A27 Arundel Bypass Environmental Assessment Report

Chapter 13 – Road Drainage and Water Environment

30 August 2019

Environmental Assessment Report Chapter 13 - Road Drainage and the Water Environment A27 Arundel Bypass – PCF Stage 2 Further Consultation

TABLE OF CONTENTS

13 ROAD DRAINAGE AND THE WATER ENVIRONMENT ...... 13-1

13.1 Introduction ...... 13-1 13.2 Legislative and policy framework ...... 13-2 13.3 Assessment methodology...... 13-9 13.4 Assessment assumptions and limitations ...... 13-19 13.5 Study Area ...... 13-23 13.6 Baseline conditions ...... 13-23 13.7 Potential impacts ...... 13-40 13.8 Design, mitigation and enhancement measures ...... 13-43 13.9 Assessment of likely significant effects ...... 13-49 13.10 Summary ...... 13-77

LIST OF TABLES Table 13-1 – Legislation, policy and guidance applicable to the road drainage and water environment assessment 13-3 Table 13-2 - Estimating the importance of water environment attributes taken from Table A4.1 of the DMRB HD 45/9 13-13 Table 13-3 - Estimating the magnitude of an impact on an attribute taken from Table A4.3 of the DMRB HD 45/9 13-15 Table 13-4 - Estimating the magnitude of an impact on an attribute taken from Table A4.5 of the DMRB HD 45/9 13-18 Table 13-5 - Estimating the significance of potential effects taken from Table A4.5 of the DMRB HD 45/91 13-19 Table 13-6 - Assessment assumptions and limitations for road drainage and water environment 13-20 Table 13-7 - Summary of baseline conditions by option for road drainage and water environment assessment 13-34 Table 13-8 - Sensitivity of identified receptors for road drainage and water environment 13-39 Table 13-9 - Construction phase potential impacts for road drainage and water environment 13-40 Table 13-10 - Operational phase potential impacts for road drainage and water environment 13-42 Table 13-11 - Road drainage and water environment construction phase likely significant effects 13-78 Table 13-12 - Road drainage and water environment operational phase likely significant effects 13-79

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Environmental Assessment Report Chapter 13 - Road Drainage and the Water Environment A27 Arundel Bypass – PCF Stage 2 Further Consultation

LIST OF FIGURES Figure 13-1 – Water Constraints Map All Variants

Figure 13-2 – Unnamed Ordinary Watercourses

Figure 13-3 – Named Ordinary Watercourses

LIST OF APPENDICES Appendix 13-1 – Environment Agency Baseline Model approval

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Environmental Assessment Report Chapter 13 - Road Drainage and the Water Environment A27 Arundel Bypass – PCF Stage 2 Further Consultation

Acronyms

ACRONYMS DEFINITION BGS British Geological Survey CEMP Construction Environmental Management Plan CIRIA Construction Industry Research Information Association DMRB Design Manual for Roads and Bridges HAWRAT Highways Agency Water Risk Assessment Tool HMWB Heavily Modified Waterbody ICM Integrated Catchment Model LTRAS Lower Tidal River Arun Strategy LWS Local Wildlife Site NGR National Grid Reference OS Ordonnance Survey PCF Project Control Framework PPG Pollution Prevention Guidelines SFRA Strategic Flood Risk Assessment SuDS Sustainable Drainage Systems

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Environmental Assessment Report Chapter 13 - Road Drainage and the Water Environment A27 Arundel Bypass – PCF Stage 2 Further Consultation

Glossary

TERM DEFINITION

Aquifer An aquifer is an underground layer of water-bearing permeable rock, rock fractures or unconsolidated materials (gravel, sand, or silt). Aquifers are sub- categorised as Principle, Secondary and Unproductive reflecting their importance as a resource (drinking water supply) and role in supporting surface water flows and wetland ecosystems. Basin Similar to a catchment, reflects the topographic area contributing to recharge of a watercourse. Bedrock The solid rock in the ground which supports all the soil above it. British Geological Provider of objective and authoritative geoscientific Survey (BGS) data, information and knowledge for the UK. Catchment The area contributing flow or runoff to a particular point on a watercourse. Climate change Long-term variations in global temperature and weather patterns both natural and as a result of human activity, primarily greenhouse gas emissions. Construction and Document setting out methods to avoid, minimise and Environmental mitigate environmental impacts on the environment Management Plan and surrounding area and the protocols to be followed (CEMP) in implementing these measures in accordance with environmental commitments during construction. Culvert Covered channel or pipe that forms a watercourse below ground level. Design Manual for The DMRB is a suite of documents which contains Roads and requirements and advice relating to works on Bridges (DMRB) motorway and all-purpose trunk roads for which one of the Overseeing Organisations is highway or road authority. Dewatering The removal of water from an aquifer via pumping (active) or gravity (passive) drainage. Environment Government Agency charged with the protection of Agency the environment Flood defence Flood defence infrastructure, such as flood walls and embankments, intended to protect an area against flooding, to a specified standard of protection. Flood event A flooding incident characterised by its level or flow

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Environmental Assessment Report Chapter 13 - Road Drainage and the Water Environment A27 Arundel Bypass – PCF Stage 2 Further Consultation

TERM DEFINITION

hydrograph Flood risk A study to assess the risk of a site or area flooding, assessment and to assess the impact that any changes or development in the site or area will have on flood risk. Floodplain Area of land that borders a watercourse, an estuary or the sea, over which water flows in time of flood, or would flow but for the presence of flood defences where they exist. Flood Zone 1 Areas deemed be at less than 0.1% chance of flooding in any year, also known as having a 1 in 1000-year chance. Flood Zone 2 Areas deemed to have between 0.1% – 1% chance of flooding from rivers in any year (between 1 in 1000 and 1 in 100 chance) or between 0.1% – 0.5% chance of flooding from the sea in any year (between 1:1000 and 1:200 chance). Flood Zone 3 Areas within flood zone 3 have been shown to be at a 1% or greater probability of flooding from rivers or 0.5% or greater probability of flooding from the sea. Flow Path The subsurface course a water molecule or solute (groundwater) would follow in a given groundwater velocity field. Fluvial Of or found in a river Freeboard The distance from the water level to the top of the channel's sides. Geo-morphology The study of the physical features of the surface of the earth and their relation to its geological structures Groundwater Water in the ground, usually referring to water in the saturated zone below the water table. (Ground) Water A distinct volume of groundwater within an aquifer or body system of aquifers, which is hydraulically isolated from nearby groundwater bodies. Groundwater Flooding caused by groundwater escaping from the flooding ground when the water table rises to or above ground level. Groundwater level Measurement of water level (head elevation) within an monitoring aquifer unit. Used to determine groundwater level variations but carried out over a large area to determine groundwater flow gradients. Can be measured within both confined (covered with an impermeable layer that leads to higher head pressures within aquifer) and unconfined aquifer

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Environmental Assessment Report Chapter 13 - Road Drainage and the Water Environment A27 Arundel Bypass – PCF Stage 2 Further Consultation

TERM DEFINITION

(water level below unsaturated zone within soil profile). Hydraulic Model A mathematical model of a water/sewer/storm system and is used to analyse the system's hydraulic behaviour. Infiltration The process by which water on the ground surface enters the soil (related to permeability). Internal Drainage A public body that manage water levels in an area, Board (IDB) known as an internal drainage district, where there is a special need for drainage. Main River A watercourse designated on a statutory map of Main rivers, maintained by the Environment Agency. Natural Flood The incorporation of natural processes, used within Management fluvial and coastal systems, to reduce the risk of flooding and coastal erosion. Ordinary A watercourse which is not a private drain and is not watercourse designated a Main river. Ordinary Permitting system used by Local Authorities to Watercourse manage flood risk caused by alterations to Consent watercourse profiles Ordnance Survey The OS is the national mapping agency for Great (OS) Britain and produces large scale maps. Outfall Place where a river, drain, or sewer empties into the sea, a river, or a lake. Overburden The material (generally comprising both rock and soil) that lies above a specific geological unit or aquifer of interest. Overland flow Flooding caused by surface water runoff when rainfall flooding intensity exceeds the infiltration capacity of the ground, or when the soil is so saturated that it cannot accept any more water. Over pumping Temporary over pumping systems are used during construction to minimise alterations to river/stream baseflow contribution. Permeability A measure of the ability of a porous material (often, a rock or an unconsolidated material) to allow fluids to pass through it. Given in units of m2. Project Control A joint Department for Transport and Highways Framework (PCF) Agency approach to managing major projects, which comprises: ƒ A standard project lifecycle

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Environmental Assessment Report Chapter 13 - Road Drainage and the Water Environment A27 Arundel Bypass – PCF Stage 2 Further Consultation

TERM DEFINITION

ƒ Standard project deliverables ƒ Project control processes

Receptor Any human or environmental aspect that is presently or potentially exposed to, and adversely affected by, the release or migration of contaminants. Recharge Downward movement of surface water to groundwater. Recharge is the primary method through which water enters an aquifer. Recharge occurs both naturally (through the water cycle) and through anthropogenic processes (i.e., "artificial groundwater recharge"), where rainwater and or reclaimed water is routed to the subsurface. Riparian In Ecology - relating to wetlands adjacent to rivers and streams. In Law - relating to or situated on the banks of a river. Runoff Water flow over the ground surface to the drainage system. This occurs if the ground is impermeable or saturated, or if rainfall is particularly intense. Standard of The estimated probability of a design event occurring, protection or being exceeded, in any year. Thus, it is the estimated probability of an event occurring which is more severe than those against which an area is protected by flood defences Strategic flood A study to examine flood risk issues on a sub-regional risk scale, typically for a river catchment or local authority assessment area during the preparation of a development plan. Source Protection Defined areas showing he risk of contamination to Zone (SPZ) selected groundwater sources used for public drinking water supply, from any activities that might cause pollution in the area. Surface Water Surface water is water on the surface of continents such as in a river, lake or wetland. Sustainable A sequence of management practices and control drainage structures, often referred to as SUDS, designed to systems (SUDS) drain surface water in a more sustainable manner. Typically, these techniques are used to attenuate rates of runoff from development sites. Superficial Unconsolidated sediments such as gravel, sand, silt Deposits and clay, often discontinuous patches or larger spreads. Tributary A river or stream flowing into a larger river or lake.

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Environmental Assessment Report Chapter 13 - Road Drainage and the Water Environment A27 Arundel Bypass – PCF Stage 2 Further Consultation

TERM DEFINITION

Phytotoxic Substance, chemical or element poisonous to plants Watercourse Any natural or artificial channel that conveys surface water.

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Environmental Assessment Report Chapter 13 - Road Drainage and the Water Environment A27 Arundel Bypass – PCF Stage 2 Further Consultation

13 Road Drainage and the Water Environment

13.1 Introduction

13.1.1.1 This chapter provides identification of baseline and an assessment of the potential impacts associated with road drainage and the water environment arising from the Scheme. This chapter has been completed in accordance with the DMRB Volume 11, Section 3, Part 10 (HD 45/09). The potential impacts based on professional judgement considered in this chapter are: ƒ Construction phase Increased pollution to the River Arun, the Binsted and Tortington Rife, and other ordinary watercourses within the Study Area from mobilised suspended solids, sediment, spillage of fuels or other harmful substances that may migrate to surface water and groundwater receptors. Impacts to hydro-morphological and ecological quality of watercourses due to works within close proximity of watercourses such as the installation and alteration of culverts, bridges and outfalls as well as realignment of watercourses, including changes associated with sediment deposition. Increased flooding associated with temporary works within areas of fluvial flood storage, works to existing watercourse alignments and culverts. Temporary works could also result in changes in flood conveyance paths, depending on their nature. Dewatering of groundwater bodies due to intrusive works e.g. cuttings, piling, foundations and other excavations. This may cause temporary alteration to groundwater flow paths and may impact upon habitats. Increased groundwater vulnerability by reducing the overall quantity of water in the aquifer and subsequently impact to the quantification status of the designated aquifer. ƒ Operational phase Increased pollution from polluted surface water runoff containing silts and hydrocarbons and phytotoxic metals such as Copper and Zinc that may migrate or be discharged to surface water features or groundwater resources via the proposed highway drainage system. Permanent impacts associated with new structures within or in close proximity to watercourses such as the installation and alteration of Page 13-1 August 2019

Environmental Assessment Report Chapter 13 - Road Drainage and the Water Environment A27 Arundel Bypass – PCF Stage 2 Further Consultation

culverts, bridges and outfalls as well as realignment of watercourses that has the potential to impact the hydro-morphological, chemical and ecological quality of watercourses. Increased flooding resulting from increased rates and volumes of surface water runoff from an increase in impermeable area and/or changes to the existing drainage regime. Increased flood risk to people and property elsewhere as a result of introducing impermeable surfaces within areas identified to be at risk of flooding within the Arun floodplain, thus impacting flood flow conveyance and reducing floodplain storage, and impact to existing flood defences. Where cutting or excavation dewatering is required for the Scheme this could permanently reduce groundwater quantities within the groundwater body during the operational phase. This could impact the quantification status of the designated aquifer. Reduced groundwater recharge due to introduction of new impermeable road surfacing/hardstanding. Alteration of natural groundwater flow paths due to the introduction of intrusive piled structures and foundations. 13.1.1.2 This chapter should be read in conjunction with: ƒ Chapter 8: Biodiversity for further information pertaining to impacts to ecology, including sensitive and/or important aquatic species and possible groundwater dependent ecosystems and a summary of the Habitats Regulations Assessment (HRA). ƒ Chapter 9: Geology and Soils for further information pertaining to the impacts relating to geology, soils and sources of land contamination, both historic and current.

13.2 Legislative and policy framework

13.2.1.1 The broad legislative and policy framework relevant to environmental assessment of the Scheme is set out in Chapter 1: Introduction of this EAR. Table 13-1 summarises the legislation, policy and guidance applicable to Road Drainage and the Water Environment assessment.

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Table 13-1 – Legislation, policy and guidance applicable to the road drainage and water environment assessment Name Summary Directives/Legislation Water The overall objective of the Water Framework Directive Framework is to bring about the effective coordination of water Directive environment policy and regulation across Europe. The 2000/60/EC main aims of this Directive are to ensure that all surface water and groundwater reach ‘good’ status (in terms of ecological and chemical quality and water quantity, as appropriate), promote sustainable water use, reduce pollution and contribute to the mitigation of flood and drought. The Directive also contains provisions for controlling discharges of dangerous substances to surface water and groundwater and includes a ‘List of Priority Substances’. Various substances are listed as either priority substances and priority hazardous substances list I or list II substances. The purpose of the Directive is to eliminate and pollution from list I substances and reduce pollution from the list of priority substances. Groundwater The Groundwater Directive aims to set groundwater Directive quality standards and introduce measures to prevent or 2006/118/EC limit pollution of groundwater, including those listed within the ‘List of Priority Substances’. This Directive has been developed in response to the requirements of Article 17 of the Water Framework Directive, specifically the assessment of chemical status of groundwater and objectives to achieve ‘good’ status. Environmental The Environmental Permitting (England and Wales) Permitting Regulations 2016 largely replaced the Water Resources (England and Act 1991 as the key legislation for water pollution in the Wales) UK. Under the Environmental Permitting Regulations, it Regulations is an offence to cause or knowingly permit a water 2016 discharge activity, including the discharge of polluting materials to freshwater, coastal waters, relevant territorial waters or groundwater, unless complying with an exemption or an environmental permit. The Environment Agency sets conditions which may control volumes and concentrations of particular substances or impose broader controls on the nature of the effluent, taking into account any relevant water quality standards from the relevant EU Directives.

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Name Summary The Regulations also assist in the management of flood risk and, as of 6 April 2016, any activity which has the potential to impact on a main river (which typically means any works in the vicinity of a main river, flood defence structure and sea defence, or in a floodplain) will require a Flood Risk Activities Permit (previously referred to as Flood Defence Consent) to be granted by the Environment Agency and specifies the appropriate conditions to ensure works do not increase flood risk or damage flood defences. Land Drainage The Land Drainage Act 1991 sets out rights and Act 1991 responsibilities for all parties in relation to land drainage, including responsibilities for maintenance and works in the vicinity of ordinary watercourses. The Act requires that an ordinary watercourse be maintained by its owner in such a condition that free flow of water is not impeded. The Act also states that any works in the vicinity of ordinary watercourses that have the potential to obstruct or alter the flow of water will require appropriate consent from the Local Authority or Internal Drainage Board. This is usually obtained as Land Drainage Consent or Ordinary Watercourse Consent. Flood and The Floods and Water Management Act 2010 was Water prepared following the Pitt Review in 2007. The Act Management created the role of the Lead Local Flood Authority Act 2010 (typically the unitary authority or county council, as applicable) to take responsibility for leading the co- ordination of local flood risk management in their areas. The Act prescribes the role of the Lead Local Flood Authority in the review and approval of surface water management systems. This has led to a recent change that requires the Lead Local Flood Authority to review and comment on significant development in regard to the recently published national standards for Sustainable Drainage Systems (Non-statutory technical standards for sustainable drainage systems, Department for Environment, Food and Rural Affairs, March 2015). The Water The Water Abstraction and Impounding (Exemptions) Abstraction Regulations 2017 provide for exemptions from the and restriction on abstraction and the restriction on Impounding impounding works in the Water Resources Act 1991. (Exemptions) Regulations 2017

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Environmental Assessment Report Chapter 13 - Road Drainage and the Water Environment A27 Arundel Bypass – PCF Stage 2 Further Consultation

Name Summary Environment The Environmental Act 1995 provides for the Act 1995 establishment of the Environment Agency and to provide for the transfer of functions, property, rights and liabilities to this corporate body. The Act also makes provision with respect to contaminated land and abandoned mines, and for the control of pollution, the conservation of natural resources and the conservation or enhancement of the environment National Policy National The National Networks National Policy Statement (NN Policy NPS) at paragraphs 5.219 recognises that infrastructure Statement for development can have adverse effects on the water National environment. Paragraph 5.220 of the NN NPS states Networks that the “Government’s planning policies make clear (NN NPS)1 that the planning system should contribute to and enhance the natural and local environment by, amongst other things, preventing both new and existing development from contributing to, or being put at unacceptable risk from, or being adversely affected by, water pollution”. The Government has issued guidance on water supply, wastewater and water quality considerations in the planning system. The NN NPS at paragraph 5.222 also states that for “those projects that are improvements to the existing infrastructure, such as road widening, opportunities should be taken, where feasible, to improve upon the quality of existing discharges where these are identified and shown to contribute towards Water Framework Directive commitments”. The NN NPS advises applicants for projects that may be affected by or may add to flood risk to seek sufficiently early pre-application discussions with the Environment Agency, and where relevant other flood risk management bodies.

1 Department of Transport, National Policy Statement for National Networks (NN NPS) December 2014. Available at: https://assets.publishing.service.gov.uk/government/uploads/system/uploads/attachment_data/file/387223/n psnn-web.pdf [Accessed in August 2019].

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Name Summary National The National Planning Policy Framework (NPPF) at Planning paragraph 155 requires that inappropriate Policy developments in areas of flood risk should be avoided Framework by directing development away from high risk areas. 2019 (NPPF)2 Where development is necessary, projects should be made safe from flooding without increasing flood risk elsewhere. The sequential test is used as the principal step to identify preferred locations (NPPF paragraph 162). If development is deemed necessary in a flood zone, an exception test can be conducted through an appraisal of risk, and appropriate reduction and management measures can be implemented.

All applications (NPPF paragraph 164) in the following areas should be accompanied by a Flood Risk Assessment – all projects in Flood Zones 2 and 3 (medium and high probability of river and tidal flooding); projects of 1 hectare or greater in Flood Zone 1 (low probability of river and tidal flooding); projects which may be at significant risk from other sources of flooding (local watercourses, surface water, groundwater or reservoirs); or where the Environment Agency has notified the local planning authority that there are critical drainage problems. Local Policy Arun District The Arun District Local Plan 2011-2031 replaced the Local Plan 2003 Arun District Local Plan in 2018. Relevant Local 2011-20313 Plan policies include: ƒ Policy W SP1 Water ƒ Policy W DM1 Water Supply and Quality ƒ Policy W DM2 Flood Risk ƒ Policy W DM3 Sustainable Urban Drainage Systems.

2 Ministry of Housing, Communities and Local Government (2019). National Planning Policy Framework (NPPF). Available at: https://assets.publishing.service.gov.uk/government/uploads/system/uploads/attachment_data/file/779764/N PPF_Feb_2019_web.pdf [Accessed in August 2019]. 3 Arun District Council, Arun District Council Local Plan 2011-2031 (2018) https://www.arun.gov.uk/download.cfm?doc=docm93jijm4n12549.pdf&ver=12567 [Accessed July 2019]

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Environmental Assessment Report Chapter 13 - Road Drainage and the Water Environment A27 Arundel Bypass – PCF Stage 2 Further Consultation

Name Summary South Downs The South Downs National Park Authority submitted its National Park Local Plan in April 2018. The final Inspectors Report Local Plan- concluded that the Local Plan is sound, subject to a 2014–20334 number of main modifications. The National Park Authority considered and adopted the Local Plan together with the Inspector’s recommended main modifications on 2 July 2019. The adopted Local Plan replaces all existing planning policies across the National Park. Relevant policies include: ƒ Core Policy SD1 Sustainable Development ƒ Core Policy SD2 Ecosystem Services ƒ Strategic Policy SD17 Protection of the Water Environment ƒ Strategic Policy SD49 Flood Risk Management ƒ Development Management SD50: Sustainable Drainage Systems.

