to rainfall is more rapid, the rate of recharge and recession is greater and groundwater levels rise more quickly and are more extreme in seasonal fluctuation. The onset of groundwater flooding also appears earlier. In 2000/2001, peak groundwater levels in the Wallington catchment occurred in December 2000, whereas in the Test and Itchen peak levels generally did not occur until late January or early February. Halcrow (2002) reported that groundwater flooding events are more frequent in the Wallington and Meon catchments and the events tend to be of shorter duration as the groundwater recession starts earlier.

4.2.1.9 In the central catchments, the onset of groundwater flooding requires a more extended period of recharge and appears to be more conditional on the antecedent conditions before this recharge occurs i.e. the aquifer needs to be more “topped up“ at the onset of the extreme rainfall events before groundwater flooding might occur. However, although groundwater flooding in these central catchments tends to be slower to start than in the eastern catchments, when it does occur, it tends to be of longer duration.

4.2.1.10 Past flooding from groundwater has been caused both directly as water levels rise above ground level, or indirectly as high groundwater causes flooding of rivers which are dominated by water emerging from aquifers (baseflow). This has been the case in a number of areas of Hampshire, such as Basingstoke and Deane Borough where flooding was mainly due to high groundwater-fed flows on the rivers Test and Loddon causing overtopping of river banks. In addition within this area there have been reports of localised flooding in the upper parts of the Loddon catchment due to high groundwater levels. The characteristic feature of groundwater flooding events is the relatively long duration compared with fluvial flooding.

4.2.2 Groundwater Flooding from Permeable Superficial Deposits

4.2.2.1 In the non-Chalk areas, groundwater flooding, where it occurs, involves more shallow seated mechanisms. In these cases, groundwater flooding is associated with the rise in groundwater level within the permeable superficial deposits (such as river terrace gravels), typically found in river valleys. Groundwater from these deposits emerges at the surface in low lying areas (otherwise isolated from the impacts of fluvial flooding) causing flooding. Such flooding is usually associated with fluvial (or tidal) flooding events, although it may both precede the onset of fluvial flooding and last longer than fluvial flooding.

4.2.2.2 There are few specific examples of groundwater flooding in permeable superficial deposits (PSDs) in Hampshire; in part as such events are often rapidly overwhelmed by the effects of fluvial or surface water flooding.

4.2.2.3 In some areas of New Forest District not normally associated with groundwater flooding, superficial deposits lying over the Tertiary deposits beneath the rivers of the New Forest are susceptible to PSD flooding. For example, in and around Brockenhurst, where substantial river terrace deposits (refer Annex B Figure 2) are coincident with local drainage to the Lymington River, flooding of this nature has

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been known to disrupt roads and pathways. [Refer Brockenhurst Parish Council website: http://www.brockenhurst.gov.uk]

4.2.2.4 Elsewhere in New Forest District, villages such as Calmore, Totton may also experience this type of flooding, particularly in dips in roads. However, most of the problems in these towns are related to surface water flooding.

4.2.2.5 In the Test Valley District, the flooding of winter 2000/2001 in Romsey was a combination of fluvial, surface water and groundwater flooding. Some properties experienced groundwater derived cellar flooding, although the root cause was fluvial flooding exacerbated by poor surface drainage. Flood durations in this 2000/2001 event were mostly only 2-3 days, much more indicative of a fluvial event than the longer duration groundwater flooding associated with the chalk.

4.2.2.6 Rather than being derived directly from the Chalk (as elsewhere in the county) the groundwater flooding experienced in Romsey (which does not lie directly on chalk strata) can be attributed to groundwater rise in the permeable superficial deposits (river gravels, river alluvium) and is associated with extreme levels and flows in the River Test.

4.2.2.7 Given it is closely associated with fluvial and surface water flooding, and its occurrence in areas outside the central chalk catchments (the focus of this GWMP) PSD flooding is best addressed in the District Level SWaMPs and through partnership with the Environment Agency.

4.3 Ecology & Environmental Designations

4.3.1.1 There are a number of local, national or international designations with respect to ecology, landscape and other areas protected by UK policy or legislation that occur in Hampshire. These designated sites are shown on Figures 1- 5 in Annex D.

4.3.1.2 A separate Environmental Report is provided in Annex D of this GWMP. This describes more fully the occurrence, extent and significance of these designated sites.

4.3.1.3 Within each individual Action Plan, the key environmental constraints are identified and where these may be impacted upon by the action plan or where the action plan may be used to enhance environmental benefit this is also identified.

4.4 Infrastructure

4.4.1 Critical Infrastructure

4.4.1.1 Critical infrastructure essentially comprises elements of infrastructure that are “those facilities, systems, sites and networks necessary for the functioning of the country and the delivery of the essential services upon which daily life in the UK depends” (see Ref 13).

4.4.1.2 Nine sectors are generally recognised: energy, food, water, transportation, communications, emergency services, health care, financial services and government.

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4.4.1.3 Hampshire County Council retain location records of critical infrastructure and other facilities, which also includes less immediately critical facilities including for example, departments stores, hotels and public houses.

4.4.1.4 For the purposes of this plan, key infrastructure location data has been extracted from these records and has been mapped (refer Annex B Figure 5). Key infrastructure considered and included in the mapping included:

Emergency Services facilities (e.g. hospitals, Police stations, Fire and rescue centres)

Key Transport links (e.g. airports, bus and rail stations)

Communication centres (e.g. telecoms facilities)

Energy facilities (e.g. power stations, sub stations)

4.4.1.5 This data, and its coincidence with recorded groundwater flooding incidents was used when considering groundwater flood risk and is referred to where relevant in each individual action plan.

4.4.1.6 As groundwater flooding emerges slowly and may last over an extended period, the consideration of critical infrastructure relates less to the needs of emergency planning and (for example) evacuation and more to how that critical infrastructure might be affected by, for example, property and facilities damage or long term limitations in access.

4.4.1.7 Groundwater issues related to sewerage and roads are discussed in Section 6.4.

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5 Groundwater flooding initial risk assessment

5.1 Existing and Historic Flooding Incidents

5.1.1.1 There are a number of recorded sources of groundwater flood incidents, the main sources of historic information are:

The Halcrow report on the winter flooding of 2002 (Ref 2);

The Defra report of 2004 (Ref 9);

Hampshire County Councils flooding records.

5.1.1.2 Additional information is available from:

The PFRA;

The Overarching SWMP and the District Level SWMPs where available;

Ward based assessments in the LFRMS;

Various information (e.g. local action plans) provided by the water utilities.

5.2 Initial site selection and intermediate level assessment

5.2.1.1 It was previously identified (section 2.4) that the GWMP falls between an intermediate and more detailed level of assessment. On this basis groundwater flood risk has been evaluated at a level of detail commensurate with what data was available. This data may be at ward, village or some other pre-determined level (e.g. village groupings related to hydrological rather than administrative groupings).

5.2.1.2 The Halcrow report identified some 105 villages affected by flooding in 2000/2001. This extreme event provides a starting point to which a risk based site selection process may be applied. The key data from this report is reproduced in Annex E Table E1.1.

5.2.1.3 As a first step in the risk assessment process, an initial comparison was made between the sites identified at highest risk of groundwater flooding in the LFRMS (based on the economic cost of groundwater flooding by ward) and an initial selection was made of the most at risk villages based on the numbers of properties flooded as identified in the Halcrow 2002 report (refer Annex E Table E1.2 and Annex B Figure 6). This simply identifies the risk ranking from most severe (rank 1) to least severe (rank 22). Note that the latter report was (mostly) based on individual villages/ settlements hence no completely direct comparison of the risk “rank” is possible, although where villages are within the wards identified in the LFRMS, these are shown on the Table in italics. Unsurprisingly, there are only a few villages outside the high risk wards identified in the LFRMS. The comparison is summarised on Table 5.1 below.

5.2.1.4 From the Halcrow (2002) report there remain a large number of villages wherein groundwater flooding was recorded during 2000/2001, albeit due to the lower numbers of properties affected they have not, at this time, been identified for

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specific action. In these locations, the generic actions as identified in Section 6 could be applied.

Table 5.1 Initial Highest Risk Villages Selection

Risk Rank

LFRMS (see note 1) Halcrow Report on 2000-2001 Flooding (see note 2)

1 Droxford, Soberton and Hambledon Hambledon

2 Fareham East (Crockerhill, Wallington) Wallington

3 Upper Meon Valley (West Meon, Exton, Corhampton)

Wickham

4 Battins (Stockheath) Rowlands Castle

5 Cheriton and Bishops Sutton (Cheriton, Bishops Sutton, Kilmeston)

Romsey

6 Ashurst, Copythorne South and Netley Marsh Kings Worthy

7 Abbey Havant

8 Clanfield and Finchdean (Finchdean, Clanfield, Charlton)

Hursley

9 Rowlands Castle Finchdean and Deanlane End

10 Town (Gosport) Kimpton

11 Wickham West Meon

12 Penton Bellinger (Kimpton, Appleshaw, Clanville, Shipton Bellinger)

Gosport

13 Upton Grey and the Candovers Exton

14 Kings Worthy Appleshaw

15 Broughton and Stockbridge Ashhurst

16 Colden Common and Twyford Preston Candover

17 Totton East Bishops Sutton

18 Bourne Valley (Vernham Dean, Upton) Corhampton and Meonstoke

19 The Alresfords(Old Alresford, New Alresford, Bighton)

Totton and Calmore

20 Itchen Valley (Easton, Avington, Ovington, Chilcomb, Nothington, Itchen Stoke)

Woodlands and Netley Marsh

21 - Bramdean

22 - Bourne Rivulet Villages (see below)

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Notes to Table 5.1

Note 1: Ward based economic cost of groundwater flooding

Note 2: Settlement ranking based on the no. of properties flooded 2000/2001, the initial selection process based on the Halcrow report actually identified 22 villages or village groupings

Note 3: Italicised villages appear in both lists

Note 4: Given recent significant works with the local community and concerns regarding sewage flooding in the Bourne Rivulet villages of Vernham Dean, Upton, Hurstbourne Tarrent, Stoke, St Mary Bourne these were brought together in the initial selection

5.2.1.5 As part of an initial assessment, this selection process allows a focus on the most at risk villages.

5.3 Detailed assessment and identifying a short list for actions

5.3.1.1 There are other factors that need to be taken into account in selecting sites for a further, more detailed risk analysis and for action plan derivation. In particular these are:

Is the flooding primarily attributable to groundwater (as opposed to fluvial) flooding?

