13 Water Resources, Drainage & Flood Risk

Introduction 13.9 Some waterbodies are designated as ‘artificial’ or ‘heavily modified’ and are not able to achieve near natural conditions. The classification of these waterbodies and the biology they represent are measured against ‘ecological potential’ 13.1 This chapter of the Environmental Statement (ES) has been prepared by Ardent Consultant Engineers (Ardent) and rather than status. For these waterbodies to reach good potential their chemistry must be good and the structural addresses the impact of the proposed 128-150 Blackfriars Road development (hereafter referred to as the ‘proposed nature of the waterbody, which harms the biology, must be essential for its valid use. These are included in the baseline development’) on Water Resources, Drainage and Flood Risk, both at the site and in the immediate surrounding area. It assessment. should be noted that due to the considerable overlap between the two subject areas, some of the impacts relating to National Legislation the hydrogeology underlying the site are also dealt with in Chapter 14: Ground Conditions of this ES. The Water Resources Act 1991 & Water Act 2003 13.2 This chapter describes the methods used to identify the baseline conditions at the proposed development site and within the surrounding area. Key water resources and receptors and their importance are identified and the assessment 13.10 The Water Resources Act 1991 (as amended) (Ref. 13-3) sets out the relevant regulatory controls that provide addresses the potential impacts of the proposed development on these resources. Consideration of impacts is made in protection to water bodies and water resources. In November 2003 the Water Act (2003) (Ref. 13-4) was passed. The the context of existing site conditions, demolition and construction works and once the proposed development is Water Act governs the control of water abstraction, discharge to water bodies, water impoundment, conservation and complete and operational. The need for mitigation measures is addressed and any residual impacts are identified. drought provision. It also introduced improvements to the Water Resources Act such as the development of Catchment Those residual impacts of moderate or major significance are the resultant likely significant environmental effects. Abstraction Management Strategies (CAMS). 13.3 This ES chapter is supported by a Flood Risk Assessment (FRA), conducted by Ardent, which is presented in ES 13.11 In addition to the above the following Acts are also relevant to the water environment: Volume III: Technical Appendix H. The FRA assesses the potential flood risk to the existing site; identifies the  The Environment Act (Ref. 13-5) (which established the Environment Agency); and potential impacts the proposed development may have upon flood risk; and sets out mitigation measures to reduce the  The Environmental Protection Act (Ref. 13-6), which provides for integrated pollution control. potential impacts identified and manage the associated risk. 13.12 A number of specific regulations have been implemented to enact the statutory law as discussed above. These 13.4 Direct consultation with external parties has been undertaken as part of the Environmental Impact Assessment (EIA) regulations include: process. In particular, the Environment Agency, Thames Water Utilities Limited (TWUL) and the London Borough of  The Anti-Pollution Works Regulations (1999) (Ref. 13-7); Southwark (LBS) have been consulted in the preparation of this ES chapter. In addition, a variety of data sources have been consulted such as published maps. Each data source is referenced as appropriate in the following sections of this  The Control of Pollution (Oil Storage) (England) Regulations (2001) (Ref. 13-8); ES chapter.  The Groundwater Regulations (England and Wales) (2009) (Ref. 13-9), which transposed the EU Groundwater Directive (2006) (2006/118/EC) (Ref. 13-10) into UK law; Legislative and Planning Policy Context  The Environmental Damage Regulations (2009) (Ref. 13-11);  The Water Resources Act (Amendment) (England & Wales) Regulations (2009) (Ref. 13-12); International Legislation  The Environmental Permitting (England and Wales) Regulations (2010) (Ref. 13-13) which control discharge of water to surface water and groundwater; and European Water Framework Directive  Water Supply (Water Quality) Regulations (2010) (Ref. 13-14). 13.5 The European Union (EU) Water Framework Directive (WFD) (Ref. 13-1) came into force in December 2000, transposed into UK law by the introduction of the Water Resources (Water Framework Directive) (England and Wales) Flood and Water Management Act 2010 Regulations 2003 (Ref. 13-2). The WFD aims to make clearer the way in which the environment is governed and 13.13 The Flood and Water Management Act 2010 (Ref. 13-15) received royal assent on 8 April 2010 and is largely aimed at integrates and supersedes a range of EU legislation which covers different aspects of water management. delivering the recommendations of the Pitt Review following the 2007 floods. 13.6 The WFD requires all waterbodies to reach at least good status or good potential by 2015 unless there are grounds for 13.14 The Flood and Water Management Act 2010 defines clearer roles and responsibilities for the implementation of departure. However, provided that certain conditions are satisfied, in some cases the achievement of good status may sustainable urban drainage systems (SuDS) in developments, by requiring drainage systems to be approved against a be delayed until 2021 or 2027. The WFD focuses on the ecological health of surface water bodies, as well as requiring set of national standards. The Act also requires a lead local flood authority to develop, maintain, apply and monitor a waterbodies to achieve traditional chemical standards. The Environment Agency has produced River Basin strategy for local flood risk management in its area. Management Plans (RBMPs) drawn up for river basin districts across England and Wales, which set out the baseline 13.15 Once enacted, Schedule 3 of the Act advocates that the Lead Local Flood Authority (established at the county or information for each waterbody and the requirements for each waterbody to reach good status or good potential. unitary local authority level) will be required to establish SuDS Approval Bodies (SABs). The date for enactment is 13.7 The WFD will help to protect and enhance the quality of: pending supplementary legislative guidance.  Surface freshwater (including lakes, streams and rivers); 13.16 It introduces changes to the rights to connect to sewers. Automatic connection rights are to be restricted only to  Groundwater; adopted sewer schemes constructed to the new National Sewer Standard (Ref. 13-16) or approved SuDS schemes  Groundwater dependent ecosystems; constructed to the new National SuDS Standard (Ref. 13-17).  Estuaries; and National Planning Policy  Coastal waters out to 1 mile from low-water. National Planning Policy Framework (2012) 13.8 For surface waters, good status is a statement of overall status consisting of a chemical and ecological component. Chemical status measures priority substances which present a significant risk to the water environment and is classified 13.17 The National Planning Policy Framework (NPPF) (Ref. 13-18) came into force on 27 March 2012 and outlines the as ‘good’ or ‘fail’. Ecological status is measured on a scale of ‘high’, ‘good’, ‘moderate’, ‘poor’ and ‘bad’. The ecological Government’s economic, environmental and social planning policies for England. The NPPF sets out the Government’s status takes into account physico-chemical elements, biological elements, specific pollutants and hydromorphology. vision of sustainable development, which should be interpreted and applied to meet local aspirations. The NPPF supersedes and replaces a number of planning policy documents that are applicable to the water environment including

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Planning Policy Statement 25 (PPS25) Development and Flood Risk (Ref 13-19) and PPS23 Planning and Pollution 13.23 The London Plan sets out an integrated economic, environmental, transport and social framework for the development Control (Ref 13-20. The NPPF sets out 12 planning principles as guidance for local planning authorities (LPAs) for the of London for the next 20-25 years. Policies of relevance to water resources and flood risk within the context of the creation of their Local Plan, of which the following are directly applicable to the water environment: proposed development include:  “10. Meeting the challenge of climate change, flooding and coastal change – Taking account of climate change  Policy 2.18 Green Infrastructure – The promotion of SuDS will improve water resources, flood mitigation and over the longer term including factors such as flood risk, coastal change, water supply and changes to biodiversity reduce flood risk; and landscape. Paragraph 100 to 108 inclusive establishes the Planning Policy relating to flood risk management”;  Policy 5.3 Sustainable Design and Construction – Promotes high standards of design in new developments to and improve environmental performance. This includes avoiding impacts from natural hazards (such as flooding);  “11. Conserving and enhancing the natural environment – Development should minimise pollution and other  Policy 5.11 Green Roof and Development Site Environs – Major developments should include roof, wall and site adverse effects on the local and natural environment and should plan positively for the creation, protection, planting in their design to achieve sustainable urban drainage by absorbing rainfall and thereby reduce flooding enhancement and management of networks of biodiversity and green infrastructure”. associated with surface water runoff; Technical Guidance to the National Planning Policy Framework  Policy 5.12 Flood Risk Management – Development proposals must comply with PPS25 (superseded by NPPF) and have regard to measures proposed in Thames Estuary 2100 Plan and Catchment Flood Management Plans. 13.18 The Technical Guidance (Ref. 13-21) provides additional information for LPAs on development in areas at risk of Developments which are required to pass the PPS25 Exceptions Test will need to address flood resilient design flooding to ensure the effective implementation of the policies in the NPPF. The guidance retains key elements of and emergency planning; PPS25 and the existing minerals policy statement and planning guidance notes; however the guidance is only an  Policy 5.13 Sustainable Drainage – Developments should utilise SuDS, aim to achieve greenfield run off rates and interim measure and is pending a wider review of guidance to support planning policy. manage surface water runoff close to source; 13.19 With respect to water resources and flood risk, local planning authorities should ensure that they:  Policy 5.14 Water Quality and Wastewater Infrastructure – Aims to protect and improve water quality and ensure  Prevent both new and existing development from contributing to or being put at unacceptable risk from, or being adequate and appropriate sewerage infrastructure; and adversely affected by unacceptable levels of land, air, water or noise pollution;  Policy 5.15 Water Use and Supplies – Developments should minimise the use of treated water by incorporating  Ensure SuDS, covering the whole range of sustainable approaches to surface drainage management are water saving measures such as reducing water consumption from 161 litres per day (l/d) to 105 l/d in residential incorporated into new developments; development. The use of water harvesting and grey water recycling schemes should also be promoted.  Ensure new development is planned to avoid increased vulnerability to impacts arising from climate change; and Revised Early Minor Alterations to the London Plan (2013)  Avoid inappropriate development in areas at risk of flooding by directing development away from areas at highest risk or where development is necessary, making it safe without increasing flood risk elsewhere. 13.24 Revised early minor alterations were made to the London Plan to ensure that the document reflected the NPPF and the 13.20 The NPPF states that Local Plans are the key to delivering sustainable development that reflects the vision and Government guidance and national legislation enacted since July 2011. This document was formally published in aspirations of local communities. Local Plans must be supported by a Strategic Flood Risk Assessment (SFRA) and October 2013. The only alteration to the policies of relevance to the water resources and flood risk is that the NPPF develop policies to manage flood risk, taking account of advice from the Environment Agency. Local Plans should apply has superseded PPS25. However, the requirements for new developments in terms of water resource and flood risk, a sequential, risk-based approach to the location of development to avoid flood risk to people and property where remains the same. possible and to manage any residual risk, taking account of the effects of climate change, by: Supplementary Planning Guidance – Sustainable Design and Construction  Applying the Sequential Test; 13.25 Section 2.3 of the Mayor of London Supplementary Planning Guidance (SPG) for Sustainable Design and Construction  If necessary, applying the Exception Test; (Ref. 13-23) states that the essential standards required of new developments include a reduction of water use per bed  Safeguarding land from development that is required for current and future flood management; space to 40m3 per year (equivalent to approximately 110 litres/head/day) and that there is 100% metering. The Mayor’s  Using opportunities offered by new development to reduce the causes and effects of flooding; and preferred standards would reduce water use to less than 25m3 per bed space per year (approximately 75  Seeking opportunities to facilitate the relocation of development, including housing, to more sustainable locations litres/head/day) and promote the use of grey water for all non-potable uses. where climate change is expected to increase flood risk. 13.26 Section 2.4.4 of the SPG indicates that the essential standards for reducing water pollution and flooding require that all 13.21 LPAs should only consider development in flood risk areas appropriate where informed by a site-specific FRA following developments use SuDS wherever practical, and achieve 50% attenuation of the undeveloped site’s surface water the Sequential Test, and if required the Exception Test, and it can be demonstrated that: runoff at peak times. The assessment assumes the undeveloped site to be the proposed development site as it exists  Within the site, the most vulnerable development is located in areas of lowest flood risk unless there are overriding prior to the development proposals (i.e the existing site). The Mayor’s preferred standards would achieve 100% reasons to prefer a different location; attenuation of the undeveloped site’s surface water runoff at peak times.  Development is appropriately flood resilient and resistant, including safe access and escape routes where required 13.27 The SPG also highlights the need for all developments to conform to the sequential test of PPS25 (superseded by the and it gives priority to the use of sustainable drainage systems; and NPPF), and identifies that development should incorporate safe access routes above the flood levels likely during the  Residual risks that remain after applying the sequential approach can be safely managed. lifetime of the new development and adopt the principles of flood resilient design. Regional Planning Policy The Mayor’s Water Strategy (2011) The London Plan (2011) 13.28 The Mayor’s Water Strategy (Ref. 13-24) details ways in which present water resources could be used more effectively, in order to tackle problems such as water supply, wastewater generation and flood risk across London. ‘Actions’ of 13.22 The London Plan was adopted in July 2011 (Ref. 13-22) and sets out a number of key policies aimed to assist relevance to water resource and flood risk issues for the proposed development site are: protection of the water environment during redevelopment and construction.  Action 5, which aims to make property more water efficient. The strategy aims to raise awareness of efficient commercial (non-domestic) water use and encourages commercial users to set internal targets and best practice