South Downs The Position Statement sets out the Authority’s position National Park in the case of any future transport infrastructure Authority projects. In considering proposals the SDNPA will be Position “mindful that the current state of congestion on the A27 Statement on can create secondary impacts within the National Park” A27 route (paragraph 6 of the Position Statement). Where corridor5 feasible, the primary impacts of any new schemes must be objectively assessed alongside potential secondary impacts. In assessing the specific impacts of any detailed options, the SDNPA (paragraph 7 of the Position Statement) will ask Highways England to use the framework of the seven Special Qualities (SQ) of the National Park. South Downs The South Downs National Park Strategic Flood Risk National Park Assessment (SFRA) supports and informs the Local Level 1 Plan, including the site allocations, by assessing the Update and impact that land use changes and development in the Level 2 area will have on flood risk. The SFRA provides the Strategic basis for applying the Sequential Test to development Flood Risk sites, thereby directing development away from areas at highest risk.

4 South Downs National Park Authority, South Downs National Park Local Plan, July 2019 https://www.southdowns.gov.uk/planning/south-downs-local-plan_2019/local-plan/ [Accessed July 2019] 5 South Downs National Park Authority 2019. South Downs National Park Authority Position Statement on A27 corridor. Available at: https://www.southdowns.gov.uk/national-park-authority/our-work/position-statements/ [Accessed July 2019]

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Environmental Assessment Report Chapter 13 - Road Drainage and the Water Environment A27 Arundel Bypass – PCF Stage 2 Further Consultation

Name Summary Assessment 20176 Guidance South East The South-East River Basin Management Plan extends River Basin from Kent to Hampshire and covers over 10,000 km2. Management Within this River Basin Management Plan there are nine Plan management catchments which include the Arun and (December Western Streams catchment. The main issues are 2015) physical modifications, pollutions from waste water, pollutions from towns and transport, changes to natural flow and water level, negative effects of invasive non- native species, and pollution from rural areas. The priority issues specifically within the Arun and Western Streams catchment are fish passage, diffuse pollution and invasive non-native species. In addition, actions will be developed to improve estuarine and coastal waters. Design Design Manual Roads Bridges Guidance (DMRB) Manual for includes all current standards, advice notes and other Roads and documents relating to the design, assessment and Bridges7 operation of trunk roads, including motorways HD 45/09 which sets out the recommended approach for evaluating impacts on the water environment. Environment The Environment Agency’s approach to groundwater Agency’s protection 2018 contains non-statutory position approach to statements which provide information about the groundwater Environment Agency’s approach to managing and protection protecting groundwater and, adopts a risk-based 20188 approach where legislation allows.

6 South Downs National Park Level 1 Update and Level 2 Strategic Flood Risk Assessment, September 2017 [Accessed July 2019] 7 Highways Agency, HD 45/09 Road Drainage and the Water Environment, Design Manual for Roads and Bridges (November 2009) 8 Environment Agency, The Environment Agency’s approach to groundwater protection. Version 1.2 (Published February 2018) Page 13-8 August 2019

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Name Summary The The Construction Industry Research and Information Construction Association provides guidance on sustainable drainage Industry systems, pollution control and groundwater control as Research and part of temporary works for construction projects. Information Association (CIRIA) notably C532 (Control of water pollution from construction sites), C648 (Control of water pollution from linear construction projects), C750 (Groundwater control, design and practice) and C753 (The SuDS Manual)9 13.3 Assessment methodology 13.3.1 Overview of assessment methodology

13.3.1.1 The road drainage and water environment assessment has been prepared in accordance with the DMRB Volume 11, Section 3, Part 10 Road Drainage and the Water Environment (HD 45/09) 10. 13.3.1.2 The DMRB HD 45/09 promotes the following approach: ƒ Estimation of the importance of the receptor ƒ Estimation of the magnitude of the impact ƒ Assessment of the significance of the impact based on the importance of the receptor and magnitude of the impact.

9 The Construction Industry Research and Information Association (CIRIA). CIRIA C532 Control of water pollution form construction sites. Guidance for consultants and contractors (2001); CIRIA C648 Control of water pollution from linear construction projects. Technical Guidance. (May2006); CIRIA C750 Groundwater control: design and practice (April 2006); CIRIA C753 The SuDS Manual (2015). 10 Highways Agency, HD 45/09 Road Drainage and the Water Environment, Design Manual for Roads and Bridges (November 2009) Page 13-9 August 2019

Environmental Assessment Report Chapter 13 - Road Drainage and the Water Environment A27 Arundel Bypass – PCF Stage 2 Further Consultation

13.3.1.3 The value and sensitivity of a potential receptor (and therefore its importance) is considered in terms of indicators such as quality, scale, rarity and substitutability. The criteria in Table A4.3 of DMRB HD 45/09 have been used to estimate the importance of the relevant road drainage and water environment attributes in the Study Area (as described in Section 13.5), provided in Table 13-2. 13.3.1.4 The criteria for assessing the magnitude of a potential effect are taken from Table A4.4 of DMRB HD 45/09, provided in Table 13-3. 13.3.1.5 The overall significance of potential effects considers both the magnitude of the impact and the importance of the receptor, provided in Table 13-4. 13.3.1.6 Mitigation measures incorporated into the design and considered standard good practice have been considered prior to undertaking the assessment of effects. Any residual effects following these measures have been identified and the need for further mitigation is outlined. Mitigation measures will be considered further during Detailed Design of the preferred option. 13.3.1.7 The assessment of potential effects on water quality, hydro-morphology, flood risk and water and groundwater conveyance is a qualitative assessment at this PCF Stage 2 (Option Selection). Hydraulic model developed for the Lower Arun 13.3.1.8 InfoWorks Integrated Catchment Model of the Lower River Arun including the Binsted and Tortington Rife was developed by WSP following a review of the Lower Tidal River Arun Strategy (LTRAS) Infoworks RS Model (2010) in June 2017. It was agreed with the Environment Agency and Highways England in July 2018 to convert the LTRAS model to an InfoWorks Integrated Catchment Model (ICM) to re-establish the baseline model. The baseline model was then used to test the operational effects of Scheme options to be built within the Arun floodplain. 13.3.1.9 The model extent is defined by the catchment area extending from the coastline (Littlehampton) to the determined upstream extent at Pallingham Weir, approximately 40km from the River Arun estuary. 13.3.1.10 The Environment Agency approved the hydraulic model, hydrology and design flows in May 2018 for use in the assessment of Scheme options. The model has been used to provide an indication of the floodplain compensation required. Initial modelling analysis in relation to the Scheme options is discussed in Section 13.9. 13.3.2 Future baseline

13.3.2.1 The anticipated changes to baseline water environment conditions by the year 2026 (the operational year) due to climate change, policy changes, or future development has been assessed by considering:

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Environmental Assessment Report Chapter 13 - Road Drainage and the Water Environment A27 Arundel Bypass – PCF Stage 2 Further Consultation

ƒ The Water Framework Directive ƒ Environment Agency Climate Change Allowances11 ƒ The Lower Tidal River Arun Flood Risk Management Strategy12. 13.3.2.2 The Scheme falls within the Arun and Western Streams management catchment under the South-East River Basin Management Plan. This management catchment specifically pinpoints fish passage, diffuse pollution and invasive non-native species as areas of concern in relation to the reasons for waterbodies not achieving ‘good’ Water Framework Directive status. The River Arun is designated as a Heavily Modified Waterbody (HMWB), with its current ecological quality assessed to be ‘moderate’ and chemical quality assessed to be ‘good’ (Cycle 2, 2016). 13.3.2.3 The water quality of the Chichester Chalk aquifer has been assessed against the objectives of the Water Framework Directive and the results show that its current quantitative status and chemical status is assessed to be ‘poor’ with no change to its chemical status expected by 2021 but with improvement to 'good' chemical status by 2027. 13.3.2.4 The water quality of the Lambeth Group aquifer to the south and west of Arundel has been assessed against the objectives of the Water Framework Directive. Cycle 2 results show that its current quantitative status is ‘poor’ with a target for improvement to ‘good’ status by 2021. Its current chemical status is already 'good’; therefore, no change is predicted. 13.3.2.5 The Scheme is located within the South-East River Basin District. In this region it is predicted that by 2115 peak river flows could increase by 35% (central allowance), 45% (higher central allowance) and 105% (upper end allowance).

11 Environment Agency: Flood risk assessments: Climate Change Allowances, https://www.gov.uk/guidance/flood-risk-assessments-climate-change-allowances scheme (2016) [Accessed April 2019] 12 Environment Agency, Lower Tidal River Arun Flood Risk Management Scheme (2012, revised 2015) https://www.gov.uk/government/publications/lower-tidal-river-arun-flood-risk-management-scheme [Accessed April 2019]

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Environmental Assessment Report Chapter 13 - Road Drainage and the Water Environment A27 Arundel Bypass – PCF Stage 2 Further Consultation

13.3.2.6 This may increase the frequency of flood risk to identified receptors and increase the extent of Flood Zones 2 and 3, resulting in a greater proportion of the Study Area at risk of fluvial flooding13. Whilst there is no guidance for the year 2027, the increase is likely to be incremental and therefore some increase in peak river flows may be experienced. The peak rainfall intensity may also increase as a result of climate change, which could potentially increase the risk of surface water flooding to the site. The Environment Agency provides guidance on the central and upper end allowances for all of England. The total potential change anticipated up to 2115 is 20% (central allowance) and 40% (upper end allowance)14. 13.3.2.7 The Lower Tidal River Arun Flood Risk Management Strategy for the management of flood risk over the next 100 years proposes: ƒ Raising of low spots in the defences at the end of their design life in Arundel Town Centre. ƒ Construction of flanking defences to manage flood risk before the defences located downstream fail. 13.3.2.8 The Lower Tidal River Arun Flood Risk Management Strategy also states that downstream of Arundel the existing earth embankments will be maintained for the next 50 years by the Environment Agency. After 50 years the strategy indicates that maintenance would stop, and new inland defences would be built to protect Arundel from flooding. The most significant change in the baseline conditions is likely to be associated with an increase in peak river flows and peak rainfall intensity associated with the potential effects of climate change. The status of the proposed changes to the planned programme of maintenance works change to maintenance operations is unknown. However, there is not likely to be any change by 2027. 13.3.3 Significance criteria

13.3.3.1 The importance of receptors identified in the Study Area has been assigned in accordance with the criteria shown in Table 13-2, and the magnitude of impact has been assigned in accordance with the criteria shown in Table 13- 3.

13 Environment Agency: Flood risk assessments: Climate Change Allowances, https://www.gov.uk/guidance/flood-risk-assessments-climate-change-allowances scheme (2016) [Accessed April 2019] 14 Environment Agency: Flood risk assessments: Climate Change Allowances, https://www.gov.uk/guidance/flood-risk-assessments-climate-change-allowances scheme (2016) [Accessed April 2019] Page 13-12 August 2019

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Table 13-2 - Estimating the importance of water environment attributes taken from Table A4.1 of the DMRB HD 45/915 Value Typical Example (Sensitivity) Descriptors Very High Very high Surface Water: importance ƒ European Commission and rarity, Designated Salmonid/Cyprinid international fishery scale and ƒ very limited Water Framework Directive Class potential for ‘High’ substitution. ƒ Site protected/designated under European Commission or UK habitat legislation (Special Areas of Conservation, Special Protection Area, Site of Special Scientific Interest, Water Protection Zones, Ramsar site, salmonid water)/ Species protected by European Commission legislation Groundwater: ƒ Principal aquifer providing a regionally important resource or supporting site protected under European Commission and UK habitat legislation ƒ Source Protection Zone 1 Flood Risk: ƒ Floodplain or defence protecting more than 100 residential properties from flooding

15 Highways Agency, HD 45/09 Road Drainage and the Water Environment, Design Manual for Roads and Bridges (November 2009) Page 13-13 August 2019

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Value Typical Example (Sensitivity) Descriptors High High Surface Water: importance ƒ Water Framework Directive Class and rarity, ‘Good’ national ƒ Major Cyprinid Fishery scale, and ƒ limited Species protected under potential for European Commission or UK substitution. habitat legislation Groundwater: ƒ Principal aquifer providing locally important resource or supporting river ecosystem ƒ Source Protection Zone 2 Flood Risk: ƒ Floodplain or defence protecting between 1 and 100 residential properties or industrial premises from flooding

Medium High or Surface Water: medium ƒ Water Framework Directive Class importance ‘Moderate’ and rarity, regional Groundwater: scale, limited ƒ Aquifer providing water for potential for agricultural or industrial use with substitution. limited connection to surface water ƒ Source Protection Zone 3 Flood Risk: ƒ Floodplain or defence protecting 10 or fewer industrial properties from flooding

Low Low or Surface Water: medium ƒ Water Framework Directive Class importance ‘Poor’ and rarity, local scale. Groundwater: ƒ Unproductive strata Flood Risk:

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Value Typical Example (Sensitivity) Descriptors ƒ Floodplain with limited constraints and a low probability of flooding of residential and industrial properties

Table 13-3 - Estimating the magnitude of an impact on an attribute taken from Table A4.3 of the DMRB HD 45/9 Magnitude Typical Criteria Example of Impact Descriptors Negligible Results in effect Surface Water: on attribute, but of ƒ No risk identified by insufficient HAWRAT (pass both soluble magnitude to and sediment-bound affect the use or integrity pollutants) ƒ Risk of pollution from spillages <0.5% Groundwater: ƒ No measurable impact upon an aquifer and risk of pollution from spillages <0.5% Flood Risk: ƒ Negligible change in peak flood level (1% annual probability) <+/- 10 mm

Minor Results in some Surface Water: Adverse measurable ƒ Failure of either soluble or change in sediment-bound pollutants in attribute’s quality HAWRAT or vulnerability” ƒ Calculated risk of pollution from spillages >0.5% annually and <1% annually Groundwater:

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Magnitude Typical Criteria Example of Impact Descriptors ƒ Potential low risk of pollution to groundwater from routine runoff – risk score 0.5% annually and <1% annually ƒ Minor effects on groundwater supported wetlands Flood Risk: ƒ Increase in peak flood level (1% annual probability) >10mm.

Moderate Results in effect Surface Water: Adverse on integrity of ƒ Failure of both soluble and attribute, or loss sediment-bound pollutants in of part of attribute HAWRAT but compliance

with Environmental Quality Standard values ƒ Calculated risk of pollution from spillages >1% annually and <2% annually Groundwater: ƒ Partial loss or change to an aquifer ƒ Potential medium risk of pollution to groundwater from routine runoff – risk score 150-250 ƒ Calculated risk of pollution from spillages >1% annually and <2% annually ƒ Partial loss of the integrity of groundwater supported designated wetlands Flood Risk: ƒ Increase in peak flood level (1% annual probability) >50 mm

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Magnitude Typical Criteria Example of Impact Descriptors Major Results in loss of Surface Water: Adverse attribute and / or ƒ Failure of both soluble and quality and sediment-bound pollutants in integrity of the HAWRAT and compliance attribute” failure with Environmental Quality Standard values ƒ Calculated risk of pollution from a spillage >2% annually ƒ Loss or extensive change to a fishery ƒ Loss or extensive change to a designated Nature Conservation Site Groundwater: ƒ Loss of, or extensive change to, an aquifer ƒ Potential high risk of pollution to groundwater from routine runoff – risk score >250 ƒ Calculated risk of pollution from spillages >2% annually ƒ Loss of, or extensive change to, groundwater supported designated wetlands Flood Risk: ƒ Increase in peak flood level (1% annual probability) >100 mm

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13.3.3.2 The Highways England Water Risk Assessment Tool (HAWRAT) and detailed hydraulic modelling have not been applied at this stage as the design of the Scheme is not sufficiently advanced to provide a meaningful quantitative assessment. A predominantly qualitative approach has been adopted that is considered appropriate to PCF Stage 2 (Option Selection), informed by preliminary drainage proposals and hydraulic modelling of the baseline condition. It is recommended that HAWRAT is applied during PCF Stage 3 (Preliminary Design) in addition to detailed hydraulic modelling to inform the Flood Risk Assessment and, if deemed required, geomorphological analysis to inform the Water Framework Directive assessment. 13.3.3.3 The significance of effect is as described as detailed in Table 13-4.

Table 13-4 - Estimating the magnitude of an impact on an attribute taken from Table A4.5 of the DMRB HD 45/916 Significance Typical Descriptors category Very Large These effects represent key actors in the decision-making Adverse process. The effects are generally, but not exclusively, associated with sites or features of international, national or regional importance that are likely to suffer a most damaging impact and loss of resource integrity. However, a major change in a site or feature of local importance may also enter this category. Large These effects are considered to be very important Adverse considerations and are likely to be material in the decision-making process. Moderate These effects may be important but are not likely to be Adverse key decision-making factors. The cumulative effects of such factors may influence decision-making if they lead to an increase in the overall adverse effect on a particular resource or receptor. Slight These effects may be raised as local factors. They are Adverse unlikely to be critical in the decision-making process but are important in enhancing the subsequent design of the project. Neutral No effects or those that are beneath levels of perception, within normal bounds of variation or within the margin of forecasting error.

16 Highways Agency, HD 45/09 Road Drainage and the Water Environment, Design Manual for Roads and Bridges (November 2009) Page 13-18 August 2019

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13.3.3.4 The significance of overall effect is determined by combining the magnitude of impact with the importance of the receptor as presented in Table 13-5.

Table 13-5 - Estimating the significance of potential effects taken from Table A4.5 of the DMRB HD 45/9117 Magnitude of impact (Degree of change)

Negligible Minor Moderate Major Very Moderate/ Large/ Neutral Very Large High Large Very Large Slight/ Moderate/ Large/

e High Neutral

c Moderate Large Very Large n a

t Medium Neutral Slight Moderate Large r o

p Slight/ Low Neutral Neutral Slight m

I Moderate 13.3.3.5 In this chapter, where an effect has been assessed as being of moderate significance or greater, it is considered to be a ‘significant effect’ in Environmental Impact Assessment terms. Where an effect is assessed as being of slight / moderate significance, the worst-case scenario is assumed and it is considered to be significant in Environmental Impact Assessment terms, given that mitigation is still to be formally developed at PCF Stage 3 (Preliminary Design). This is discussed in further detail in Chapter 4: Environmental Assessment Methodology.

13.4 Assessment assumptions and limitations

13.4.1.1 The assumptions and limitations which apply to this assessment are outlined in Table 13-6. For each assumption or limitation an explanation of the possible result of the assumption has been provided as well as a description of any corrective actions that have been taken to adjust for any limitations.

17 Highways Agency, HD 45/09 Road Drainage and the Water Environment, Design Manual for Roads and Bridges (November 2009) Page 13-19 August 2019

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Table 13-6 - Assessment assumptions and limitations for road drainage and water environment Assumption or Result of Assumption Correction for Limitation or Limitation assumption or limitation It is assumed that Changes to the Appropriate checks third party data baseline condition have been undertaken used to form the could give rise to informed by baseline inconstancies and professional assessment is inaccuracies that may judgement. No reliable and alter the assessment inconsistencies have accurate due to the content and required been identified within credibility of source mitigations; however, PCF Stage 2 (Option this is considered Selection). unlikely due to the reputable sources of baseline information used. The widened bridge The level of design is Should the design Option 1V5 and considered to be change this should be Option 1V9 will proportionate to PCF discussed with the require new bridge Stage 2 (Option Environment Agency abutments and is Selection). This will and the assessment assumed to be need to be reviewed updated during PCF along the same during PCF Stage 3 Stage 3 (Preliminary alignment as the (Preliminary Design). Design). existing bridge abutments. The current Not anticipated to At PCF Stage 3 understanding of significantly change the (Preliminary Design) the drainage regime assessment in PCF close consultation with will be confirmed Stage 2 (Option the Environment following on from Selection). Agency and other consultation with Statutory the Environment Environmental Bodies Agency and Lead will be held Local Flood Authority during PCF Stage 3 (Preliminary Design).

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Assumption or Result of Assumption Correction for Limitation or Limitation assumption or limitation The current Not anticipated to Should the design understanding of significantly change the change this should be the Scheme design assessment in PCF discussed with the indicates that the Stage 2 (Option Environment Agency assessment will not Selection). and the assessment consider impacts updated. related to changes in catchment hydrology of the River Arun and scour due to the bridge piers assumed to not be within channel. The aim of the site Not anticipated to This is appropriate to visits have been for significantly change the assessment in PCF site familiarisation assessment in PCF Stage 2 (Option only. No primary Stage 2 (Option Selection). data has been Selection). collected. This chapter has Not anticipated to The mitigation been written based significantly change the measures will be on the assumption assessment in PCF refined during PCF that the proposed Stage 2 (Option Stage 3 (Preliminary mitigation measures Selection). Design). will be adopted. This chapter has Not anticipated to This is proportionate to been written based significantly change the assessment in PCF on the current assessment in PCF Stage 2 (Option design freeze Stage 2 (Option Selection). available which Selection). shows the River Arun crossing on an embankment.

