Land Off Rawreth Lane, Rayleigh,

Flood Risk Assessment

Project number: 60469673

September 2020

Land Off Rawreth Lane, Rayleigh Essex Project number: 60469673

Quality information

Prepared by Checked by Verified by Approved by Helen Judd Sarah Littlewood Peter Mansell Dan Scurlock Principal Water & Flood Principal Water & Flood Technical Director Associate Director Risk Consultant Risk Consultant

Revision History

Revision Revision date Details Authorized Name Position

1 July 2020 Draft for Client Dan Scurlock Associate Director Comment

2 August 2020 Draft for Legal Dan Scurlock Associate Director Review

3 2nd Sep 2020 Draft following Dan Scurlock Associate Director Legal Review

4 14th September Final for planning Dan Scurlock Associate Director submission

Distribution List

# Hard Copies PDF Required Association / Company Name

- 1 Countryside Properties (UK) Limited

Prepared for:

Countryside Properties (UK) Limited

Prepared by:

AECOM Limited Midpoint, Alencon Link Basingstoke Hampshire RG21 7PP

T: +44(0)1256 310200 aecom.com

© 2020 AECOM Limited. All Rights Reserved.

This document has been prepared by AECOM Limited (“AECOM”) for sole use of our client (the “Client”) in accordance with generally accepted consultancy principles, the budget for fees and the terms of reference agreed between AECOM and the Client. Any information provided by third parties and referred to herein has not been checked or verified by AECOM, unless otherwise expressly stated in the document. No third party may rely upon this document without the prior and express written agreement of AECOM.

AECOM

Land Off Rawreth Lane, Rayleigh Essex Project number: 60469673

Table of Contents

1. Introduction ...... 5 1.1 Terms of Reference ...... 5 1.2 Background...... 5 1.3 Aims and objectives ...... 5 1.4 Methodology ...... 6 2. Site Description...... 7 2.1 Location ...... 7 2.2 Local Water Features ...... 7 2.3 Flood Zone...... 8 2.4 Topography ...... 9 2.5 Geology, Soils and Hydrogeology ...... 9 3. Development Proposals ...... 10 3.1 Proposed Development ...... 10 3.2 Development Lifetime ...... 10 3.3 Development Vulnerability Classification ...... 10 4. Flood Risk to the Proposed Development...... 12 4.1 Overview ...... 12 4.2 Fluvial Flood Risk ...... 12 4.3 Tidal Flood Risk ...... 14 4.4 Surface Water Flood Risk and Overland Flow ...... 16 4.5 Groundwater Flood Risk ...... 17 4.6 Sewer Flood Risk ...... 18 4.7 Artificial Sources...... 18 4.8 Summary of Flood Risk to the Proposed Development ...... 18 5. Flood Risk from the Proposed Development ...... 20 5.1 Overview ...... 20 5.2 Tidal Flood Risk ...... 20 5.3 Fluvial Flood Risk ...... 20 5.4 Surface Water Flood Risk and Overland Flow ...... 21 5.5 Groundwater Flood Risk ...... 21 5.6 Sewer Flood Risk ...... 21 5.7 Artificial Sources...... 22 5.8 Summary of Flood Risk from the Proposed Development ...... 22 6. Mitigation Measures ...... 23 6.1 Overview ...... 23 6.2 Mitigation of Groundwater Flood Risk ...... 23 7. Planning Policy ...... 24 7.1 National Planning Policy Framework: ...... 24 7.2 Local Planning Policy: District Council Local Development Framework Core Strategy ...... 25 7.3 Council Local Development Framework Allocations Plan ...... 26 8. Residual Flood Risk...... 27 8.1 Overview ...... 27 8.2 Blockages at structures along Rawreth Brook ...... 27 8.3 Failure or Exceedance of Sewer Network...... 27 9. Summary ...... 29 9.1 Overview ...... 29 9.2 Flood Risk – To the Proposed Development ...... 29 9.3 Flood Risk – From the Proposed Development...... 29