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benchmarks for water use reduction. Thames Water estimate that overall commercial demand will grow by 8%  Incorporate SuDS and reduce water run-off from the site by at least 50%. In this area this is likely to be achieved over the next 25 years. The policy recognises that a significant proportion of commercial water use is from the through green roofs, collection tanks and permeable landscaping of the public realm; services sector (for example 16% from hotels, bars and restaurants) and it therefore holds significant potential to  Avoid polluting or damaging the ecology of the River Thames. Proposals to use water from the River to cool save water. A number of water saving technologies are outlined, such as the replacement of urinals with waterless buildings must demonstrate that they will not negatively impact on the River quality or ecology, either individually varieties; and or in combination with other similar schemes. Consent from the Environment Agency will be required; and  A number of water saving technologies are outlined; and  Meet the preferred standards set out in the Sustainable Design and Construction SPD. In particular major  Action 18, which encourages the use of green roofs, rainwater harvesting, grey water recycling and sustainable development should achieve at least Code for Sustainable Homes (CfSH) Level 4 and BREEAM Excellent. drainage to relieve the pressures on the drainage systems, thereby reducing flood risk and water demand. 13.36 The SPD identifies the need to respond to flooding. Stating that the area is within the River Thames flood zone and Local Planning Policy although it is defended to a high level, there is a small risk that the defences may fail and development needs to take this into account. The Southwark SFRA identified that if the flood defences were to fail, the area would flood very London Borough of Southwark Core Strategy (2011) quickly. There are also large areas of hard surfaces which, coupled with an old Victorian sewer system, also pose a 13.29 The LBS Core Strategy (Ref. 13-25) is part of the Development Plan along with the saved Southwark Plan and London flood risk. Plan. These are the main documents used to make planning decisions and set the strategy for development in Elephant and Castle Supplementary Planning Document and Opportunity Area Planning Framework Southwark. The Core Strategy was adopted by Council Assembly on 6 April 2011. Strategic Policies and Strategic (2012) Objectives relating to the water environment are: 13.37 The southern part of the proposed development site is located in the Elephant and Castle Opportunity Area (Ref. 13-  Strategic Policy 13 – High environmental standards: Requiring developments to minimise water use and use local 28). sources of water where possible. Allowing development to occur in the protected Thames flood zone as long as it is designed to be safe and resilient to flooding and meets the Exceptions Test. Requiring developments to help 13.38 SPD 19 Energy, water and waste states the following requirements; reduce flood risk by reducing water run-off, using sustainable SuDS and avoiding the paving over of gardens and  “Development will be required to meet the highest possible environmental standards, in line with our Core Strategy creation of hard standing areas. and the London Plan, including targets based on the CfSH and BREEAM”.  Strategic Objective 2B. Promote sustainable use of resources helping Southwark to become a green and  “In line with Core Strategy policy 13, we will require development to reduce water use and use water as efficiently environmentally sustainable borough. New developments will be built to high environmental standards to reduce as possible. To achieve CfSH Level 4, residential developments should reduce potable water consumption below the impact on the environment and adapt to climate change, focussing on flood risk, waste management, 105L per person per day. Highly efficient water saving fixtures, fittings and appliances should be used and biodiversity and water quality. development should connect to a local water supply or borehole where this is available”. London Borough of Southwark, Southwark Unitary Development Plan (2007) Saved Policies 13.39 Elephant and Castle is within a flood risk zone and therefore development will need to be made safe from flooding through the site layout and the design of buildings. New development will be required to incorporate drainage measures 13.30 The Southwark Plan (Ref. 13-26) sets out how Southwark Council, as the Local Planning Authority (LPA) will use its to help reduce and slow the amount of run-off leaving a site. Development will need to manage surface water on-site or planning powers to influence development. The Plan explains why planning decisions are made, and the objectives and as close to the site as possible, using SuDS techniques. Where possible, greenfield run-off rates should be achieved targets that the LPA is seeking to achieve. It provides the framework for guiding Southwark’s development, taking on-site. account of how much it has changed, and looking forward to how this may continue in the future. Blackfriars Road Supplementary Planning Document (2014) 13.31 The Strategic Policies of the Plan set out the overall direction for the physical and spatial aspects of the Community Strategy. 13.40 The Blackfriars Road SPD (Ref 13-29) was published in on 28 January 2014. The SPD does not make reference to 13.32 The site is located in the London South Central/Central Activity Zone which is a strategic regeneration priority area water resources, drainage or flood risk. identified in the London Plan. Other Relevant Policy and Guidance 13.33 In addition to the Strategic Policies, the Southwark Plan has the following Saved Policies relevant to this chapter that 13.41 Southwark Council is the Lead Local Flood Authority (LLFA) under the Flood and Water Management Act 2010. have not been replaced by the Core Strategy; Southwark have developed a Surface Water Management Plan and are currently working through the plan to help  “Policy 3.9 Water: All developments should incorporate measures, to: i) Reduce the demand for water; and, ii. reduce the risks to our residents, businesses and the environment. Southwark are also developing a Local Flood Risk Recycle grey water and rainwater. In addition, all new developments must use preventative measures to ensure Strategy (LFRS), which they will be consulting on in the near future. that they do not lead to a reduction in water quality. New developments should not result in an increase in surface run-off, which could result in increased flood risk and pollution. Policy 3.9 is not superseded by the Core Strategy”. London Regional Flood Risk Appraisal (2009) Draft Bankside, Borough and London Bridge Supplementary Planning Document (2010) 13.42 The London Regional Flood Risk Appraisal (RFRA) (Ref. 13-30) seeks to ensure that the overall flood risk in Greater London does not increase. The RFRA contains 19 recommendations to be implemented by the Environment Agency 13.34 This Draft Opportunity Area Supplementary Planning Document (SPD) was published in February 2010 and is currently and other agencies. out for consultation (Ref. 13-27). The northern part of the site is located within the SPD Area. 13.43 Those recommendations of particular relevance to the proposed development include: 13.35 Section 4.4.1 Guidelines for development states that all developments should:  Recommendation 5 – Developments should reduce surface water discharge in line with Policy 5.13 of the London  Avoid sensitive uses such as residential accommodation, schools and nurseries at ground and basement floor Plan; level unless a site specific flood risk assessment demonstrates that flood risk poses a low hazard to the site;  Recommendation 6 - Regeneration and redevelopment of London’s fluvial river corridors offer a crucial opportunity  Be designed to be flood resilient, particularly basement and ground floor levels; to reduce flood risk. SFRAs and policies should focus on making the most of this opportunity through appropriate  Incorporate green roofs and habitat features; location, layout and design of development and the River Thames Catchment Flood Management Plan. In

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particular, opportunities should be sought to: set back development from the river edge to enable sustainable and London Borough of Southwark Surface Water Management Plan (2011) cost effective flood risk management options; ensure that the buildings with residual flood risk are designed to be 13.55 A Surface Water Management Plan (SWMP) was carried out by URS Scott Wilson & Capita Symonds on behalf of the flood compatible or flood resilient; use open spaces within developments, which have a residual flood risk to act as LBS and completed in September 2011 (Ref. 13-34). flood storage areas; and 13.56 As part of Phase 2 Risk Assessment, direct rainfall modelling has been undertaken across the entire borough for five  Recommendation 8 – Organisations responsible for development with large roof areas should investigate specified return periods. The results of this modelling have been used to identify Local Flood Risk Zones (LFRZs) providing additional surface water run-off storage. where flooding affects houses, businesses and/or infrastructure. Those areas identified to be at more significant risk Thames Estuary 2100 Plan have been delineated into Critical Drainage Areas (CDAs) representing one or several LFRZs as well as the contributing catchment area and features that influence the predicted flood extent. 2008. 13.44 The Thames Estuary 2100 Plan (TE2100) (Ref. 13-31) is the result of a detailed assessment of the options available to manage flood risk and their economic costs, benefits and environmental impacts. It sets out the strategic direction for 13.57 An initial overview of the flooding issues in the LBS, based on the Environment Agency 's Flood Map for Surface Water managing flooding across the estuary, and contains recommendations on what actions the Environment Agency and (FMfSW) and historic flooding records in the Borough indicate that several areas, including Dulwich, Herne Hill, others will need to take in the short (next 25 years), medium (25-40 years) and long term (to the end of the century). It Peckham and Camberwell are affected by multiple sources of flood risk. also identifies sites where intertidal habitat (saltmarsh and mudflat) could be created to replace habitats that are being 13.58 The Surface Water Management Plan does not show the site to be located with a LFRZ or CDZ. lost due to rising sea levels. Pollution Prevention Guidance Notes 13.45 The TE2100 Plan is based on current guidance on climate change, but is adaptable to changes in predictions for sea level rise and climate change over the century. 13.59 The Environment Agency Pollution Prevention Guidance (PPG) Notes provide advice on statutory responsibilities and good environmental practice. The Guidance Notes of particular relevance to the proposed development include: 13.46 A public consultation on the TE2100 Plan ran between April and July 2009. The finalised TE2100 Plan has been approved by the Environment Agency Board and submitted to the Department for the Environment, Food and Rural  PPG 1: General Guide to the Prevention of Pollution (Ref. 13-35), which provides an introduction to pollution Affairs (Defra). prevention and the pollution prevention guidance notes;  PPG 2: Above Ground Oil Storage Tanks (Ref. 13-36), which provides guidance to those responsible for the London Borough of Southwark Preliminary Flood Risk Assessment (2011) storage of oil on construction sites. The document provides guidance on location, bunding, protection and 13.47 An interim draft Preliminary Flood Risk Assessment (PFRA) was completed by URS/Scott Wilson for the LBS and operation of oil stored in addition to maintenance and brief guidance on dealing with spills; submitted to the Environment Agency in June 2011 (Ref. 13-32).  PPG 3: Use and Design of Oil Separators in Surface Water Drainage Systems (Ref. 13-37), which provides 13.48 A PFRA is a high level screening exercise to identify areas of significant flood risk within a given study area. The PFRA guidance on when oil separators are appropriate and what size and type of separator is required; involves collecting information on past (historic) and future (potential) floods, assembling the information into a PFRA  PPG 5: Works In, Near or Liable to Affect Watercourses (Ref. 13-38) which provides guidance on general report with supplemental Annexes, and identifying Flood Risk Areas. precautions to take when working in the vicinity of a watercourse, along with more specific measures to prevent 13.49 The primary driver behind the PFRA is the Flood Risk Regulations 2009, which came into law on the 10 December contamination and to minimise any adverse impacts; 2009 and seek to transpose the European Councils’ Floods Directive (Directive 2007/60/EC on the assessment and  PPG 6: Working at Construction or Demolition Sites (Ref. 13-39) is a document that mirrors much of PPG 5 but management of flood risks) into domestic law in England and Wales and to implement its provisions. with particular emphasis on the situations likely to occur at demolition and construction sites; 13.50 The purpose of the PFRA report under the Regulations is to provide the evidence for identifying areas susceptible to  PPG 7: Refuelling Activities (Ref. 13-40), which provides information on the correct delivery, storage and flood risk. The report will also provide a useful reference point for all local flood risk management and inform local flood dispensing of fuel to help reduce the risk of pollution; and risk strategies.  PPG 21: Pollution Incident Response Planning (Ref. 13-41) assists those developing site-specific pollution London Borough of Southwark Strategic Flood Risk Assessment (2008) incident response plans to prevent and mitigate damage to the environment caused by accidents such as spillages and fires. 13.51 A Stage 1 Strategic Flood Risk Assessment (SFRA) was completed by Jacobs Engineering on behalf of the LBS in February 2008 (Ref. 13-33). Assessment Methodology and Significance Criteria 13.52 The SFRA indicates the proposed development site to be wholly located within Flood Zone 3a (high probability of flooding), identified as comprising land assessed as having a 0.5% chance of flooding in any given year from tidal Assessment Methodology sources. The proposed development site is however shown as being in an area which benefits from Thames tidal flood defences. 13.60 Baseline conditions have been established through a desk study and consultation with the following bodies: 13.53 The SFRA shows the site to be located in the zone with a rate of inundation of less than six hours if the River Thames  Environment Agency; defences were to be breached. The proposed development site is also identified as being located in a Low Degree of  TWUL; and Flood Hazard area.  The LBS. 13.54 The proportion of the LBS situated within Zone 3a High Probability is a particularly vibrant part of London and future 13.61 As part of the robust consultation process formal requests for information relating to flood risk were issued to the above investment and regeneration is paramount. Prohibiting future residential development in these areas is likely to have a Consultess and the responses collated and reviewed. Where appropriate follow up calls and emails have been detrimental impact upon the economic and social welfare of the existing community, and consequently there are clearly undertaken to clarify any ambiguous data. The technical content of the Flood Risk Assessment (FRA) has also been other non-flooding related planning 'needs' that warrant further consideration of these areas. Therefore, following the discussed. The correspondence details are included within the FRA presented in ES Volume III: Technical Appendix application of the Sequential Test, the Council and potential future developers are required to work through the H. Exception Test, where applicable.