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Assumption or Result of Assumption Correction for Limitation or Limitation assumption or limitation The use of intrusive Potential changes in Throughout the design piled structures for natural groundwater process changes to the the floodplain hydraulics and flow design will be reviewed crossing has not pathways due to by road drainage and been assessed for intrusive piled water environment groundwater structures will not be specialists to seek to impacts considered in detail at avoid adverse impacts PCF Stage 2 (Option to groundwater Selection). This issue receptors including will be common to all water users. Scheme options and is a matter for detailed design work in PCF Stage 3 (Preliminary Design). Attenuation No attenuation Environmental Impact ponds/basins will ponds/basins are Assessment Statement be located on and proposed within Chalk to include assessment founded within Principal Aquifer on specific pond/basin Secondary A aquifer ground material. This locations. These ground materials if will help avoid potential locations will be unproductive strata contamination and determined in PCF locations are not adverse impacts on the Stage 3 (Preliminary suitable for groundwater body. Design). infiltration to ground. British Geological Potential susceptibility The BGS susceptibility Survey to groundwater flooding to groundwater flooding Susceptibility to in the Study Area map to be obtained for Groundwater consideration during Flooding map not PCF Stage 3 consulted for EAR (Preliminary Design). BGS geology maps and borehole logs have been consulted to inform groundwater flood risk. This issue is typically designed out as part of the civil design and drainage strategy.

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13.5 Study Area

13.5.1.1 The Study Area in relation to groundwater features and groundwater abstractions is up to a minimum of 1 kilometre from the furthest extent of the Scheme options. This distance is based on professional judgement of the assessor from experience of similar schemes and current knowledge of the area. 13.5.1.2 A buffer was applied to create the surface water Study Area. This involved creating a minimum of a 1 kilometre buffer from the furthest extent of the Scheme options as illustrated on Figure 13-1. This is considered a conservative approach based on professional judgement and experience of working in the area. 13.5.1.3 This Study Area will be used to assess the potential direct impacts of the Scheme options such as pollutants transported in surface water runoff, pollutants conveyed in drainage systems, pollutants migrating to groundwater features, potential increases in runoff and works within river channels. 13.5.1.4 Potential receptors of high importance and above that are located at a distance greater than 1 kilometre from the Scheme options have been assessed based on whether they are considered to be hydraulically connected to the Study Area. These features may include surface water abstractions, downstream watercourses and main rivers (such as the River Arun). 13.5.1.5 The Study Area for the assessment of flood risk has been defined by the extent by which flood risk may be influenced and the extent of relevant flood zones. This is driven by the need to consider the impact of the Scheme to people and property elsewhere, regardless of their location, although for a scheme such as this it is typical to consider risks up to a distance of 1 kilometre from the Scheme. If the assessment undertaken during PCF Stage 3 (Preliminary Design) indicates an increased risk at a distance further than 1 kilometre from the Scheme, the Study Area would be extended accordingly. Figures supporting this chapter are: ƒ Figure 13-1: showing the extent of the Study Area in relation to the water environment constraints ƒ Figure 13-2: labelled with the network of drains within the Study Area ƒ Figure 13-3: labelled with main rivers and named ordinary watercourses within the Study Area.

13.6 Baseline conditions

13.6.1.1 The baseline conditions described for the Road Drainage and the Water Environment assessment are derived from the following sources:

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ƒ Desk study sources: Arun District Combined Level 1 and Level 2 Strategic Flood Risk Assessment 201618 Arun District Strategic Flood Risk Assessment 200819 British Geological Survey Online Viewer20 Defra Magic online geographical information portal21 Environment Agency main river map22 Environment Agency online catchment data explorer23 Environment Agency online flood map for planning24 Environment Agency risk long term flood risk map (outlining surface water and artificial flooding from reservoirs in this instance)25 Groundsure Report (2015)26 Ordnance Survey (OS) mapping27 Technical Note from the Lower Tidal River Arun Strategy (LTRAS) Atkins, June 201328 ƒ Field survey sources: Study Area walkover (selective relevant areas) undertaken on 22 February 2018 to make field observations. Site visit to Binsted and Tortington Rife undertaken 22 October 2018, 2018 to make field observations. ƒ Additional sources: InfoWorks ICM developed by WSP in 201729

18 Arun District Council, Appendix H Arun District Strategic Flood Risk Assessments (2016) https://www.arun.gov.uk/planning-policy-flood-risk [Accessed April 2019] 19 Arun District Council, Map H Arun District Strategic Flood Risk Assessments (2008) https://www.arun.gov.uk/planning-policy-flood-risk [Accessed April 2019] 20 British Geological Society, Geology of Britain viewer http://mapapps.bgs.ac.uk/geologyofbritain/home.html [Accessed April 2019] 21 Defra, MAGIC Map, http://magic.defra.gov.uk [Accessed April 2019] 22 Environment Agency, Main River Map, [online] available at: https://www.arcgis.com/apps/webappviewer/index.html?id=17cd53dfc524433980cc333726a56386 [Accessed April 2019] 23 Environment Agency, Catchment Explorer [online] available at: https://environment.data.gov.uk/catchment- planning/ [Accessed April 2019] 24 Environment Agency, Flood Map for Planning [online] available at: https://flood-map-for- planning.service.gov.uk [Accessed April 2019] 25 Environment Agency flood map for planning Available at: https://flood-warning- information.service.gov.uk/long-term-flood-risk [Accessed April 2019] 26 GroundSure Insights Ltd. (April 2015). Arundel.- Appendix 9-1 27Ordnance Survey (OS), OS Maps (2019) [online] Available at: https://osmaps.ordnancesurvey.co.uk/ [Accessed February 2018]. 28 Environment Agency, Lower Tidal River Arun flood risk management scheme (2012, revised 2015) https://www.gov.uk/government/publications/lower-tidal-river-arun-flood-risk-management-scheme [Accessed April 2019]. 29 Infoworks Integrated Catchment Model of the Lower Arun Catchment (2017) WSP. Page 13-24 August 2019

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Consultation with the Environment Agency, the Lead Local Flood Authority and other Statutory Environmental Bodies. 13.6.2 Summary of baseline conditions for the Scheme

Main rivers 13.6.2.1 A review of OS mapping indicates that the River Arun, designated as a main river under the jurisdiction of the Environment Agency, flows through the centre of Arundel, flowing in a southerly direction to discharge to the sea approximately 6.5 kilometres downstream of Arundel at Littlehampton. 13.6.2.2 The River Arun is assessed by the Environment Agency against objectives of the Water Framework Directive and is classified as a heavily modified waterbody, with its current ecological quality assessed to be ‘moderate’ and chemical quality assessed to be ‘good’ (cycle 2, 2016). 13.6.2.3 A review of the Environment Agency ‘main river map’30 confirms two further main rivers in the Study Area as shown in Figure 13-3. Tortington Rife is designated a main river at its channel through Spinningwheel Copse at National Grid Reference 498950, 105990. Binsted Rife is designated a main river at Little Danes Wood at National Grid Reference 497800, 106500 before its confluence with the Tortington Rife (498707,104563) as shown in Figure 13-3. Both watercourses discharge into the River Arun just south of the Ship and Anchor Marina Campsite. 13.6.2.4 Tortington Rife and Binsted Rife have not been assessed against the objectives of the Water Framework Directive. Decisions on what constitutes a Water Framework Directive Waterbody is overseen by the Environment Agency. Ordinary watercourses 13.6.2.5 There is a large network of named and unnamed ordinary watercourses within the Study Area as shown in Figure 13-1. The Scheme crosses a number of named ordinary watercourses; these include those: ƒ Located to the east of the River Arun (labels with the prefix EAST_AQ on Figure 13-2) including Warning Camp Ditch, Station Ditch and Brookfield Stream ƒ Immediately west of the River Arun (labels with the prefix WEST_AQ on Figure 13-2) including Tortington Upper Ditch and Spring Ditch

30 Environment Agency, Main River Map, [online] available at: https://www.arcgis.com/apps/webappviewer/index.html?id=17cd53dfc524433980cc333726a56386 [last accessed April 2019] Page 13-25 August 2019

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ƒ Ordinary watercourses to the west of the River Arun which are tributaries of the Tortington Rife (labels with the prefix TORT_AQ in Figure 13-2) flowing through Binsted Wood and from the South Downs National Park. 13.6.2.6 The Environment Agency in this region acts as the Internal Drainage Board and therefore holds jurisdiction over the Internal Drainage Board designated watercourses within the Study Area as shown in Figure 13-2. Consultation with the Environment Agency confirms that the Internal Drainage Board watercourses broadly aligns with the named ordinary watercourses within Flood Zone 3 as shown in Figure 13-2. 13.6.2.7 Ordinary watercourses are within the jurisdiction of West Sussex County Council as Lead Local Flood Authority under Land Drainage Act 1991. The West Sussex County Council has confirmed that Arun District Council acts on behalf of the West Sussex County Council regarding proposed work in or adjacent to ordinary watercourses. 13.6.2.8 Water quality within the ordinary watercourses within the Study Area is not monitored against the objectives of the Water Framework Directive. Decisions on what constitutes a Water Framework Directive Waterbody is overseen by the Environment Agency. The ecological value of the ordinary watercourses has been assessed as part of Chapter 8: Biodiversity. Other surface water features 13.6.2.9 The Arundel Wetland Centre is located north of Ford Road Roundabout at National Grid Reference 502200, 107800. The wetland centre is thought to be predominantly fed by the underlying chalk important to the local area acting as both a nature reserve providing habitat to local wildlife as well as an area of recreational amenity. This will be confirmed during PCF Stage 3 (Preliminary Design). 13.6.2.10 The ponds that have been assessed for ecological significance are discussed in Chapter 8: Biodiversity. Surface water abstractions and discharge points 13.6.2.11 A Groundsure report (2015)31 identified several licensed surface water abstractions within the Study Area, from Station Ditch, Brookfield Stream and other unnamed watercourses. Abstractions from these surface waterbodies were reported to be used for agricultural, aquaculture, irrigation or industrial purposes.

31 GroundSure Insights Ltd. (April 2015). Arundel.- Appendix 9-1

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13.6.2.12 The Groundsure report (2015)32 identified 47 active discharge points. The discharge points include discharges of road drainage to surface water features, including the River Arun. Groundwater features 13.6.2.13 British Geological Survey mapping shows that the Scheme options are founded upon London Clay Formation, Lambeth Group (clay, silt and sand), Spetisbury Chalk Member, Tarrant Chalk Member and Lewes Nodular Chalk bedrock geology. These are in part overlain by a mixture of superficial deposits which include Head Deposits, River Terrace Deposits, Raised Beach Deposits, Raised Storm Beach Deposits, Raised Marine Deposits and Alluvium. 13.6.2.14 The Lewes Nodular Chalk, Tarrant Chalk Member and Spetisbury Chalk Member (White Chalk Subgroup) are classified by the Environment Agency as a Principal Aquifer, described as layers of rock or drift deposits that have high intergranular or fracture permeability, meaning they usually provide a high level of water storage and may support water supply or river base flow on a strategic scale. The Chalk at this location is overlain by approximately 10-30m of alluvium (clay), as per British Geological Survey borehole logs TQ00NW5 and TQ00NW12633 respectively. 13.6.2.15 The Lambeth Group is classified by the Environment Agency as a Secondary A Aquifer, described as permeable layers capable of supporting water supplies at a local rather than a strategic scale, and in some cases forming an important source of base flow to rivers. The Head Deposits, River Terrace Deposits, Raised Beach Deposits, Raised Storm Beach Deposits, Raised Marine Deposits and Alluvium are also classified as Secondary A Aquifer by the Environment Agency.

32 GroundSure Insights Ltd. (April 2015). Arundel.- Appendix 9-1 33British geological Survey borehole logs available at http://mapapps2.bgs.ac.uk/geoindex/home.html and http://mapapps.bgs.ac.uk/GeoRecords/GeoRecords.html.

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13.6.2.16 The Head Deposits are also classified as Secondary Undifferentiated aquifer by the Environment Agency. Secondary Undifferentiated aquifers are defined by the Environment Agency as “assigned in cases where it has not been possible to attribute either category A or B to a rock type. In most cases, this means that the layer in question has previously been designated as both minor and non-aquifer in different locations due to the variable characteristics of the rock type”34. Secondary B aquifers are defined by the Environment Agency as “predominantly lower permeability strata which may in part have the ability to store and yield limited amounts of groundwater by virtue of localised features such as fissures, thin permeable horizons and weathering”35. This indicates that groundwater may be present in the Head Deposits, however this groundwater may be finite in extent. 13.6.2.17 The London Clay Formation will be predominantly, if not entirely, unproductive strata due to the low permeability of the London Clay Formation. British Geological Survey borehole SU90NE23, located at British National Grid reference (498120,106400), shows that the Lambeth Group possesses a thickness of approximately 40m, which increases towards the centre of the Study Area. The London Clay Formation is present in the central area only (immediately south of Arundel). The British Geological Survey borehole logs located within the London Clay Formation outcrop do not clearly denote the contact boundaries between the London Clay Formation and the below lying Lambeth Group; this is likely due to the geology boundary being a graded boundary. The London Clay Formation is estimated to locally be 1-15m thick where present. Further detail of the geology underlying the Study Area is provided in Chapter 9: Geology and Soils. 13.6.2.18 Review of Defra Magic Interactive Mapping21 groundwater map indicates that the Inner Zone (Zone 1) of a designated groundwater Source Protection Zone is located approximately 250m to the north of the existing A27. None of the Scheme options pass through this Source Protection Zone. The Source Protection Zone is mapped in Figure 13-1. 13.6.2.19 The Environment Agency’s Water Abstraction Licences map (now no longer available) and Groundsure report (2015)36 identify several licensed groundwater abstractions within the Study Area. Water abstracted from these abstraction points is reported to be used for potable use and for agricultural, aquaculture and irrigation uses. The abstraction licence borehole construction details are unknown; however, these are likely to be founded in the Chalk Group.

34 Environment Agency Aquifer Designation Map Summary http://apps.environment- agency.gov.uk/wiyby/117020.aspx 35 Environment Agency Aquifer Designation Map Summary http://apps.environment- agency.gov.uk/wiyby/117020.aspx 36 GroundSure Insights Ltd. (April 2015). Arundel.- Appendix 9-1 Page 13-28 August 2019

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13.6.2.20 The Groundsure report (2015) identifies six active sewage discharge points to groundwater within 1 kilometre of the Scheme options. 13.6.2.21 Groundwater quality is monitored against the objectives of the Water Framework Directive for the Chalk and Lambeth Group aquifers. 13.6.2.22 The water quality of the Chalk aquifer to the north of Arundel has been assessed by the Environment Agency to have current quantitative status of ‘poor’, and with a chemical status of ‘poor’ with no change expected by 2021 and aiming for improvement to ‘good’ chemical status by 2027. 13.6.2.23 The water quality of the Lambeth Group aquifer to the south and west of Arundel has been assessed by the Environment Agency to have current quantitative status of ‘poor’ and current chemical status of ‘good’, with the objective to achieve ‘good’ quantitative status by 2021. 13.6.3 Flood risk

Historical flooding 13.6.3.1 The Arun District Strategic Flood Risk Assessments undertaken in 200837 and 201638 gives an overview of major historic flood incidents over last 60 years. The Strategic Flood Risk Assessment states that previous recorded flood incidents were due to heavy rainfall, high groundwater levels, high river flows and high tides (but not necessarily in combination) within the Study Area. These were namely to the south of Arundel and in the vicinity of Ford Road roundabout in the centre of Arundel. 13.6.3.2 The source of flooding in the centre of Arundel is identified as fluvial and from sewers following on from high intensity rainfall events in 1974, 2000 and 2012. 13.6.3.3 Email correspondence received on 17 May 2018 from the Environment Agency confirms that there have been no major recorded fluvial events within the Study Area in recent years due to the current defences in place. The Environment Agency stated that the last recorded flood event within the Study Area was recorded to have taken place in 2014. The 2014 event affected most of the River Arun and Rother catchments. Tidal and fluvial flood risk 13.6.3.4 The Environment Agency’s Flood Map for Planning39 indicates that there is fluvial and tidal flood risk associated with the River Arun, Tortington Rife and Binsted Rife.

37 Arun District Council, Map H Arun District Strategic Flood Risk Assessments (2008) https://www.arun.gov.uk/planning-policy-flood-risk [last accessed April 2019] 38 Arun District Council, Appendix H Arun District Strategic Flood Risk Assessments (2016) https://www.arun.gov.uk/planning-policy-flood-risk [last accessed April 2019] 39 Environment Agency, Flood Map for Planning [online] available at: https://flood-map-for- planning.service.gov.uk [last accessed April 2019] Page 13-29 August 2019

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13.6.3.5 Consultation with the Environment Agency confirmed that whilst there is some fluvial interaction the predominant source of flooding is tidal. All options are identified to cross Flood Zones 2 and 3 as presented in Figure 13-1. Definitions of the categories are provided in the glossary. 13.6.3.6 The River Arun is currently defended by raised earth embankments that run along the stretch of the channel to Littlehampton. The Lower Arun Flood Risk Management Strategy40 states that these were originally designed with a standard of protection of a 1 in 50-year flood event but now are thought to have a standard of protection as low as a 1 in 33-year flood due to the degradation of these defences41. 13.6.3.7 The earth embankments will not be maintained in the future as discussed in Section 13.3.2. To address the planned deterioration of the earth embankments, the 2014 Lower Tidal River Arun Flood Risk Management Strategy42 has been prepared by Atkins on behalf of the Environment Agency. It is a long-term plan that highlights the most cost effective and environmentally preferred method to manage the risk of main river flooding over the next 100 years. 13.6.3.8 Arundel is located in the Lower Tidal River Arun Flood Risk Management Strategy Unit SU5 where the preferred option is to “Sustain to a 1 in 75-year standard of protection”. The strategy outlines that there will be maintenance of defences through Arundel to raise low spots. The defences in SU5 will be replaced at the end of their residual life. Flanking defences will be required to manage flood risk in Strategy Unit SU5 before flood defences downstream fail. 13.6.3.9 Strategy Unit SU6 (located downstream of Strategy Unit SU5) is called Arundel to Littlehampton and includes the Binsted Rife and Tortington Rife. The area downstream opens into a broad floodplain and is largely rural and agricultural. Here the existing defences consist of earth embankments with concrete protection. The Environment Agency’s preferred option is to maintain the defences for 50 years. After 50 years the strategy indicates that maintenance would stop, and new inland defences would be built to protect Arundel from flooding.

40 Environment Agency, Lower Tidal River Arun flood risk management scheme (2012, revised 2015) https://www.gov.uk/government/publications/lower-tidal-river-arun-flood-risk-management-scheme [Accessed April 2019]. 41 Environment Agency, Lower Tidal River Arun flood risk management scheme (2012, revised 2015) https://www.gov.uk/government/publications/lower-tidal-river-arun-flood-risk-management-scheme [Accessed April 2019]. 42 Environment Agency, Lower Tidal River Arun flood risk management scheme (2012, revised 2015) https://www.gov.uk/government/publications/lower-tidal-river-arun-flood-risk-management-scheme [Accessed April 2019].

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13.6.3.10 Fluvial and tidal flooding associated with the minor tributaries feeding into Binsted Rife and Tortington Rife is not illustrated on the Environment Agency’s Flood Map for Planning43, most likely due to the small size of the catchments. However, review of the Environment Agency’s Risk of Flooding from Surface Water map44 illustrates the likely flood extent associated with these watercourses. The mapping indicates that flow largely stays within the channels of the two watercourses until the confluence of Binsted Rife and Tortington Rife south west of Decoy reservoirs at National Grid Reference 498700, 104400. 13.6.3.11 A summary of Scheme option specific fluvial flood risk is presented in Table 13-7. Flood risk from surface water 13.6.3.12 Review of the Environment Agency’s Risk of Flooding from Surface Water map45 indicates a risk of flooding from surface water sources within the Study Area as presented in Figure 13.1. Flooding from surface water is typically associated with natural overland flow paths and local depressions in topography, where surface water runoff can accumulate during or following heavy rainfall events. 13.6.3.13 Fluvial flooding from watercourses with catchments less than 3 km2 is not mapped on the Environment Agency’s Flood Map for Planning. However, due to the way in which the Risk of Flooding from Surface Water map is produced, areas identified as being at risk of flooding from surface water often overlap with areas identified as being at risk of fluvial flooding. Thus, in locations where no fluvial flood risk mapping exists, the Environment Agency’s Risk of Flooding from Surface Water map may provide an alternative indication of potential fluvial flood risk associated with smaller catchments. A review of the Environment Agency’s Risk of Flooding from Surface Water map shows such areas along the alignment of a number of small watercourses located to the west of Ford Road, isolated areas along the existing A27 alignment as well as in the centre of Arundel. 13.6.3.14 A summary of Scheme option specific surface water flood risk is presented in Table 13-7.