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Land Off Rawreth Lane, Rayleigh Essex Project number: 60469673

9.4 Planning Policy ...... 29 9.5 Recommended Mitigation ...... 29 Appendix A Redline Boundary...... 30 Appendix B Topographic Survey ...... 31 Appendix C Proposed Development Plans ...... 32 Appendix D Outline Drainage Strategy...... 33 Appendix E Model Build Report ...... 34 Appendix F Anglian Water Correspondence ...... 35

Figures

Figure 2-1 Site Location (Contains Ordnance Survey data © Crown copyright and database right 2020)...... 7 Figure 2-2 Site overview (Contains Ordnance Survey data © Crown copyright and database right 2020) ...... 8 Figure 4-1 Environment Agency Flood Map for Planning ...... 12 Figure 4-2 Flood modelling extents ...... 13 Figure 4-3 Flood Mapping with Proposed Development Plans (refer to Appendix C for landuse descriptions) ...... 14 Figure 4-4 2017 Modelled Tidal Extents (Contains Ordnance Survey data © Crown copyright and database right 2020) ...... 15

Tables

Table 4-1 Extracted Peak Water Levels from Environment Agency 2017 River Crouch Modelling (mAOD) ...... 15 Table 4-2 Summary of Flood Risk to the Proposed Development...... 19 Table 5-1 Summary of Flood Risk from the Proposed Development ...... 22 Table 7-1 PPG (Table 3) Flood risk vulnerability and flood zone ‘compatibility’...... 24 Table 7-2 Peak river flow allowances by river basin district (Ref: Flood risk assessments: climate change allowances Guidance by Environment Agency, February 2016) ...... 25

AECOM

Land Off Rawreth Lane, Rayleigh Essex Project number: 60469673

1. Introduction 1.1 Terms of Reference 1.1.1 AECOM has been commissioned by Countryside Properties (UK) Limited to prepare a flood risk assessment (FRA) to support a new outline planning application which re-plans part of a previously consented planning application for a residential mixed-used development at a site “Land off Rawreth Lane”, Rayleigh, Essex (hereinafter referred to as the ‘Site’). Hereinafter the subject of this application is referred to as the ‘Proposed Development’.

1.1.2 This FRA has been prepared in accordance with the National Planning Policy Framework (NPPF)1 and supporting Planning Practice Guidance (PPG)2. 1.2 Background 1.2.1 In June 2016 outline planning permission was granted for a residential-led mixed use development of 500 homes to the west of Rayleigh (reference 15/00362/OUT) following the inclusion of the Site in Rochford District Council’s Development Plan. 1.2.2 This permission also included: reserving land for a potential new primary school; areas for non- residential uses (suitable for a range of uses including, health or medical, creche, day nursery or day centre, small scale retail, food and drink establishments, or a residential institution); open spaces; landscaping; footpath and cycle links; drainage and infrastructure works.

1.2.3 Construction of the development commenced in May 2019 and the first new homes are expected to be completed and occupied in autumn 2020. 1.2.4 The new 2020 outline planning application for the Site re-plans part of the originally consented scheme, and has the effect of the amount of land within the Site for residential purposes by circa 3.5 hectares (ha) by reducing the open space, and increasing the density on some previously approved parcels, such that overall, the number of residential units would increase compared to the original approval by up to 222 homes, and the non-residential built floorspace would increase by up to 500m². 1.2.5 The red line boundary for the 2020 outline planning application is included in Appendix A and hereinafter is referred to as the ‘Site’. 1.3 Aims and objectives 1.3.1 As stated in paragraph 30 of the PPG2 , the purpose of a site specific FRA is “… to assess the flood risk to and from a development site. Where necessary the assessment should accompany a planning application submitted to the local planning authority. The assessment should demonstrate to the decision-maker how flood risk will be managed now and over the development’s lifetime, taking climate change into account, and with regard to the vulnerability of its users.”