Have any of the mitigation works identified in the 2002 report (or other works subsequently) been undertaken that may address (or reduce) the level of groundwater flood risk?

Has any further data been gathered that further informs the flood risk (e.g. evidence for frequency of occurrence)?

Are there factors other than property flooding to be considered (e.g. impact on critical infrastructure including key roads, impacts on foul drainage provision, environmental impacts)?

Are there other flood risks (e.g. surface water flooding) that should be taken into account and which may impact on overall (“cumulative”) flood risk?

Can villages be grouped together (as has been done with the Bourne Rivulet villages) and considered as a single “unit” both with respect to risk and with respect to actions?

5.3.1.2 When these factors are taken into consideration, 8 sites (Wallington; Wickham; Gosport; Ashurst; Havant; Totton & Calmore; Woodlands & Netley Marsh; Romsey) were eliminated as the cause of flooding was not attributable to groundwater. This also applies to Fareham East; Battins and Abbey (part of Romsey).

5.3.1.3 As these sites had previously been identified in the LFRMS as being at risk from groundwater flooding, (i.e. prior to more detailed investigation) and as they will not be addressed herein, it is important that the flood risk in these settlements is

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properly addressed as part of the appropriate District Surface Water Management Plan.

5.3.1.4 A further 3 sites (Kimpton; Exton; Bramdean) eliminated from consideration as they already have adequate mitigation plans in place.

5.3.1.5 This left a final selection of 11 sites for further analysis.

5.3.1.6 It is presently planned to address the 10 most significantly at risk sites within the GWMP. Although the data used for the identifying these 10 settlements (from 11) was primarily based on the number of properties affected by the floods that occurred during winter 2000-2001, further selection criteria were adopted qualitatively to arrive at a preferred list of settlements. The other criteria included:

Flooding frequency

The impact of road flooding

Impacts arising from sewage flooding

5.3.1.7 The risk assessment process and methodology used to derive the short list for action are described further in Annex E.

5.3.1.8 The developed final risk ranking and short list of settlements for action is provided below:

Table 5.2 Final risk ranking

Village No. of Properties Flooded 2000/2001

Ranking by properties flooded

Flood Frequency ranking

Road flooding ranking

Sewer flooding ranking

Overall Risk Rank

Hambledon 96 1 8 =2 =4 1

Rowlands Castle 23 2 =4 =7 =7 2

Kings Worthy 21 3 7 =7 =1 3

Finchdean and Deanlane End

18 =4 =4 =7 =1 4

Hursley 18 =4 6 =2 =4 5

Bishops Sutton 12 =8 1 1 =7 6

Appleshaw 12 =8 3 =2 4 7

Bourne Rivulet villages 14 7 2 11 3 8

West Meon 16 6 =8 =2 =7 9

Preston Candover 12 =8 =8 =2 =7 10

.

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5.4 Summary of at Risk Areas

5.4.1.1 The summaries below, based primarily on the events of 2000/2001, describe the characteristics of the flooding events, at each of the most at risk villages. The locations of these are shown on Figure 5.1 below. The numbering on the map reflects the overall risk rank given in Table 5.2 above.

Figure 5.1 Distribution of the highest risk sites

5.4.2 Hambledon

5.4.2.1 There is a significant history of flooding in Hambledon, with 8 incidents in the 40 years prior to the event of 2000/2001, 4 of which led to significant property damage. Further flooding occurred in 2003 and again in 2012/2013. Despite the record recorded rainfall and high groundwater conditions, flooding experienced in 2012/2013 was not as extreme as that experienced in 2000/2001.

5.4.2.2 The 2000/2001 event comprised significant long term groundwater flooding and groundwater levels reached their highest levels locally since records began in about 1960. This in turn caused the Chalk aquifer storing the groundwater effectively to

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“overflow”, and discharge via springs and seepages into the normally dry valleys occupied by East Street, West Street and Lower West Street.

5.4.2.3 In all a total of 124 properties were affected by groundwater flooding. Of these, 50 properties suffered ground floor flooding and a further 46 properties suffered cellar flooding, and 28 were affected by external flooding.

5.4.2.4 Substantial commercial losses were suffered as a result of the flooding.

5.4.2.5 The flood water in both East Street and West Street was contaminated with sewage, due to the sewerage system becoming overwhelmed by floodwater ingress.

5.4.2.6 Resulting flows on the roads themselves were high and, because the road surface is above the ground floor level of some adjacent properties, several such properties suffered internal flooding.

5.4.2.7 Frequent episodes of high rainfall contributed to the floodwaters periodically until they receded. The excess surface water on the roads also flowed into, and overwhelmed, the sewerage system.

5.4.2.8 A major cause of flooding in Hambledon is the decline in drainage pathways which allow flood water to pass through the village without causing harm. This overall flow capacity has been significantly reduced over the last 100 years (see extract from the Halcrow 2002 report in box below). The reduced ability to drain water at the surface may also lead to the “backing up” of groundwater (as it is unable to drain away) and exacerbate problems derived from extreme groundwater levels, including spring emergence.

5.4.3 Rowlands Castle

5.4.3.1 Significant flooding occurs regularly in the Lavant valley (see also Finchdean). In Rowlands Castle, the floods of 1959, 1968, 1976, 1988, 1994 and 1995 were recorded (by local residents) as heavy or very heavy events.

5.4.3.2 Flooding was experienced in Finchdean Road in the 1960s, 1976, 1988, 1994, 1995 and 2000/2001.

The capacity of the surface water drainage system through the village has been reduced

over the years, with road widening, culverting and some ditch infilling. Due to the regular

occurrence of flooding in Hambledon historically, a “great ditch” is understood to have

existed through the village for the purpose of transferring floodwater when necessary. By the

1920’s, the ditch had been replaced in part by a 9” (225mm) diameter pipe and in 1944 it

was completely culverted to permit parking of tanks as part of the preparation for D-Day.

Posford Haskoning also report that the level of the highway is some 500mm higher than it

was 100 years or so ago. (Halcrow 2002)

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5.4.3.3 Throughout the village and its surrounding area, the 2000/2001 event is reported to have been the worst event.

5.4.3.4 Flooding in Rowlands Castle is not just associated with the flood flows in the West Lavant Stream. For example, flooding in Redhill Road and The Green are related to emergence of groundwater which cannot drain. The latter flooding is independent of the flows in the West Lavant Stream, occurs at times of high rainfall and is generally confined to road flooding, although some property flooding has been recorded.

5.4.3.5 During the 2000/2001 event, 11 properties suffered internal flooding in Finchdean Road and an additional property suffered cellar flooding. A further 10 properties were recorded as having suffered from internal flooding. Of these, 8 properties also suffered from contaminated water flooding or impeded foul water drainage

5.4.3.6 Road flooding was also severe and access was cut off to some 55 properties in Finchdean Road. This resulted from surface floodwaters which flowed out of bank along the West Lavant Stream. Floodplain flows outflanked the “Stansted Park” wall (which offers some protection) and flooded Finchdean Road, overwhelming the road drainage.

5.4.3.7 High groundwater around the affected properties could not drain away and caused internal and external flooding. Groundwater ingress into septic tanks caused contamination of floodwaters and impeded foul drainage at some houses.

5.4.4 Kings Worthy

5.4.4.1 Minor groundwater flooding is understood to occur more often than once in 5 years in Kings Worthy, but serious flooding is relatively rare, having last occurred there about 50 years ago.

5.4.4.2 During the floods of 2000/2001, 9 properties suffered internal flooding, 12 properties had flooding beneath floor level (basements and cellars) and 3 had problems with toilet flushing due to surcharged sewers. The flooding episode lasted 60-106 days. Residents used pumps to discharge the water, although discharge (of this water) to soakaways is believed to have resulted in recirculation of that water.

5.4.4.3 Property flooding was directly or indirectly related to springflow and all the properties flooded were on or close to Springvale Road, a major thoroughfare through the village that follows a normally dry Chalk valley. Due to high groundwater levels, a number of springs broke out around the road and in the fields to the north-east, and the resulting surface flow overwhelmed the surface drainage system in the road.

5.4.4.4 Issues with the surface water system that were reported at the time have partly been addressed by Winchester City Council through culvert clearance. There were outstanding deficiencies still reported in 2002, although it is not known if further action has been undertaken since then.

5.4.4.5 There is currently no Environment Agency Groundwater Flood Alert service provided to Kings Worthy, and it needs to be considered whether and how this service can be extended to include Kings Worthy.