43 Environment Agency, Flood Map for Planning, https://flood-map-for-planning.service.gov.uk [Accessed February 2019] 44 Environment Agency flood map for planning Available at: https://flood-warning- information.service.gov.uk/long-term-flood-risk [Accessed April 2019] 45 Environment Agency flood map for planning Available at: https://flood-warning- information.service.gov.uk/long-term-flood-risk [Accessed April 2019]

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Flood risk from reservoirs (other sources)

13.6.3.15 The Arundel Strategic Flood Risk Assessment46 states that reservoir flooding is very different from other forms of flooding. However, the potential for this source of flooding on a local scale should be considered during the planning process and the hazards associated with the source of flooding be studied in detail as part of site-specific flood risk assessments. It may happen with little or no warning and evacuation will need to happen immediately. The likelihood of such flooding is very difficult to estimate, but it is less likely than flooding from rivers or surface water. Baseline conditions by Scheme option 13.6.3.16 Table 13-7 summarises the baseline conditions for each Scheme option where it differs from the general description given above with further clarification given below. Fluvial and Tidal Flooding 13.6.3.17 The extent of fluvial and tidal flood risk discussed in Table 13-7 is defined as Flood Zone 3 by the Environment Agency Flood Map for Planning. A review of the Lower River Arun hydraulic model shows an undefended scenario which is supportive of the extents presented by the Environment Agency Flood Map for Planning. 13.6.3.18 The ordinary watercourses are described as minor tributaries in Table 13-7 as they feed into main tributaries of the River Arun (the Binsted and Tortington Rife) as shown in Figure 13-2. Surface water flood risk 13.6.3.19 The assessment of surface water flood risk discussed in Table 13-7 describes the high-risk category which is defined as an area which has a chance of flooding of greater than 3.3% (1 in 30-year flood event). Flood risk from reservoirs (other sources). 13.6.3.20 Arundel Wetland Centre is a source of flooding from reservoir failure as shown in the Environment Agency long term flood risk map47. This will be investigated further during PCF Stage 3 (Preliminary Design). 13.6.3.21 Option 1V5 and Option 1V9 are approximately 0.8 kilometre away at their nearest point from the Arundel Wetland Centre north of Mill Road (NGR 502200, 107800). The maximum flood extents do not reach the existing road, however in the event of a breach, flood waters are shown to be conveyed downstream within the River Arun channel.

47Environment Agency flood map for planning Available at: https://flood-warning- information.service.gov.uk/long-term-flood-risk [Accessed January 2019]

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13.6.3.22 Option 3V1, Option 4/5AV1, Option 4/5AV2 and Option 5BV1 are not within close proximity at their nearest point from the Arundel Wetland Centre north of Mill Road (NGR 502200, 107800). The maximum flood extents do not reach the existing road, however in the event of a breach, flood waters are shown to be conveyed downstream within the River Arun channel. Groundwater abstractions 13.6.3.23 Licensed and unlicensed groundwater abstractions are present within 1 kilometre of the Scheme. Of note, these abstractions are likely founded within the Chalk.

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Table 13-7 - Summary of baseline conditions by option for road drainage and water environment assessment Key Option 1V5 Option 1V9 Option 3V1 Option 4/5AV1 Option 4/5AV2 Option 5BV1 Environmental Value Main River- River Option 1V5 runs from Option 1V9 runs from Option 3V1 runs from Option 4/5AV1 runs from Option 4/5AV2 runs from Option 5BV1 runs from Arun Crossbush Junction across Crossbush Junction across Crossbush Junction through Crossbush Junction through Crossbush Junction through Crossbush Junction through undeveloped land east of undeveloped land east of an area of low-lying an area of low-lying an area of low-lying an area of low-lying the River Arun crossing the River Arun crossing agricultural land crossing agricultural land crossing agricultural land crossing agricultural land crossing cross the River Arun along cross the River Arun along over the River Arun with a over the River Arun with a over the River Arun with a over the River Arun with a the existing bridge location the existing bridge location clear span structure to be clear span structure to be clear span structure to be clear span structure to be at NGR 501400, 106800. at NGR 501400, 106800. constructed south east of constructed south east of constructed south east of constructed south east of The Environment Agency The Environment Agency Tortington Priory at NGR Tortington Priory at NGR Tortington Priory at NGR Tortington Priory at NGR has highlighted that the has highlighted that the 500700,104800. 500700,104800. 500700,104800. 500700,104800. current flood defences current flood defences under the existing A27 road under the existing A27 road bridge appear to be shifting bridge appear to be shifting sideways. sideways. Main River- This Scheme option does This Scheme option does This Scheme option does This Scheme option This Scheme option This Scheme option Binsted Rife* not cross watercourse or not cross watercourse or not cross watercourse or crosses main river (AQ100) crosses main river (AQ100) crosses main river (AQ100) minor tributaries. minor tributaries. minor tributaries. at NGR 497800, 106400 to at NGR 497800, 106400 to immediately west of the join onto the existing A27 at join onto the existing A27 at Avisford Park Golf Club at Yapton Lane through Little Yapton Lane South of Little NGR 498000, 105900. Danes Wood. Danes Wood. Main River- This Scheme option does This Scheme option does This Scheme option This Scheme option This Scheme option This Scheme option Tortington Rife* not cross watercourse or not cross watercourse or crosses seven minor crosses main river (AQ066) crosses main river (AQ60) crosses main river (AQ60) minor tributaries. minor tributaries. tributaries associated with at NGR 498900,105900 at NGR 499500, 105400 at NGR 499500, 105400 the Tortington Rife (AQ056, and 10 minor tributaries and 10 minor tributaries and 10 minor tributaries AQ57B, AQ070, AQ068, associated with the associated with the associated with the AQ073, AQ074, AQ075). Tortington Rife (AQ044, Tortington Rife (AQ044, Tortington Rife (AQ044, AQ046B, AQ047, AQ048A, AQ046B, AQ047, AQ048A, AQ046B, AQ047, AQ048A, AQ045B, AQ052, AQ054, AQ045B, AQ052, AQ054, AQ045B, AQ052, AQ054, AQ57A, AQ065, AQ078). AQ57A, AQ064, AQ067). AQ57A, AQ064, AQ067). Ordinary This Scheme option cross This Scheme option cross This Scheme option This Scheme option This Scheme option This Scheme option Watercourses* an area to the east of the an area to the east of the crosses seven ordinary crosses seven ordinary crosses seven ordinary crosses seven ordinary River Arun where there is a River Arun where there is a watercourses to the east of watercourses to the east of watercourses to the east of watercourses to the east of complex number of ordinary complex number of ordinary the River Arun (AQ015A, the River Arun (AQ015A, the River Arun (AQ015A, the River Arun (AQ015A, watercourses (AQ034, watercourses (AQ034, AQ014A, AQ010, AQ007, AQ014A, AQ010, AQ007, AQ014A, AQ010, AQ007, AQ014A, AQ010, AQ007, AQ030A, AQ030B, AQ024, AQ030A, AQ030B, AQ024, AQ004, AQ001). AQ004, AQ001). AQ004, AQ001) AQ004 and AQ001) AQ028, AQ029, AQ035, AQ028, AQ029, AQ035, To the west of the River To the west of the River To the west of the River To the west of the River AQ092) including Station AQ092) including Station Arun the option crosses 13 Arun the option crosses 11 Arun the option crosses 11 Arun the option crosses 10 Ditch as shown in Figure Ditch as shown in Figure ordinary watercourses ordinary watercourses ordinary watercourses ordinary watercourses 13-2 and Figure 13-3. 13-2 and Figure 13-3. associated with the associated with the associated with the associated with the Tortington Rife (AQ044, Tortington Rife (AQ044, Tortington Rife (AQ044, Tortington Rife (AQ044, AQ046B, AQ047, AQ048, AQ046B, AQ047, AQ048A, AQ046B, AQ047, AQ048A, AQ046B, AQ047, AQ048A, AQ051, AQ052, AQ056, AQ045B, AQ052, AQ054, AQ045B, AQ052, AQ054, AQ045B, AQ052, AQ054, AQ057, AQ068, AQ050, AQ57A, AQ065, AQ066, AQ57A, AQ060, AQ064, AQ57A, AQ060, AQ064), AQ073, AQ074, AQ075) as AQ078) and the Binsted AQ067) and the Binsted the Binsted Rife (AQ100) Rife (AQ100) as shown in Rife (AQ100) as shown in and LID_AQ101 to the

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Key Option 1V5 Option 1V9 Option 3V1 Option 4/5AV1 Option 4/5AV2 Option 5BV1 Environmental Value shown in Figure 13-2 and on Figure 13-2 and Figure Figure 13-2 and Figure 13- western extent of the Figure 13-3. 13-3. 3. scheme at Walberton Green (NGR 497000, 106000) as shown in on Figure 13-2 and Figure 13-3. Flood risk- fluvial Option 1V5 crosses fluvial Option 1V9 crosses and Option 3V1 crosses fluvial Option 4/5AV1 crosses Option 4/5AV2 crosses Option 5BV1 crosses fluvial and tidal sources and tidal Flood Zone 3 east tidal Flood Zone 3 east of and tidal Flood Zone 3 east fluvial and tidal Flood Zone fluvial and tidal Flood Zone and tidal Flood Zone 3 east of the River Arun between 3 east of the River Arun 3 east of the River Arun of the River Arun between of the River Arun between the River Arun between the the Arun Valley Railway between the Arun Valley between the Arun Valley the Arun Valley Railway the Arun Valley Railway and Arun Valley Railway and the (NGR 501700, 105600) to Railway NGR 501700, Railway NGR 501700, (NGR 501700, 105600) to the Ford Road roundabout. Ford Road Roundabout, the far western extent at the 105600) to the far western 105600) to the far western the far western extent at the including the widening of Tortington Priory Farm to extent at the Tortington extent at the Tortington Tortington Priory Farm to the west of the River Arun Priory Farm to the west of Priory Farm to the west of the west of the River Arun the roundabout. (NGR 500500, 105500. the River Arun (NGR the River Arun (NGR (NGR 500500, 105500). 500500, 105500). Fluvial 500500, 105500). Flood risk and tidal flood risk associated with the Flood risk associated with a associated with the Tortington Common network of ordinary Tortington Common at NGR NGR499000, 105700. Land watercourses to the western 499700, 105300. Land within this area is extent of the scheme at within this area is predominantly agricultural, Walberton Green (NGR predominantly agricultural, although review of 497000, 106000). although review of Ordnance Survey mapping Ordnance Survey mapping indicates that individual indicates that individual properties are located in properties are located in close proximity to the close proximity to the mapped flood extents. mapped flood extents. Flood risk- Review of Environment Review of Environment The area to the north of The area to the east of the The area to the east of the The area to the east of the surface water Agency Risk of Flooding Agency Risk of Flooding Havenwood Park at the B2132 Yapton Lane shown B2132 (Yapton Lane) B2132 (Yapton Lane) from Surface Water map from Surface Water map western extent of Option to be at high risk of surface shown to be at high risk of shown to be at high risk of shows localised areas along shows localised areas along 3V1 is shown to be at high water flooding. It is likely surface water flooding. It is surface water flooding. It is Option 1V5 to be Option 1V9 to be risk of surface water that the A27 creates a likely that the A27 creates a likely that the A27 creates a susceptible to surface water susceptible to surface water flooding. It is likely that the barrier to overland flows barrier to overland flows barrier to overland flows flood risk. flood risk. The Scheme A27 creates a barrier to and water is ponding and water is ponding and water is ponding The Scheme option option continues down the overland flows and water is adjacent to the A27. adjacent to the A27. adjacent to the A27. continues down the existing existing A27 and crosses ponding adjacent to the A27 and crosses areas areas along the A27. Limited areas within Option Limited areas within Option Limited areas within Option along the carriageway at carriageway at risk of Localised ponding in high 4/5AV1 likely to be 4/5AV2 likely to be 5BV1 likely to be associated risk of surface water surface water flooding: risk surface water flooding associated with depressions associated with depressions with depressions in local flooding: ƒ Encroachment on areas within Option 3V1 is in local topography. in local topography. topography. ƒ High risk ponding areas at high risk likely to be associated with depressions in local Surface water flood risk is Surface water flood risk is Surface water flood risk is along the existing of surface water topography. shown in Figure 13-1. shown in Figure 13-1. shown in Figure 13-1. A27 into the area flooding. Surface water flood risk is around Scotland shown in Figure 13-1. Barn

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Key Option 1V5 Option 1V9 Option 3V1 Option 4/5AV1 Option 4/5AV2 Option 5BV1 Environmental Value ƒ High risk overland ƒ High risk ponding flow path from along the existing Goblestubbs A27 into the area Copse ponding around Scotland along the existing Barn A27 into the land ƒ High risk overland around flow path from Havenwood Goblestubbs Park/Bickklin Copse ponding Piece along the existing A27 into the land The existing A27 is slightly raised therefore surface around water is unlikely to pond on Havenwood the main carriageway. Park/Bickklin Water is likely to be Piece conveyed away from carriageway. However, The existing A27 is slightly surcharging of drainage raised therefore surface systems could occur in the water is unlikely to pond on event of intense sustained the main carriageway. rainfall. Water is likely to be Surface water flood risk is conveyed away from shown in Figure 13-1. carriageway. However, surcharging of drainage systems could occur in the event of intense sustained rainfall. Surface water flood risk is shown in Figure 13-1. Principal Aquifer- The Lewes Nodular Chalk is The Lewes Nodular Chalk is Option 3V1 crosses the The Lewes Nodular Chalk is The Lewes Nodular Chalk is The Lewes Nodular Chalk is Lewes Nodular unlikely to be encountered unlikely to be encountered Lewes Nodular Chalk to the not encountered by this not encountered by this not encountered by this Chalk by this option based on the by this option based on the far western extent of the Scheme option. Scheme option. Scheme option. available desk study data. available desk study data. Scheme option. At this location the Scheme option is mainly underlain by head deposits, however, the Chalk is directly exposed at surface to the north east of Paine’s Wood. Principal Aquifer- Option crosses the Options crosses the A small section of Option The Spetisbury Chalk The Spetisbury Chalk The Spetisbury Chalk Spetisbury Chalk Spetisbury Chalk Member Spetisbury Chalk Member 3V1 is located upon the Member is not encountered Member is not encountered Member is not encountered Member to the far western extent of to the far western extent of Spetisbury Chalk Member, by this Scheme option. by this Scheme option. by this Scheme option. the option. the option. to the north west of

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Key Option 1V5 Option 1V9 Option 3V1 Option 4/5AV1 Option 4/5AV2 Option 5BV1 Environmental Value At this location the options At this location the options Scotland Barn near the far are directly underlain by are directly underlain by western extent of the Head and Storm Beach Head and Storm Beach Scheme option. deposits. deposits. At this location the Scheme option is mainly underlain by Head deposits, however, the Chalk may be directly exposed at surface to the north west of Scotland Barn. Secondary A This Scheme option This Scheme option This Scheme option This Scheme option This Scheme option This Scheme option Aquifer- Lambeth crosses the Lambeth Group crosses the Lambeth Group crosses the Lambeth Group crosses the Lambeth Group crosses the Lambeth Group crosses the Lambeth Group Group at two locations; from the at two locations; from the at two locations; from the at two locations; to the far at two locations; to the far at two locations; to the far north of Scotland Barn to north of Scotland Barn to north of Scotland Barn to western extent of the western extent of the western extent of the the Hospital and between the Hospital and between the middle section of Scheme option and as the Scheme option and as the Scheme option and as the the River Arun and railway the River Arun and railway Torrington Common and Scheme option crosses the Scheme option crosses the Scheme option crosses the line. line. between the River Arun and River Arun. River Arun. River Arun. To the west the railway line. To the west the Lambeth To the west the Lambeth Lambeth Group is mainly Near the railway line the Near the railway line the Group is mainly underlain Group is mainly underlain underlain by Head Deposits Lambeth Group is overlain Lambeth Group is overlain Near the railway line the by Raised Storm Beach by Head Deposits and near with a small coverage of by Raised Marine Deposits. by Raised Marine Deposits. Lambeth Group is overlain Deposits and near the River the River Arun the Lambeth Raised Beach Deposits. by Raised Marine Deposits. Arun the Lambeth Group is Group is overlain by Raised Near the River Arun the overlain by Raised Marine Marine Deposits. Lambeth Group is overlain Deposits. by Raised Marine Deposits. Secondary A Alluvium is not encountered Alluvium is not encountered Alluvium is not encountered The option crosses Alluvium The option crosses Alluvium The option crosses Alluvium Aquifer- Alluvium by this Scheme option. by this Scheme option. by this Scheme option. Deposits to the north east of Deposits to the south of Deposits to the east of the Meadow Lodge to the Little Danes Wood to the Avisford park Golf Club to centre of this Scheme west and near the Meadow the west and near the option. Lodge to the centre of this Meadow Lodge to the Scheme option. centre of this Scheme option. Secondary A This Scheme option This Scheme option River Terrace Deposits are This Scheme option This Scheme option This Scheme option Aquifer- River crosses the River Arun crosses the River Arun not encountered by this crosses the River Terrace crosses the River Terrace crosses the River Terrace Terrace Deposit floodplain underlain by floodplain underlain by Scheme option. Deposits near Church Farm Deposits to the west of Deposits to the north east of River Terrace Deposits. River Terrace Deposits. to the east of Binsted and Oakley Cottages and near Walberton, west of Oakley near New Barn at New Barn at Tortington. Cottages and near New Tortington. Barn at Tortington. Secondary A This Scheme option This Scheme option The centre of the Scheme The centre of the Scheme The centre of the option To the east the Scheme Aquifer- Raised crosses two outcrops of crosses two outcrops of option crosses two outcrops option crosses three crosses three outcrops of option crosses three Beach Deposits Raised Beach deposits from Raised Beach deposits from of Raised Beach Deposits. outcrops of Raised Beach Raised Beach Deposits. outcrops of Raised Beach east of the railway line to east of the railway line to This Scheme option Deposits. To the east the Scheme Deposits from the far the far east extent of the the far east extent of the crosses two outcrops of This Scheme option option crosses two outcrops western option extent to Scheme option. Scheme option. Raised Beach deposits from crosses two outcrops of of Raised Beach deposits Avisford. east of the railway line to Raised Beach deposits from from east of the railway line The centre of the Scheme east of the railway line to option crosses three

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Key Option 1V5 Option 1V9 Option 3V1 Option 4/5AV1 Option 4/5AV2 Option 5BV1 Environmental Value the far east extent of the the far east extent of the to the far east extent of the outcrops of Raised Beach Scheme option. Scheme option. Scheme option. Deposits. To the east the Scheme option crosses two outcrops of Raised Beach deposits from east of the railway line to the far east extent of the Scheme option. Secondary A This Scheme option This Scheme option The option crosses a The west of the option a Raised Storm Beach Raised Storm Beach Aquifer- Raised crosses a section of Raised crosses a section of Raised section of Raised Storm section of Raised Storm Deposits are not Deposits are not Beach Deposits Storm Beach Deposits and Storm Beach Deposits and Beach Deposits and Raised Beach Deposits and Raised encountered by this encountered by this and Raised Storm Raised Beach Deposit to Raised Beach Deposit to Beach Deposit to the west Beach Deposit to the west Scheme option. Scheme option. Beach Deposits the west of the option; from the west of the option; from of the option; from north of of the option; from Barn’s north of Paine’s Wood to north of Paine’s Wood to Paine’s Wood to the north Copse to the east of Church the north west of Scotland the north west of Scotland west of Scotland Barn. Farm. Barn. The Scheme option Barn. The Scheme option To the centre of the crosses a second outcrop of crosses a second outcrop of The Scheme option crosses Scheme option Raised Raised Beach Deposit near Raised Beach Deposit near two other sections of Beach Deposits are present the railway line to the east the railway line to the east Raised Beach Deposit; one to the west of Binsted Park of the Study Area. of the Study Area. near Priory Farm and the to new Barn, Torrington and other near the railway line to the south of Priory Farm. to the east of the Study To the east of the Scheme Area. option Raised Beach Deposits are present near the railway line. Secondary A/B This Scheme option This Scheme option This Scheme option This Scheme option This Scheme option This Scheme option Aquifer - Head - crosses the Head Deposits crosses the Head Deposits crosses the Head Deposits crosses three outcrops of crosses three outcrops of crosses four outcrops of from the far western option from the far western option from the far western option Head Deposits from the far Head Deposits from the far Head Deposits from the far extents to the north-east extents to the north-east extent to the north west of western option extent to western option extent to western option extent to corner of Stewards Copse. corner of Stewards Copse. Scotland Barn and from the Fairmeads Farm. Fairmeads Farm. Fairmeads Farm. south border of Tortington Common to the north of New Barn, Tortington. * Watercourses have been numbered using a naming convention developed by the Biodiversity team, as shown in Figure 13-2.

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13.6.4 Identified receptors

13.6.4.1 The receptors identified within the Study Area are listed in Table 13-8 with an assessment of their importance. The importance of receptors was determined following the guidance outlined in Table 13-2.

Table 13-8 - Sensitivity of identified receptors for road drainage and water environment Receptor Importance River Arun High - A main river under the jurisdiction of the Environment Agency. Current Water Framework Directive classification is moderate. The river flows through a popular urban area and is used for boating and riverside walks. Binsted Rife Medium - No known designations, although the and Tortington location of surface water features within the Binsted Rife - (Other Wood Complex LWS (main river) most likely provides Main Rivers) local importance to the overall value of these areas. They support local abstractions for non-potable uses. Ordinary Low - ditches and other unnamed ordinary Watercourses watercourses, including Internal Drainage Board designated, providing a drainage function to the low lying agricultural land within the Study Area. Groundwater – High - Lewes Nodular Chalk, Tarrant Chalk Member Principal and Spetisbury Chalk Member aquifers to the north of Aquifers A27 has current Water Framework Directive classification of poor, although the aquifers support a designated Source Protection Zone. Groundwater – Medium - Most of the Scheme options are underlain Secondary A by Secondary A Aquifer of the Sussex Lambeth Aquifers Group, with current Water Framework Directive classification of poor. The aquifers support local abstractions for non-potable uses. The full list of on-site Secondary A superficial aquifers are as follows; Head, River Terrace Deposits, Raised Beach Deposits, Raised Storm Beach Deposits, Raised Marine Deposits and Alluvium deposits. Groundwater – Low – A selection of Head deposits are classified as Secondary Secondary Undifferentiated Aquifers which have Undifferentiated limited permeability and ability to transmit Aquifer groundwater. Groundwater - High - The licensed groundwater abstractions and Users surface water features are dependent on groundwater.