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13.62 In addition, the FRA, presented in ES Volume III: Technical Appendix H, assesses sources of flood risk using Table 13-1 Methodology for Determining Importance of a Resource/Receptor available data on flood zones and flood levels of watercourses relative to the proposed development site. Other Importance Criteria Typical Example potential sources of flood risk such as surface water run-off and groundwater have also been assessed. EU Designated Salmonid/Cyprinid fishery 13.63 The methodology used to identify the baseline conditions at the proposed development site and to assess the potential WFD Class ‘High’ impacts to water resources/receptors, drainage and flood risk as a result of the proposed development, has involved Site protected/designated under EU or UK habitat the following stages: legislation (Special Area of Conservation (SAC), Special Resource/receptor has a high quality Protection Areas (SPA), Site of Special Scientific Interest  Baseline: Identification of resources and determination of their importance; Very High and rarity on regional or (SSSI), Water Protection Zone (WPZ), Ramsar site, salmonid water)/ Species protected by EU legislation  Preparation of a conceptual site model, identifying feasible pollution sources and pathways during the demolition national scale Floodplain or defence protecting more than 100 residential and construction and operational phases of the proposed development; properties from flooding Environment Agency Flood Zone  Determination of the magnitude of the impacts of the proposed development on these resources/receptors, 3b including an assessment of any residual impacts following mitigation; Environment Agency Source Protection Zone 1 or 2 Principal Aquifer providing locally important resource or  Evaluation of the significance of the impacts relative to the quality and quantity of the resources/receptors; and Resource/receptor has a high quality supporting river ecosystem High  Identification of suitable and appropriate mitigation measures, for all stages of the proposed development (i.e. and rarity on local scale Environment Agency Flood Zone 3a demolition and construction; and operation) and an indication of how these measures will affect the significance of Environment Agency Source Protection Zone (SPZ) residual impacts. Secondary Aquifer Resource/receptor has a medium WFD Class ‘Moderate’ Significance Criteria Medium quality and rarity on local Floodplain or defence protecting 10 or fewer industrial scale properties from flooding 13.64 There are three stages to the assessment of the impact on water resources as follows: Environment Agency Flood Zone 2 WFD Class ‘Poor’ 1. The methodology for assessing the importance of a receptor has been adapted from the Highways Agency’s Resource/receptor has a low quality Low Unproductive strata Design Manual for Roads and Bridges (DMRB) Road Drainage and the Water Environment, ‘Reporting of and rarity on local scale Environment Agency Flood Zone 1 Significance of Potential Effects’ (HD45/09) (Ref. 13-42). The Importance of a resource/receptor (classed as very high, high, medium or low) is based on the ability of the resource/receptor to absorb change and the relative importance of the receptor using the scale in Table 13.1. The importance is also determined by professional Table 13-2 Terms Used to Describe the Magnitude of the Potential Impacts on the Water judgement based on best management practices and published data on the resources/receptors importance. Resource/Receptor 2. The magnitude of the potential impact (classed as large, medium, small or negligible) is determined based on Magnitude Criteria Examples Table 13-2, the assessor’s knowledge of the proposed development and also taking into account the impact both Results in loss of resource//receptor -loss of EU designated Salmonid fishery pre- and post-mitigation; and - change in General Quality Assessment (GQA) grade of river reach 3. The significance of a potential impact (classed as major, moderate or minor) is determined by the interaction of Large - compromise employment source importance and magnitude, whereby the impacts can be beneficial, adverse or negligible. The impact significance - loss of flood storage/increased flood risk matrix is set out in Table 13.3. - pollution of potable source of abstraction 13.65 An impact can be temporary or permanent, with impacts quantified as being short-term (0-5 years), medium term (5-10 Results in impact on integrity of -loss in productivity of a fishery resource/receptor or loss of part of - contribution of a significant proportion of the effluent in the years) or long-term (>10 years). Medium resource receiving river, but insufficient to change its GQA grade 13.66 The significance criteria also takes into account: - reduction in the economic value of the feature  The duration involved; Results in minor impact on -measurable changes in attribute, but of limited size and/or Small  The reversibility of the impact; and resource/receptor proportion Results in an impact on -discharges to watercourse but no significant loss in quality,  The number of receptors. resource/receptor but of insufficient fishery productivity or biodiversity Negligible 13.67 The following impact significance categories have been used: magnitude to affect the use/integrity - no significant impact on the economic value of the feature - no increase in flood risk  Negligible: An imperceptible or no impact to water resources;  Beneficial: A beneficial/positive impact on water resources; or  Adverse: A detrimental/negative impact on water resources. Table 13-3 Criteria for Estimating the Significance of Impacts (adverse/beneficial/negligible) 13.68 When an impact is considered to be beneficial or adverse, the following levels of significance are stated, as calculated Magnitude of Importance of resource/receptor in Table 13-3): change Very High High Medium Low  Minor: An example is a limited, very short or highly localised impact (i.e. small magnitude of change) on a water High Major Major Moderate Minor resource of high or medium quality or importance; or a wide extent or long duration (i.e. a large magnitude) impact Medium Major Moderate Minor Negligible on a water resource of medium quality or importance; Small Moderate Minor Negligible Negligible  Moderate: Medium magnitude of change on a water resource of high quality; or a large (reversible) impact on a Negligible Minor Negligible Negligible Negligible water resource of medium quality or importance; and  Major: A medium or large magnitude of change on a water resource of high or very high quality or importance.

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Baseline Conditions 13.74 The River Neckinger is shown on the Lost Rivers of London (Ref. 13-44) and its documented path lay approximately 500m to the south of the proposed development site (Figure 13-1). This river has been lost to the urbanisation of Hydrology London. 13.75 Figure 13-2 is an extract of SFRA (Ref 13-33) Figure A and shows the general topography of the LBS. The land Surface Water Resources typically falls from Dulwich and Sydenham in the south of the Borough towards the River Thames. The northern part of 13.69 The proposed development site is located in the Thames River Basin District, as defined by the WFD and described in the Borough falls generally from west to east. the Thames River Basin Management Plan (Ref.13-43). The Thames River Basin District is one of the most populated 13.76 The proposed development site is located in the higher north-western part of the Borough (approx. 3-4m Above parts of Britain. The district covers both rural and urban environments stretching from the Thames estuary, including Ordnance Datum (AOD)) with lower elevations encountered to the east and south of the proposed development site in London, to the limestone hills of the Cotswolds. Water supports these landscapes and their wildlife, and it is vital to the Bermondsey and Camberwell. livelihoods of those who live and work here. 13.70 The Thames River Basin District is one of the driest in the UK with rainfall levels below the national average. The River Figure 13-2 Topography of the LBS (Extract of SFRA Figure A) Thames is an important water source providing two-thirds of London’s drinking water. Water supply is taken from the freshwater section of the river upstream of Teddington weir.

Figure 13-1 Lost Rivers of London

13.71 No surface water bodies are present within the proposed development site and the nearest major surface water body is the River Thames, approximately 1km north of the proposed development site. The River Thames is designated as 13.77 This area of London is highly urbanised and as such the hydrology is defined by the urban nature. being a tidal watercourse in this location with the section of river influenced by tidal activities extending upstream to 13.78 Pluvial modelling undertaken as part of the Surface Water Management Plan has identified that flooding within the LBS Teddington Lock. is typically shallow and widely dispersed across much of the Borough, but deeper flooding is predicted across the 13.72 Whilst the River Thames poses a potential risk of flooding to properties within the LBS, all property within the Borough central belt of the borough (north of the A202). Historical records indicate that flooding is largely a result of the local are currently protected from combined tidal and fluvial flooding by the River Thames Tidal Defences (TTD) up to the 1 drainage network and TWUL sewer capacity; the majority of the borough is served by combined sewers which, in many in 1000 year event. cases, were designed and built in the late 1800s, and subsequent urbanisation and cross-connection means that it is 13.73 Aside from the River Thames, there are no other watercourses within the LBS that may pose a potential risk of flooding likely that the sewers across the LBS will have varying standards of capacities, particularly in the north of the Borough. to properties within the Borough, although it is interesting to note the historic presence of the River Neckinger. 13.79 Potential risks of flooding from non-river related sources are therefore sewer surcharging and surface water flooding as a result heavy rainfall and/or blocked gullies.

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13.80 Hydrologically, the urban drainage has some capacity to absorb change without significantly altering its present Figure 13-3 Map of CSOs and Sewage Treatment Works character. The urban catchment is constrained in its nature by the built environment and topography. Existing drainage infrastructure has little ability to absorb change and significant changes would disrupt the urban drainage system and flood risk. The urban hydrology is assessed to have medium importance. Water Supply (River Thames) 13.81 TWUL supplies water to London. The majority of London’s water supplies come from the River Thames and the River Lee, with about 70% of all the water taken from the River Thames upstream of Teddington Weir. It is then stored in reservoirs around the capital. The remainder is abstracted from the aquifer underneath London. 13.82 The water supply resource has a rarity on a regional scale. The water supply resource provided by the River Thames means the river is assessed to have high importance. Water Quality (River Thames) 13.83 As a result of the requirements of the WFD, there are two classifications to assess the status of waterbodies, ecological and chemical. These classifications have been assessed as part of the River Basin Management Plan (RBMP) for the Thames River Basin District. 13.84 The River Thames is classified as a Heavily Modified Waterbody (HMWB), which means that it has been artificially altered for coastal protection, flood protection and navigation, therefore is not able to achieve near natural conditions. 13.85 The classification of HMWBs and the biology they represent are measured against Ecological Potential rather than Status (Ref. 13-40, Annex A). For these waterbodies to reach good potential their chemistry must be good and the structural nature of the waterbody, which harms the biology, must be essential for its valid use. 13.86 The stretch of the River Thames adjacent to the proposed development site is classified under the WFD as being of Moderate Ecological Potential and is expected to remain the same in 2015; it is predicted to reach good potential by 2027. This section of the river is currently Failing to Achieve Good chemical status. 13.87 According to the London State of the Environment (SOE) Report (2011) (Ref. 13-45), around 39 million tonnes of diluted but untreated sewage is discharged annually into the Thames Tideway. 13.88 Combined Sewer Overflows (CSOs) are a significant contributor to Tideway water quality problems with 57 CSOs (63% of which are thought to be unsatisfactory) discharging into the Thames between Hammersmith and Woolwich. Figure Geology and Hydrogeology 13.3 shows the location of CSO along the River Thames (Ref. 13-46). Geology 13.89 Ecological status is determined using criteria to assess compliance with the WFD. Both sections of the Tidal Thames in London (from Teddington to Battersea, and Battersea to Mucking) are classified as ’Moderate’ under the WFD 13.95 Chapter 14: Ground Conditions of this ES contains a full review of the geology and the hydrogeology of the area. definitions and can therefore be considered to be of a medium quality 13.96 According to the British Geological Society (BGS) online datasets the superficial geology is formed of the Kempton Park 13.90 The SOE suggests Dissolved oxygen (DO) is the most important indicator of the status of water quality in the Thames Gravel formation consisting of sand and gravel, locally with lenses of silt, clay or peat. The bedrock geology is the London Tideway. Under the WFD, the DO status for middle section of the Thames from Battersea to Mucking, is classified as Clay Formation (clay & silt). ‘moderate’ in the SOE, and can therefore be considered to be of a medium quality . 13.97 The geological conditions beneath the proposed development site have been assessed with reference to BGS Map Sheet 13.91 Published data on DO shows the condition of the Thames in the vicinity of the proposed development site as gradually 270 ‘South London’, scale 1:50:000, Solid and Drift Edition (Ref 13-48). The geological sequence is anticipated to improving. The existence of combined sewers and storm overflows from treatment works into the River Thames make it comprise: challenging to improve the water quality.  Made ground; 13.92 The Thames Tideway Tunnel project by TWUL aims to tackle the problem of overflows from the capital’s Victorian  Kempton Park Gravel – Thames River Terrace Deposits; sewers and therefore protect the River Thames from increasing pollution for at least the next 100 years. On 27 March  London Clay Formation - Stiff bluish Clay that becomes brown when weathered; 2013, the Planning Inspectorate accepted the application for development consent with a decision expected in late  Lambeth Group - Clay with inter-bedded sand; summer/early autumn 2014 (Ref. 13-47).  Thanet Sand Formation - Blue green sand; and 13.93 The proposed Thames Tunnel is designed to capture flows from 34 unsatisfactory CSOs along the tideway for treatment at Beckton Sewage Treatment Works (STW). The proposed 20-mile (32km) Thames Tunnel will run from  White Chalk Subgroup - Regionally, the Cretaceous Chalk underlies the Thanet Sand and comprises micritic west to east London, beneath the River Thames. limestone with flint nodules. 13.94 From a Water Quality point of view the tidal River Thames receptor is assessed to be of medium importance in terms of 13.98 The BGS publishes numerous historic borehole records online, and there are a number of historic borehole log in the the current levels of pollution and in terms of supporting wildlife, recreation and amenity vicinity of the proposed development site. Borehole sample TQ37NW/2305 at Georges Circus, undertaken in 1989 by Terresearch Ltd, indicates 3m of made ground above 7m of sandy flint gravel above a sandy clay.