1.3.2 The following objectives have been achieved to fulfil this aim: • Gather desktop information relating to geology, topography and local water features that may influence the risk of flooding to the Proposed Development; • Identify and quantify the vulnerability of the Proposed Development to flooding from different sources and identify potential flood risk reduction measures;

1‘National Planning Policy Framework’ (February 2019) available at https://www.gov.uk/government/publications/national- planning-policy-framework--2 Accessed 24th June 2020. 2 ‘Flood risk and Coastal Change’ (2014) available at https://www.gov.uk/guidance/flood-risk-and-coastal-change Accessed 24th June 2020.

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Land Off Rawreth Lane, Rayleigh Essex Project number: 60469673

• Assess the risk of flooding from all sources (tidal, fluvial, surface water, groundwater, sewers and ordinary watercourses) to and from the Proposed Development allowing for the effects of climate change over the lifetime of the Proposed Development; and, • Assess the remaining ‘residual’ risk after risk reduction measures have been taken into account and demonstrate that this is acceptable for the Proposed Development. 1.4 Methodology 1.4.1 AECOM’s approach to FRAs is based on the industry standard Source-Pathway-Receptor model. The Source-Pathway-Receptor model firstly identifies the causes or ‘sources’ of flooding to and from a development. This identification is based on a review of available information such as mapping, local conditions and consideration of the effects of climate change. The nature and likely extent of flooding arising from any one source is considered, e.g. whether such flooding is likely to be localised or widespread. 1.4.2 As well as flooding from more obvious sources such as rivers and the sea, assessment of other flooding sources, this includes groundwater flooding, surface water flooding, sewer flooding and flooding from artificial sources. 1.4.3 The presence of a flood source does not always imply a risk. For example, the presence of a sewer does not necessarily increase the risk of flooding unless the sewer is local to the development and ground levels encourage surcharged flows to accumulate. The exposure pathway or ‘flooding mechanism’ determines whether there is a risk of exposure to a flood source. If a flooding mechanism is not present, then potential risk from the associated flood source is considered to be negligible.

1.4.4 If a flood source and flooding pathway are identified, then assessment of the flood risk to the receptor is determined by combining the probability of the flood event occurring with the severity of impact (or consequences) if the flood event were to occur. Receptors include any people or buildings which are connected to the source by a pathway. 1.4.5 The potential severity of the impact is determined through consideration of a combination of flood source type, flood mechanisms present, layout and design of the proposed receptor and vulnerability of the proposed receptor. 1.4.6 In summary, for a particular flood risk to exist, all the elements of the Source-Pathway-Receptor model must be present. Effective mitigation measures can be provided to reduce the magnitude of flood risk by removing one element of the model, such as a pathway. The incorporation of flood defence or flood resilience measures into building receptors and the provision of safe access and egress plans for users of a development are all strategies which, if utilised correctly, will reduce or remove the pathway element of flood risk.

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Land Off Rawreth Lane, Rayleigh Essex Project number: 60469673

2. Site Description 2.1 Location 2.1.1 The Site relating to this application covers an area of 15.87 hectares (ha.) and is currently being redeveloped for a residential mixed-use by Countryside Properties (UK) Limited. The approximate national grid reference for the centre of the Site is TQ 79244 92418. The location of the Site can be seen in Figure 2-1 and the redline boundary is included in Appendix A.

2.1.2 The Site is located to the north west of the urban extent of Rayleigh, Essex. Rawreth Lane passes along the northern border of the Site and London Road (A129) passes along the southern boundary. Further arable farmland is present to the west of the Site. 2.1.3 To the east of the Site lies the Rawreth Industrial Estate, with sections of residential areas to the north east (Laburnum Way) and south east (Cheapside West). Lower Barn Farm is located to the south of the Site. Rawreth Hall is located to the north west of the Site.