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Receptor Importance Floodplain – Very High - The identified flood defences and River Arun associated fluvial and/or tidal floodplain provide protection to more than 100 residential properties from flooding Floodplain – Low - Flood risk predominantly within rural areas with other surface few properties identified to be located in close waters features proximity to Environment Agency flood zone mapped extents.

13.7 Potential impacts

13.7.1 Construction phase

13.7.1.1 The potential impacts based on professional judgement relating to the construction phase of the Scheme are outlined in Table 13-9.

Table 13-9 - Construction phase potential impacts for road drainage and water environment Potential Impact Description of the Scoped Impact Geomorphology and Increased pollution Increased pollution risks water quality from mobilised suspended solids, spillage of fuels or other harmful substances that may migrate to surface water and groundwater receptors. Impacts to the Works within or in close hydro-morphological proximity to and ecological watercourses such as quality of the installation and watercourses alteration of culverts, bridges and outfalls as well as realignment of watercourses, including changes associated with sediment deposition.

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Potential Impact Description of the Scoped Impact Flooding Temporary works Construction activities within channel and that take place within floodplain the floodplain could result in a loss of floodplain storage. Temporary works could also result in changes in flood conveyance paths, depending on their nature. Groundwater Cutting and other Intrusive structures (e.g. excavation including cuttings) or ponds below groundwater the water table or dewatering potentiometric surface may require groundwater dewatering during the construction phase. Dewatering the aquifer may alter current groundwater flow directions and reduce groundwater resources locally. Increased Where soil stripping groundwater and/or excavations are vulnerability proposed, aquifer overburden will be reduced/removed which could lead to temporarily increased groundwater vulnerability (to pollution) during the construction phase.

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13.7.2 Operational phase

13.7.2.1 The potential impacts based on professional judgement relating to the operational phase of the Scheme are outlined in Table 13-10.

Table 13-10 - Operational phase potential impacts for road drainage and water environment Potential Impact Description of the Scoped Impact Geomorphology Increased Polluted surface water runoff and water pollution containing silts and hydrocarbons quality and phytotoxic chemicals that have the potential to migrate or be discharged to surface water features or groundwater resources via the proposed highway drainage system (including increased spillage risk) posing a risk to the water quality in the River Arun, other watercourses or groundwater. Permanent New structures may cause impacts impact to the associated with hydromorphological, chemical new structures and ecological quality of the within or in close watercourses and drains within proximity to this area. watercourses Flooding Increased Loss of fluvial floodplain storage, fluvial/tidal most notably associated with the flooding of the River Arun between Ford Road Arun and the Arun Valley Railway. Impacts to flood Increased flood risk to people flow conveyance and property elsewhere as a of the Binsted result of the Scheme has Rife, Tortington potential to effect flood flow Rife and ordinary conveyance and reducing watercourses floodplain storage, and impact to existing flood defences. Increased flood Introduction of new impermeable risk from surface surfaces, leading to increased water discharge runoff and increased flood risk.

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Potential Impact Description of the Scoped Impact Groundwater Cutting Cutting or ponds below the water groundwater table or potentiometric surface dewatering may require the permanent removal of groundwater (dewatering), altering groundwater flow path and reducing groundwater resources locally. Foundations If the Scheme foundations are impacting located within the groundwater groundwater flow table then groundwater mounding and emergence (flooding) may occur. Reduced There will be a reduction of area groundwater for natural groundwater recharge recharge due to hardstanding for the proposed road.

13.8 Design, mitigation and enhancement measures

13.8.1 Embedded in current design

13.8.1.1 At this stage of the Scheme, the design has adopted the provision of clear span structures over the Binsted and Tortington Rife. The piers will be set back away from the mapped flood zone extents to not cause an increase in flooding, maintain bankside riparian habitat and not impact flow dynamics. In PCF Stage 3 (Preliminary Design) further opportunities for mitigation will be embedded into the design with opportunities for additional mitigation to be provided to sensitive areas as the design progresses. 13.8.2 Future design

13.8.2.1 The Scheme options should avoid the risk of flooding to people and property elsewhere. Flood risk might increase as a result of the Scheme through the reduction of floodplain storage, impacts to existing flood defences, obstruction to flow conveyance, or an increase in the rate and volume of surface water runoff. The design of the Scheme options has applied the following design considerations. These key considerations will continue to be applied in PCF Stage 3 (Preliminary Design) and through design development:

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ƒ No net loss of fluvial floodplain storage, most notably associated with the River Arun between Ford Road and the Arun Valley Railway. Impacts can be mitigated through limiting land-take within the identified fluvial floodplain, the provision of like-for-like floodplain compensation, or by limiting lost fluvial storage by building the Scheme on a structure. ƒ No increased flood risk to people and property associated with impacts to tidal flood conveyance and storage. A meeting with the Environment Agency on the 24th July 201748 confirmed that compensation will not be required for tidal flood water storage. However potential impacts on flow paths and tidal risk should be fully considered. Should tidal flooding be the only mechanism detrimentally affected by the Scheme, a solution will need to be developed to maintain the existing flood depth. That is, ensuring conveyance of flow to enable the existing floodplain to ebb and flow and maintaining current flood depths. ƒ Ensure the Scheme will remain operational. The Environment Agency confirmed that as the road will qualify as a Nationally Significant Infrastructure Project pursuant to the Planning Act 2008, and as it crosses a functional floodplain it will need to remain operational and safe for users in times of flood. The Environment Agency advised that they expect an allowance of 600 millimetres freeboard (including 105% Climate Change allowance) above the modelled flood level to be applied to the design of the road. ƒ No notable impact on flood flow conveyance associated with Tortington Rife and Binsted Rife. Impacts could be mitigated through avoiding proposed structures that would impede the flow of water up to and including the 1 in 100 annual exceedance probability fluvial flood event and taking tidal effects into account. The Environment Agency confirmed that they would expect any bridge or deck soffits to be 600 millimetres above either the 1 in 100 annual exceedance probability fluvial event plus 105% climate change allowance, or 1 in 200 exceedance annual probability tidal event including sea level rise as a result of climate change in 2115, whichever is greatest. ƒ Provision of clear span bridges wherever possible, noting that this will be of key importance for the proposed crossings of the Binsted Rife and Tortington Rife (classified as main rivers), and maintaining sufficient flow capacity for the 1 in 100 annual probability fluvial flood event taking tidal effects into account for the River Arun, in line with the current design.

48 Arundel A27 Bypass Flood Risk Meeting, 24th July 2017. Held in Highways England office. Page 13-44 August 2019

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ƒ Provision of appropriately sized culverts for all crossings of other ordinary watercourses and drains in accordance with the Design Manual for Roads and Bridges, at minimum maintaining the capacity of the channel. Consideration will also need to be given to maintaining connectivity for terrestrial and aquatic ecology. ƒ Ensuring no reduction in the standard of protection served by existing flood defences, or impact to the ability to access these defences for maintenance. ƒ Providing a robust surface water drainage system that ensures discharge from the Scheme does not increase flood risk elsewhere up to and including the 1 in 100 annual exceedance probability rainfall events. The need to provide attenuation and restrict the rate and volume of discharge will need to be agreed with West Sussex County Council as Lead Local Flood Authority. ƒ Consideration of the potential effects of climate change over the lifetime of the Scheme and in accordance with Environment Agency guidance, noting that tide levels are likely to rise by approximately 1.21m, river flows are likely to increase by approximately circa.35-105% and rainfall intensity is likely to increase by 20-40% in accordance with updated Environment Agency projections published in March 2016. It is also important to note that climate change predictions for the UK are currently being revised and amended climate change allowances may need to be taken into account during further assessments required to inform PCF Stage 3 (Preliminary Design). 13.8.2.2 At this stage of the assessment the provision of suitable mitigation measures such as floodplain compensation (that may require additional land take) and the design of structural elements are assumed to be embedded within the design of the Scheme. The assessment of potential effects therefore assumes that mitigation measures will be designed into the Scheme at PCF Stage 3 (Preliminary Design) and assesses the impacts and residual risk of the Scheme are reported in this chapter ‘post-mitigation’. 13.8.2.3 The Scheme seeks to avoid an adverse effect on water quality that could result in adverse effects on local surface water and groundwater abstractions. Consideration will need to be given to the treatment of runoff prior to discharge and the measures that will be required in the event of spillage. Multi-stage proposals that maximise passive treatment through the use of sustainable drainage systems are recommended. The Scheme may also offer improvement opportunities to provide improved drainage, most notably for Option 1V5 and Option 1V9 which utilise the existing road alignment.

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13.8.2.4 The design of culverts will take ecological considerations into account to not impede passage of aquatic species, where appropriate, and maintain appropriate flow dynamics. 13.8.2.5 Inspection of the flood defences will be required to inform the design of the Scheme options. An inspection of existing structures will be required to identify any remedial work for water and drainage purposes. 13.8.2.6 Where intrusive structures are to be constructed within permeable materials, it will be necessary to define groundwater levels at least one full year in advance of construction to determine potential risks and develop appropriate mitigation. If groundwater interceptions arise, then further groundwater investigation or mitigation will be required. Potential mitigation measures for cuttings and attenuation ponds are described as: ƒ Passive dewatering systems such as the installation of perimeter drains and permeable blankets to remove groundwater. ƒ Active dewatering systems such as dewatering wells to remove groundwater. ƒ Lining of attenuation ponds to prevent groundwater ingress, giving due consideration to risks of upheave. ƒ The use of perimeter sheet piled walls toed into low permeable material will prevent groundwater ingress into the proposed structure cavity, meaning dewatering is confined to the construction phase. Groundwater mounding and recess on the hydraulic upgradient and downgradient side of the wall may occur. 13.8.2.7 Where dewatering is determined to be required, a quantitative assessment will be needed to assess potential impacts to local groundwater users, groundwater abstractions, surface water features and hydrogeologically sensitive habitats and, where necessary, develop appropriate mitigation strategies.

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13.8.3 Construction phase mitigation measures

13.8.3.1 A Construction Environmental Management Plan (CEMP) be prepared and adopted before the construction phase to limit the risk of pollutants entering surface water features or discharging to ground. The CEMP will detail the procedures and methods to minimise the potential environmental risks associated with construction. Activities would be undertaken in accordance with appropriate good practice guidance, such as CIRIA’s control of water pollution from construction sites (C532). Although withdrawn, the Pollution Prevention Guidelines (PPG) published by the Environment Agency still provide good practice guidance, particularly PPG1 - General guide to the prevention of water pollution; PPG 5 - Works in, near or liable to affect watercourses; and PPG 6 - Working at construction and demolition sites. 13.8.3.2 The CEMP will also describe the procedures to be followed in the event of an environmental emergency such as a fuel or chemical spillage and will include register of licences/permits needed to protect water environment/work within/near watercourses. Typical mitigation measures for inclusion in the CEMP are provided below. These measures are not a complete list and will be further refined during PCF Stage 3 (Preliminary Design). ƒ Minimise areas of exposed surface by only removing vegetation when necessary and keep gradients as shallow as possible to prevent soil erosion ƒ Construction of crossing and other activities in the vicinity of water courses will require site specific construction environmental management measures. ƒ Enforce tight control of site boundaries including minimal land clearance and restrictions on the use of machinery adjacent to water bodies. Where possible, do not locate stockpiles within 10m of water bodies, tidal extent or drainage lines. ƒ Construction materials, such as concrete, should be mixed in designated areas located away from water bodies and drainage lines. ƒ Construction workers should be made aware of the risks associated with flooding out of watercourses should large rainfall events occur during construction and to be aware that this is an area with a tidal range. 13.8.3.3 The following construction phase mitigation measures are also considered standard best practice to protect the quality of groundwater resources: ƒ Where below ground surface construction is required on aquifer material, borehole monitoring of groundwater levels will be needed to confirm whether groundwater interceptions could arise.

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ƒ Mitigations for cutting and attenuation pond construction may include, but are not limited to, active dewatering systems such as the sump pump and dewatering wells to remove groundwater prior to and during construction. ƒ Where dewatering is determined to be required a quantitative risk assessment will be required should there be potential for the dewatering activities to impact upon groundwater aquifers, groundwater dependant habits, and/or groundwater linked surface water features. ƒ Any intrusive works undertaken throughout the year that may intercept groundwater could be completed during the summer months in order to prevent having to complete groundwater dewatering i.e. groundwater levels may be at shallower depths during the winter months. Any seasonal changes in groundwater level; will be assessed further at PCF Stage 3 (Preliminary Design). ƒ The use of perimeter sheet piled walls toed into low permeable material would prevent groundwater ingress into a proposed structure cavity, meaning dewatering would be confined to the internal space and no external dewatering impacts would occur. Groundwater mounding and recess on the hydraulic upgradient and downgradient side of the wall may occur. ƒ Where appropriate consider the use of discharging runoff to ground to prevent aquifer quantity losses taking into account of surface water runoff quality in potential pre-treatment requirements. 13.8.4 Operation phase mitigation measures

13.8.4.1 Operational phase mitigation measures at this stage are those outlined in Section 13.8.1 and 13.8.2. Once these mitigation measures are adopted and embedded into design they will form part of the operational phase mitigation measures. 13.8.5 Opportunities for enhancement

13.8.5.1 No opportunities for enhancements have been identified with regard to road drainage and the water environment. Opportunities will continue to be developed as the Scheme design develops.

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13.9 Assessment of likely significant effects

13.9.1 Discussion

13.9.1.1 The Scheme has the potential to impact the water environment during construction and operation. An assessment of the potential significant effects is provided below. This takes into consideration mitigation measures that are good practice such as the implementation of a CEMP. This assessment additionally takes into consideration mitigation that will be included in the embedded and future design of the Scheme, such as the provision of clear- span structures crossing Binsted Rife and Tortington Rife with abutments set back from the mapped fluvial flood extents, floodplain compensation, maintaining river and floodplain connectivity, the provision of appropriate drainage and appropriate culvert design for land drain crossings. A more detailed assessment of required mitigation measures will be undertaken during PCF Stage 3 (Preliminary Design) and will be used to inform the design of the Scheme. 13.9.2 Future Baseline/Do Minimum Scenario

13.9.2.1 There is a potential for the predominantly freshwater ordinary watercourses shown in Figure 13-2 to eventually become a tidally influenced environment (which is of a higher salinity) if the existing earth embankments are no longer maintained, as the Lower Arun Flood Risk Management Strategy suggests. This can significantly alter existing characteristics of the catchment including the ecology over time. 13.9.2.2 The potential future cessation of maintenance and subsequent deterioration of the raised earth flood defences along the River Arun can also increase the susceptibility of the agricultural land within the Study Area to flooding. 13.9.3 Option 1V5 and Option 1V9 – construction phase

Post-mitigation assessment of effects 13.9.3.1 Option 1V5 and Option 1V9 are considered together as the proposed alignments are largely similar with regard to the water environment, however the assessment highlights specific differences in the design of the two Scheme options. 13.9.3.2 Option 1V5 and Option 1V9 largely follow the alignment of the existing A27 therefore the risk to the quality of the water environment is likely to be comparatively minimal during construction. This is based on the assumption that appropriate pollution control measures outlined within a CEMP are implemented during construction. 13.9.3.3 The greatest risks to water quality during construction will be associated with works within the channel of the River Arun: Page 13-49 August 2019

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ƒ Option 1V5 proposes to extend the current River Arun road bridge. ƒ Option 1V9 proposes to remove the existing River Arun road bridge and replace with a clear span structure to allow for the dual carriageway width. Geomorphology and water quality Increased pollution 13.9.3.4 It is proposed within Option 1V5 and Option 1V9 to extend the current River Arun road bridge to allow for the dual carriageway. The greatest risks to water quality during construction will be associated with the construction of new abutments and embankment adjacent to river, as well as temporary works within the river channel The impacts are most likely to be associated with runoff from earth stockpiles or occur during the construction of the Scheme. In addition to this, some increase in sedimentation contained within overland flow from the construction working areas is likely to occur due to the likely proximity of works to the River Arun. However, it is a large tidal waterbody which is subject to increased sediment levels during large tidal flows and where sediment entering the watercourse will be dispersed quickly through the tidal flow regime. Provided correct working procedures and practices proposed within the CEMP are adopted and care is taken to avoid pollution, the impacts during the construction phase would reduce greatly. Therefore, the magnitude of the potential impact to the quality of the River Arun is considered likely to be minor adverse. Consequently, there is likely to be a direct but temporary effect on the River Arun, with the significance assessed as slight adverse (not significant). 13.9.3.5 Groundwater flow paths may be altered due to the introduction of intrusive piled structures, but this is dependent on pile density, depth and orientation to groundwater flow. This will be assessed in PCF Stage 3 (Preliminary Design) as the design is progressed. There is potential for the piles to hydraulically connect waterbodies if the piles are constructed at significant depth. In addition to this, piles may create migration pathways for contaminants. 13.9.3.6 Option 1V5 and Option 1V9 do not cross Binsted Rife or Tortington Rife.

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13.9.3.7 Option 1V5 and Option 1V9 requires the construction of new carriageway within currently undeveloped land to the east of Arundel as the options cross the Arun Valley Railway. The most likely risks are associated with increased sedimentation from exposed earth and construction of the earth embankments, as well as increased risk of hydrocarbons associated with mechanical plant. The works could result in some measurable change in water quality in the receiving watercourses as increased sediment loads entering smaller watercourses may take longer to settle out or be dispersed through normal processes. Construction related impacts are considered to be direct and temporary as water quality within the watercourses would improve over time as sediments settle and pollutants are treated by entrapment, dilution and natural processes. The CEMP is likely to adequately manage risks of pollution and spillage from mechanical plant. The impact to the ordinary watercourses that drain between the Arun Valley Railway line is considered to be minor adverse. Given the low importance of these features, the likely temporary significance of effect is neutral (not significant). Impacts to the hydro morphological and ecological quality of watercourses 13.9.3.8 The existing A27 and Arun Valley Railway will already provide a barrier to the movement of aquatic species. The work required to construct the Scheme can cause the temporary loss of riparian vegetation, damage to existing substrate and changes to flow dynamics. However, the works are unlikely to pose significant impact to the hydro-morphological and ecological quality of the River Arun and ordinary watercourses within the Study Area. The duration of this work is temporary and is expected to return to a condition similar to the baseline within an estimated two years of construction. Therefore, impacts are considered to be of insufficient magnitude to affect the use or integrity of the watercourse. The impacts are likely to be negligible. The resulting overall temporary significance of effect is likely to be neutral (not significant).

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Flooding

Flooding associated with temporary works 13.9.3.9 Option 1V5 proposes to maintain the existing River Arun road bridge with an additional structure to provide for more lanes. Option 1V9 proposes to remove the existing bridge and construct a new clear span structure over the River Arun. Temporary works during construction may need to be located in the River Arun floodplain could potentially reduce channel width if a dry working area is required within the channel. Placing structures in the channel could also affect flood flow conveyance and pose risk of debris accumulating at temporary structures, further reducing channel capacity. In addition to this, the implementation of the CEMP and an appropriate flood response strategy is expected to appropriately manage these risks. The impact magnitude is assessed to be negligible, with an overall temporary significance of effect of neutral (not significant). 13.9.3.10 Temporary works will also be required within the floodplain associated network of ordinary watercourses to the east of Arundel. The main risk associated with temporary loss of floodplain storage and flow conveyance across the floodplain. This is unlikely to cause a notable increase in flood risk elsewhere as the works are temporary and the likelihood of a significant flood event happening is relatively low. The flow in smaller watercourses is likely to be maintained by over pumping and provision of temporary channels to maintain connectivity. The magnitude of impact to the network of ordinary watercourses of is considered to be low. The overall significance of effect is considered to be neutral (not significant). Groundwater

Groundwater quality impacts 13.9.3.11 Option 1V5 and Option 1V9 will require the construction of new carriageway within currently undeveloped land to the east of Arundel, where the Scheme crosses the Arun Valley Railway. The new carriageway construction will require soil stripping and cuttings, piling, reducing aquifer overburden and consequently creating shorter/quicker/direct pathways for rainfall recharge and contamination, increasing groundwater vulnerability. 13.9.3.12 Assuming that appropriate pollution control measures as outlined within a CEMP are implemented, the risk to groundwater quality is likely to be comparatively minimal during the construction of the Scheme. 13.9.3.13 The magnitude of the potential impact to groundwater quality of the Chalk, Lambeth Group and superficial aquifers is considered likely to be negligible and therefore the overall significance of effect is considered neutral (not significant).