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Hydrogeological Setting and Designations Thames). The current condition grade for defences in the area of the proposed development site is 2 (Good), on a scale of 1 (very good) to 5 (very poor). 13.99 Environment Agency maps show that the proposed development site is not located within an inner (Zone 1) or outer (Zone 2) Source Protection Zone (SPZ). The nearest outer SPZ is located approximately 1,500 metres south-west of 13.115 It is also understood that the future flood levels at the proposed development site are predicted to reduce over time. the proposed development site, which extends to around the Oval & Vauxhall rail station. Some of the levels are lower for the more extreme probabilities when including climate change because the hydraulic model takes into account the Thames Barrier closure rule and assumes that it remains unchanged up to 2107 (2107 13.100 Environment Agency maps locate the proposed development site within a Secondary A Aquifer (Superficial deposits). epoch). Increased sea levels and fresh water flows mean that the Thames Barrier closure rule will be met more often. Secondary A Aquifer is defined as permeable layers capable of supporting water supplies at a local rather than This means that a smaller number of tides will be allowed to flow up into central London each year. strategic scale, and in some cases forming an important source of base flow to rivers. 13.116 In-channel flood levels for various return periods have been provided by the Environment Agency and are taken from 13.101 However, perched groundwater may be present in the underlying soil strata but this is unlikely to pose a flood risk. the Tidal Thames Joint Probability Extreme Water Levels study completed by Halcrow in 2008. The modelled node 13.102 According to the River Basin Management Plan (Annex A), the groundwater chemical status is currently Poor. closest to the site is Node 2.34. Water levels at this node are 4.95m AOD for the 0.5% 2005 baseline (reducing to 13.103 The existing groundwater quality is assessed as having medium importance, as it is located above a Secondary A 4.94m in 2107) and 4.99m AOD for the 0.1% 2005 baseline (reducing to 4.98m in 2107). Aquifer. 13.117 Flood levels at the proposed development site have been taken from Tidal Thames Breach modelling study completed Groundwater Abstractions and Discharges by the Environment Agency in March 2012. 13.118 This modelling simulates tidal breaches along the Thames from Teddington to the Mar Dyke and River Darent. A series 13.104 The underlying chalk geology forms the predominant groundwater aquifer, which provides around 40% of public water of approximately 100 tidal models were developed for the Environment Agency at pre-determined breach locations. supply. Current assessments show that groundwater is fully used over much of the Thames River Basin District. Defences are assumed to breach down to the ground level behind the defence. Therefore it is essential to maintain and improve the quantity and quality of groundwater (Ref. 13-43). 13.119 Based on the 2008 Extreme Water Level Modelling, the 0.5% probability of annual exceedance (1 in 200 year joint 13.105 London Abstraction Licensing Strategy (February 2013) (Ref.13-49) outlines how the WFD’s main objectives are to probability - Thames Barrier Operational) tidal event was modelled for all breach locations with a current year baseline protect and enhance the water environment and ensure the sustainable use of water resources for economic and social of 2005. In addition, for breaches downstream of the Thames Barrier, the 1 in 200 year plus climate change event development. Catchment Abstraction Management Strategies (CAMS) set out how to manage the water resources of a (2107 epoch) was also modelled. catchment and contribute to implementing the WFD. 13.120 The breach model indicates that only a portion of the proposed development site would be at risk of flooding as a result 13.106 Confined Chalk underneath London is designated as a Principal Aquifer. The groundwater flow within this water body is of a breach of the flood defences, as shown in Figure 13-4. drawn towards central London. The source of this groundwater comes from the unconfined areas upstream, mainly outside the London CAMS catchment. 13.121 The breach model indicates that the eastern edge of the proposed development site north of Library Street and adjacent to Bazeley House and potentially the southern site boundary adjacent Borough Road would be affected. 13.107 The major pressure in the London CAMS area is the population growth resulting in requirements for new housing and increased demand for water for domestic and business use. In recent years, a dramatic rise in the groundwater heating 13.122 Breach model site specific flood levels are shown to vary from a maximum of 3.55m AOD on the eastern edge of the and cooling schemes has been observed in response to policies on reducing carbon dioxide emissions. These site to 3.3m AOD in the south western corner of the proposed development site. It should be noted that usual practice schemes are particularly popular in central London. in breach modelling is to use filtered LiDAR data. LiDAR data is an accurate ground survey acquired by aerial surveys using Light Distance And Ranging (LiDAR), it has been used for a number of years to collect highly detailed ground 13.108 The guiding principles for managing the resource within the Confined Chalk include, prevent flooding infrastructure terrain models to inform flood risk planning. The raw data captured includes all buildings, railway bridges, viaducts, under London, like the London Underground and building foundations; and, maintain the groundwater levels above the pylons, trees cars and other features, which when viewed from above in the LiDAR data would be represented as solid chalk to prevent aquifer dewatering and reduce risk of derogation. blocks. These ‘blocks’ would therefore impede flood flow, and with respect to pylons and tree canopies, create an 13.109 According to their Water Resource Management Plan (WRMP), TWUL also has a programme to provide an additional artificial representation of the ground, by creating ridges or ‘lumps’ in the LiDAR which when viewed from the ground 28 megalitres per day (Ml/d) of water through the development of small groundwater abstraction schemes by 2015 would not exist. Subsequently, for floodplain modelling the buildings and other features are removed to ensure that flow (Ref. 13-50). paths are not artificially impeded. The LiDAR data with the buildings and other features removed is referred to as the 13.110 According to the UK Groundwater Forum's website, in south west London, groundwater levels have declined at rates of ‘Filtered LiDAR’, this represents a bare earth model and is the standard data source used for floodplain modelling. around 5 metres (m) per year in response to GARDIT abstractions and other water company abstractions to the south. 13.123 Using the worst case breach level of 3.55m, Figure 13-5 shows the extent of the flooding based on the topographic 13.111 The groundwater potable water supply resource is assessed as having high importance due to the contributions it survey levels. makes to London’s water supply. 13.124 The SFRA shows that the proposed development site is located within a zone determined to have a low degree of flood Flood Risk hazard. River Thames 13.125 The current flood management regime (flood defences, including Thames Barrier) mean that any anticipated changes (climate change) are planned into the management and the proposed development site is determined to have a low 13.112 A site specific FRA has been produced by Ardent Consulting Engineers (February 2014) and is provided in ES Volume degree of flood hazard. III: Technical Appendix H. The FRA addresses the flood risk at the proposed development. 13.126 The existing flood risk from the River Thames is assessed as having medium importance. 13.113 The proposed development site is located within Flood Zone 3a (high probability of flooding) which is identified as comprising land assessed as having a 0.5% chance of flooding in any given year from tidal sources. The proposed development site is however in an area which benefits from Thames tidal flood defences.

13.114 It is understood that the River Thames tidal flood defences provide a standard of defence in excess of the present day

1 in 1,000 (0.1% AEP) event. The defences are all raised, man-made and privately owned. It is the riparian owners' responsibility to ensure they are maintained to a crest level of 5.41 m AOD (the Flood Defence Level in this reach of the

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Figure 13-4 EA Breach Model Results (0.5% AEP) Figure 13-5 Extent of Flooding for 0.5% AEP based on Topographic Survey

Groundwater 13.127 As the London Underground (northern line) runs in the vicinity of the site, the risk of groundwater flooding is negated by the GARDIT principles, whereby to prevent ground water rising to a level to affect foundations and the tube network, groundwater abstraction takes place to maintain groundwater at a safe level.

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Water Supply Infrastructure 13.136 In 2010 TWUL opened the UK’s first large-scale desalination plant (up to 150 Ml/d). In times of drought or other emergency, this enables water to be taken from the tidal Thames and remove the salt to produce drinking water. 13.128 Most of London’s water system is based on Victorian piping. More than half of TWUL’s water mains are over 100 years According to the WRMP, TWUL also has a programme to provide an additional 28 Ml/d of water through the old; around a third are over 150 years old (Ref. 13-51). development of small groundwater abstraction schemes by 2015. 13.129 The water industry was privatised in 1989 and TWUL is a private business tasked with supplying water to London and 13.137 TWUL has been consulted regarding the existing drainage and water supply network in the surrounding area, and has meeting its shareholders expectations. supplied asset location plans detailing the water supply network surrounding the proposed development site (refer 13.130 TWUL supplies water to London. As previously mentioned, the majority of London’s water supplies come from the River Figure 13.7). Thames and the River Lee, with about 70% of all the water taken from the River Thames upstream of Teddington Weir. 13.138 The plans indicate 200mm and 315mm diameter (high-density polyethylene) HDPE water mains on Blackfriars Road It is then stored in reservoirs around the capital. The remainder is abstracted from the aquifer underneath London. with two connections shown to the proposed development site. The 200mm pipe becomes 250mm at St Georges 13.131 The EA’s consultation on ‘Identifying Areas of Water Stress for the UK’ (Ref. 13-46) identifies London as an area of Circus and continues south. There is a trunk main located at St Georges Circus. There is a 125mm diameter main in serious water stress. Library Street connecting into a 180mm main on Borough Road. This 180mm main connects into the 250mm main on 13.132 Average domestic consumption in Southwark in 2010-11 was 166.5 litres per person per day. The 5-year average in St Georges Circus. Pipes in the area appear to have all been upgraded to HDPE. the LBS is 161 litres per person per day (2006-07 to 2010-11). 24% of households have a water meter; an increase 13.139 Although the pipe network in the immediate vicinity of the proposed development site is constructed in HPPE, from 15% in 2000-01 (Ref. 13-52). throughout London, Victorian era water mains exist and high leakage occurs within the network, this is why TWUL are 13.133 Reservoir storage is used by TWUL to balance supply with water taken from the Thames when flows are high. The in the process of replacing the Victorian mains with HDPE. London Ring Main links the water treatment plants around London. 13.140 The water supply infrastructure (including storage, treatment and distribution) is considered to be of medium 13.134 In December 2011, TWUL produced its Final Draft Water Resource Management Plan (WRMP) (Ref. 13-49), which importance on a local, district and regional level with little capacity to absorb change. The rate of any change needs to sets out forecasts for water supply and demand and identifies the measures proposed to meet consumers’ needs over be in accordance with regional water resource planning. Following initial discussions between Thames Water and the the next 25 years. Applicant, it was likely that some form reinforcement to the existing Thames Water infrastructure may be required offsite. However, with the Applicant incorporating technological which focus on using less water and the incorporation 13.135 The forecasts indicate that the London Water Resource Zone (WRZ) will have a deficit of 367 mega litres per day (Ml/d) of a rainwater harvesting system to collect water for irrigation purposes, it is anticipated that the impact will be low. by 2040. To meet this deficit, TWUL aim to introduce a number of management and supply measures. Figure 13-6 shows the water resource options over the period 2015-2040. These include, leakage reduction (mains replacement programme) metering, water efficiency and wastewater re-use from the Becton Sewage Treatment Works (150 Ml/d). Figure 13-7 Extract of TWUL Potable Water Supply Network

Figure 13-6 TWUL WRMP – Water Resource Options (2015-2040).