Figure 2-1 Site Location (Contains Ordnance Survey data © Crown copyright and database right 2020) 2.2 Local Water Features 2.2.1 As shown Figure 2-1, the Site is divided by the Rawreth Brook. The Rawreth Brook is classified as an Environment Agency Main River3 and is a tributary of the River Crouch (which is tidally influenced). This river flows from the south of Grosvenor Road (south east of the Site) in a north westerly direction, before joining the River Crouch upstream of Battlesbridge (X577518, Y194163). To the west of the Site, a Main River channel draining from the south joins the

3 A main river is defined by the environment agency as “Main rivers are watercourses shown on the statutory main river maps held by the Environment Agency, the Department of Environment, Food and Rural Affairs (in ) and the Welsh Assembly Government (in Wales). They can include any structure or appliance for controlling or regulating the flow of water into, in o r out of the channel. The Environment Agency has permissive powers to carry out works of maintenance and improvement on these rivers. Our formal consent is required for works that affect a main river.” (Environment Agency available online at http://www.geostore.com/environment-agency/WebStore?xml=environment-agency/xml/dataLayers_MR.xml)

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Land Off Rawreth Lane, Rayleigh Essex Project number: 60469673

Rawreth Brook. These channels are designated Main Rivers; therefore, the Environment Agency have discretionary flood risk management, enforcement and maintenance powers on them. In addition, there are several land drainage ditches that flow from the north and south of the Site to the Rawreth Brook. 2.2.2 To the west of the Site, there is an overflow channel from the Rawreth Brook that flows to the north, before entering a pond and flowing in a north westerly direction towards Rawreth. This overflow channel is located opposite the point of the confluence of the main river channel that drains from the south. 2.2.3 To the west of the Site, a section of the Rawreth Brook is culverted as part of a crossing between the fields. This is located approximately 60m from the western boundary of the Site. A drainage ditch, draining form the south of the Site, joins the Rawreth Brook at this point. The topographic survey for the Site (Appendix B) identifies the culvert to have a diameter of 750 mm.

Figure 2-2 Site overview (Contains Ordnance Survey data © Crown copyright and database right 2020) 2.3 Flood Zone 2.3.1 The Environment Agency’s Flood Map for Planning (Rivers and Sea)4 shows that the Site lies within Flood Zone 1, Flood Zone 2 and Flood Zone 3 associated with the Rawreth Brook. These are defined as: • Flood Zone 1 Low Probability – Land having less than 0.1% (1 in 1000 year) annual exceedance probability (AEP) of river or sea flooding; • Flood Zone 2 Medium Probability – Land having between a 1% (1 in 100 year) and 0.1% (1 in 1000 year) AEP of river flooding, or land having between a 0.5% (1 in 200 year) and 0.1% (1 in 1000 year) of sea flooding; and, • Flood Zone 3 High Probability – Land having a 1% (1 in 100 year) AEP of greater of river flooding, or Land having a 0.5% (1 in 200 year) AEP of greater of sea flooding.

4 ‘Environment Agency Flood Map for Planning’ available at https://flood-map-for-planning.service.gov.uk/, accessed 24th June 2020.

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Land Off Rawreth Lane, Rayleigh Essex Project number: 60469673

The Site is not shown to benefit from defences. 2.4 Topography 2.4.1 A topographic survey of the Site was completed in 2009 by Survey Solutions and is included in Appendix B. 2.4.2 The general slope of the Site is from east to west. There is also a slope from the north and the south towards the centre of the Site towards the line of the Rawreth Brook. The lowest point in the topography is therefore towards the west of the Site, where levels are at 7.8 meters above Ordnance Datum (mAOD), as the Rawreth Brook flows west out of the Site. 2.4.3 The highest points are to the south east and the north east of the Site, where the ground levels are at 15.6mAOD and 27.6mAOD respectively. Within the northern part of the Site, there is a section with a steeper slope of approximately 1 in 20 that runs across the Site from west to east.