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5.4.5 Finchdean and Deanlane End

5.4.5.1 Significant flooding occurs regularly in the Lavant valley and is understood to have occurred in the 1960s, 1976, 1988, 1994 and 1995. Flooding of the roads in Finchdean occurs regularly, at least every 7-10 years, although none have been as severe as the 2000/2001 event.

5.4.5.2 During the winter of 2000/2001, at Finchdean, 7 properties and at Deanlane End 4 properties suffered internal flooding. One house suffered from external contaminated water flooding, 3 houses suffered from prolonged internal dampness and 3 houses had water under the floorboards. In addition access was cut off to a large number of properties in Finchdean Road, Rowlands Castle.

5.4.5.3 Surface floodwaters originated from groundwater emerging in the valleys above Finchdean and within the villages. Water is understood to have flowed towards Finchdean along the roads from Chalton and Idsworth. Both these roads have winterbournes alongside them.

5.4.5.4 Spring water flowed out of bank along the watercourse through Finchdean, along both sides of the railway line and through Deanlane End before joining the West Lavant Stream flowing into Rowlands Castle.

5.4.5.5 It is understood that flooding under the railway bridge in Dean Lane occurs regularly when the watercourse flows, approximately every 2 years.

5.4.5.6 During Winter 2012/2013 actions by the EA, Hampshire County Council Emergency Planning and Highways, the District Council, the Parish Council and local riparian owners was undertaken to clear ditches. This action appeared to manage the worst effects of flooding, although roads were flooded for about a month and a number of properties had to pump from sumps to control groundwater.

5.4.6 Hursley

5.4.6.1 Hursley has a previous history of flooding. In 1995, heavy winter rainfall raised the groundwater level and caused flooding to many properties, including 17 whose cellars flooded. Some properties were flooded in 1994, but the damage that occurred then was substantially less. We understand that flooding also occurred in the village in 1963 and 1967.

5.4.6.2 During the winter of 2000-01, 18 properties suffered from flooding caused by groundwater. Of these, 1 property was affected internally, 12 properties had flooded cellars/damp floors, and 3 of these properties and 5 other properties suffered external flooding contaminated with sewage. Significant road flooding also occurred in parts of the village.

5.4.6.3 Extreme groundwater levels led to exceptional spring flows within the village. Runoff from periodic episodes of heavy rainfall further increased surface flows. The high groundwater levels also caused the local Chalk aquifer effectively to “overflow”, by discharging via springs.

5.4.6.4 The resulting spring flow, combined with direct runoff from periodic severe rainfall events, caused surface flooding. This floodwater, and possibly groundwater as well, inundated the sewerage system causing it to overflow in places.

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5.4.6.5 Although some improvements to surface water drainage had been made prior to these events and some significant surface water flooding problems resolved, 2000/2001 still resulted in significant flooding along the A3090 and adjacent properties.

5.4.6.6 The flooding at Hursley in 2000/2001, and prior to that could be attributed directly (in the case of cellar flooding) or indirectly to high groundwater levels. Some property owners successfully utilised pumps to prevent/minimise the ingress of groundwater into their cellars

5.4.7 Bishops Sutton

5.4.7.1 Bishops Sutton is located in a valley with fairly steep sides (about 1 in 15). Extreme high groundwater levels appear to generate groundwater flow from the valley sides. The southern valley side seems to be most prone to the emergence of groundwater and can cause flooding of cellars and ground floors of some properties in the village as well as flooding of the roads.

5.4.7.2 Prior to the reported incidents of the winter of 2000/2001, there are no official records of previous groundwater flood events on the same scale. During this event 12 properties flooded which included 7 properties with cellar flooding (one of which appears to flood every 3 years or so) and 4 with ground floor flooding. 1 property was flooded externally by (sewage) contaminated water. No commercial properties suffered.

5.4.7.3 Severe flooding of the main road (A31) about 1km from Bishop’s Sutton village during 2000/2001 required emergency pumping and road raising works. Although it is believed that a more permanent solution has now been put in place.

5.4.7.4 The Ford Stream provides the main watercourse for the drainage of groundwater and surface run-off. During the winter of 2000/2001, the unusually high run-off discharge, pumped floodwaters from the A31 and from cellars, and the constrictions within the channel caused the Ford Stream to be overwhelmed. This in turn may have diminished the stream’s capacity to draw down the high groundwater levels in parts of the village affecting the level of cellar and internal flooding in properties which had not previously been affected.

5.4.8 Appleshaw

5.4.8.1 Prior to 1994-995, it is understood that flooding in Appleshaw occurred every 6-7 years up until the 1960s. Serious flooding is reported to have occurred in 1919/20, 1928, 1947, 1951/52 and 1960/61. There was no further flooding until 1994/1995 – a lull in serious flooding of approximately 30 years. Despite this lull, the occurrence of groundwater flooding has been estimated as being a 1 in 25 year event.

5.4.8.2 As with other parts of Hampshire, the flood events of the winter of 2000/2001 are the most extreme experienced to date. During 2000/2001 in Appleshaw and Redenham, 4 properties where flooded internally, 7 properties experienced cellar flooding, and 1 of these properties and 1 other property suffered external sewage flooding. Additional properties where flooded externally, due to localised overflowing from the surface drainage system.

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5.4.8.3 The Southern Water pumping station in the village was overwhelmed by the flow in the sewers, which apparently contained a significant floodwater component. Southern Water had to pump sewage into the surface water drainage network for a period of 5 months.

5.4.8.4 The winter rainfall and extreme groundwater levels led to exceptional springflows within the village. Runoff from periodic episodes of heavy rainfall further increased surface flows.

5.4.8.5 A surface water by pass channel has been constructed around Appleshaw, although it is not clear how this has affected overall groundwater flood risk within the village it is understood that during the winter 2012/2013 it flowed for the first time in response to the extreme rainfall experienced.

5.4.9 Bourne Rivulet Villages

5.4.9.1 The Bourne Rivulet Villages of Vernham Deane, Upton, Hurstbourne Tarrant, Stoke and St Mary Bourne have a history of groundwater flooding, with groundwater flooding recorded in all these villages in 1994/95; 2000/2001 and 2002/3. During 2000/2001 thirteen properties in the valley experienced internal flooding and a number of properties suffered from external flooding with (sewage) contaminated water.

5.4.9.2 Although within each settlement relatively few properties experience internal groundwater flooding, within the valley as a whole, there have been significant flooding problems related to infiltration into the sewage system. This has not only led to internal and external sewage flooding but has also led to the need to apply emergency pumping of sewage into the Bourne rivulet. This is a sensitive issue particularly given the cress industry in lower parts of the valley.

5.4.9.3 There have been significant efforts in recent years by Southern Water to address the issue of sewer flooding, and the current infiltration reduction plan for the valley is well developed with implementation expected imminently. However until that time that these issues are resolved, the villages are identified as being at high risk and on this basis a settlement action plan developed.

5.4.10 West Meon

5.4.10.1 There is a history of flooding in West Meon, with records of 8 homes flooding at Long Priors in 1979. In additional there is regular (possibly annual) flooding of the A32 and High Street associated with the overtopping of the River Meon, although an number of flood events recorded during 200/2001 were clearly the result of groundwater emergence.

5.4.10.2 The winter of 2000/01 was the wettest water year (March-April) on record with a probability of occurrence that was less frequent (rarer) than once in 100 years. As a result, groundwater levels during the autumn of 2000 were unusually high, and then rose to previously unrecorded levels locally during the following winter. This led to exceptional spring flows within the village. Runoff from periodic episodes of heavy rainfall further increased surface flows.

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5.4.10.3 During this winter 2000/2001 event, the drainage of the exceptional flows arising in the catchment of the River Meon caused the river to be overwhelmed within West Meon. The river overtopped and damaged its banks in a number of places and sheet flow caused flooding of properties in the village. Despite clearance during the preceding summer, villagers believe that the conveyance of the River Meon channel was impeded by vegetation and other constrictions that exacerbated the flooding.

5.4.10.4 In addition, groundwater flowed along the valley sides and emerged as springs at the foot of the valley. This groundwater run-off overwhelmed road drainage in places and could not flow freely into the River Meon. This led to groundwater flooding in sixteen properties (excluding external ‘clean’ flooding). There were reports of 3 properties with cellar flooding, 11 with ground floor flooding and 3 with contaminated (sewage) ground floor flooding. No commercial properties flooded. Some properties that suffered only external flooding had substantial damage and some external flood waters are also understood to have contained sewage.

5.4.11 Preston Candover

5.4.11.1 In 2000/2001, the flooding in Preston Candover was caused primarily by high groundwater levels and associated exceptional springflows. Groundwater levels reached previously unrecorded highs in response to rainfall with an estimated probability of occurrence that was less frequent (rarer) than once in 200 years.

5.4.11.2 The ephemeral head of the Candover Stream (classified as ‘non-main river’ through the village) emerged near Stenbury Drive during the winter 2000/01, approximately 1 kilometre further up valley then under “normal” winter conditions.

5.4.11.3 The springflow collected on the B3046 and flowed through the village towards Church Lane. Resulting flow in the road could not easily drain away due to the various blockages in the drainage channel, and the saturated state of surrounding land. Frequent episodes of high rainfall contributed to surface runoff to the floodwaters periodically until they receded.

5.4.11.4 At Preston Candover, 9 properties suffered ground floor flooding during the winter 2000-01. Three properties suffered cellar flooding, 2 with an associated loss of stock and revenue. Approximately 14 properties had problems with their septic tanks and significant damage to the road surface occurred.