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Foul and Surface Water Drainage 13.146 One 225mm sewer is built over and crosses under part of the proposed development site from manhole 7501. It is not clear which properties/sites feed into the various sewers, as the records indicate flows in two manholes adjacent to the 13.141 The proposed development site currently drains to TWUL combined sewers. As such the site contributes to potential site flowing out in two directions. surcharging of combined sewers and CSOs located at the River Thames. 13.147 Historic plans concerning the network have been found dating back to 1848. The sewer in Library Street was diverted 13.142 The LBS (and therefore the proposed development site) is served by Crossness sewage treatment works (STW). on its present route circa 1888, however, there is no information regarding the manhole in Library Street (7505) and the Crossness STW is located in south east London. In 2009 it served a population equivalent of 1,890,000. Crossness direction of flows other than it was reconstructed in 1900. TWUL consider that there is no opportunity to divert the flows STW is permitted to discharge 597,000m3/d of treated sewage effluent into the Thames Tideway under dry weather away from this system or abandon this part of the network. As such, TWUL have agreed in principle to the continuance conditions (Ref. 13-53). of the build over of the 225mm sewer. 13.143 As outlined in the Water Quality (Thames River) section above, CSOs are a significant contributor to Tideway water 13.148 The 225mm sewer under the building is in good condition and is constructed of ductile iron. This was presumably re- quality problems with 57 CSOs (63% of which are thought to be unsatisfactory) discharging into the Thames between laid when Hill House was constructed. Hammersmith and Woolwich. 13.149 There is at least one 150mm diameter connection from Hill House into the Trunk Sewer on Blackfriars Road. There 13.144 An extract of TWUL sewer records is provided in Figure 13-8. TWUL records show the Battlebridge Sewer (a 1372mm may be other connections, such as to a 225mm sewer going south in Library Street from Erlang House (not proven) by 914mm Trunk Combined Sewer) running southwards along Blackfriars Road to the west of the proposed and possible direct connections from Hill House to the Trunk Sewer. development site with an invert level adjacent to the proposed development site of approximately - 1.93 mAOD. 13.150 TWUL state that there are no likely capacity problems as long as discharge was on a like for like basis, or the Surface

Water run off was restricted to 50% of existing peak run off rates (as per the London Plan 2011 requirements). Figure 13-8 Extract of TWUL Drainage Network 13.151 The existing impermeable area is estimated to be 7740m2 (approximately 99% impermeable). It is assumed that open

Top of sewer run space at south end has no positive drainage. beneath existing building 13.152 Existing peak runoff rates for an assumed critical 5 minute storm are 108l/s (1 year Average Recurrence Intervals (ARI), 243 l/s (30 year ARI) and 310 l/s (100 year ARI). 13.153 Existing foul drainage runoff is not known, however, 5 l/s has been estimated. This figure is based on the existing site Erlang House, Hill House and Milcote House collectively providing approximately 129,608sqft (12,040m2) of office (Class B1) accommodation. For office space accommodation, Thames Water criteria attributes a value of 2 750l/100m /day for foul flows (Dry Weather Flow - DWF). Based on the above criteria and applying a 6.6 DWF peaking factor for a 12 hour day will result in a peak foul flow of 13.8l/s. This has been conservatively rounded down to 13l/s.

13.154 Surface and foul water flows contribute to CSO and STW overflow events. Existing capacity issues may result in

localised flooding in the LBS. The age of the infrastructure and the unknown nature of some of the network means there can be constraints to re-development. The quality of existing runoff from the highly urbanised catchment is High Level considered to be low. Overflow MH7505 13.155 The existing foul and surface water drainage infrastructure attribute is assessed as having medium importance. Summary of Resource Importance

13.156 Table 13-4 summarises the importance assigned to the various water resources/receptors discussed within the baseline conditions section of this chapter.

Table 13-4 Summary of Water Resource/Receptor Importance

Flap Valve Water Resources/ Receptor Importance Summary MH 7401 The River Thames is Nationally significant and water supply is of high importance. The River Thames is an River Thames– Water Supply High important water source providing two-thirds of London’s drinking water. Note that water supply is sourced upstream of Teddington weir. The River Thames is Nationally significant and water quality is of high importance for a number of reasons. Medium River Thames – Water Quality Water quality is currently at risk from CSOs the water

quality is planned to improve from Moderate to Good potential by 2027

Groundwater (Secondary Aquifer) – Water Medium Water quality is of high importance but it is resilient to Quality some change 13.145 The local drainage is combined in 225mm and 300mm diameter sewer runs that flow in various directions to the east of Water supply is high importance due to supply potable Groundwater (Principal Aquifer) – Water High water to London and managing water levels in relation the proposed development site along Library Street and Davidge Street, before connecting to the Trunk sewer. Supply/Abstraction & Discharge to the underground network etc. Flood Risk Medium Existing management strategies incorporate allowance

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Water Resources/ Receptor Importance Summary Table 13-5 Potential Contamination Sources and Activities, Pathways and Receptors during the for change (climate change). There is a residual risk of Demolition and Construction Phases flooding from a breach of the flood defences. Sources The water supply infrastructure is considered to be of medium importance on a local, district and regional Demolition activities and materials level with little capacity to absorb change. The rate of any change needs to be in accordance with regional TWUL water supply infrastructure Medium water resource planning. Localised soil and groundwater contamination in Made Ground and underlying strata London is an area of serious water stress. The existing water supply infrastructure is old and TWUL are Off-site soil and groundwater contamination migrating on-site currently replacing water mains throughout London

Surface and foul water flows contribute to CSO and STW overflow events. Existing capacity issues may Pathways result in localised flooding in the LBS. The age of the TWUL Foul Drainage (Sewer) Network Medium infrastructure means there can be constraints to re- development The quality of existing runoff from the Groundwater dewatering activities highly urbanised catchment is consider to be low

Creation of direct preferential pathways to ground and surface water

Potential Impacts and Mitigation Measures Surface water runoff

13.157 The following paragraphs detail the assessment of potential impacts on the water environment from the demolition and Piling through the London Clay, excavations and dewatering construction phase and the operation of the proposed development.

13.158 This section addresses: Existing buried obstructions, foundations etc.  Short-term, medium term (demolition and construction), long-term (complete and operational development) impacts, and direct and indirect impacts; Preferential pathways such as piling  Quantitative impact assessment (where possible); and  Mitigation measures describe design mitigation, management controls, physical and compensation measures. Drainage routes Demolition and Construction Impacts Sewer infrastructure and CSOs 13.159 The proposed development comprises the demolition and redevelopment of the existing Hill House, Milcote House and

Erlang House at 128 – 150 Blackfriars Road. The proposed development will provide a Gross Internal Area (GIA) of up to 40,211m2. Two landscaped publically accessible pedestrian walkways between the blocks are also proposed. Migration of groundwater

Proposed ground floor uses are retail/café/restaurant, and own door duplex office units. The proposed residential element will include the provision 336 residential units provided as both market and affordable. Receptors

13.160 The overall construction period is presently estimated at approximately 3.5 years. 13.161 Examples of potential pollution sources, pathways and receptors in the context of water resources for the demolition TWUL Foul Drainage (Sewer) Network

and construction phase are presented in Table 13-5. River Thames

Groundwater

13.162 Potential impacts arising from demolition and construction that could impact surface and groundwater comprise the following:  The mobilisation/release of contaminants including; suspended sediments, oils/hydrocarbons, concrete and cement products from demolition and construction practice techniques and machinery;  Flood Risk;  Disturbance of groundwater;  Disturbance of contaminated land;  Disturbance of existing drainage systems;  Water supply; and

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 Wastewater generation.  A Pollution Prevention Plan/ Environmental Management Plan (EMP) will be put into place; Mobilisation of Contaminants  Properly contained wheel wash facilities will be used where required to isolate sediment rich run-off; and  Drainage of surface run-off and de-watering effluents to settling tanks to remove suspended solids prior to Potential Impacts discharge to sewer. 13.163 The mobilisation/release of contaminants during the demolition and construction phase of the project could include; 13.175 Measures will be taken to protect controlled waters from the release of oils and hydrocarbons at the proposed suspended sediments, oils/hydrocarbons, concrete and cement products from construction practice techniques and development site. These measures comprise: machinery.  Oils and hydrocarbons will be stored in designated locations with specific measures to prevent leakage and 13.164 Potential sources of suspended sediments during the demolition and construction of the proposed development include release of their contents. This will include the siting of storage areas away from surface water drains on an excavations, exposed ground and stockpiles, plant and wheel washing and dust and sediment generated during impermeable base. An impermeable bund with no outflow will be manufactured to contain capacity of 110% of the demolition activities. The major pathway for suspended sediments to reach controlled water bodies is through runoff contents. Valves and trigger guns will be protected from vandalism and kept locked when not in use; during rainfall events or when areas are being washed down. This may cause sediment-laden water to enter the local  Wherever possible, plant and machinery will be kept away from the drainage system and will have drip trays drainage network, reach the River Thames via CSOs or infiltrate down into the ground. beneath oil tanks/engines/gearboxes/hydraulics, which will be checked and emptied regularly via a licensed waste 13.165 Suspended sediments can result in the suffocation of fish, smothering of plants, reduced levels of light within water disposal operator; bodies and decreased water quality of surface water abstractions. Any organic matter contained within the sediment  Following the discharge of surface run-off and de-watering effluents to settling tanks the drainage will be routed to can increase the Biochemical Oxygen Demand (BOD) of the water and result in a lowering of DO. Suspended oil interceptors prior to discharge to sewer; and sediments are also a major transport mechanism for low-solubility contaminants that can bind to sediment particles and  An emergency spillage action plan will be produced, which site staff will be reminded to read and understand prior enter water bodies resulting in adverse impacts to the receiving water body. to any on-site works. On-site provisions will be made to contain a serious spill or leak through the use of booms, 13.166 Water supply from the Thames River is upstream of the proposed development site and therefore not impacted on by bunding and absorbent material. demolition and construction activities. 13.176 A number of precautions will be taken on-site to reduce the potential magnitude of these impacts, including: 13.167 The release of sediment can block up existing gullies and foul drainage infrastructure increasing the risk of localised  The majority of concrete used will be pre-mixed and delivered from an off-site source, thereby negating the need flooding and increasing the requirement for maintenance by TWUL. to mix concrete on-site and reducing the potential for creation of alkaline wastewater; 13.168 The main source for oils and hydrocarbons at the proposed development site will be from potential spillages and leaks  Wherever possible, any mixing and handling of wet concrete on-site will be undertaken in designated impermeable associated with plant machinery and fuel storage. The pathways for oils and hydrocarbons to reach receptors could be areas, away from any drainage channels or surface water; and via surface water runoff, the foul drainage network and through infiltration.  A designated impermeable area will be used for any washing down or equipment cleaning associated with 13.169 The release of oils and fuel can result in additional loadings on downstream STW, and a reduction in quality of local concrete or cementing processes. Wastewater will then be discharged to the foul drainage system or contained groundwater. If oils are released via CSOs, the result can be the poisoning of fish, the creation of oily surface films on and removed by tanker to a suitable discharge location. water and a reduction in the quality of industrial and potable abstractions. Oils also bind to sediments, strata and 13.177 Either Barratt London (the Applicant) or the Principal Contractor will prepare a detailed Construction Method Statement organisms and can form emulsions that float on the water surface and upon breakdown by the action of microbes can (CMS) through which mitigation and compliance with the LBS Environmental Code of Construction Practice and the lower the DO content of the water. ‘Considerate Constructors Scheme’ will be achieved. Refer to Chapter 5: Demolition and Construction for more details. 13.170 Concrete and cement products are highly alkaline and their release into controlled waters could have an adverse 13.178 Alongside (or part of) the CMS, and drawing on this ES, will be a CEMP which will cover environmental issues relating impact on fauna and on the water quality in general, resulting in a poor taste and an increase in pH to levels above the to on-site activities during the demolition and construction phase. Refer to Chapter 5: Demolition and Construction for legal drinking water standards. more details. 13.171 Construction processes that can result in the release of concrete and cement include on-site concrete mixing and the washing down of areas where mixing has taken place. This leads to large quantities of wastewater runoff, which can Residual Impact flow into the surface water drainage system and infiltrate the ground. 13.179 The control measures set out above will aim to reduce the volume of potentially contaminated wastewater and therefore 13.172 It is estimated that the release of contaminants could produce an impact of medium magnitude on: the local drainage the magnitude of the potential impacts on surface water, groundwater and the foul drainage network will be negligible. network; groundwater (quality and supply); and a small magnitude impact on the water quality of the River Thames. 13.180 The residual impact significance is negligible on the River Thames, groundwater and local drainage systems. 13.173 The pre-mitigation potential impact significance is therefore minor adverse on the foul drainage infrastructure and 13.181 Table 13-6 summarises the impacts to water resources as a result of the mobilisation of contaminants pre and post groundwater quality and negligible for the Thames River water quality. The pre-mitigation potential impact on mitigation. groundwater supply is medium.