2.4.4 From the east to the west of the Site, following the channel of the river, the ground levels fall from 12.2mAOD to 7.8mAOD (this is a gradient of approximately 1:600). 2.5 Geology, Soils and Hydrogeology 2.5.1 The bedrock geology at the Site is predominantly the London Clay Formation (clay, silt and sand) overlain in some places by superficial Head Deposits (comprising of sand and gravel). The central part of the Site, adjacent to the Rawreth Brook has superficial Alluvium deposits5. 2.5.2 There are three shallow boreholes on or near the Site5. In the northern part of the Site, there are two borehole records (TQ79SE2 and TQ79SE3) to the east of Rawreth Hall. These record the geology to be clay dominated. The groundwater levels are recorded to be at 6.71m below ground level (approximately 13.3 mAOD) and 3.66 m below ground level (approximately 17.3 mAOD).

2.5.3 A borehole record further to the south (TQ79SE13), adjacent to Rawreth Brook, records the presence of superficial Head Deposits and Alluvium to 1.1m below ground level. London Clay was present below the superficial deposits to the base of the borehole at 2.5 m below ground level. 2.5.4 The topsoil in the northern part of the Site is a slowly permeable seasonally wet base rich and loamy and clayey soil. The topsoil around Rawreth Brook and the southern part of the Site is a loamy clayey soil with impeded drainage6. 2.5.5 The Defra aquifer designation mapping7 identifies the superficial deposits across the Site to be classified as aquifers. The Alluvium is considered to be Secondary A aquifers that are capable of supporting water supplies at local scales and can be important in forming base flows to rivers. The Head Deposits are classified as secondary undifferentiated aquifers due to the variable geology. 2.5.6 The northern part of the Site, dominated by the London Clay, is classified as unproductive strata. That is, the clay has low permeability and will have negligible significance on water supply or river base flow.

5 British Geological Survey ‘Geology of Britain Viewer’ available online at http://www.bgs.ac.uk/data/mapViewers/home.html accessed June 2020. 6 Cranfield Soil and Agrifood, ‘Soilscapes’ available online at: https://www.landis.org.uk/soilscapes/ June 2020. 7 Defra ‘Magic Maps’ available online at https://magic.defra.gov.uk/MagicMap.aspx accessed June 2020.

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Land Off Rawreth Lane, Rayleigh Essex Project number: 60469673

3. Development Proposals 3.1 Proposed Development 3.1.1 The Proposed Development Plans are included in Appendix C and cover an area of 15.87 ha.

3.1.2 The proposals are for the erection of residential development and the provision of non- residential floorspace (falling within uses classes A1 and/or A3 and/or A4 and/or D1b) with associated open space, landscaping, parking, servicing, utilities, footpath and cycle links, drainage and infrastructure works. 3.1.3 The original 2016 outline permission granted consent for 500 residential units (by reason of Condition 6 of 15/00362/OUT). A total of 312 homes have been granted Reserved Matters approval pursuant to the original 2016 outline permission. This 2020 outline planning application is for an increase in the residential land by circa 3.5 ha. It is understood that the housing will be a mix of sizes and no basement dwellings are proposed. 3.1.4 The 2016 outline permission included an element of non-residential development on the Site by reason of the description of the development (which included reference to A1/A3/A4/C2/D1a and D1b uses) and the land use parameter plan, which included a parcel of land of 0.15 ha for health purposes and 0.38 ha on the ‘island site’ for any of the uses applied for. 3.1.5 The 2020 outline application will adopt the same approach by including flexibility for either an A1 use (retail), A3 use (restaurant), A4 use (Pub) and/or D1b use (crèche), on a parcel of land of 0.3 ha, as shown on the new proposed land use parameter plan. As with the existing approval, Countryside Properties (UK) Limited anticipate having a s106 obligation that requires the owner to market the non-residential parcel of land for any of these uses, and in the event that there are no offers, the non-residential parcel would be greenspace.