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Groundwater dewatering impacts 13.9.3.14 Where cuttings or below ground surface structures (such as attenuation ponds) are proposed on aquifer ground materials, these structures may intercept groundwater. Where interceptions occur, groundwater removal or dewatering will be required to construct the cuttings and/or ponds. Groundwater dewatering can impact upon the groundwater flow net and provision of water to local groundwater users or ecological habitats dependant on groundwater flow. 13.9.3.15 A ground investigation and subsequent groundwater level monitoring will be required to determine if groundwater will be intercepted by these proposed features. 13.9.3.16 Option 1V5 and Option 1V9 includes a <4.2m deep cutting between Chainage 720m and 1250m. The cutting is founded on 6.3m of made ground and a further 8.75m of Lambeth Group according to BGS borehole log TQ00NW160. As the cutting is located on top of a topographical high, groundwater is not anticipated to be encountered within the Head or Lambeth Group deposits. However, should the Head deposits or Lambeth Group beds be water bearing at this location then they will require dewatering to construct the cutting. 13.9.3.17 The cutting may intercept the Lambeth Group, which is defined as a medium value receptor. The temporary construction works of the cutting have the potential requirement for dewatering. After following the embedded construction mitigation listed in Section 13.8.3 above, the impact magnitude of dewatering at this location is assessed as negligible and therefore the overall significance of the dewatering is considered neutral (not significant). 13.9.3.18 There are three drainage ponds/basins proposed for Option 1V5 and Option 1V9. Attenuation pond/basin construction will be located on and founded within Secondary A aquifer ground material. These ponds/basins may intercept groundwater in the Secondary A aquifers, which are defined as medium value receptors. The temporary construction works of the ponds have the potential to require dewatering. The impact magnitude of dewatering at this location is assessed as minor and therefore the overall significance of the dewatering is considered slight adverse (not significant). 13.9.3.19 As no groundwater dewatering is anticipated in the Chalk, no impact to local groundwater abstractions is expected. Therefore, a no change of effect is predicted.

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13.9.3.20 Proposed intrusive piled structures on aquifer ground materials may potentially intercept groundwater and hydraulically connect waterbodies. Hydrogeological assessments should be completed for the proposed piled structures to assess and mitigate any impact upon the groundwater flow as well as impacts on local groundwater users and groundwater dependant ecosystems. 13.9.3.21 A ground investigation and subsequent groundwater level monitoring will be required to determine if groundwater will be intercepted by these proposed features. 13.9.3.22 The magnitude of the potential impact to groundwater flow is considered to be minor adverse with the overall significance of effect being slight adverse (not significant). 13.9.4 Option 1V5 and Option 1V9 – operation phase

Geomorphology and water quality

Increased pollution 13.9.4.1 During operation, surface water runoff has the potential to contain silts and hydrocarbons that are washed off hard paved areas. These can increase water turbidity, deplete oxygen levels and be toxic to the aquatic environment. Uncontrolled discharge via infiltration to ground can also cause permanent deterioration of groundwater quality. Pollution of waterbodies from surface water runoff containing silts and hydrocarbons is considered a direct permanent impact. Although pollutants can be treated by natural processes in the waterbody the absence of adequate mitigation would result in a continuous discharge of polluting substances to waterbodies. The Scheme will be mitigated by a proposed surface water drainage system. This will include appropriate pollution control measures for new sections of road and may offer an opportunity for betterment for existing sections of road if the existing drainage systems are upgraded in line with the SuDS Manual Developed by CIRIA (C753). The magnitude of the impact posed to water quality during operation is likely to be negligible, with overall significance of effect being neutral given the appropriate mitigation measures are incorporated into design (not significant).

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Permanent impacts to the hydro morphological and ecological quality of watercourse 13.9.4.2 The works are unlikely to pose significant permanent impact to the hydro- morphological and ecological quality of the River Arun and ordinary watercourses within the Study Area provided the inclusion embedded mitigation through design. The crossing of the existing land drains in the vicinity of the Arun Valley Railway may remove riparian aquatic habitat and impact aquatic connectivity, although the existing A27 and Arun Valley Railway will already provide a barrier to the movement of aquatic species and therefore the impacts are likely to be negligible. The resulting overall significance of effect is likely to be neutral (not significant).

Flooding Increased fluvial/tidal flooding of the River Arun 13.9.4.3 Loss of fluvial floodplain storage, broadly associated with the River Arun between Ford Road and the Arun Valley Railway, could result in the loss of fluvial floodplain storage and impacts to fluvial and tidal flood flow conveyance. This may adversely impact adjacent property and infrastructure. It is assumed that the flow capacity of the drains can be maintained through the Scheme design. 13.9.4.4 The mitigation measures have not yet been developed or determined at this stage of design. Initial modelling of required compensation land indicates Option 1V5 and Option 1V9 requires a larger amount of floodplain compensation area in comparison to Option 3V1, Option 4/5AV1, Option 4/5AV2 and Option 5BV1. Professional judgement, using knowledge and experience of similar schemes, identified typical mitigation measures which are likely to include but are not limited to: floodplain compensation; upstream Natural Flood Management options for compensatory flood storage; provision of flood relief culverts to maintain floodplain connectivity; in addition to maintaining the capacity of the River Arun by providing a clear span structure. There is scope for further refinement, but this would be undertaken once the preferred route is determined, in PCF Stage 3 (Preliminary Design). Therefore, the significance of effect is likely to be neutral (not significant). This significance of effect assumes that all required mitigation measures will be incorporated into the preliminary design of the Scheme. Impacts to flood flow conveyance of ordinary watercourses 13.9.4.5 Increased flood risk to people and property as a result of the Scheme has the potential to affect flood flow conveyance and reduce floodplain storage. Given the inclusion of floodplain compensation and maintenance of flood flow conveyance embedded in the design of the Scheme, the significance of the effect is likely to be neutral (not significant).

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Increased flood risk from surface water discharge 13.9.4.6 The introduction of impermeable surface area within the Study Area may lead to an increase in generated surface water runoff from the Scheme. During PCF Stage 3 (Preliminary Design), a surface water drainage system will be designed to attenuate surface water runoff. The overall significance of effect is considered to be neutral (not significant). Groundwater

Groundwater recharge impacts 13.9.4.7 Option 1V5 and Option 1V9 requires the construction of new carriageway within currently undeveloped land to the east of Arundel as the Scheme crosses the Arun Valley Railway. On construction completion the new road surface hardstanding will collect rainfall which would have otherwise naturally recharged groundwater aquifers. 13.9.4.8 For the regional bedrock aquifers, and the regionally significant outcrops of superficial aquifers, the new road surface hardstanding area is relatively small in comparison to the groundwater body recharge catchments, therefore the impact magnitude of groundwater recharge impacts due to new carriageway construction is considered to be negligible. Given the medium- high importance of the groundwater aquifers, the overall significance of effect is likely to be neutral (not significant). 13.9.4.9 For local superficial aquifers where the new road surface hardstanding area is proportionate in size to the groundwater body recharge catchments, a minor impact is anticipated. Given the medium importance of the superficial groundwater aquifers, the overall significance of effect is likely to be slight adverse (not significant). 13.9.5 Option 3 V1 - construction phase

13.9.5.1 Option 3V1 will cross a number of ordinary watercourses and land drains within Binsted Wood Complex LWS and a number of land drains between Ford Road and the Arun Valley Railway as well as the River Arun as illustrated in Figure 13-1.

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Geomorphology and water quality

Increased pollution 13.9.5.2 Option 3V1 requires the construction of an embankment across the River Arun (NGR 500700, 104800). The greatest risks to water quality during construction will be associated with the construction of new abutments and embankment adjacent to river, as well as temporary works within the river channel. The impacts are most likely to be associated with runoff from earth stockpiles during high rainfall events and/or flooding. In addition to this, some increase in sedimentation contained within overland flow from the construction working areas is likely to occur due to the likely proximity of works to the River Arun. However, it is a large tidal waterbody which is subject to increased sediment levels during large tidal flows and sediment entering the watercourse will be dispersed quickly through the tidal flow regime. Provided correct working procedures and practices proposed within the CEMP are adopted and care is taken to avoid pollution, the impacts during the construction phase would reduce greatly. Therefore, the magnitude of the potential impact to the quality of the River Arun is considered likely to be minor adverse. Consequently, there is likely to be a direct but temporary effect on the River Arun, with the significance assessed as slight adverse (not significant). 13.9.5.3 Groundwater flow paths may be altered due to the introduction of intrusive piled structures, but this is dependent on pile density, depth and orientation to groundwater flow. This will be assessed in PCF Stage 3 (Preliminary Design) as the design is progressed. There is potential for the piles to hydraulically connect waterbodies if the piles are constructed at significant depth. In addition to this, piles may create migration pathways for contaminants. 13.9.5.4 Option 3V1 requires the construction of new carriageway within currently undeveloped land to the east of Arundel as the options cross the Arun Valley Railway and a clear span structure crossing the Tortington Rife. The most likely risks are associated with increased sedimentation from exposed earth as well as increased risk of hydrocarbons associated with mechanical plant. The works could result in some measurable change in water quality in the receiving watercourses as increased sediment loads entering smaller watercourses may take longer to settle out or be dispersed through normal processes. Construction related impacts are considered to be direct and temporary as water quality within the watercourses would improve over time as sediments settle and pollutants are treated by entrapment, dilution and natural processes. The CEMP likely to adequately manage risks of pollution and spillage from mechanical plant.

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13.9.5.5 The magnitude of impact to the Tortington Rife is considered to be minor adverse, given the medium importance of these receptors the likely temporary significance of effect is slight adverse (not significant). 13.9.5.6 The magnitude of impact to the ordinary watercourses that drain between the Arun Valley Railway line is considered to be minor adverse. Given the low importance of these features, the likely temporary significance of effect is neutral (not significant).

Impacts to the hydro morphological and ecological quality of watercourses 13.9.5.7 The works are unlikely to pose significant permanent impact to the hydro- morphological and ecological quality of the River Arun, Tortington Rife and ordinary watercourses within the Study Area. The existing A27 and Arun Valley Railway will already provide a barrier to the movement of aquatic species. The work required to construct the Scheme can cause the temporary loss of riparian vegetation, damage to existing substrate and changes to flow dynamics. However, the works are unlikely to pose significant impact to the hydro-morphological and ecological quality of the River Arun and Tortington Rife and ordinary watercourses within the Study Area as the duration of this work is temporary, and will return to a condition similar to the baseline condition within an estimated two years of construction and therefore impacts are considered to be of insufficient magnitude to affect the use or integrity of the watercourse. The impacts are likely to be negligible. The resulting overall significance of effect is likely to be neutral (not significant).

Flooding

Flooding associated with temporary works 13.9.5.8 Temporary works associated with the Scheme within the floodplain and channel of the River Arun and any reduction in the capacity of the watercourse or floodplain (or impacts to existing flood defences) could increase flood risk predominantly to urban areas of Arundel and to Tortington Priory Farm to the south of Option 3V1. Works required for construction of a road bridge could reduce channel width if a dry working area is required within the channel and floodplain. Placing structures in the channel could also affect flood flow conveyance and pose risk of debris accumulating at temporary structures and further reducing channel capacity. This is unlikely to cause a notable increase in flood risk elsewhere as works are temporary and the likelihood of a significant flood event happening is relatively low and the connectivity of watercourse will be maintained. The magnitude of the impact will be heavily dependent on local conditions; however, the implementation of the CEMP and an appropriate flood response strategy will manage these risks. The impact magnitude during construction is considered to be negligible, with a significance of effect of neutral (not significant).

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13.9.5.9 Temporary works will be required within the floodplain of the River Arun and the network of ordinary watercourses to the east of Arundel. The works are not considered to pose increased flood risk elsewhere during the construction of other crossings of the ordinary watercourses and land drains within Binsted Wood Complex LWS. The impact magnitude is assessed to be negligible, with an overall significance of effect of neutral (not significant).

Groundwater

Groundwater quality impacts 13.9.5.10 Option 3V1 proposes a new route through the Torrington Common area, where Head Deposits, Raised Beach Deposits, River Terrace Deposits, Raised Marine Deposits, Lambeth Group and London Clay Formation are present. All geologies apart from the London Clay Formation are classified as Secondary A aquifers and are considered medium value receptors. 13.9.5.11 Option 3V1 requires the construction of new carriageway within currently undeveloped land to the west and east of Arundel. The new carriageway construction will require soil stripping and cuttings, reducing aquifer overburden and consequently creating shorter/quicker/direct pathways for rainfall recharge and contamination, increasing aquifer vulnerability. Assuming that appropriate pollution control measures as outlined within a CEMP are implemented, the risk to groundwater quality is likely to be comparatively minimal during construction. 13.9.5.12 The magnitude of the potential impact to groundwater quality of the Chalk, Lambeth Group and superficial aquifers is considered likely to be negligible and therefore the overall significance of effect is considered neutral (not significant).

Groundwater dewatering impacts 13.9.5.13 Where cuttings or below ground surface structures (such as attenuation ponds) are proposed on aquifer ground materials, these structures may intercept groundwater. Where interceptions occur, groundwater removal or dewatering will be required to construct the cuttings and/or ponds. Groundwater dewatering can impact upon the groundwater flow and provision of water to local groundwater users or ecological habitats dependant on groundwater flow. 13.9.5.14 A ground investigation and subsequent groundwater level monitoring will be required to determine if groundwater will be intercepted by these proposed features.

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13.9.5.15 Option 3V1 includes two cuttings, one <5m deep cutting between chainage 3120m to 3710m and the other <6m deep cutting between approximately chainage 3970m to 4850m. No suitable BGS borehole logs are available in close proximity of these cuttings, however, the most westerly cutting is anticipated to be founded on Raised Beach Deposits and Lambeth Group and the second most westerly cutting is likely to be founded in Lambeth Group. Both cuttings are located near the top of a topographical highs and groundwater is not anticipated to be encountered within either the Raised Beach Deposits or Lambeth Group aquifers. However, the Raised Beach Deposits and Lambeth Group aquifers could be water bearing at this location and may require dewatering to construct the cutting. 13.9.5.16 The cuttings may intercept the Raised Beach Deposits and Lambeth Group aquifers, which are defined as medium value receptors. The temporary construction works of the cutting have the potential to require dewatering. The impact magnitude of dewatering at this location is assessed as minor and therefore the overall significance of the dewatering is considered slight adverse (not significant). 13.9.5.17 There are two drainage ponds/basins proposed for Option 3V1. Attenuation pond/basin construction will be located on and founded within Secondary A aquifer ground material. These ponds/basins may intercept groundwater in the Secondary A aquifers, which are defined as medium value receptors. The temporary construction works of the ponds have the potential to require dewatering. The impact magnitude of dewatering at this location is assessed as minor and therefore the overall significance of the dewatering is considered slight adverse (not significant). 13.9.5.18 As no groundwater dewatering is anticipated in the Chalk, no impact to local groundwater abstractions is expected. Therefore, the overall significance of neutral is predicted (not significant).

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13.9.6 Option 3V1 - operation phase

Geomorphology and water quality

Increased pollution 13.9.6.1 During operation, surface water runoff has the potential to contain silts and hydrocarbons that are washed off hard paved areas. These can increase water turbidity, deplete oxygen levels and be toxic to the aquatic environment. Uncontrolled discharge via infiltration to ground can also cause permanent deterioration of groundwater quality. Pollution of waterbodies from surface water runoff containing silts and hydrocarbons is considered a direct permanent impact. Although pollutants can be treated by natural processes in the waterbody the absence of adequate mitigation would result in a continuous discharge of polluting substances to waterbodies. Pollution as a result of the Scheme will be mitigated by the proposed surface water drainage system. This will include appropriate pollution control in line with the SuDS Manual Developed by CIRIA (C753). The magnitude of the impact posed to water quality during operation is likely to be negligible, with overall significance of effect being neutral given the appropriate mitigation measures are incorporated into design (not significant). Permanent impacts to the hydro morphological and ecological quality of watercourses 13.9.6.2 The works may pose risks to the hydro-morphological and ecological quality of the River Arun and Tortington Rife and ordinary watercourses within the Study Area by removing ecological habitat and severing connectivity. Appropriate culvert design measures of maintaining hydrological connectivity, creation of a natural bed and maintaining the low flow channel, the design of the culverts can be undertaken in such a way as to not increase velocity. The resulting overall significance of effect is likely to be neutral (not significant). 13.9.6.3 From a hydro morphological perspective, if there are no changes in bed gradient, no changes in erosion or deposition and no watercourse reprofiling is undertaken, the magnitude of impact is likely to be negligible. There may be permanent loss of bankside habitat along the length of the proposed culverts, however Option 3V1 alignment crosses approximately perpendicular to most watercourses and field drains. This is likely to result in the smallest length of watercourse disturbance. With the detailed mitigation measures and further assessment of ecological and hydro morphological impacts, the residual effect is likely to be neutral (not significant).

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Flooding

Increased fluvial/tidal flooding of the River Arun 13.9.6.4 The greatest flood risks during operation will be associated with permanent works within the floodplain and channel of the River Arun. Any reduction in the capacity of the watercourse or floodplain (or impacts to existing flood defences) could increase flood risk to urban areas of Arundel and to Tortington Priory Farm to the south of Option 3V1 alignment. 13.9.6.5 The construction of an earth embankment could pose a risk as this will introduce a physical barrier to the movement of water and displace floodplain storage. The mitigation measures are dependent on additional land take and detailed hydraulic modelling which will be used to inform the design of the Scheme at PCF Stage 3 (Preliminary Design). 13.9.6.6 The mitigation measures have not yet been developed or determined at this stage of design. However, initial modelling of required compensation land indicates Option 3V1 requires significantly less land take than Option 1V5 and 1V9. Professional judgement using knowledge and experience of similar schemes identified typical mitigation measures which are likely to include but are not limited to: floodplain compensation; upstream Natural Flood Management options for compensatory flood storage; provision of flood relief culverts to maintain floodplain connectivity; in addition to maintaining the capacity of the River Arun by providing a clear span structure. 13.9.6.7 The specific mitigation measures will require consultation and approval by the Environment Agency, landowners and other Statutory Environmental Bodies. There is scope for further refinement, but this would be undertaken in PCF Stage 3 (Preliminary Design). Given the very high importance of the River Arun floodplain, the significance of effects is likely to be neutral (not significant) with mitigation measures embedded in the design. This significance of effect assumes that all required mitigation measures will be incorporated into the design of the Scheme at PCF Stage 3 (preliminary design). 13.9.6.8 Culverts through the embankment will need to be appropriately designed to maintain the capacity of the channel of the land drains and ordinary watercourses. Consideration will also need to be given to maintaining connectivity for aquatic ecology. The magnitude of the impact will be heavily dependent on the characteristics of flooding in this area and will need to be informed through detailed hydraulic analysis. With flood flow conveyance and floodplain compensation mitigation measures in place, the magnitude of impacts is likely to be negligible. Given the very high importance of the River Arun floodplain, the overall significance of effect is likely to be neutral assuming that sufficient mitigation measures embedded into the design.

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13.9.6.9 Option 3V1 will also cross the extensive network of land drains to the west and east of the River Arun and Option 3V1 will cross the Tortington Rife through Spinningwheel Copse. With the inclusion of floodplain compensation, provision of culverts of adequate size and maintenance of flood flow conveyance embedded in the design of the Scheme, the significance of the effect is likely to be neutral (not significant).

Increased flood risk from surface water discharge 13.9.6.10 The introduction of impermeable surface area within the Study Area may lead to an increase in generated surface water runoff from the Scheme. During PCF Stage 3 (Preliminary Design), a surface water drainage system will be designed to attenuate surface water runoff from the majority of the Scheme prior to discharge. The overall significance of effect is considered to be neutral (not significant).

Impacts to flood flow conveyance of the Tortington Rife and ordinary watercourses 13.9.6.11 Option 3V1 will cross the extensive network of watercourses to the east and west of the of the River Arun, including the Tortington Rife. With floodplain compensation, provision of culverts of adequate size and maintenance of flood flow conveyance embedded in the design of the Scheme, the significance of the effect is likely to be neutral (not significant). Groundwater Groundwater dewatering impacts 13.9.6.12 Where cuttings or below ground surface structures (such as attenuation ponds) are proposed on aquifer ground materials, these structures may intercept groundwater. Where interceptions occur, groundwater removal or dewatering will be required to operate the proposed cutting or ponds. Groundwater dewatering can impact upon the groundwater flow and provision of water to local groundwater users or ecological habitats dependant on groundwater flow. 13.9.6.13 Option 3V1 includes two cuttings, one <5m deep cutting between chainage 3120m to 3710m and the other <6m deep cutting between chainage 3970m to 4850m. No suitable BGS borehole logs are available in close proximity of these cuttings, however, the most westerly cutting is anticipated to be founded on Raised Beach Deposits and Lambeth Group and the second most westerly cutting is likely to be founded in Lambeth Group. Both cuttings are located near the top of a topographical highs and groundwater is not anticipated to be encountered within either the Raised Beach Deposits or Lambeth Group aquifers. However, the Raised Beach Deposits and Lambeth Group aquifers could be water bearing at this location and may require dewatering to operate the cutting.