Mitigation 13.174 A number of measures will be employed at the proposed development site during the demolition and construction phase to prevent the potential release of suspended sediments and to reduce any associated impacts. These comprise:  Cut-off ditches and/or geotextile silt-fences, which will be installed around excavations or exposed ground and stockpiles to prevent the uncontrolled release of sediments from the site;  Site access points which will be regularly cleaned to prevent build-up of dust and mud;  Earth movement will be controlled to reduce the risk of demolition and construction silt combining with the site run- off;

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Table 13-6 Mobilisation of Contaminants: Summary of Impacts Disturbance of Groundwater Potential Impact Residual Impact

Pre-Mitigation Post-Mitigation Potential Impacts Resource/Receptor Magnitude of Significance of Magnitude of Significance of Resource/Receptor 13.190 Consideration should be given to the possibility of encountering perched groundwater within and around the perimeter Importance impact impact impact Impact River Thames Water of the proposed development site during excavations for foundations and proposed basement levels. Medium Small Negligible Negligible Negligible Quality 13.191 Proposed piling will include secant or contiguous piled wall around the perimeter of the proposed development site and Groundwater quality Medium Medium Minor (Adverse) Negligible Negligible bearing piles throughout. The piled wall will be installed around the perimeter of the new basement. These piles will Moderate Groundwater supply High Medium Negligible Negligible (Adverse) penetrate approximately 20 metres (m) below the basement level. Refer to Chapter 5 Demolition and Construction for TWUL more details. Foul Drainage (Sewer) Medium Medium Minor (Adverse) Negligible Negligible 13.192 Excavations and piling have the potential to provide a direct pathway for pollutants to reach groundwater, resulting in a Network potential impact on groundwater quality. The pre-mitigation impact magnitude is likely to be medium and the significance of the impact on groundwater quality is likely to be minor adverse. Flood Risk Mitigation Potential Impacts 13.193 The following mitigation measures will be implemented for controlling groundwater during excavations:  If perched groundwater is encountered during establishment of the basement and core foundations, dewatering 13.182 The proposed development site is not at significant risk of flooding. Identified flood risks are outlined in the FRA may be required. The most appropriate methods to dewater excavations will be selected, for example, prior to provided in ES Volume III: Technical Appendix H. There are however minor temporary risks of flooding from tidal, dewatering the perimeter of the excavation could be enclosed with either sheet-pile or a diaphragm wall. pluvial and potentially groundwater sources during the demolition and construction phase. Piezometers (standpipes) could then be placed outside the sheet pile wall to monitor groundwater levels; and 13.183 The overall demolition and construction period is presently estimated at 3.5 years.  Water arising from excavations will need to be disposed of to the local sewer network (subject to agreement with 13.184 The probability of an event occurring during a discrete period of time is given by the formula; TWUL) if uncontaminated and following the removal of silt via settlement ponds or alternative measures.  Pr = 1 – [1-(1/T)]L However, if the water arising is found to be contaminated, then this will have to be removed off site via tankers to  Where, Pr = probability, T = return period, L = period of time. be suitably disposed of. 13.185 Using the above formula, the 0.5% AEP tidal breach flood risk would have a probability of 1.7% of occurring during the Residual Impact demolition and construction phase. 13.194 With these control measures in place, the likely potential residual impacts on groundwater from the proposed 13.186 The FRA describes that the proposed development site is defined as having a low degree of flood hazard in the SFRA. development are assessed as negligible (Table 13-8). 13.187 The magnitude of impact pre-mitigation is small and the significance is negligible.

Mitigation Table 13-8 Disturbance of Groundwater: Summary of Impacts Potential Impact Residual Impact 13.188 Measures need to be employed during the demolition and construction phase to ensure surface water runoff from the Pre-Mitigation Post-Mitigation proposed development site is attenuated and discharged responsibly to ensure flood risk is not increased off site as a Resource/Receptor Magnitude of Significance of Magnitude of Significance of Resource/Receptor result of the demolition and construction phase. It is recommended that the attenuation structures (in the form of pipes Importance impact impact impact Impact and lined geo-cellular tanks, as detailed in the Flood Risk Assessment) proposed for the operational phase of the Groundwater – Water proposed development are constructed early on to contribute to the management of surface waters from the proposed Quality Medium Medium Minor (Adverse) Negligible Negligible

development site. Residual Impact Disturbance of Contaminated Land 13.189 The implementation of the above mitigation measures will help to reduce the potential probability of flooding and as a Potential Impacts result will reduce the residual risk to negligible. 13.195 There are potential sources of contamination, which is likely to be caused from the previous uses of the site. Previous uses include; housing, tobacco factory and a public house. Refer to Chapter 14: Ground Conditions for more details. Table 13-7 Flood Risk: Summary of Impacts However, a detailed intrusive site investigation is recommended to be undertaken during the detailed design phase, to Potential Impact Residual Impact

Pre-Mitigation Post-Mitigation confirm the likely sources of any contamination issues found on site. Resource/Receptor Magnitude of Significance of Magnitude of Significance of Resource/Receptor 13.196 A site visit last year undertaken by RSA Geotechnics also identified potential on-site sources of contamination which Importance impact impact impact Impact included the existing buildings, car park areas, underground oil tanks, large generators and an on-site electricity Flood Risk Medium Small Negligible Negligible Negligible substation. 13.197 The disturbance of contaminated land could mobilise pollutants that could then migrate via a pathway to a receptor. At risk receptors are Thames River quality, groundwater quality and TWUL foul drainage (sewer) network.

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13.198 Chapter 14: Ground Conditions states that the greater proportion of any contamination present is anticipated to be  All existing utilities will be identified and marked prior to works commencing; contained within the made ground. Given that the proposed development includes extending the existing basement  Signs will be used to warn of the presence of the drainage system; areas to provide one site-wide basement, most or all of the made ground is anticipated to be removed, which will  Surface water flows attenuated on-site with controlled discharge rates; therefore also remove the expected source of the contamination.  Measures as outlined in previous paragraphs (13.174 – 13.178) to be implemented to protect sewer integrity from 13.199 It is possible however that undiscovered areas of contamination could exist, with the potential for disturbance and the the release of sediment, oils, hydrocarbons, cement etc. re-mobilisation of contaminants into surface water (via surface water runoff into the drainage network) or groundwater  Any damage to the drainage network will be immediately repaired; and (via preferential pathways or infiltration), which could have a potential impact of medium magnitude on all the risk receptors. This would lead to minor adverse impacts on the River Thames water quality, TWUL foul drainage (sewer)  An emergency spillage action plan will be produced to ensure spillages and leakages are immediately contained. network and groundwater quality. 13.207 The build over section of the existing 225 sewer will have to be accurately located and protected during demolition and construction (protective wide steel plate over compressible cushion or similar) with piling a minimum clearance (usually Mitigation 1.5m minimum) and sewer CCTV surveyed after, all to TWUL approval. 13.200 In the event that contamination is discovered, all work will stop immediately and measures will be taken to prevent Residual Impact disturbance and mobilisation of contaminants. Depending on the type of contamination, treatment of contaminants in- situ should be explored or removed via tankers for off-site disposal, before continuation of any works 13.208 The measures described above will reduce the magnitude of impact and likelihood of any pollution incidents, and manage pathways. This will reduce the magnitude of potential impacts to negligible. The significance of the potential Residual Impact residual impact is negligible (Table 13-10). 13.201 Therefore, with the appropriate methodology and control measures in place, the potential magnitude of impacts associated with the presence of undiscovered areas of contamination on-site will be reduced to negligible. The Table 13-10 Disturbance of Existing Drainage: Summary of Impacts significance of the potential residual impact is therefore also considered to be negligible (Table 13-9). Potential Impact Residual Impact

Pre-Mitigation Post-Mitigation Resource/Receptor Magnitude of Significance of Magnitude of Significance of Resource/Receptor Table 13-9 Disturbance of Contaminated Land: Summary of Impacts Importance impact impact impact Impact Potential Impact Residual Impact River Thames Water

Pre-Mitigation Post-Mitigation Quality Medium Small Negligible Negligible Negligible Resource/Receptor Magnitude of Significance of Magnitude of Significance of Resource/Receptor Importance impact impact impact Impact Groundwater – Water River Thames Water Quality Medium Small Negligible Negligible Negligible Quality Medium Medium Minor (Adverse) Negligible Negligible TWUL Foul Drainage Medium Small Negligible Negligible Negligible Groundwater – Water (Sewer) Network Quality Medium Medium Minor (Adverse) Negligible Negligible

TWUL Foul Drainage Medium Medium Minor (Adverse) Negligible Negligible Water Supply Demand (Sewer) Network Potential Impacts Existing Drainage Systems 13.209 Processes during the demolition and construction phase of the proposed development may require significant volumes of water. Potential Impacts 13.210 Generally the source of water is either mains water or water abstracted from surface water. Mains water use puts 13.202 Disturbance of the existing drainage network increases the likelihood of pollutants (via surface water or foul water) pressure on the water supply resources and supply system. being re-released in an uncontrolled manner. These pollutants could damage the quality receiving waterbody and also 13.211 It is expected that water supply to the proposed development site during the demolition and construction phase will be impact the aquatic ecology. Pathways include infiltration, vertical and lateral preferential pathways, surface water runoff provided via the existing TWUL network in the surrounding area and that the supply for demolition and construction and the upstream drainage network. Uncontrolled surface water flows will contribute to the frequency of CSOs into the purposes will require a building water supply licence from TWUL. River Thames. 13.212 Water supply for demolition and construction processes, therefore, may represent a short term, increase in supply 13.203 During demolition and construction on-site, the combined sewage network will be expected to transport surface water, volumes to the proposed development site. The magnitude of impact on water supply resources (Thames River and sewerage and wastewater generated, with consent from TWUL. groundwater) is assessed as being negligible whereas the magnitude on local infrastructure is assesses as being small. 13.204 If the drainage network is damaged during demolition and construction, this could potentially have an impact of small The significance of these impacts is negligible in all cases. magnitude on groundwater quality and also the River Thames water quality. Damage or blockages to the existing sewer infrastructure would also have an impact of small magnitude. Mitigation 13.205 The resultant significance is negligible in all cases based on the resource/receptors importance. 13.213 Demolition and construction works require water for a number of activities. A WRAP report (December 2012) (Ref. 13- 54) outlines the priority for implementing water conservation measures on construction sites is on reducing water Mitigation wastage with the following site processes identified as likely to be the most water wasting activities: 13.206 A number of mitigation measures will be implemented on-site to both prevent any potential damage to drainage  dust suppression, to include general, site road and wheel washing; networks and hence prevent release of these contaminants:  hydro-demolition with high pressure water;