5.5 Future / Potential Groundwater Flood Risk

5.5.1 Indicators based on historic events

5.5.1.1 Records of historic flooding, particularly from the events of 2000/2001, included clearly defined occurrences of groundwater flooding and form our best means of evaluating future groundwater flooding risk.

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5.5.1.2 Those areas within which the groundwater flood alert service is currently in operation (refer Annex B, Figure 4) – and which is based largely on the experience of 2000/2001, will remain the most susceptible to groundwater flooding.

5.5.1.3 However, despite the extreme represented by the events of 2000/2001, this may not give a full picture of future events.

5.5.1.4 Exceptional rainfall occurred throughout 2012. As a result, recorded groundwater levels in the winter of 2012/2013 exceeded most “trigger levels” set by the Environment Agency, which continued to issue and update groundwater flood alerts (in most areas where this service is provided) throughout the winter. However, despite these exceptional conditions, the extensive groundwater flooding of 2000/2001 has not been repeated this winter.

5.5.1.5 Further investigation to compare the 2000/2001 and 2012/2013 events would provide a greater understanding of the mechanisms of groundwater flooding in the county.

5.5.1.6 Whilst the focus in this GWMP is on areas of the Chalk, groundwater flooding associated with shallow superficial deposits (river terrace deposits gravels etc. – see section 4.2.2) needs to be supplemented by further information in order for us to fully understand these processes.

5.5.2 Understanding of future groundwater flood risk

5.5.2.1 Our understanding of groundwater flood risk as a whole is in its infancy and to date ”prediction” of future flooding events is relatively unsophisticated compared to modelling of fluvial or even surface water flood events. This is, primarily due to a lack of data and the complexity of groundwater flow behaviour and groundwater emergence. There is no currently available standard “method” to predict the future risk of groundwater flooding and existing approaches have tended to focus on the susceptibility of areas to groundwater flooding.

5.5.2.2 Although predictive groundwater models can be developed (on a similar basis to numerical groundwater resources models) in general terms they require a large amount of good quality, site-specific data. Even then they may produce results with a high degree of uncertainty attached. Furthermore, most existing models that utilise appropriate data sets are designed for regional water resources management and are often unsuitable for forecasting groundwater flood risk at a local level without significant changes.

5.5.3 Potential impacts from climate change

5.5.3.1 Most climate change models indicate we are likely to experience drier summers, albeit with more intense rainfall when it occurs and wetter winters. A review of how climate change impacts may affect Hampshire is provided in the LFRMS (Ref 6).

5.5.3.2 As groundwater flooding occurs primarily as a response to extended periods of rain during late autumn and early winter, there may be an increased risk of groundwater flooding arising from these changing rainfall patterns. However, this is far from certain and the complex relationship between rainfall, recharge, groundwater

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storage and flow is such that we cannot currently predict what the effects of climate change might be with respect to groundwater flood risk.

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6 Settlement risk assessment and measures assessment 6.1 Introduction

6.1.1.1 Section 5 has highlighted the areas in Hampshire most at risk of groundwater flooding. This section now considers what actions might be taken to address / mitigate that risk. It deals with generic actions that can be applied across the board and suggests which organisation or body might be best placed to deliver them. More detailed bespoke actions for each individual area are set out the action plans in Annex F.

6.2 Overall Approach – Generic Measures

6.2.1.1 Irrespective of any site specific measures, a range of generic measures can be identified that help to address and manage groundwater flood risk. In summary these measures can be identified as:

Development management;

Emergency planning;

Drainage infrastructure maintenance;

Installation of dewatering systems at local or household level;

Installation of structural resistance and resilience measures

Development of a flood warning system (see section 7.1)

6.2.1.2 These measures are best developed with a good understanding of the groundwater flooding mechanisms in the area of concern (refer Annex C). This understanding should be based on:

Geology (including bedrock and superficial deposits)

Groundwater levels and flow

Topography

Surface water drainage including both fluvial and manmade drainage networks (such as road drainage)

Foul drainage networks

Local Flood History

Key flood receptors (properties, including basements, roads and other significant infrastructure)

6.2.1.3 The potential costs and benefits of any proposed measures may then be set in the context of this local analysis.

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6.3 Planning for groundwater flooding

6.3.1 Development (Planning) Management

6.3.1.1 For all proposed new developments within an area that could include high groundwater flood risk (see 6.3.1.3 below) a groundwater flood risk assessment should be undertaken. The assessment should include as much site-specific data as possible (including evidence from local sources such as Parish Councils and Flood Action Groups).

6.3.1.2 Planning management is essential to control inappropriate (new) development and drainage in areas that may be prone to groundwater flooding. This may include, for example:

Allowing infiltration drainage only where it can be demonstrated that it does not contribute to the overall risk of groundwater flooding (i.e. appropriate mitigation or management of that risk is included in the design of the drainage);

Restrictions on private sewerage (such as cesspits) and requiring “sealed” foul drainage systems;

Controls on ground floor levels of new developments;

A presumption against the construction of basements1;

Controls on development of all sub surface structures, including foundations;

Ensuring access routes will remain free of groundwater flooding and do not constrain the free flow of groundwater or emergent groundwater

Requirements for specification of materials resilient to long term exposure to flooding;

Consultation with local communities on groundwater flooding and groundwater emergence (this may be included as part of a Local Planning Authorities existing public consultation process, or depending on how future government guidance will evolve, as part of the consultation process

1 Although the owners/ developers of the basement may be the most likely to suffer from groundwater flood

risk, the deeper foundations associated with the basement may impede groundwater flow just below the

ground surface and encourage it to emerge, potentially increasing flood risk for other receptors

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required for an application to the SUDS Approval Body of Hampshire County Council) .

6.3.1.3 At minimum, such planning management measures should be required, in all areas:

Where there have been records of previous local groundwater flooding particularly where this occurs within the same groundwater catchment;

Further, and unless local conditions, records or lines of evidence can be used to demonstrate otherwise, these management measures should be applied in particular to areas:

Which are subject to the groundwater flood alert service from the Environment Agency;

Which have been identified with a groundwater flood susceptibility of ≥ 75% (according to Environment Agency groundwater flood susceptibility mapping).

6.3.1.4 Further information on potential development within Hampshire is provided in the LFRMS (Ref 6).

6.3.2 Local planning

6.3.2.1 Groundwater flood risk should be a material consideration when preparing local plans and the kinds of potential restrictions on development outlined above must be taken into consideration. Where necessary and where these areas cannot (for other reasons) be avoided, the additional cost of developing mitigation, including appropriate flood risk management infrastructure should be recognised in the plans.

6.3.3 Infiltration Drainage and Soakaways

6.3.3.1 Under the Flood and Water Management Act and under emerging National Standards for Sustainable Drainage (SuDS) infiltration may be identified as the preferred drainage option.

6.3.3.2 However in areas susceptible to groundwater flooding, infiltration drainage, for example as part SuDS schemes for new developments, should not be permitted unless it can be demonstrated to be appropriate through production of a local groundwater flood risk assessment (see also section 6.3.1.2).

6.3.3.3 Individual recommendations with respect to infiltration drainage are made within each settlement action plan (see Annex F), but as a general rule, unless a developer can demonstrate through the groundwater flood risk assessment that infiltration drainage either has no adverse impact on groundwater flood risk or could lead to improvements in (all types of) flood risk there should be a presumption against infiltration drainage in those areas identified in section 6.3.1.3 above.

6.3.3.4 The LFRMS provides further information with regard to the implementation of the Flood and Water Management Act, Lead Local Flood Authority responsibilities, the requirements of SuDS Approval Bodies (SABs) and the potential implications of the National Standards for Sustainable Drainage.

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6.3.4 Emergency Planning

6.3.4.1 Hampshire County Council has prepared a Multi Agency Flood Response Plan which outlines the response arrangements in place for a co-ordinated multi agency response to major flooding. This can be found at:

http://documents.hants.gov.uk/flood-water-management/HampshireMultiAgencyFloodResponsePlanPublicVersion2012.pdf

6.3.4.2 The LFRMS (LFRMS - Annex I) provides information on preparation for flooding, which applies to all forms of flooding and Hampshire County Council provides advice on its website:

http://www3.hants.gov.uk/emergency_flooding

http://www3.hants.gov.uk/emergencyplanning/severeweather/flooding-advice/sandbags.htm

6.3.4.3 Other guidance is available from:

Environment Agency website

What to do before, during and after a flood (Environment Agency Publication)

Flooding from groundwater (Environment Agency publication)

Ready for Flooding (National Flood Forum publication)

Which can be found at the following:

http://www.environment-agency.gov.uk/homeandleisure/floods/114720.aspx

http://publications.environment-agency.gov.uk/pdf/FLHO1110BTFK-e-e.pdf

http://publications.environment-agency.gov.uk/PDF/FLHO0911BUGI-E-E.pdf

http://nationalfloodforum.org.uk/?page_id=14

6.4 Drainage Infrastructure Maintenance

6.4.1 Conveyance

6.4.1.1 Fundamentally the damage caused by emergent groundwater, as with all forms of flooding can in part be managed by improved conveyance and clearance of drainage pathways, retaining water within drainage channels, reducing the potential for back up in water courses and moving the flood water away from potential receptors. This includes appropriate maintenance and management of ordinary watercourses, other surface water drainage, highway ditches (that often follow valley floors), clearance and maintenance of culverts etc. Maintaining land drainage may also help reduce levels within the groundwater catchment.