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13.9.6.14 The cutting may intercept the Raised Beach Deposits and Lambeth Group aquifers which are defined as medium value receptors. The operation of the cutting could require dewatering. The impact magnitude of dewatering at this location is assessed as minor and therefore the overall significance of the dewatering is considered slight adverse. 13.9.6.15 The proposed attenuation ponds may intercept groundwater contained in the Secondary A aquifer ground materials, which are defined as medium value receptors, during the operation phase. The operation of the ponds have the potential to require dewatering. The impact magnitude of dewatering at the attenuation pond locations is assessed as minor and therefore the overall significance of the attenuation pond dewatering is considered slight adverse. Groundwater recharge impacts 13.9.6.16 Option 3V1 requires the construction of new carriageway within currently undeveloped land to the west and east of Arundel. On construction completion the new road surface hardstanding will collect rainfall which would have otherwise naturally recharged groundwater aquifers. 13.9.6.17 For the regional bedrock aquifers, and the regionally significant outcrops of superficial aquifers, the new road surface hardstanding area is relatively small in comparison to the groundwater body recharge catchments, therefore the impact magnitude of groundwater recharge impacts due to new carriageway construction is considered to be negligible. Given the medium importance of the groundwater aquifers, the overall significance of effect is likely to be neutral. 13.9.6.18 For local superficial aquifers where the new road surface hardstanding area is proportionate in size to the groundwater body recharge catchments, a minor impact is anticipated. Given the medium importance of the superficial groundwater aquifers, the overall significance of effect is likely to be slight adverse. 13.9.7 Option 4/5AV1, Option 4/5AV2 and Option 5BV1 – construction phase

13.9.7.1 Option 4/5AV1, Option 4/5AV2 and Option 5BV1 may have an impact on the ordinary watercourses and land drains flowing south from Binsted Wood Complex LWS as the watercourses exit the wooded area. Option 4/5AV1, Option 4/5AV2 and Option 5BV1 will additionally cross a number of land drains between Ford Road and the Arun Valley Railway, the River Arun and the Binsted Rife as illustrated in Figure 13-1.

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Geomorphology and water quality Increased pollution 13.9.7.2 Option 4/5AV1, Option 4/5AV2 and Option 5BV1 requires the construction of an embankment across the River Arun (NGR 500700, 104800). The greatest risks to water quality during construction will be associated with the construction of new abutments and embankment adjacent to river, as well as temporary works within the river channel. The impacts are most likely to be associated with runoff from earth stockpiles during high rainfall events and/or flooding. In addition to this, some increase in sedimentation contained within overland flow from the construction working areas is likely to occur due to the likely proximity of works to the River Arun. However, it is a large tidal waterbody which is subject to increased sediment levels during large tidal flows and sediment entering the watercourse will be dispersed quickly through the tidal flow regime. Provided correct working procedures and practices proposed within the CEMP are adopted and care is taken to avoid pollution, the impacts during the construction phase would reduce greatly. Therefore, the magnitude of the potential impact to the quality of the River Arun is considered likely to be minor adverse. Consequently, there is likely to be a direct but temporary effect on the River Arun, with the significance assessed as slight adverse (not significant). 13.9.7.3 Groundwater flow paths may be altered due to the introduction of intrusive piled structures, but this is dependent on pile density, depth and orientation to groundwater flow. This will be assessed in PCF Stage 3 (Preliminary Design) as the design is progressed. There is potential for the piles to hydraulically connect waterbodies if the piles are constructed at significant depth. In addition to this, piles may create migration pathways for contaminants.

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13.9.7.4 Option 4/5AV1, Option 4/5AV2 and Option 5BV1 requires the construction of new carriageway within currently undeveloped land to the east of Arundel as the Scheme options cross the Arun Valley Railway and a clear span structure crossing the Binsted and Tortington Rife. The most likely risks are associated with increased sedimentation from exposed earth as well as increased risk of hydrocarbons associated with mechanical plant. The works could result in some measurable change in water quality in the receiving watercourses as increased sediment loads entering smaller watercourses may take longer to settle out or be dispersed through normal processes. Construction related impacts are considered to be direct and temporary as water quality within the watercourses would improve over time as sediments settle and pollutants are treated by entrapment, dilution and natural processes. The CEMP likely to adequately manage risks of pollution and spillage from mechanical plant. The impact to the ordinary watercourses that drain between the Arun Valley Railway line is considered to be minor adverse. 13.9.7.5 The magnitude of impact to the Binsted Rife and Tortington Rife is considered to be minor adverse, given the medium importance of these receptors and the likely temporary significance of effect is slight adverse (not significant). 13.9.7.6 The magnitude of impact to the ordinary watercourses that drain between the Arun Valley Railway line is considered to be minor adverse. Given the low importance of these features, these receptors the likely temporary significance of effect is neutral (not significant). Impacts to the hydro morphological and ecological quality of watercourses 13.9.7.7 Option 4/5AV1, Option 4/5AV2 and Option 5BV1 requires the construction of new carriageway within currently undeveloped land to the east of Arundel as the Scheme options cross the Arun Valley Railway and clear span structures across the Binsted Rife and Tortington Rife. The most likely risks are associated with increased sedimentation from exposed earth and construction of the earth embankments, as well as increased risk of hydrocarbons associated with mechanical plant. The works could result in some measurable change in water quality in the receiving watercourses as increased sediment loads entering smaller watercourses may take longer to settle out or be dispersed through normal processes. Construction related impacts are considered to be direct and temporary as water quality within the watercourses would improve over time as sediments settle and pollutants are treated by entrapment, dilution and natural processes. The CEMP likely to adequately manage risks of pollution and spillage from mechanical plant. The impact to the ordinary watercourses that drain between the Arun Valley Railway line is considered to be minor adverse. Given the low importance of these features, the likely temporary significance of effect is neutral (not significant).

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Flooding Flooding associated with temporary works 13.9.7.8 Temporary works associated with the Scheme within the floodplain and channel of the River Arun and any reduction in the capacity of the watercourse or floodplain (or impacts to existing flood defences) could increase flood risk predominantly to urban areas of Arundel and to Tortington Priory Farm. Works required for construction of a road bridge could reduce channel width if a dry working area is required within the channel and floodplain. Placing structures in the channel could also affect flood flow conveyance and pose risk of debris accumulating at temporary structures and further reducing channel capacity. This is unlikely to cause a notable increase in flood risk elsewhere as works are temporary and the likelihood of a significant flood event happening is relatively low and the connectivity of watercourse will be maintained. The magnitude of the impact will be heavily dependent on local conditions; however, the implementation of the CEMP and an appropriate flood response strategy will manage these risks. The impact magnitude during construction is considered to be negligible, with a significance of effect of neutral (not significant). 13.9.7.9 Temporary works will be required within the floodplain of the River Arun and the network of ordinary watercourses to the east of Arundel. The works are not considered to pose increased flood risk elsewhere during the construction of other crossings of the ordinary watercourses and land drains within Binsted Wood Complex LWS. The impact magnitude is assessed to be negligible, with an overall significance of effect of neutral (not significant). Groundwater Groundwater quality impacts 13.9.7.10 Option 4/5AV1, Option 4/5AV2 and Option 5BV1 creates a new route through the Walberton and Tortington areas, where Head Deposits, Raised Beach Deposits, River Terrace Deposits, Raised Marine Deposits, Lambeth Group and London Clay Formation are present. All geologies (apart from the London Clay Formation) are classified as Secondary A aquifers and are considered Medium value receptors. 13.9.7.11 Option 4/5AV1, Option 4/5AV2 and Option 5BV1 requires the construction of new carriageway within currently undeveloped land for most of the alignment. This will require soil stripping and cuttings, reducing aquifer overburden and consequently creating shorter/quicker/direct pathways for rainfall recharge and contamination, increasing aquifer vulnerability. Appropriate pollution control measures will be outlined within a CEMP and implemented, the risk to groundwater quality is likely to be comparatively minimal during Scheme construction.

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13.9.7.12 The magnitude of the potential impact to groundwater quality of the Lambeth Group and superficial aquifers is considered to be negligible, with an overall significance of effect of neutral (not significant). Groundwater dewatering impacts 13.9.7.13 Where cuttings or below ground surface structures (such as attenuation ponds) are proposed on aquifer ground materials, these structures may intercept groundwater. Where interceptions occur, groundwater removal or dewatering will be required to construct the cuttings and/or ponds. Groundwater dewatering can impact upon the groundwater flow and provision of water to local groundwater users or ecological habitats that are dependent on groundwater flow. 13.9.7.14 A ground investigation and subsequent groundwater level monitoring will be required to determine if groundwater will be intercepted by these proposed features. 13.9.7.15 Option 4/5AV2 includes three cuttings, one <8m deep cutting between chainage 725m to 1450m, a ~4m deep cutting between chainage 1500m to 1850m and a ~5m deep cutting between chainage 3100m and 3720m. 13.9.7.16 The <8m deep cutting between chainage 725m to 1450m is founded on <1.5m of Head Deposits, ~2.5m Raised Beach Deposits and at least 10m of clay rich Lambeth Group according to BGS borehole log SU90NE128. As the cutting is located on top of a topographical high, groundwater is not anticipated to be encountered within the Head Deposits or Raised Beach Deposits, however, these could be water bearing at this location. If the deposits are water bearing, then they will require dewatering to construct the cutting. 13.9.7.17 The cutting between chainage 725m to 1450m may intercept Head Deposits, Raised Beach Deposits and Lambeth Group aquifers, which are defined as medium value receptors. The temporary construction works of the cutting have the potential to require dewatering. The impact magnitude of dewatering at this location is assessed as negligible and therefore the overall significance of the dewatering is considered neutral (not significant). 13.9.7.18 The ~4m deep cutting between chainage 1500m to 1850m is founded on Head Deposits and London Clay Formation. No suitable BGS borehole logs in the vicinity of this cutting are available. Large quantities of groundwater are not anticipated to be encountered within the Head Deposits at this location, however, these deposits could contain finite quantities of groundwater. If the deposits are water bearing, they will require dewatering to construct the cutting.

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13.9.7.19 The cutting between chainage 1500m to 1850m may intercept Head Deposit aquifer, which is defined as a medium value receptor. The temporary construction works of the cutting have the potential to require dewatering. The impact magnitude of dewatering at this location is assessed as negligible and therefore the overall significance of the dewatering is considered neutral (not significant). 13.9.7.20 The ~5m deep cutting between chainage 3100m and 3720m is founded on <1.5m of Head Deposits, ~3m Raised Beach Deposits and at least 2.5m of London Clay Formation according to BGS borehole log TQ00NW135. As the cutting is located at the bottom of a topographical low, groundwater is anticipated to be encountered within the superficial deposits at this location. 13.9.7.21 The cutting between chainage 3100m and 3720m will likely intercept groundwater within the Head Deposit and Raised Beach Deposits which are defined as medium value receptors. The temporary construction works of the cutting have the potential to require dewatering. The impact magnitude of dewatering at this location is assessed as minor and therefore the overall significance of the dewatering is considered slight adverse (not significant). 13.9.7.22 There are three drainage ponds/basins proposed for Option 4/5AV1. Attenuation pond/basin construction will be located on and founded within Secondary A aquifer ground material. These ponds/basins may intercept groundwater in the Secondary A aquifers, which are defined as medium value receptors. The temporary construction works of the ponds have the potential to require dewatering. The impact magnitude of dewatering at this location is assessed as minor and therefore the overall significance of the dewatering is considered slight adverse (not significant). 13.9.7.23 As no groundwater dewatering is anticipated in the Chalk, no impact to local groundwater abstractions is expected. Therefore, a no change of effect is predicted. 13.9.7.24 Option 4/5AV1 includes three cuttings, one <5m deep cutting between chainage 1000m and 1600m, a <5.5m deep cutting between chainage 1825m to 2360m and a ~5m deep cutting between chainage 4100m and 4800m. The most easterly cutting of Option 4/5AV1 predominately follows the most easterly cutting of the Option 4/5AV2 alignment, which is assessed above, therefore, this cutting will not be reassessed. 13.9.7.25 The <5m deep cutting between Chainage 1000m and 1600m is founded on 6m+ of Head Deposits, according to BGS borehole log SU90NE90, which will be founded on Lambeth Group bedrock. As the cutting is located on top of a topographical high, groundwater is not anticipated to be encountered within the Head Deposits. If the deposits are water bearing, then they will require dewatering to construct the cutting.

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13.9.7.26 The cutting between chainage 1000m and 1600m may intercept Head Deposits aquifer, which is defined as medium value receptor. The temporary construction works of the cutting have the potential to require dewatering. The impact magnitude of dewatering at this location is assessed as negligible and therefore the overall significance of the dewatering is considered neutral (not significant). 13.9.7.27 The <5.5m deep cutting between chainage 1825m to 2360m is founded on <1.6m of Head Deposits, ~6.6m of London Clay Formation and Lambeth Group, as per local BGS borehole log SU90NE42, which will be founded on Lambeth Group bedrock. As the cutting is located on top of a topographical high, groundwater is not anticipated to be encountered within the Head Deposits or Lambeth Group. If the deposits are water bearing, then they will require dewatering to construct the cutting. 13.9.7.28 The cutting between chainage 1825m to 2360m may intercept Head Deposit aquifer, which is defined as a medium value receptor. The temporary construction works of the cutting have the potential to require dewatering. The impact magnitude of dewatering at this location is assessed as negligible and therefore the overall significance of the dewatering is considered neutral. 13.9.7.29 There are three drainage ponds/basins for Option 4/5AV2. It is anticipated that attenuation pond/basin construction will be located on and founded within Secondary A aquifer ground material. These ponds/basins may intercept groundwater in the Secondary A aquifers, which are defined as medium value receptors. The temporary construction works of the ponds have the potential to require dewatering. The impact magnitude of dewatering at this location is assessed as minor and therefore the overall significance of the dewatering is considered slight adverse (not significant). 13.9.7.30 As no groundwater dewatering is anticipated in the Chalk for Option 4/5AV2, no impact to local groundwater abstractions is expected. Therefore, the overall significance of effect is neutral (not significant). 13.9.7.31 Corridor 5BV1 includes two cuttings, one <7m deep cutting between chainage 820m and 2090m and a <5.5m deep cutting between chainage 4100m and 4800m. The most easterly cutting of Option 5BV1 predominately follows the most easterly cutting of the Option4/5AV1, which is assessed above, therefore, this cutting will not be reassessed. 13.9.7.32 The <7m deep cutting between chainage 820m and 2090m is founded on Head Deposits, Raised Beach Deposits, and River Terrace Deposits overlaying London Clay Formation bedrock. No suitable BGS borehole logs in the vicinity of this cutting are available for review. Groundwater may be encountered within the above listed superficial Deposits. If the deposits are water bearing, then they will require dewatering to construct the cutting.

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13.9.7.33 The cutting between chainage 820m and 2090m may intercept groundwater in the Head Deposits, Raised Beach Deposits, and River Terrace Deposits aquifers, which are defined as medium value receptor. The temporary construction works of the cutting have the potential to require dewatering. The impact magnitude of dewatering at this location is assessed as minor and therefore the overall significance of the dewatering is considered slight adverse (not significant). 13.9.7.34 There are four drainage pond/basin proposed for Option 5BV1. Attenuation pond/basin construction will be located on and founded within Secondary A aquifer ground material. These ponds/basins may intercept groundwater in the Secondary A aquifers, which are defined as medium value receptors. The temporary construction works of the ponds have the potential to require dewatering. The impact magnitude of dewatering at this location is assessed as minor and therefore the overall significance of the dewatering is considered slight adverse (not significant). 13.9.7.35 As no groundwater dewatering is anticipated in the Chalk for Option 5BV1, no impact to local groundwater abstractions is expected. Therefore, the overall significance of effect is neutral (not significant). 13.9.8 Option 4/5AV1, Option 4/5AV2 and Option 5BV1 – operation phase

Geomorphology and water quality Increased pollution 13.9.8.1 During operation, surface water runoff has the potential to contain silts and hydrocarbons that are washed off hard paved areas. These can increase water turbidity, deplete oxygen levels and be toxic to the aquatic environment. Uncontrolled discharge via infiltration to ground can also cause permanent deterioration of groundwater quality. Pollution of waterbodies from surface water runoff containing silts and hydrocarbons is considered a direct permanent impact. Although pollutants can be treated by natural processes in the waterbody the absence of adequate mitigation would result in a continuous discharge of polluting substances to waterbodies. Pollution as a result of the Scheme will be mitigated by the proposed surface water drainage system. This will include appropriate pollution control in line with the SuDS Manual Developed by CIRIA (C753). The magnitude of the impact posed to water quality during operation is likely to be negligible, with overall significance of effect being neutral given the appropriate mitigation measures are incorporated into design (not significant).

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Permanent impacts to the hydro morphological and ecological quality of watercourses 13.9.8.2 The works may pose risks to the hydro-morphological and ecological quality of the River Arun and Tortington Rife and ordinary watercourses within the Study Area by removing ecological habitat and severing connectivity. Appropriate culvert design measures of maintaining hydrological connectivity, creation of a natural bed and maintaining the low flow channel, the design of the culverts can be undertaken in such a way as to not increase velocity. The resulting overall significance of effect is likely to be neutral (not significant). 13.9.8.3 From a hydro morphological perspective, if there are no changes in bed gradient, no changes in erosion or deposition and no watercourse reprofiling is undertaken, the magnitude of impact is likely to be negligible. There will be a permanent loss of bankside habitat along the length of the proposed culverts; however, the Scheme alignment crosses approximately perpendicular to most watercourses and field drains, resulting in the smallest length of watercourse disturbance. With the detailed mitigation measures and further assessment into of ecological and hydro morphological impacts, the residual effect is likely to be neutral (not significant). Flooding

Increased fluvial flooding 13.9.8.4 The greatest flood risks during operation will be associated with permanent works within the floodplain and channel of the River Arun. Any reduction in the capacity of the watercourse or floodplain (or impacts to existing flood defences) could increase flood risk to urban areas to the south of the Scheme.

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Environmental Assessment Report Chapter 13 - Road Drainage and the Water Environment A27 Arundel Bypass – PCF Stage 2 Further Consultation

13.9.8.5 The construction of an earth embankment could pose a risk as this will introduce a physical barrier to the movement of water and displace floodplain storage. The mitigation measures are dependent on additional land take and detailed hydraulic modelling which will be used to inform the design of the Scheme in PCF Stage 3 (Preliminary Design). The compensation measures have not yet been developed or determined at this stage of design. The mitigation measures have not yet been developed or determined at this stage of design, however initial modelling of required compensation land indicates Option 4/5AV1, Option 4/5AV2 and Option 5BV1 requires significantly less land take than Option 1V5 and 1V9. Professional judgement based on knowledge and experience of similar schemes identified typical mitigation measures which are likely to include but are not limited: to floodplain compensation; upstream Natural Flood Management options for compensatory flood storage; provision of flood relief culverts to maintain floodplain connectivity; in addition to maintaining the capacity of the River Arun by providing a clear span structure. 13.9.8.6 The specific mitigation measures will require consultation and approval by the Environment Agency, landowners and other Statutory Environmental Bodies. There is scope for further refinement, but this would be undertaken once the preferred route is determined, in PCF Stage 3 (Preliminary Design). Given the very high importance of the River Arun floodplain, the significance of effect is likely to be neutral (not significant) with the mitigation measures embedded in the design. This significance of effect assumes that all required mitigation measures will be incorporated into the Scheme in PCF Stage 3 (Preliminary Design). 13.9.8.7 Culverts through the embankment will need to be appropriately designed to maintain the capacity of the channel of the land drains and ordinary watercourses. Consideration will also need to be given to maintaining connectivity for aquatic ecology. The magnitude of the impact will be heavily dependent on the characteristics of flooding in this area and will need to be informed via detailed hydraulic analysis. With flood flow conveyance and floodplain compensation mitigation measures in place, the magnitude of impacts is likely to be negligible. Given the very high importance of the River Arun floodplain, the overall significance of effect is likely to be neutral assuming that sufficient mitigation measures embedded into the design. 13.9.8.8 Option 4/5AV1, Option 4/5AV2 and Option 5BV1 will also cross the extensive network of land drains to the west and east of the River Arun. With the inclusion of floodplain compensation, provision of culverts of adequate size and maintenance of flood flow conveyance embedded in the design of the Scheme, the significance of the effect is likely to be neutral (not significant).

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Environmental Assessment Report Chapter 13 - Road Drainage and the Water Environment A27 Arundel Bypass – PCF Stage 2 Further Consultation

Impacts to flood flow conveyance of the Binsted and Tortington Rife and ordinary watercourses 13.9.8.9 Option 4/5AV1, Option 4/5AV2 and Option 5BV1 will cross the extensive network of watercourses to the east and west of the of the River Arun and the Binsted Rife and Tortington Rife. With floodplain compensation, provision of culverts of adequate size and maintenance of flood flow conveyance embedded in the design of the Scheme, the significance of the effect is likely to be neutral (not significant). Increased flood risk from surface water discharge 13.9.8.10 The introduction of impermeable surface area within the Study Area may lead to an increase in generated surface water runoff from the Scheme. During PCF Stage 3 (Preliminary Design), a surface water drainage system will be designed to attenuate surface water runoff from the majority of the Scheme prior to discharge. The overall significance of effect is considered to be neutral (not significant).