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 cleaning, to include ready mixed concrete wagons and other applications; and Mitigation  commissioning and testing of building plant/services. 13.220 The use of the water efficient fixtures and fittings and the use of mitigation measures to prevent silty water ingress can 13.214 The WRAP report identifies a number of measure to help conserve water on a construction site including; help to reduce the volume of water entering the TWUL sewer network, thereby reducing flood risk and impact on water  Construction companies should ensure all water sources are accurately quantified, though mains water is quality of the River Thames by reducing the volume discharged via CSOs. particularly important. This may include installing sub-meters at strategic locations around the distribution network, Residual Impact and/or utilising metered standpipes;  Using water saving devices and alternative dust suppression methods; and 13.221 The post mitigation residual impact remains negligible.  Using alternative cleaning methods. 13.215 All relevant contractors will be required to undertake opportunities to minimise and reduce the use of water, including; Table 13-12 Wastewater: Summary of Impacts Potential Impact Residual Impact  Implementation of staff based initiatives such as turning off taps when not in use both on-site and within site Pre-Mitigation Post-Mitigation offices; Resource/Receptor Magnitude of Significance of Magnitude of Significance of Resource/Receptor  Use of recycling water systems such as wheel washes; and Importance impact impact impact Impact River Thames - Water  Use of a rainwater harvesting system for use in equipment and vehicle washing will also be investigated. Quality Medium Small Negligible Negligible Negligible Residual Impact TWUL Foul Drainage Medium Small Negligible Negligible Negligible 13.216 Water saving measures will be adopted where possible and so, any potential impact on the water supply resources and (Sewer) Network infrastructure would be removed. The significance of potential residual impacts on water demand from the River Thames, groundwater and TWUL infrastructure remains negligible post-mitigation. Completed Operational Development

Table 13-11 Water Supply System: Summary of Impacts 13.222 The potential sources, pathways and receptors in the context of water resources for the completed operational proposed development are presented in Table 13-13. Potential Impact Residual Impact

Pre-Mitigation Post-Mitigation Resource/Receptor Magnitude of Significance of Magnitude of Significance of Resource/Receptor Table 13-13 Potential Contamination Sources and Activities, Pathways and Receptors for the Operation of Importance impact impact impact Impact River Thames Water the Proposed Development Supply High Negligible Negligible Negligible Negligible Sources

Groundwater – Water Leaks, spillages, (fertilisers, pesticides, fuel, hydrocabons) Supply High Negligible Negligible Negligible Negligible Flood Risk TWUL Infrastructure – Water Supply Network Medium Small Negligible Negligible Negligible Disturbance of groundwater

Increased wastewater generation

Increased demand for potable water Wastewater Generation Potential Impacts Pathways

13.217 Wastewater is generated during the demolition and construction phase via effluent from sanitary facilities provided on- Creation of direct contact pathways to ground and surface water

site. It is expected that foul water generated at the site will be drained via the existing TWUL combined drains in the Lateral migration of groundwater surrounding area, following treatment if required. If dewatering is required during excavations, then abstracted water may be discharged to the TWUL network, following sediment removal. The demolition and construction activities may Site layout and topography (hardstanding, surface water drains) result in an increase in the volumes of wastewater generated which would in turn lead to an increase in pressure on the Drainage/service runs local sewer network capacity and the receiving Crossness STW. It can also lead to a potential increase in the volume of water spilled into the River Thames, via CSOs in the TWUL network. Basement structure, foundations and piles 13.218 The rate at which the proposed development site can discharge to the TWUL sewer network is restricted by the size of Preferential pathways such as piling the existing sewer connections. If no additional connections to the sewer network are obtained, then the maximum discharge into the sewer network will not exceed the existing situation. If wastewater is generated at a greater volume TWUL sewage infrastructure than it can be discharged to the sewer network, then it will be stored or tankered off-site. Receptors 13.219 The magnitude of impact on the TWUL infrastructure and the River Thames prior to mitigation is considered to be small. The significance of the impact on the Thames water quality & TWUL infrastructure is negligible prior to mitigation. TWUL Sewers/treatment works

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TWUL Reservoirs Table 13-14 Mobilisation of Contaminants: Summary of Impacts Potential Impact Residual Impact River Thames Pre-Mitigation Post-Mitigation Resource/Receptor Magnitude of Significance of Magnitude of Significance of Groundwater Resource/Receptor Importance impact impact impact Impact River Thames Water Quality Medium Small Negligible Negligible Negligible 13.223 Potential impacts arising from the completed and operational development comprise the following:  The mobilisation/release of contaminants; Groundwater – Water  Flood Risk; Quality Medium Medium Minor Adverse Negligible Negligible  Disturbance of groundwater; TWUL Foul Drainage Medium Small Negligible Negligible Negligible  Water Demand; and (Sewer) Network  Surface water and Wastewater generation. Mobilisation of Contaminants (Impacts and Mitigation) Flood Risk Potential Impacts Potential Impacts 13.224 Typical sources of pollution from the complete development include oil leaks and petrol spillages from vehicles or 13.230 A FRA has been undertaken and is provided within ES Volume III: Technical Appendix H presenting the flood risk storage facilities and from application of fertiliser, pesticides and herbicides to landscaped areas. Pollutants can be information to and from the site. This confirms the proposed development’s location in Flood Zone 3 (defended) with a mobilised in surface water runoff and enter the surface water drainage network. The release of chemicals in this way is risk of flooding from a breach of the tidal defences. The proposed development is considered to have a small impact for anticipated to have a small magnitude of impact on the surface water environment, as the quantities are likely to be potential flooding. relatively small and dilution will be available within the environment (for example, in surface water runoff, the receiving 13.231 This site-specific FRA aims to demonstrate that the proposed development will be safe for its lifetime taking account of sewer network and the River Thames). In the unlikely event that the pollutants enter the on-site drainage system there the vulnerability of its users, without increasing flood risk elsewhere, and, where possible, will reduce flood risk overall. is a risk of them entering the River Thames system through CSOs associated with the TWUL network. Prior to mitigation the impact significance of flooding on and off-site is negligible. 13.225 The low volume of any potential spill could result in a small impact on the TWUL drainage network and on the River Mitigation Thames water quality and a medium impact on groundwater quality. The resultant significant pre-mitigation is negligible for both the TWUL drainage network and the River Thames water quality and minor adverse for groundwater. 13.232 The following measures to reduce any risk of flood will be incorporated into the proposed development: Mitigation  The integration of SuDS to reduce the runoff rate from the proposed development site (designed for up to and including the 100 year event and plus an allowance of 30% increase in rainfall due to climate change); 13.226 The main pathway for these pollutants to impact the groundwater environment is via infiltration through soft landscaped  Locating all residential accommodation above the flood level (at first floor and above); areas and via preferential pathways. However, due to the majority of the proposed development site containing  Ensuring flow routes for flood water into the basement are removed; impermeable surfaces, limited soft landscape areas (greenroofs only) and an extensive basement, it is expected that the impact would be negligible on the underlying groundwater.  Reducing the number of flow routes into the building; 13.227 As with the demolition and construction phase of the proposed development, there remains a risk of a spillage of  Providing safe access and egress for all uses from the site; and contaminating material, for example fuels and oils, which could potentially be released to ground and surface waters.  Providing a flood evacuation/response plan. The risk of this occurring can be managed by operational measures. The use of oil trays on construction plant and Residual Impact bunds around fuel storage areas and secure compounds will provide the relevant mitigation to minimise the risk of accidental spillages. These practices are covered by the Environment Agency Pollution Prevention Guidelines. The 13.233 Following the implementation of mitigation measures, the proposed development site is assessed to have negligible drainage of the basement will be via sumps with sump pumps and therefore oil alarms can be used to warn if there is a residual impact in respect to flood risk. risk in concentration in any water entering the sumps. Any spills occurring within the basement will be pumped to combined Thames Water sewers to the east of the site. Table 13-15 Flood Risk: Summary of Impacts 13.228 The majority of impermeable area is either building roofs or paved pedestrian areas. The risk of contamination from the Potential Impact Residual Impact

roofs is small due to the inclusion of greenroofs. The small risk relates to when fertiliser is applied to the roof areas Pre-Mitigation Post-Mitigation Resource/Receptor Magnitude of Significance of Magnitude of Significance of (particularly in their establishment phase) which could runoff into the sewers. A management plan will be in place to Resource/Receptor Importance impact impact impact Impact ensure excessive fertilisers are not applied. The management plan will quantify application rates and dosages of Flood Risk Medium Small Negligible Negligible Negligible particular fertilizers. As external hardstanding areas are pedestrianised only, the risk of pollution includes gross pollutants (general rubbish) and sediments. The management plan will identify a maintenance and cleaning regime to prevent the build-up of sediment and rubbish within external hardstanding areas. Disturbance of Groundwater Residual Impact Potential Impacts 13.229 With good site management, the potential residual impact on water quality of the River Thames, groundwater and the 13.234 The proposed basement is a larger footprint to the existing basement. However, it is not anticipated this will have any TWUL sewer network will be negligible (Table 13-14). impacts on perched groundwater.

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13.235 Considering that the hydraulic regime in the surrounding environment is already significantly influenced by existing in- Table 13-17 Water Supply System: Summary of Impacts situ deep basements/foundations then the magnitude of impact is considered to be negligible on shallow groundwater Potential Impact Residual Impact

and therefore the significance is evaluated as negligible and therefore no mitigation measures are proposed. Pre-Mitigation Post-Mitigation Resource/Receptor Magnitude of Significance of Magnitude of Significance of Resource/Receptor Importance impact impact impact Impact Table 13-16 Disturbance of Groundwater: Summary of Impacts River Thames Water Supply Potential Impact Residual Impact High Small Minor (Adverse) Small Negligible

Pre-Mitigation Post-Mitigation

Resource/Receptor Magnitude of Significance of Magnitude of Significance of Resource/Receptor Groundwater – Water Importance impact impact impact Impact Supply High Small Minor (Adverse) Small Negligible Groundwater Quality Medium Negligible Negligible Negligible Negligible

TWUL Infrastructure – Water Supply Network Medium Small Negligible Small Negligible

Water Demand Potential Impacts Surface Water and Wastewater Generation 13.236 An indication of the proposed water demand volumes have been calculated based on Construction Industry Research Potential Impacts and Information Association (CIRIA) report C657 (Ref.13-55) and Buildings Services Research and Information Association (BSRIA) guidance (Ref. 13-56) for commercial demand and the CfSH (Level 4) requirements for residential: 13.243 The foul water generated on-site will be discharged into the TWUL network (indicative peak foul flow calculation of 25  35 kilolitres/day (kl/day) for offices, retail, café & supermarket (based on approximately 1,550m2 of retail/cafe and l/second). 2,726m2 GIA of offices); and 13.244 The volume of wastewater generated at the proposed development site will present an increase in the volume of foul  100 kl/day for residential use (based on an occupancy population of 2.5 people per property, which equates to water from the baseline conditions (estimated at 13 l/s) approximately 840 people and 105 l/person/day). 13.245 If the capacity of the TWUL sewer network is reached then foul water would be discharged directly into the River 13.237 Although the proposed development aims to incorporate best practices for water demand, including CfSH Level 4 for Thames via CSOs. This would cause a short-term impact of small magnitude which would result in a negligible impact residential dwellings and BREEAM Excellent for commercial, the proposed development is expected to increase the significance on the Thames River water quality. water supply requirements above the baseline. The increase in water demand is expected to have a minor adverse 13.246 The impact on the TWUL infrastructure is small with the resultant significance being negligible. impact on potable water supply resources (Thames River and Groundwater). Mitigation Mitigation 13.247 The increase in foul flows from the baseline condition is mitigated by restricting the surface water flows to the combined 13.238 The development aims to reduce water consumption by 40% under a notional baseline performance (estimated sewer. The surface water flows are restricted to 63% of the estimated existing 1 in 1 year peak runoff rate. The peak average from the BREEAM guidance on non-domestic water reduction). It is proposed that commercial water efficiency surface water runoff rate of 108 l/s is restricted to 40 l/s. Therefore the combined discharge is estimated to be reduced is achieved by installing low flush toilets, low flow taps and low flow showers. It is also proposed that mains water leak from 121 l/s to 65 l/s. Dry weather baseflows will, however, be increased to the STWs. detection system, pulsed out water meter and flow control devises are fitted in each toilet area. 13.248 Surface water flow attenuation is proposed in a number of strategically located geo-cellular storage crates with 13.239 The residential element of the proposed development proposes to use ultra-low flush WCs, low volume baths, and attenuation provided for critical storm events up to and including the 1 in 100 year (plus 30% allowance for the climate regulated showers and taps and low water appliances. A rainwater harvesting system is also proposed to collect water change) event. for irrigation purposes. This will use a pump to deliver water to conveniently located irrigation points provided for the Residual Impact rooftop landscaped amenity terraces. 13.240 As water efficiency incorporated into the development is mandatory (refer Southwark SPDs) there is minimal mitigation 13.249 The residual impact and significance on the drainage infrastructure and the River Thames water quality is considered to proposed. The incorporation of rainwater harvesting will reduce the demand for potable water. be negligible post mitigation.