6.4.1.2 Increased conveyance, including maintaining the upper parts of the natural watercourse (i.e. winterbourne stretches of chalk streams - see Annex C) will help drain the groundwater body and bring down groundwater levels through encouraging natural recession.

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6.4.1.3 However undertaken, means of improving conveyance must be carried out with recognition that this could increase downstream flood risk as flows are passed down the catchment. Any such approach must therefore be integrated within the catchment as a whole.

6.4.1.4 Channel maintenance and clearance responsibilities for the management of rivers, ordinary watercourses, highway drainage and minor channels and land drains are set out in the LFRMS.

6.4.1.5 Fluvial and surface water flood events may, in part, be addressed by providing additional flood storage within the flood plain. This storage serves to retain peak flood flows and helps reduce downstream risk.

6.4.1.6 However, the lack of a peak in groundwater derived flood flow and its slow rate of recession (i.e. high flows are maintained over a long period) is such that use of storage within a broader floodplain is unlikely to significantly reduce downstream flood risk.

6.4.1.7 Although improved conveyance can address some of the issues caused by groundwater once it has emerged at the surface and essentially becomes a surface flow problem, there are some fundamental characteristics of groundwater flooding which cannot be addressed by conveyance improvements, for example:

During a groundwater flood event, the locations of groundwater emergence may be new (or previously unrecorded) and there may be no established drainage pathway for discharge.

Emergence may occur directly beneath properties (e.g. through floorboards or into basements) or other receptors.

Surcharging of sewers, cess pits and other sub surface drainage

6.4.1.8 Therefore, where circumstances occur, other actions may be required. These include developing resilience and resistance and the use of dewatering (or other groundwater management methods), described below.

6.4.2 Flood Resistance and Resilience

6.4.2.1 While it is almost impossible to completely flood-proof a property, there are measures that can be taken to reduce the impact of flood damage and to aid recovery from damage once the flood event has passed. Although many of the measures used to provide resistance and resilience to surface water and fluvial flooding are also suited to groundwater flooding, many traditional methods of flood protection, such as sandbags, may not be effective against flooding from groundwater. This is because water can come up through the floor and remain for a long time.

6.4.2.2 There are differences in impacts related to the long duration of groundwater flooding (weeks compared with days). These include potential structural impacts on foundations and impacts on sub surface drainage (both main sewer systems and local systems such as cess pits and soakaways).

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6.4.2.3 Whilst the duration of groundwater flooding is problematic, as it generally takes some time to build up, there is generally a greater length of time to move valuable items or undertake a planned “evacuation”

6.4.2.4 Resistance measures are intended to limit entry of water to the building. Those that may be effective in a building include:

Installing waterproof floors and sealing walls (including making good pointing, rendering etc.);

Similarly sealing (tanking) basements and using sump pumps for clearance if water ingress cannot be prevented;

Covering susceptible ingress points such as airbricks (e.g. flood proof airbricks are available) and sealing weep holes;

One-way valves, toilet plugs and pipe bungs may prevent the entry of water from flooded sewers;

‘Sump and pump’ – the use of a drain around a property to intercept rising groundwater and direct it to a sump, from where it is pumped to disposal (see dewatering below).

6.4.2.5 Resilience involves modifying the interior of a building, for example by using materials that are less prone to damage by floodwater and/ or dry quickly so that the post-flooding clean-up will be easier, cheaper and quicker. Any surface water / fluvial resilience measure will be equally suitable for groundwater flooding. Typical measures include:

Mounting electrical sockets, fittings and equipment at high level above expected flood water;

Using solid or tile floors rather than fitted carpets;

Having readily demountable equipment (such as TVs etc.) that can be moved to a safe location;

Raise less easily demountable portable equipment (e.g., kitchen fittings) to high level;

Using plaster and other building materials that are more resilient to long periods under damp conditions.

6.4.2.6 The Environment Agency provides advice on preparing properties for flooding in the following publications:

Homeowners Guide to Flood Risk , which lists various measures that are applicable to flooding in general;

Flooding from groundwater- Practical advice to help homeowners reduce the impact of flooding from groundwater which provides information specific to groundwater flooding.

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These can be found at:

(http://www.knowyourfloodrisk.co.uk/pdf/protection-guide.pdf)

(http://publications.environment-agency.gov.uk/PDF/FLHO0911BUGI-E-E.pdf)

respectively.

Parish Councils and Flood Action Groups (see section 7.2) may also provide more localised advice on preparing properties for flooding.

6.4.3 Dewatering

6.4.3.1 Dewatering to alleviate groundwater flooding could include, for example:

Continually pumping out a flooded basement to prevent further damage;

Installation of a groundwater control system around a property (e.g. using French drains and a pumped sump) to prevent groundwater emerging from beneath an individual building up through the floorboards;

Employing a series of abstraction wells to locally reduce the groundwater level (e.g. within a valley floor location);

Overpumping existing water supply wells to drawn down groundwater on a more regional basis.

6.4.3.2 Whichever means is to be adopted (apart from the latter example) there must be a route available to dispose of the abstracted water. In most cases, groundwater flooding will coincide with (or be the cause of) overwhelmed surface water drainage systems. Finding a suitable location to discharge the pumped water (i.e. one that does not increase downstream risk) may be problematic. As noted above (see section 6.4.1.5 and 6.4.1.6), storing the water is unlikely to be practical (unless the flooding is tidally controlled) due to the long duration of events and difficulty of providing the storage volume needed.

6.4.3.3 Assuming the floodwater can be disposed of, dewatering is only likely to be a suitable solution for highly sensitive receptors or structures whose stability could be affected by groundwater flooding.

6.4.3.4 Apart from simple basement pumping, most of these dewatering approaches also may require significant design effort to ensure they will work appropriately. This would include local desk study possibly accompanied by site investigations and a monitoring programme prior to establishing a viable dewatering design.

6.4.3.5 Overpumping of existing water supply wells will only work if the water supply wells are sufficiently close to reduce groundwater levels beneath impacted receptors.

6.4.3.6 In both these latter cases of more “regional” dewatering, unless pumped wells are in the immediate vicinity of the impacted location, they are unlikely to have a significant effect, there would be a number of complex issues to address (including disposal of the pumped water) and the benefit cost of any such approach is likely to be very questionable.

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6.4.4 Management of sewage flooding

6.4.4.1 While it may be possible to manage sewage flooding through use of one way valves and sealed systems where this relates to individual cess pit or septic tank drainage, where mains drainage is involved, any such effort is a larger undertaking.

6.4.4.2 During the winter of 2000/2001 and again during 2012/2013 the foul sewerage in a number of areas has experienced infiltration into the system which causes it to become overloaded with water. In some more sensitive locations this occurs on a frequent basis (for example at Hambledon and through the villages of the Bourne Rivulet) This means that some householders are unable to flush their toilets, manholes pop up and it can cause “sewage flooding” in the settlement and downstream pollution to local watercourses. The water utility company may have to pump direct from the downstream end of the system, potentially direct to a watercourse, so potentially exacerbating pollution problems.

6.4.4.3 Sewer flooding and drainage are the responsibility of the water companies in Hampshire (Southern Water, Thames Water, and Wessex Water).

6.4.4.4 The water companies have plans and procedures in place detailing their responses to groundwater sewer infiltration issues in general and developing the most appropriate mitigation/ control measures for each site where these issues are known to occur. These plans include as much site specific information as is available and are updated as new information is identified. Where actions are planned to address flood risk, it is essential to consider these holistically, i.e. the impact of the action plan on all aspects of drainage (including the foul sewage system) must be considered.

6.4.5 Road Traffic Management

6.4.5.1 As well as potentially overwhelming road drainage (and indeed roads in valley floors may become a “preferred” route for the passage of water during a flood event), groundwater flooding may cause significant damage to the road structure, including road sub-base and surface and verges.

6.4.5.2 Due to the typically long duration of groundwater flooding, long term diversions may be needed to direct road traffic away from flooded areas. This may have significant repercussions with respect to access to properties, access for emergency services or access to critical infrastructure.

6.4.5.3 As well as setting up diversions, it may be necessary for road traffic to pass through areas of shallow flooding, which has its own risks including:

Driver/vehicle safety risks;

Potential for vehicle “bow-waves” to increase the penetration of floodwaters into properties.

As a minimum, the introduction of temporary traffic calming measures is required to address these risks.

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6.5 Introduction - settlement risk assessment and action plans

6.5.1 Approach

6.5.1.1 A detailed action plan has been produced for each of the top ten settlements at high risk of groundwater flooding. These action plans address the potential risk of groundwater flooding in an identified settlement, likely damage to property, mitigation that has been carried out to date, along with any further actions and mitigation that are proposed or to be considered.

6.5.1.2 A detailed map of the area is also included with each action plan. The action plans for the top 10 in the ranking at risk from groundwater flooding can be seen in Annex F.

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7 Managing residual risk 7.1 Introduction

7.1.1.1 Although the settlement specific plans identify a number of physical measures (for example improvements to conveyance or reactive maintenance measures), due to the nature and characteristics of groundwater flooding, there remain elements of residual risk that cannot be addressed in this way.

7.1.1.2 These residual risks need to be addressed by a range of awareness raising measures, that may include, for example, promotion of the flood alert service offered by the Environment Agency, development of local and personal flood action plans and development of flood action groups. These measures are discussed further below. Further information dissemination should encourage local residents whose properties are at risk to apply their own resilience and resistance measures (as identified in Section 6).

7.2 Environment Agency Flood Warnings

7.2.1 Overall Approach

7.2.1.1 The Environment Agency flood warning service has three types of warnings that help prepare for flooding and take appropriate action. They are:

Flood Alert

Flood Warning

Severe Flood Warning

Further details of what these different types of warning mean are given in Annex G1.