Groundwater Groundwater dewatering impacts 13.9.8.11 Where cuttings or below ground surface structures (such as attenuation ponds) are proposed on aquifer ground materials, these structures may intercept groundwater. Where interceptions occur, groundwater removal or dewatering will be required to operate the cuttings and/or ponds. Groundwater dewatering can impact upon the groundwater flow net and provision of water to local groundwater users or ecological habitats dependant on groundwater flow. 13.9.8.12 A ground investigation and subsequent groundwater level monitoring will be required to determine if groundwater will be intercepted by these proposed features. 13.9.8.13 Option 4/5AV2 includes three cuttings, one <8m deep cutting between chainage 725m to 1450m, a ~4m deep cutting between chainage 1500m to 1850m and a ~5m deep cutting between chainage 3100m and 3720m. 13.9.8.14 The cutting between chainage 725m to 1450m may intercept Head Deposits, Raised Beach Deposits and Lambeth Group aquifers, which are defined as medium value receptors. During the operation phase the cutting may require dewatering. The impact magnitude of dewatering at this location is assessed as negligible and therefore the overall significance of the dewatering is considered neutral (not significant).

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Environmental Assessment Report Chapter 13 - Road Drainage and the Water Environment A27 Arundel Bypass – PCF Stage 2 Further Consultation

13.9.8.15 The cutting between chainage 1500m to 1850m may intercept Head Deposit aquifer, which is defined as a medium value receptor. During the operation phase the cutting may require dewatering. The impact magnitude of dewatering at this location is assessed as negligible and therefore the overall significance of the dewatering is considered neutral (not significant). 13.9.8.16 The cutting between chainage 3100m and 3720m will likely intercept groundwater within the Head Deposit and Raised Beach Deposits which are defined as medium value receptors. During the operation phase the cutting may require dewatering. The impact magnitude of dewatering at this location is assessed as minor and therefore the overall significance of the dewatering is considered slight adverse (not significant). 13.9.8.17 The proposed attenuation ponds may intercept groundwater contained in the Secondary A aquifer ground materials, which are defined as medium value receptors, during the operation phase. The operation of the ponds have the potential to require dewatering. The impact magnitude of dewatering at the attenuation pond locations is assessed as minor and therefore the overall significance of the attenuation pond dewatering is considered slight adverse (not significant). 13.9.8.18 Option 4/5AV1 includes three cuttings, one <5m deep cutting between chainage 1000m and 1600m, a <5.5m deep cutting between chainage 1825m to 2360m and a ~5m deep cutting between chainage 4100m and 4800m. Please note that the most easterly cutting of Option 4/5AV1 predominately follows the most easterly cutting of the Corridor 4/5AV2 alignment, this cutting will not be reassessed. 13.9.8.19 The <5m deep cutting between chainage 1000m and 1600m is founded on Head Deposits overlaying Lambeth Group bedrock. The cutting may intercept Head Deposits aquifer, which is defined as medium value receptor. During the operation phase the pond may require dewatering. The impact magnitude of dewatering at this location is assessed as negligible and therefore the overall significance of the dewatering is considered neutral (not significant). 13.9.8.20 The <5.5m deep cutting between chainage 1825m to 2360m is founded on Head Deposits, London Clay Formation and Lambeth Group bedrock. The cutting may intercept groundwater in the Head Deposit aquifer, which is defined as a medium value receptor. During the operation phase the pond may require dewatering. The impact magnitude of dewatering at this location is assessed as negligible and therefore the overall significance of the dewatering is considered neutral (not significant).

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Environmental Assessment Report Chapter 13 - Road Drainage and the Water Environment A27 Arundel Bypass – PCF Stage 2 Further Consultation

13.9.8.21 The proposed attenuation ponds may intercept groundwater contained in the Secondary A aquifer ground materials, which are defined as medium value receptors, during the operation phase. The operation of the ponds have the potential to require dewatering. The impact magnitude of dewatering at the attenuation pond locations is assessed as minor and therefore the overall significance of the attenuation pond dewatering is considered slight adverse (not significant). 13.9.8.22 Option 5BV1 includes two cuttings, one <7m deep cutting between chainage 820m and 2090m and a <5.5m deep cutting between chainage 4100m and 4800m. The most easterly cutting of Option 5BV1 predominately follows the most easterly cutting of Option 4/5AV1, which is assessed above in Paragraph 13.9.8.17. 13.9.8.23 The <7m deep cutting between Chainage 820m and 2090m is founded on Head Deposits, Raised Beach Deposits, and River Terrace Deposits overlaying London Clay Formation bedrock. The cutting may intercept groundwater in the Head Deposits, Raised Beach Deposits, and River Terrace Deposits aquifers, which are defined as medium value receptor. During the operation phase the pond may require dewatering. The impact magnitude of dewatering at this location is assessed as minor and therefore the overall significance of the dewatering is considered slight adverse (not significant). 13.9.8.24 The proposed attenuation ponds may intercept groundwater contained in the Secondary A aquifer ground materials, which are defined as medium value receptors, during the operation phase. The operation of the ponds have the potential to require dewatering. The impact magnitude of dewatering at the attenuation pond locations is assessed as minor and therefore the overall significance of the attenuation pond dewatering is considered slight adverse (not significant).

Groundwater recharge impacts 13.9.8.25 Option 4/5AV1, Option 4/5AV2 and Option 5BV1 requires the construction of new carriageway within currently undeveloped land for most of the alignment. On construction completion the new road surface hardstanding will collect rainfall which would have otherwise naturally recharged groundwater aquifers.

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Environmental Assessment Report Chapter 13 - Road Drainage and the Water Environment A27 Arundel Bypass – PCF Stage 2 Further Consultation

13.9.8.26 For the regional bedrock aquifers, and the regionally significant outcrops of superficial aquifers, the new road surface hardstanding area is relatively small in comparison to the groundwater body recharge catchments, therefore the impact magnitude of groundwater recharge impacts due to new carriageway construction is considered to be negligible. Given the medium- high importance of the groundwater aquifers, the overall significance of effect is likely to be neutral (not significant). 13.9.8.27 For local superficial aquifers where the new road surface hardstanding area is proportionate in size to the groundwater body recharge catchments, a minor impact is anticipated. Given the medium importance of the superficial groundwater aquifers, the overall significance of effect is likely to be slight adverse (not significant).

13.10 Summary

13.10.1.1 A summary of the likely significance of effects during the construction and for the operational phase, with mitigation measures, is provided within Table 13- 11 and Table 13-12.

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Table 13-11 - Road drainage and water environment construction phase likely significant effects Option Option Corridor Impact Option 1V5 Option 1V9 Option 3V1 4/5AV1 4/5AV2 5BV1 Increased pollution to Slight Slight Slight Slight Slight Slight the River Arun adverse adverse adverse adverse (not adverse (not adverse (not (not (not (not significant) significant) significant) significant) significant) significant) Increased pollution to n/a n/a Slight Slight Slight Slight other main rivers adverse (not adverse (not adverse (not adverse (not Geomorphology significant) * significant) significant) significant) and water quality Increased pollution for Neutral (not Neutral (not Neutral (not Neutral (not Neutral (not Neutral (not works near the ordinary significant). significant). significant). significant). significant). significant). watercourses Impacts to the hydro Neutral (not Neutral (not Neutral (not Neutral (not Neutral (not Neutral (not morphological and significant) significant) significant). significant). significant). significant). ecological quality of watercourses Temporary works within Neutral (not Neutral (not Neutral (not Neutral (not Neutral (not Neutral (not the floodplain significant) significant) significant). significant). significant). significant). associated with the Flooding River Arun and the network of ordinary watercourses Pond dewatering will Slight Slight Slight Slight Slight Slight remove groundwater adverse adverse adverse adverse adverse adverse Groundwater from the aquifer unit (not (not (not (not (not (not (Secondary A significant) significant) significant) significant) significant) significant) Aquifers).

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Environmental Assessment Report Chapter 13 - Road Drainage and the Water Environment A27 Arundel Bypass – PCF Stage 2 Further Consultation

Option Option Corridor Impact Option 1V5 Option 1V9 Option 3V1 4/5AV1 4/5AV2 5BV1 Risks to water quality of Neutral (not Neutral (not Neutral (not Neutral (not Neutral (not Neutral (not all groundwater significant) significant) significant) significant) significant) significant) aquifers.

Table 13-12 - Road drainage and water environment operational phase likely significant effects Option Option Impact Option 1V5 Option 1V9 Option 3V1 Corridor 5BV1 4/5AV1 4/5AV2 Increased Neutral (not Neutral (not Neutral (not Neutral (not Neutral (not Neutral (not pollution to the significant) significant) significant). significant). significant). significant). River Arun, other watercourses and groundwater Geomorphology and water Permanent Neutral (not Neutral (not Neutral (not Neutral (not Neutral (not Neutral (not quality impacts significant) significant) significant) significant) significant) significant) associated with new structures within or in close proximity to watercourses Increased Neutral* (not Neutral* Neutral* (not Neutral* Neutral* (not Neutral* (not fluvial/tidal significant). (not significant). (not significant). significant). flooding significant). significant). Flooding Impacts to flood Neutral* (not Neutral* Neutral* (not Neutral* Neutral* (not Neutral* (not flow conveyance significant) (not significant) (not significant) significant) of the Binsted significant) significant) Rife, Tortington

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Environmental Assessment Report Chapter 13 - Road Drainage and the Water Environment A27 Arundel Bypass – PCF Stage 2 Further Consultation

Option Option Impact Option 1V5 Option 1V9 Option 3V1 Corridor 5BV1 4/5AV1 4/5AV2 rife and ordinary watercourses Increased flood Neutral* (not Neutral* Neutral* (not Neutral* Neutral* (not Neutral* (not risk associated significant) (not significant) (not significant) significant) with surface water significant) significant) discharge Pond dewatering Slight Slight Slight Slight Slight Slight adverse will remove adverse adverse adverse adverse adverse (not significant) groundwater from (not (not (not (not (not the aquifer unit significant) significant) significant) significant) significant) (Secondary A Aquifers). Lesser Neutral (not Neutral (not Neutral (not Neutral (not Neutral (not Neutral (not groundwater significant) significant) significant). significant). significant). significant). recharge due to Groundwater new hardstanding (Regionally present aquifers) Lesser Neutral (not Neutral (not Neutral (not Neutral (not Neutral (not Neutral (not groundwater significant) significant) significant). significant). significant). significant). recharge due to new hardstanding (Local superficial aquifers) *Assumed that appropriate mitigation is in place.

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Figures © Crown copyright and database rights 2019 Ordnance Survey 100030649. Kilometres You are permitted to use this data solely to enable you to respond to, or interact with, 0 1 the organisation that provided you with the data. You are not permitted to copy, DO NOT SCALE sub-licence, distribute or sell any of this data to third parties in any form. SAFETY, HEALTH AND ENVIRONMENTAL Drawing Status Suitability Project Title KEY: REGIONAL INVESTMENT PROGRAMME INFORMATON FINAL S0 OPTION 1V5 FLOOD ZONES A27 ARUNDEL In addition to the hazards/risks normally associated with the types of work Drawing Title OPTION 1V9 ENVIRONMENT AGENCY - FLOOD ZONE 3 detailed on this drawing, note the following significant residual risks WSP House OPTION 3V1 (Reference shall also be made to the design hazard log). ENVIRONMENT AGENCY - FLOOD ZONE 2 70 Chancery Lane FIGURE 13-1: Construction OPTION 4/5AV1 RISK OF FLOODING FROM SURFACE WATER London WATER CONSTRAINTS MAP OPTION 4/5AV2 WC2A 1AF HIGH (PROBABILITY OF OCCURRENCE 1 IN 30 YEARS) Tel: +44 (0)20 7314 5000 OPTION 5BV1 ALL VARIANTS MEDIUM (PROBABILITY OF OCCURRENCE BETWEEN 1 IN 30 YEARS AND 1 IN Maintenance / Cleaning www.wsp.com Scale Drawn Checked Aproved Authorised 1KM WATER CONSTRAINTS STUDY AREA 100 YEARS) Copyright © WSP Group (2019) 1:25,000 AS LM MD PA RIVERS LOW (PROBABILITY OF OCCURRENCE BETWEEN 1 IN 100 YEARS AND 1 IN 1,000 Client Original Size Date Date Date Date MAIN RIVERS YEARS) Use A3 27/06/19 27/06/19 27/06/19 27/06/19 ORDINARY WATERCOURSES GROUNDWATER SOURCE PROTECTION ZONES Drawing Number Project Ref. No. Project Originator Volume 70052558 SURVEYED WATERCOURSES ZONE I - INNER PROTECTION ZONE Decomissioning / Demolition HE551523-WSP-GEN- Revision ZONE II - OUTER PROTECTION ZONE P01.1 --- First Issue ------SWI-GI-DR-0163 ZONE III - TOTAL CATCHMENT Rev. Date Description By Chk'd App'd P01 Location Type Role Number

Path: \\uk.wspgroup.com\central data\Projects\700525xx\70052558 - CDF A27 AB Further Consultation\02 WIP\GI GIS\Mxd\EAR\HE551523-WSP-GEN-SWI-GI-DR-0163_P01_WaterConstraints_All_Variants.mxd: Plotted by: UKAXS091 Date: Jun 27, 2019 - 03:56PM WAT_AQ096

WAT_AQ088

EAST_AQ092 ARUNDEL EAST_AQ028 TORT_AQ075 EAST_AQ035 WAT_AQ089 EAST_AQ095 TORT_AQ076 EAST_AQ029 LID_AQ101 TORT_AQ071 EAST_AQ036 EAST_AQ038 TORT_AQ078 WAT_AQ086 EAST_AQ039 TORT_AQ077 TORT_AQ112 EAST_ EAST_ WAT_AQ087 AQ041 EAST_AQ040 EAST_AQ026 AQ037 EAST_ EAST_AQ031B TORT_AQ074 AQ042 EAST_AQ031A TORT_AQ073 TORT_AQ069 WEST_AQ085 EAST_AQ032 TORT_AQ072 TORT_AQ068 TORT_AQ070 EAST_AQ025 EAST_AQ024 EAST_AQ043

EAST_AQ027 LID_AQ104 TORT_AQ056 EAST_ EAST_AQ099 TORT_AQ059 TORT_AQ057B EAST_AQ023 BIN_AQ100 AQ113 EAST_AQ022 EAST_AQ030B WEST_AQ049 EAST_AQ097 EAST_AQ018C TORT_ EAST_AQ005 EAST_ EAST_ TORT_AQ066 WEST_AQ048B EAST_AQ017 AQ055 AQ030A AQ021 EAST_AQ002 LID_AQ105 WEST_AQ050 EAST_ EAST_AQ018B EAST_AQ034 Walberton Binsted AQ011 EAST_AQ001B EAST_AQ020 WEST_AQ051 EAST_ AQ093 EAST_AQ098 TORT_AQ058 WEST_AQ044 AQ006 EAST_AQ018A EAST_ TORT_AQ065 TORT_AQ091 AQ003 EAST_AQ015A Crossbush EAST_AQ004 EAST_ EAST_AQ001A TORT_AQ067 AQ014

EAST_ WEST_AQ048A EAST_ AQ012 EAST_AQ015B AQ111 AQ010 WEST_AQ047 EAST_AQ007

EAST_AQ013 TORT_AQ052 EAST_AQ008 WEST_AQ046B WEST_AQ045A TORT_AQ053

TORT_AQ064 Tortington TORT_AQ057A TORT_AQ054 WEST_AQ046A EAST_AQ009 u n WEST_AQ045B A r r e EAST_AQ106 EAST_AQ107 TORT_AQ060 EAST_AQ019 v i

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Kilometres © Crown copyright and database rights 2018 Ordnance Survey 100030649. 0 1 You are permitted to use this data solely to enable you to respond to, or interact with, the organisation that provided you with the data. You are not permitted to copy, DO NOT SCALE sub-licence, distribute or sell any of this data to third parties in any form. SAFETY, HEALTH AND ENVIRONMENTAL Drawing Status Suitability Project Title KEY: REGIONAL INVESTMENT PROGRAMME INFORMATON FINAL S0 OPTION 1V5 INDICATIVE CATCHMENT WATERCOURSES A27 ARUNDEL BYPASS In addition to the hazards/risks normally associated with the types of work Drawing Title OPTION 1V9 detailed on this drawing, note the following significant residual risks BINSTED STREAM ARUNDEL CASTLE (Reference shall also be made to the design hazard log). WSP House FIGURE 13-2: OPTION 3V1 EAST OF ARUN Construction 70 Chancery Lane UNNAMED ORDINARY CHURCH/CATHEDRAL London OPTION 4/5AV1 LIDSEY RIFE WC2A 1AF Tel: +44 (0)20 7314 5000 WATERCOURSES OPTION 4/5AV2 TORTINGTON STREAM Maintenance / Cleaning www.wsp.com Scale Drawn Checked Approved Authorised OPTION 5BV1 SPRING DITCH Copyright © WSP Group (2019) 1:20,000 AS LM MD PA Client Original Size Date Date Date Date WEST OF ARUN Use A3 27/06/19 27/06/19 27/06/19 27/06/19 Drawing Number Project Ref. No. Project Originator Volume 70052558 Decomissioning / Demolition HE551523-WSP-GEN- Revision Name must be checked against the lecal Environment Agency knowledge / Watercourses naming convention example: TORT_AQ067 = Catchment_Aquatic Survey reference P01.1 --- First Issue ------NOTES: the data source for the catchments is the LiDAR tiles of the Environment Agency (2017): https://data.gov.uk/publisher/environment-agency. SWI-GI-DR-0006 Rev. Date Description By Chk'd App'd P01 Labelled watercourses outside of the defined catchments are in an unknown catchment, which will be confirmed with the Environment Agency in due course. Location Type Role Number The watercourses are verified through site survey or extracted from 1:25,000 series Ordnance Survey basemaps where there was no access Path: \\uk.wspgroup.com\central data\Projects\700525xx\70052558 - CDF A27 AB Further Consultation\02 WIP\GI GIS\Mxd\Environment\WORKING\HE551523-WSP-GEN-SWI-GI-DR-0006_P01_Arundel_Style_Guide_Drawing_Watercourses.mxd: Plotted by: UKAXS091 Date: Jun 27, 2019 - 03:53PM ARUNDEL

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Kilometres © Crown copyright and database rights 2018 Ordnance Survey 100030649. 0 1 You are permitted to use this data solely to enable you to respond to, or interact with, the organisation that provided you with the data. You are not permitted to copy, DO NOT SCALE sub-licence, distribute or sell any of this data to third parties in any form. SAFETY, HEALTH AND ENVIRONMENTAL Drawing Status Suitability Project Title KEY: REGIONAL INVESTMENT PROGRAMME INFORMATON FINAL S0 OPTION 1V5 INDICATIVE CATCHMENT MAIN DITCHES A27 ARUNDEL BYPASS In addition to the hazards/risks normally associated with the types of work Drawing Title OPTION 1V9 WATERCOURSES detailed on this drawing, note the following significant residual risks BINSTED STREAM (Reference shall also be made to the design hazard log). WSP House FIGURE 13-3: OPTION 3V1 EAST OF ARUN ARUNDEL CASTLE Construction 70 Chancery Lane London NAMED ORDINARY OPTION 4/5AV1 LIDSEY RIFE WC2A 1AF WATERCOURSES CHURCH/CATHEDRAL Tel: +44 (0)20 7314 5000 OPTION 4/5AV2 TORTINGTON STREAM Maintenance / Cleaning www.wsp.com Scale Drawn Checked Approved Authorised OPTION 5BV1 SPRING DITCH Copyright © WSP Group (2019) 1:20,000 AS LM MD PA Client Original Size Date Date Date Date WEST OF ARUN Use A3 09/08/19 09/08/19 09/08/19 09/08/19 Drawing Number Project Ref. No. Project Originator Volume 70052558 Decomissioning / Demolition HE551523-WSP-GEN- Revision P01.1 --- First Issue ------NOTES: the data source for the catchments is the LiDAR tiles of the Environment Agency (2017): https://data.gov.uk/publisher/environment-agency. SWI-GI-DR-0214 Rev. Date Description By Chk'd App'd P01 Labelled watercourses outside of the defined catchments are in an unknown catchment, which will be confirmed with the Environment Agency in due course. Location Type Role Number The watercourses are verified through site survey or extracted from 1:25,000 series Ordnance Survey basemaps where there was no access Path: \\uk.wspgroup.com\central data\Projects\700525xx\70052558 - CDF A27 AB Further Consultation\02 WIP\GI GIS\Mxd\Environment\Water Environment\HE551523-WSP-GEN-SWI-GI-DR-0214_P01_Arundel_Style_Guide_Drawing_Watercourses_Named.mxd: Plotted by: UKAXS091 Date: Aug 09, 2019 - 04:30PM

Appendix 13-1: Environment Agency Baseline Model Approval

Ms Sophie Hartfield Our ref: HA/2017/119374/04-L02 Highways England Your ref: - Bridge House 1 Walnut Tree Close Date: 05 August 2019 Guildford Surrey GU1 4LZ

Dear Ms Hartfield

BASELINE FLOOD RISK MODEL - IMPROVEMENTS TO A27 CORRIDOR AT ARUNDEL

We can confirm that we are satisfied that the baseline model that has been produced for improvements to the A27 corridor at Arundel is appropriate for use in design modelling for the scheme. This followed a final review of the model that was completed by the Environment Agency in June 2018.

As you are aware we will continue to work with you and your teams as you progress the scheme.

Yours sincerely,

Hannah Hyland Planning Specialist

Direct dial 0203 0257088 Direct e-mail [email protected]

Environment Agency, Guildbourne House Chatsworth Road, Worthing, West Sussex, BN11 1LD. Customer services line: 03708 506 506