Residual Impact Table 13-18 Wastewater Generation: Summary of Impacts 13.241 As a result of the mitigation measures and the wider strategic measures of TWUL to safeguard water supply the Potential Impact Residual Impact

residual impact on the water supply receptors is assessed as negligible. Pre-Mitigation Post-Mitigation Resource/Receptor Magnitude of Significance of Magnitude of Significance of Resource/Receptor 13.242 The increased demand will put increased pressure on the water supply network, including, storage reservoirs, Importance impact impact impact Impact treatment plants, regional and local distribution. The increased demand is assessed to have a minor adverse impact River Thames Water pre-mitigation and a residual impact of negligible significance for the water supply network post mitigation. Quality Medium Small Negligible Negligible Negligible

TWUL Foul Drainage (Sewer) Network and Medium Small Negligible Negligible Negligible STW

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Significance of Significance of Residual Impacts Summary and Conclusions Geographical Description Resource/Receptor Potential Impacts Residual Impact Nature of Impact Scale of Impact Pre mitigation Post Mitigation 13.250 Table 13-19 summaries the impacts pre-mitigation and the residual impacts (post-mitigation) during both demolition and Infrastructure construction and operational phases. River Thames – Water Negligible Negligible Negligible Local 13.251 No likely significant environmental effects (any residual impact of moderate or major impact significance) are predicted Surface Water and Quality Wastewater TWUL Foul Drainage for the Water Resources, Drainage and Flood risk of the proposed development, provided that the mitigation measures generation (Sewer) Network and Negligible Negligible Negligible Local as discussed throughout this chapter are applied. STW

Table 13-19 Summary of Residual Impacts for Demolition and construction and Operational Phases Cumulative Impacts Significance of Significance of Geographical Description Resource/Receptor Potential Impacts Residual Impact Nature of Impact Scale of Impact Cumulative Effect of Individual Impacts on a Single Receptor Pre mitigation Post Mitigation Demolition and construction 13.252 The combined effect of individual impacts occur when a single receptor is affected by more than one impact at any point River Thames – Water in time. An exercise which tabulated the residual impacts of this ES against relevant receptors, and so identifies the Negligible Negligible Negligible Local Quality potential for combined cumulative impacts has been undertaken. Reference should be made to Chapter 18: Impact Groundwater – Water Minor Adverse Negligible Negligible Local Interactions and Cumulative Impact Assessment of this ES. Mobilisation of Quality contaminants Groundwater – Supply Moderate Adverse Negligible Negligible District Combined Impacts of the Proposed Development with Other Development Schemes TWUL Foul Drainage Minor Adverse Negligible Negligible Local (Sewer) Network 13.253 The demolition and construction impacts, as-well as the operational impacts, of the proposed development in Flood Risk Flood Risk Negligible Negligible Negligible Local combination with other proposed schemes is detailed below. The details of the 18 cumulative schemes to be assessed Disturbance to Groundwater – Water Minor Adverse Negligible Negligible Local are set out in Chapter 2: EIA Methodology of this ES. Groundwater Quality River Thames – Water Demolition and Construction related Cumulative Impacts Minor Adverse Negligible Negligible Local Quality Disturbance of Groundwater – Water 13.254 In terms of the demolition and construction phase, the key cumulative impacts are assessed as being from: the Contaminated Land Minor Adverse Negligible Negligible Local Quality mobilisation of contaminants; flood risk; water supply demand; and sewer infrastructure. TWUL Infrastructure Minor Adverse Negligible Negligible Local 13.255 Demolition and construction impacts are typically short-term, however, the cumulative impact may extend the duration River Thames – Water Negligible Negligible Negligible Local Quality to medium term. Disturbance to Groundwater – Water existing drainage Negligible Negligible Negligible Local 13.256 Given that all demolition and construction activities for the schemes considered in the cumulative impact assessment Quality systems should be undertaken to best management practices the impact of the cumulative scheme is expected to be similar to TWUL Foul Drainage Negligible Negligible Negligible Local (Sewer) Network the impact of the proposed development and therefore any cumulative impact is considered to be negligible. River Thames – Water Negligible Negligible Negligible Local Supply Operational related Cumulative Impacts Water Supply Groundwater – Water Negligible Negligible Negligible District 13.257 In terms of the operational phase, the key cumulative impacts are assessed as being from; demand Supply TWUL Water Supply  Flood risk; Negligible Negligible Negligible Local Infrastructure  Water supply; and River Thames – Water Negligible Negligible Negligible Local Wastewater Quality  Wastewater generation. generation TWUL Foul Drainage Negligible Negligible Negligible Local 13.258 It is anticipated that the schemes considered in the cumulative impact assessment will incorporate SuDS. The residual (Sewer) Network Operational impact from the proposed development is negligible, however, the cumulative impact could be considered to be minor River Thames – Water beneficial to the existing sewer infrastructure in terms of reducing flood risk and CSOs into the River Thames. Negligible Negligible Negligible Local Quality 13.259 The cumulative scheme development sites are all likely to fall within Flood Risk Zone 3a, being at risk of tidal flooding Mobilisation of Groundwater – Water Minor Adverse Negligible Negligible Local and defended by the Thames Tidal Defences. Given that the cumulative schemes will be required to comply with NPPF contaminants Quality TWUL Foul Drainage requirements, will incorporate SuDS and flow restrictions plus the implementation of flood resilience and flood response Negligible Negligible Negligible Local (Sewer) Network plans the cumulative impact is assessed as minor beneficial. Flood Risk Flood Risk Negligible Negligible Negligible Local 13.260 As a result of the cumulative schemes the combined pressures on water supply will increase. This may vary depending Disturbance of Groundwater – Water Negligible Negligible Negligible Local on the inclusion of alternative water supplies into the developments. However, based on the importance of the water groundwater Quality River Thames – Water supply resources, the cumulative significance is assessed as minor adverse. Minor Adverse Negligible Negligible Local Supply 13.261 Similarly, the cumulative development schemes are likely to increase wastewater generation. However, this should be Water Supply Groundwater – Water Minor Adverse Negligible Negligible District mitigated through the predicted reduction in surface water flows to the existing TWUL combined sewers. The demand Supply TWUL Water Supply Negligible Negligible Negligible Local cumulative impact is negligible.

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References Ref. 13-36 EA, ‘Pollution Prevention Guidelines 02: Above Ground Oil Storage Tanks’. Ref. 13-37 EA, ‘Pollution Prevention Guidance 03: Use and Design of Oil Separators in Surface Water Drainage Systems’. Ref. 13-1 Commission of the European Communities, (2000); Directive 2000/60/EC ‘The Water Framework Directive’. Ref. 13-38 EA, ‘Pollution Prevention Guidelines 05: Works in, near or liable to affect watercourses’. Ref. 13-2 Her Majesty’s Stationery Office (HMSO), (2003); ‘The Water Resources (Water Framework Directive) (England and Ref. 13-39 EA, ‘Pollution Prevention Guidelines 06: Working at construction or demolition Sites’. Wales) Regulations’. Ref. 13-40 EA, ‘Pollution Prevention Guidelines 07: Refuelling Facilities’. Ref. 13-3 HMSO, (1991); ‘The Water Resources Act’. Ref. 13-41 EA, ‘Pollution Prevention Guidelines 21: Pollution Incident Response Planning’. Ref. 13-4 HMSO, (2003); ‘The Water Act’. Ref. 13-42 The Highways Agency (2009); Design Manual for Roads and Bridges Volume 11, Section 3, part 10. Road Ref. 13-5 HMSO, (1995); ‘The Environment Act’. Drainage and the Water Environment HD45/09 Ref. 13-6 HMSO, (1990); ‘Environment Protection Act’ (c.43). Ref. 13-43 EA, (2009); ‘River Basin Management Plan – Thames River Basin District’. Including Annex A Ref. 13-7 HMSO, (1999); The Anti-Pollution Works Regulations. Ref. 13-44 Lost Rivers of London. https://londonbygaslight.wordpress.com/category/rivers/londons-lost-rivers/ Ref. 13-8 HMSO, (2001); The Control of Pollution (Oil Storage) (England) Regulations. Ref. 13-45 GLA, EA, NE, FC, (2011) London State of Environment Report 2011 Ref. 13-9 HMSO, (1998); ‘The Groundwater Regulations’. Ref. 13-46 River Thames Data and Trends on Water Quality Ref. 13-10 European Commission, (2006); Directive 2006/118/EC, on the protection of groundwater against pollution and http://www.environment-agency.gov.uk/research/library/publications/41015.aspx deterioration, PE-CONS 3639/1/100 Rev 1 Luxembourg. Ref. 13-47 Thames Water Thames Tideway Tunnel Ref. 13-11 HMSO, (2009); ‘The Environmental Damage Regulations’. http://www.thamestidewaytunnel.co.uk/ Ref. 13-12 HMSO, (2009); ‘The Water Resources (Amendment) (England and Wales) Regulations’. Ref. 13-48 BGS Map Sheet 270 ‘South London’, scale 1:50:000, Solid and Drift Edition Ref. 13-13 HMSO, (2010); ‘The Environmental Permitting (England and Wales) Regulations’. Ref. 13-49 EA, (2003), London Abstraction licensing strategy Ref. 13-14 HMSO, (2000); ‘The Water Supply (Water Quality) Regulations 2000’. Ref. 13-50 The Environment Agency’s consultation on ‘Identifying Areas of Water Stress for the UK’ Ref. 13-15 HMSO, (2010); ‘The Flood and Water Management Act’. Ref. 13-51 London Assembly, (2003); London’s Water Supply Ref. 13-16 Department for Environment, Food and Rural Affairs, (December 2011); Draft – ‘National Build Standards for the Ref. 13-52 EA, (2011); London Borough of Southwark Environmental Fact Sheet design and construction of new gravity foul sewers and lateral drains’. Ref. 13-53 Thames Water Utilities Ltd, (2013); ‘Final Draft Water Management Plan’. Ref. 13-17 DEFRA, (December 2011); Draft - ‘National Standards for Sustainable Urban Drainage Systems’. Ref. 13-54 WRAP, (December 2012) Auditing of water use on construction sites -Phase I & Phase II Ref. 13-18 Department for Communities and Local Government (DCLG), (2012); ‘National Planning Policy Framework’. Ref. 13-55 CIRIA C657, 2006, Water Key Performance Indicators and Benchmarks for Offices and Hotels Ref. 13-19 DCLG (2010) Planning Policy Statement 25 (PPS25); Ref. 13-56 BSRIA, (2011): Rule of Thumb Guidelines for Building Services. BG9/2011 Ref. 13-20 Office of the Deputy Prime Minister (ODPM) (2004); Planning Policy Statement 23: Planning and Pollution Control Ref. 13-21 DCLG, (2012), ‘Technical Guidance to the National Planning Policy Framework’. Ref. 13-22 Greater London Authority, (2011); ‘The London Plan’ (and GLA, (2013); Revised Early Minor Alterations to the London Plan). Ref. 13-23 Greater London Authority(GLA), (May 2006); ‘Supplementary Planning Guidance – Sustainable Design and Construction’. Ref. 13-24 GLA, (2011); ‘The Mayor’s Water Strategy’. Ref. 13-25 London Borough of Southwark (LBS), (2011), Core Strategy. Ref. 13-26 LBS, (2007), Southwark Plan. Ref. 13-27 LBS, (2010). Draft London Borough of Southwark Bankside, Borough and London Bridge Supplementary Planning Document (SPD) Ref. 13-28 LBS, (2012). Elephant and Castle Supplementary Planning Document (SPD) and Opportunity Area Planning Framework (OAPF) Ref. 13-29 LBS (2014) Blackfriars Road Supplementary Planning Document (SPD) Ref. 13-30 GLA, (2009); London Regional Flood Risk Appraisal. Ref. 13-31 Environment Agency (EA), Thames Estuary 2100 Plan (TE2100). Ref. 13-32 URS/Scott Wilson, (2011) Preliminary Flood Risk Assessment Ref. 13-33 Jacobs, (2008). Strategic Flood Risk Assessment Ref. 13-34 URS/Scott Wilson, (2011). Surface Water Management Plan Ref. 13-35 EA; ‘Pollution Prevention Guidelines 01: General Guide to the Prevention of Pollution’ http://www.environment- agency.gov.uk/

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