7.2.2 Groundwater Flood Information and Warnings

7.2.2.1 As groundwater flooding rises more slowly than fluvial flooding, there is a lesser requirement for immediate action and there is unlikely to be a danger to life. On this basis (refer definitions in Annex G2) the Environment Agency do not issue “Flood Warnings” or “Severe Flood Warnings” for this type of flooding and for groundwater flooding the Environment Agency only issue “Flood Alerts.”

7.2.2.2 The groundwater flood information service provided by the Environment Agency comprises a number of elements:

Provision of advice on overall groundwater conditions through monthly regional water situation reports (refer Annex G2);

Provisions of more specific advice on groundwater levels through groundwater briefing notes (refer Annex G2);

A targeted groundwater flood warning service through issue of groundwater “Flood Alerts” for specific locations and communities (see below and Annex G3);

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7.2.2.3 This targeted groundwater flood warning service is provided to some areas within Hampshire, particularly areas with a known history of groundwater flooding. The flood warning service is found at:

http://www.environment-agency.gov.uk/homeandleisure/floods/58417.aspx

Groundwater “Flood Alerts” are issued to subscribers to Floodline Warnings Direct.

[http://www.environment-agency.gov.uk/homeandleisure/floods/38289.aspx]

Individuals can sign up to Floodline Warnings Direct by calling Floodline on 0845 988 1188 or Typetalk 0845 602 6340.

Further details of the groundwater flood warning service are provided in Annex G3 including identification of the “Flood Alert” areas with additional direct dial contact numbers.

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7.2.3 The Flood Forecasting Centre and Flood Guidance Statement

7.2.3.1 The Flood Forecasting Centre (FFC), established in 2009, issues daily advice regarding flood risk through the Flood Guidance Statement (FGS). The FGS provides an overview of flood risk across England and Wales over a 5 day period which is issued to Category 1 and Category 2 responders to assist with emergency planning and decision making.

7.2.3.2 The FGS highlights risk for all types of flooding in one place including river, tidal/coastal, surface water and groundwater flood risk. It includes current warnings in place and a best judgement on what may be expected to happen. There is no public access to these warnings, which are issued at least once a day (from 10.30 a.m.) and up to 3 times a day when flood risk are high (from a scale of very low, low, medium, high).

7.2.3.3 Further details of emergency planning in Hampshire are provided in the Hampshire County Multi Agency Flood Response Plan (Ref 11).

7.2.3.4 A typical flood guidance statement is shown in Annex G4.

7.3 Forming Flood Action Groups

7.3.1 Promotion of Flood Action Groups

7.3.1.1 Hampshire County Council remains committed to the formation of Local Flood Action Groups (FAGs) as a key measure in the management of flood risk at a local level. Through its Emergency Planning and Resilience Unit it comes under the wider remit of “Community Resilience”. Community Resilience aims to identify local resources and equipment to support the response of the statutory services. Communities at risk from groundwater flooding have demonstrated that with the support of the response agencies (local authority, environment agency etc.) they are able to co-ordinate local issues by acting as a single point of contact. This co-ordination starts with the establishment of a Flood Action Group

7.3.1.2 Flood Action Groups provide a representative “grass roots” voice for their community and should aim to work in partnership with the Agencies and Authorities whose work involves flood risk. They should aim to:

Address concerns over malfunctioning assets and other issues;

Remain in touch with plans for and needs of their community;

Act as a point of liaison with riparian land owners

Assist the Local Authority in identifying particularly vulnerable members of their community to enable the appropriate support when required;

Understand procedures already in place with respect to routine maintenance and emergency services / local authority protocol;

Provide a voice with respect to the future flood risk of their community through consultation;

Identify and implement ‘flood warden’ schemes;

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Create awareness of flood risk within the wider community;

Make preparations to manage and reduce the impact on the community should a flood event occur (e.g. through development of emergency action plans and assisting with warning and informing).

7.3.1.3 The National Flood Forum provides guidance and support for local communities that wish to develop FAGs, provides “tools” to ensure their success and sustainability and will initiate the first meeting with appropriate professionals. The National Flood Forum is found at:

http://nationalfloodforum.org.uk

“How To Form A Flood Group « National Flood Forum”

Further information on the formation of Flood Action Groups and those already established in Hampshire is provided in Annex H1.

7.3.1.4 The Hambledon Village Plan is attached in Annex H2 as an example of a local flood action plan, from a community that has experienced regular flooding problems. Hambledon remains the village at greatest risk from groundwater flooding in Hampshire. The present draft settlement action plan for Hambledon will require close liaison with the community to ensure it takes into account their local experience.

7.3.2 The Parish Lengthsmen Scheme Pilots

7.3.2.1 Hampshire County Council (Economy, Transport and Environment Department) has been trialling a scheme to reintroduce the modern equivalent of ‘parish lengthsmen’ in a small number of areas to carry out routine maintenance works on roads within the parish. Initial trials in Test Valley and the Meon Valley during 2011 were followed by further trials in Winchester, Fordingbridge, Minstead and Fleet. A further extension of the trial has been agreed for 2013/14.

7.3.2.2 The lengthsmen scheme allows for a local level of (maintenance) responsibility (primarily) for County highways but also for other community assets. Examples of these responsibilities include maintenance of road drainage including grips, ditches and channels and rodding of (off highway) pipes as well as maintenance duties for land drainage. The role also allows for reporting duties.

7.3.2.3 Potentially this lengthsmen role could not only provide better local maintenance for flood conveyance but also report on significant issues (for example collapsed drainage, significant blockage) or help with reporting during actual flood incidents.

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8 Environmental Assessment 8.1 Introduction

8.1.1.1 A Strategic Environmental Assessment (SEA) has been carried out as part of the GWMP. This has been based largely on the SEA carried out for the LFRMS, although it has been more targeted at the aims and objectives of the GWMP. The SEA also takes into account the requirements of the Water Framework Directive (WFD) and the Habitats and Birds Directives; these are described in Sections 8.3 and 8.4. The principal output of the SEA will be an “Environmental Report”, which is provided as Annex D to this GWMP. However, environmental constraints and opportunities, if applicable, will also be added to the GWMP Action Plans.

8.2 Strategic Environmental Assessment

8.2.1.1 SEA is the systematic appraisal of the potential environmental impacts of policies, plans, strategies and programmes, before they are approved. It ensures that any implications for the environment are fully and transparently considered before final decisions are taken and is required by an EC Directive (2001/42/EC). The Directive is implemented in England through the Environmental Assessment of Plans and Programmes Regulations (SI 1633 2004). This legislation makes SEA a legal requirement for certain plans and programmes which are likely to have significant effects on the environment.

8.2.1.2 The GWMP is not a statutory plan. Local authorities need to decide if a GWMP requires SEA by making a ‘screening decision.’ Whether a GWMP will require SEA will depend on a number of factors, including whether it applies over a wide area, its environmental effects and its statutory status. HCC, in consultation with Halcrow, concluded that, due to the potential for significant effects on the environment, and in accordance with good practice, an SEA of the GWMP should be undertaken on a “precautionary” basis.

8.2.1.3 The Environmental Report summarises the environmental baseline for the County, focusing on issues that are specifically relevant to groundwater flood risk. It also includes consideration of the cumulative environmental effects of flood risk from groundwater sources in addition to the flood risk associated with surface water, ordinary water courses, main rivers, the sea and the sewerage network, where these sources are relevant.

8.2.1.4 The environmental baseline has been used to develop SEA ‘objectives’, formulated to help protect the environment. These objectives have been used to assess the environmental effects of the GWMP “action plans” and the results used to help select a preferred approach for groundwater management, meets environmental objectives and complies with legal requirements to protect the environment.

8.2.1.5 Sites designated for their nature conservation, landscape or cultural heritage importance, critical infrastructure and potential sources of pollution (historic landfill sites) have been identified in relation to where action plan measures are likely to take place and are listed in each of the action plans they relate to, in order to illustrate potential constraints and opportunities for groundwater management measures.

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8.2.1.6 The key findings of the SEA are that the majority of measures within the GWMP are likely to have a positive effect on the environment.

8.2.1.7 However, the eventual actual effects on receptors are difficult to predict at a strategic level because impacts are often specific to certain locations and design details of eventual GWMP groundwater flood risk mitigation measures.

8.2.1.8 On this basis, environmental constraints have been identified within each settlement action plan. An EIA screening opinion, which determines whether an EIA will be required, will need to be obtained from Natural England for any measures that could potentially have a significant effect on the environment.

8.2.1.9 If required, any project level environmental assessment or appraisal should feed into the choice of location and design for any of these locally based schemes and include measures to mitigate any adverse effects, for example through Construction Environmental Management Plans (CEMPs).

8.2.1.10 The statutory consultees for SEA (English Heritage, the Environment Agency and Natural England) and key stakeholders will have opportunity to comment on the SEA findings.

8.3 Habitats and Birds Directives

8.3.1.1 Due to the potential for the GWMP to have significant effects on sites of international nature conservation importance (Ramsar sites and Natura 2000 sites – Special Areas of Conservation (SACs), Special Protection Areas (SPAs)) in the Hampshire area, these sites have been mapped and taken into consideration in the SEA. Baseline data collection on international sites has been integrated with the SEA process.

8.3.1.2 The protection of these internationally designated sites is required in order to comply with the EU Habitats Directive (EU Council Directive 92/43/EEC on the Conservation of Natural Habitats and Wild Fauna and Flora) and the EU Birds Directive 2009/147/EC (on the Conservation of Wild Birds), and the transposing U.K. Regulations (The Conservation of Habitats and Species (Amendment) Regulations 2012, SI No. 1927).

8.4 Water Framework Directive (WFD)

8.4.1.1 The Water Framework Directive (WFD) is a European Directive which introduces a new strategic planning process to manage, protect and improve the water environment. It came into force on 22 December 2000 and was transposed into UK law in 2003. The Directive aims to help to protect and enhance the quality of:

Surface freshwater (including lakes, streams and rivers);

Groundwater;

Groundwater dependant ecosystems;

Estuaries;

Coastal waters out to one mile from low-water.

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8.4.1.2 The WFD establishes a framework for the protection of water bodies (including terrestrial ecosystems and wetlands directly dependent on them) which aims to;

Prevent deterioration in the classification status of aquatic ecosystems, protect them and improve the ecological condition of waters;

Achieve at least ‘good’ status for all waters by 2015. Where this is not possible, ‘good’ status should be achieved by 2021 or 2027;

Promote sustainable use of water as a natural resource;

Conserve habitats and species that depend directly on water;

Progressively reduce or phase out release of individual pollutants or groups of pollutants that present a significant threat to the aquatic environment;

Progressively reduce the pollution of groundwater and prevent or limit the entry of pollutants; and

Contribute to mitigating the effects of floods and droughts

8.4.1.3 The GWMP needs to be assessed for WFD compliance to ensure that local measures to reduce flood risk comply with the WFD, and should contribute to achieving WFD objectives.

8.4.1.4 The Environment Agency has advised that ‘WFD assessment can be incorporated into the SEA’ for a Local Flood Risk Management Strategy (LFRMS), which has also been prepared by HCC. The same approach has therefore been taken for the GWMP, i.e. a detailed WFD Assessment has not been undertaken. As a result of this, the SEA Objectives covering water quality, resource availability and hydromorphology and their underlying assessment criteria are designed in order to fulfil the requirements of the WFD. In general, the spirit of the WFD is to work with natural processes or soft engineering solutions to flood management, rather than hard engineering. The GWMP may therefore need to consider this in relation to its policies and action plans.

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9 Options Evaluation, Implementation and Recommendations

9.1 Generic Measures

9.1.1 Planning

9.1.1.1 The generic measures described in Section 6.2-6.4 will need to be integrated into the planning process. This will necessarily entail a level of collaboration between District Level planning authorities and counterparts at Hampshire County Council (for example staff forming the SuDs approval bodies).

9.1.1.2 Additionally, opinions may need to be sought from specialist expertise available at the Environment Agency (for example hydrogeologists), particularly where there is a need for advice regarding groundwater flood risk (for example, with respect to the evaluation of a groundwater flood risk assessment submitted in support of a planning application).

9.1.1.3 There will remain an element of shared responsibility and the inclusion of a wider stakeholder group (for example Parish Councils, Flood Action Groups) may be required during planning. Where sewage infrastructure (including for example the installation of new infrastructure) may be impacted, the involvement of the water companies will be a vital part in the decision making process.

9.1.2 Other generic Measures

9.1.2.1 Maintenance of conveyance should be part of “business as usual”, although where high groundwater flood risks have been identified (see also site specific action plans), there may be a need to review both routine maintenance processes (for example; type of proposed action, frequency, inspection and monitoring) and develop more specific reactive measures.

9.1.2.2 Both these actions may entail additional cost although utilisation of locally based resources (such as the increased use of Lengthsmen- as described in Section 7.2.2) may offset some of this additional cost.

9.1.2.3 The water companies ongoing Infiltration Reduction Plans should be taken forward to address issues related to groundwater surcharging of sewers and associated flooding. These plans should be co-ordinated with District and Hampshire County Council (as well as the Environment Agency) to ensure actions are focussed on those communities at highest risk.

9.1.2.4 It is important to ensure that the implications of all mitigation actions are effectively communicated between partners and stakeholders mitigation.

9.1.3 Promotion of generic measures

9.1.3.1 Hampshire County Council, District Councils and the Environment Agency should continue to promote the adoption of generic measures through established channels, such as through the Hampshire Association of Local Councils (HALC),

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meeting with Parish Councils and Flood Action Groups and through Local Resilience Forums.

9.1.3.2 Those measures that should be the particular focus of promotion should be:

Adoption of good practice with respect to the maintenance of conveyance among riparian landowners.

Encouraging at risk groups to sign up for the Environment Agency Flood Warning service

9.2 Site Specific Measures

9.2.1.1 The individual site specific risk assessments identify more localised measures targeted at those settlements at highest risk from groundwater flooding.

9.2.1.2 A significant number of these actions relate to routine and localised maintenance of conveyance channels and local application of the generic measures described above.

9.2.1.3 Where specific actions require the implementation of more capital intensive schemes (such as the installation of new highway drainage, new culverts, opening of new channels etc.) these should be subject to appropriate benefit cost analysis. Any such analysis should take into account the higher costs of damages associated with groundwater flooding related to the longer duration flooding that is normally experienced.(Ref 1).

9.2.1.4 Where more intensive schemes are proposed, it is essential to ensure that risks to downstream receptors is not increased as a result, additionally it is essential that the potential environmental impact is taken into account (for example, excavations may need archaeological surveys). Local environmental constraints are identified in each site specific action plan.

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10 Review and Monitoring 10.1 On going review and updates of the GWMP

10.1.1.1 As with the SWMPs, the GWMP is a live document that will require update and review as additional information becomes available. This may include for example, taking on board fresh information with respect to groundwater flooding incidents, or issues (such as sewer flooding) brought on by groundwater emergence and flow. Changes to legislation will also need to be taken on board, for example the introduction of the National SuDs standards (refer section 6.3.3) may lead to additional pressure to introduce infiltration drainage which will need to be reviewed with respect to the GWMP (and vice versa).

10.1.1.2 The overall generic action plan and individual action plans will need to be reviewed and updated as and when measures (for example, enhanced drainage or sealing of sewer systems) are put in place.

10.2 Collection and Maintenance of Groundwater flooding records

10.2.1 Monitoring and Recording Groundwater Levels

10.2.1.1 As part of its duties to manage the water environment, the Environment Agency gathers and interprets data on groundwater levels from an extensive network of monitoring sites. This data is usually stored either in their WISKI database (time series data) or in the boreholes, wells springs database (BWS).

10.3 Collection and recording groundwater flood data during a flood event

10.3.1.1 As part of its responsibilities (under FWMA 2010) Hampshire County Council is required to investigate the causes and effects of significant groundwater flooding incidents and to make recommendations to avoid that risk re-occurring, including the recording of these incidents as they happen.

10.3.1.2 As part of the Local Flood Risk Management Strategy Hampshire County Council produced a form to allow residents and other respondents to record significant flood incidents to improve the accuracy of information it records on flooding in the county. However this does not include a place to record information on basement flooding or on the back up or malfunction of foul drainage systems, both of which often occur as a result of groundwater flooding. For future use, it is proposed that the format of the reporting questionnaire should be updated to replicate the pro forma developed for Defra (see 10.3.1.4 below).

10.3.1.3 During 2007, Defra undertook a review of the collation, monitoring and risk assessment of groundwater flooding (Ref 8), which identified a number of drawbacks in the current processes for collection of information on groundwater flooding, particularly inconsistencies on how such information was collected, recorded, stored and accessed. The study concluded that the Environment Agency National Flood and Coastal Defence Database (NFCDD) had the greatest potential for hosting a national database of records of flooding from all sources, including groundwater. However, since that study, it is understood that this has not been

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pursued and the recording of groundwater flooding event information remains sporadic.

10.3.1.4 Further, the Defra 2007 study (Ref 8) identified that during a groundwater flooding event, the use of trained or “aware” personnel, collecting data in accordance with an established protocol (e.g. using a robust pro-forma, as attached in Annex I) would offer a standardised and robust approach to data collection that would provide a better record for analysis of such events in future.

10.3.1.5 It is not known whether such methods have been adopted (or indeed have been applied during the current 2012/2013) winter where groundwater levels have been extreme and some groundwater flooding has occurred.

10.3.1.6 Monitoring of groundwater flooding requires a different approach to the monitoring of other forms of flooding (including fluvial and surface water flooding), in particular:

There are significant differences in duration and extent that might be expected from a fluvial event or surface water event;

Local groundwater behavioural characteristics will dictate which groundwater flooding events should be monitored;

Flood risk levels will be locally variable.

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11 Conclusions

This section will be completed during finalisation of the report and following completion of the consultation process

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12 References 1) An assessment of the additional flood losses associated with groundwater

flooding: a report to Hampshire County Council and Winchester City Council. FHRC. Sept 2006.

2) Environment Agency – Southern Region Hampshire and Isle of Wight Area. Winter 2000-2001 Flooding in Hampshire. Final Overview Report. Halcrow. September 2002

3) Hampshire Surface Water Management Plan (SWMP) Strategic Assessment and Background Information. Hampshire County Council. April 2012.

4) Surface Water Management Plan Technical Guidance. Defra. March 2010.

5) Preliminary Flood Risk Assessment 2011-2017. Hampshire County Council. June 2011

6) Hampshire Local Flood Risk Management Strategy. Draft for Consultation. March 2013

7) McKenzie, A.A., Bloomfield, J.P., Hulbert, A. and Rutter, H.K., 2009. Confidence and Groundwater Flood Susceptibility Mapping.

8) Making Space for Water Project – HA-5 - Groundwater Flooding Records Collation, Monitoring and Risk Assessment. Defra (Jacobs 2007)

9) Strategy for Flood and Coastal Erosion Risk Management: Groundwater Flooding Scoping Study (LDS 23). Defra May 2004

10) Environment Agency (Unpublished) Groundwater Flooding Procedures Solent and South Downs Area. Updated August 2012

11) Hampshire County Multi Agency Flood Response Plan. Version 1.0 Hampshire County Council (Emergency Planning Unit). September 2012

12) Groundwater Flood Risk management: Advances Towards Meeting the Requirements of the EU Floods Directive. Cobby. D et al Journal of Flood Risk Management 2009 (1-9)

13) Strategic Framework and Policy Statement on Improving the Resilience of Critical Infrastructure to Disruption from Natural Hazards. Cabinet Office. March 2010.

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13 Abbreviations and Acronyms

Abbreviation/ Acronym Description CFMP Catchment Flood Management Plan

Defra Department for Environment, Food and Rural Affairs

EA Environment Agency

EU European Union

FAG Flood Action Group

FFC Flood Forecasting Centre

FGS Flood Guidance Statement

FRA Flood Risk Assessment

FRM Flood Risk Management

FRR Flood Risk Regulations 2009

FWMA Flood and Water Management Act 2010

GWMP Groundwater Management Plan

HCC Hampshire County Council

LLFA Lead Local Flood Authority

LRF Local Resilience Forum

LFRMS Local Flood Risk Management Strategy

NPPF National Planning Policy Framework

PFRA Preliminary Flood Risk Assessment

RBMP River Basin Management Plan SAC Special Area of Conservation

SEA Strategic Environmental Assessment

SFRA Strategic Flood Risk Assessment

SFRM Strategic Flood Risk Management

SI Site Investigation

SPA Special Protection Area

SSSI Sites of Special Scientific Interest

SPZ Source Protection Zone

SuDS Sustainable Drainage Systems

SWMP Surface Water Management Plan

WFD Water Framework Directive

WWPS Waste Water Pumping Station

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Glossary

Term Definition

ArcGIS Software package used for spatial mapping and analysis of data.

Anticline Upwardly arched folds of Sedimentary rocks put under pressure by movement in the Earth. See also syncline.

Aquifer Layer of water-bearing permeable rock, sand or gravel which is capable of providing significant amounts of water.

Borehole A narrow diameter drilled shaft or well. An abstraction borehole is used for groundwater supply (for public or private use). An observation borehole or monitoring borehole is used to measure groundwater level and may also be used to take groundwater samples

Catchment Flood Management Plan (CFMP)

Strategic planning tool through which the Environment Agency works with other key decision-makers within a river catchment to identify and agree policies for sustainable flood risk management.

Cat 1

Responder

Those organisations at the core of the response to most incidents (emergency services, local authorities, Environment Agency, local health organisations)

Cat 2

Responder

Cooperating organisations involved in the response to an incident. (Health and Safety Executive, transport and utility companies)

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Critical (National) Infrastructure

The Government defines CNI as: “Those infrastructure assets (physical or electronic) that are vital to the continued delivery and integrity of the essential services upon which the UK relies, the loss or compromise of which would lead to severe economic or social consequences or to loss of life”

The “National Infrastructure” is categorised into nine sectors: energy, food, water, transportation, communications, emergency services, health care, financial services and government.

[Source: Ref 13: Strategic Framework and Policy Statement on Improving the Resilience of Critical Infrastructure to Disruption from Natural Hazards. Cabinet Office. March 2010]

Environment Agency

The Environment Agency is the leading public body for protecting and improving the environment in England and Wales today and for future generations. The organisation is responsible for wide-ranging matters, including the management of all forms of flood risk, water resources, water quality, waste regulation, pollution control, inland fisheries, recreation, conservation and navigation of inland waterways.

It will also have a new strategic overview for all forms of inland flooding.

Flood Risk Assessment (FRA)

An assessment of the likelihood and consequences of flooding in a development area so that development needs and mitigation measures can be carefully considered.

Groundwater Water found underground within porous soils and rocks.

Groundwater flooding

Flooding caused by raised groundwater levels, typically following prolonged rain. High groundwater levels may result in increased overland flow flooding

Lead Local Flood Authority (LLFA)

Lead Local Flood Authorities are unitary authorities or County Councils, and have been established as part of the Flood and Water Management Act. LLFAs are responsible for leading the co-ordination of flood risk management in their area, but can delegate flood or coastal erosion functions to another risk management authority by agreement.

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Local Resilience Forums (LRF)

LRFs are multi-agency forums, bringing together all organisations who have a duty to co-operate under the Civil Contingencies Act, and those involved in responding to emergencies. They prepare emergency plans in a co-ordinated manner.

Main River

Main Rivers are usually larger streams and rivers, but also include smaller watercourses of strategic drainage importance. A main river is defined as a watercourse shown as such on a main river map, and can include any structure or appliance for controlling or regulating flow or water in, into or out of a main river. The Environment Agency’s powers to carry out flood defence works apply to main rivers only. Main rivers are designated by Defra.

Ordinary Watercourse

An ordinary watercourse is any other river, stream, ditch, cut, sluice, dyke or non-public sewer which is not a Main River. The local authority or Internal Drainage Board has powers over such watercourses.

Overland Flow/Surface Water Run-Off

Water flowing over the ground surface that has not reached a natural or artificial drainage channel.

Permeability The ability of a fluid, like water or oil, to pass from one pore space to another.

Intrinsic permeability is a primary feature of the strata (such as the pore spaces between mineral grains). Secondary permeability is that permeability related to post depositional features such as fractures and fissures. In the Chalk in particular these may be further increased in size by the dissolution action of groundwater or percolating rainwater.

Pluvial Flooding

‘Pluvial’ flooding (or surface runoff flooding) is caused by rainfall and is that flooding which occurs due to water ponding on or flowing over the surface before it reaches a drain or watercourse.

Pore Space Spaces or voids between grains in the rocks in which air, water, other fluids or fine-grained mineral cements can be present. (BGS)

Preliminary Flood Risk Assessment (PFRA)

Requirement under the EU Floods Directive/Flood Risk Regulations. The LLFA must complete a preliminary assessment report on past and future flood risk, and identify significant flood risk areas using national datasets.

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Resilience Measures

Resilience measures are designed to reduce the impact of water that enters property and businesses, and could include measures such as raising electrical appliances.

Resistance Measures

Resistance measures are designed to keep flood water out of properties and businesses, and could include flood guards for example.

Riparian Owners

A riparian owner is someone who owns land or property adjacent to a watercourse. A riparian owner has a duty to maintain the watercourse and allow flow to pass through freely.

Risk In flood risk management risk is defined as the probability of a flood occurring x consequence of the flood.

River Basin Management Plan (RBMP)

A management plan for all river basins required by the Water Framework Directive. These documents will establish a strategic plan for the long-term management of the River Basin District, set out objectives for water bodies and, in broad terms, what measures are planned to meet these objectives, and act as the main reporting mechanism to the European Commission.

Surface water Management Plan (SWMP)

A Surface Water Management Plan (SWMP) is a plan which outlines the preferred surface water management strategy in a given location. In this context surface water flooding describes flooding from sewers, drains, groundwater, and runoff from land, small water courses and ditches that occurs as a result of heavy rainfall.

Source Protection Zones (SPZ)

Zones defined by the Environment Agency for groundwater sources (wells, boreholes and springs used for public drinking water supply) showing the risk of contamination from any activities that might cause pollution in the area.

Spot flow gauging Non continuous gauging of river flows, carried out at a specific location, but at discreet intervals. Often carried out by hand held flowmeters, flow gauging frequency varies but might typically be once monthly. Winterbournes will only be gauged when there is detectable flow.

Stakeholders Individuals and organisations that are actively involved in a project, or whose interests may be affected as a result of a project’s execution.

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Strategic Flood Risk Assessment (SFRA)

A SFRA provides information on areas at risk from all sources of flooding. The SFRA should form the basis for flood risk management decisions, and provides the basis from which to apply the Sequential Test and Exception Test (as defined in PPS25) in development allocation and development control process.

Surface Water Flooding

In the context of this report, surface water flooding describes flooding from sewers and ordinary water courses that occurs as a result of heavy rainfall.

Sustainable Urban Drainage Systems (SuDS)

Sustainable drainage systems or sustainable (urban) drainage systems: a sequence of management practices and control measures designed to mimic natural drainage processes by allowing rainfall to infiltrate and by attenuating and conveying surface water runoff slowly compared to conventional drainage. SuDS can operate at different levels; ideally in a hierarchy of source control, local control and regional control.

Syncline A downward fold of sedimentary rock put under pressure by Earth movements. See also anticline

Water and Sewerage Company (WaSC)

Set up under the Water Industry Act 1991. Ten regional water and sewerage operators provide sewerage services in England and Wales. They are South West Water, Wessex Water, Southern Water, Thames Water, Anglian Water, Severn Trent Water, Yorkshire Water, United Utilities, Northumbrian Water and Welsh Water.

Water Cycle Strategy

Plan for new development in a holistic manner to ensure the sustainable and timely provision of necessary water services infrastructure.

Water Framework Directive (WFD)

EC water legislation designed to improve and integrate the way water bodies are managed throughout Europe. The WFD came into force on in December 2000. Member States must aim to reach good chemical and ecological status in inland and coastal waters by 2015.