3.1.6 A new road and bridge are planned to be the primary access and egress which links London Road (A129) in the south with Rawreth Lane in the north. This road does not form part of this application and has been granted reserved matters pursuant to the 2016 outline planning permission. The Rawreth Brook crossing will be the subject of a standalone reserved matters application pursuant to 15/00362/OUT. 3.1.7 A Sustainable Drainage System is proposed to be incorporated as part of the Proposed Development which takes into account the additional impermeable area. The general principals of the proposed drainage will be to implement various SuDS depending on the discharge options available. The techniques planned include permeable paving, swales, rainwater butts and five attenuation ponds which finally discharge to the Rawreth Brook at a controlled rate. The SuDS will be maintained for the lifetime of the Proposed Development by either Anglian Water, or a management company as outlined in Reserved Matters approvals referenced above. Further detail on the outline drainage strategy is included in Appendix D.

3.1.8 The Design and Access Statement provides a detailed overview of the development proposals. 3.2 Development Lifetime 3.2.1 The design life of the Proposed Development is considered to be 100 years for this FRA. 3.3 Development Vulnerability Classification 3.3.1 The NPPF1 considers the vulnerability of different types of development to flooding. The vulnerability classifications are detailed in Table 2 of the PPG2. The Proposed Development can be classified as: • ‘More Vulnerable’ – ‘Buildings used for dwelling houses, student halls of residence, drinking establishments, nightclubs and hotels.’ (NB. this does not include basement dwellings);

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Land Off Rawreth Lane, Rayleigh Essex Project number: 60469673

• ’Less Vulnerable’ – ‘Buildings used for shops; financial, professional and other services; restaurants, cafes and hot food takeaways; offices; general industry, storage and distribution; non-residential institutions not included in the ‘more vulnerable’ class; and assembly and leisure.’; • ‘Water Compatible’ – ‘Water transmission infrastructure’, ‘sewage transmission infrastructure’ and ‘amenity open space’.

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Land Off Rawreth Lane, Rayleigh Essex Project number: 60469673

4. Flood Risk to the Proposed Development 4.1 Overview 4.1.1 The NPPF1 requires the effects of all forms of flood risk to and from a development to be considered within an FRA. This section of the FRA assesses the flood risk, using the source- pathway-receptor model posed to the Proposed Development from fluvial and tidal sources; directly from rainfall on the ground surface; rising groundwater; overwhelmed sewers and drainage systems; and from artificial sources such as reservoirs, canals and lakes. After assessing each source, it can be identified where further mitigation measures are needed. 4.2 Fluvial Flood Risk 4.2.1 Flooding from fluvial sources can occur through inundation of floodplains from watercourses; inundation of areas outside the floodplain due to the influence of bridges, embankments and other features that artificially raise water levels.

4.2.2 The Rawreth Brook (shown in Figure 2-2) flows through the Site and the Environment Agency Flood Map for Planning4 (Figure 4-1) shows that the Rawreth Brook presents a source of flooding at the Site and therefore a potential flood risk to the Proposed Development.

Figure 4-1 Environment Agency Flood Map for Planning 4.2.3 The Rawreth Brook was modelled in for the Environment Agency using ISIS 1D software as part of the South Essex Flood Risk Study (completed in 2008). 4.2.4 As part of this FRA an Environment Agency hydraulic model, which includes the Rawreth Brook has been updated to improve the representation of fluvial flood risk at the Site. AECOM updated the Environment Agency 1D ISIS model in 2015 by coupling it with TUFLOW, creating a 1D-2D ISIS-TUFLOW model in the vicinity of the Site. This allowed the floodplain across the Site to be represented in more detail (in 2D) and better represent the flood routing mechanisms in the

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Land Off Rawreth Lane, Rayleigh Essex Project number: 60469673

floodplain. Peak flood levels from this phase of modelling were used to inform the design of the proposed access road across the Site. Further detail on the modelling methodology is included in Appendix E.

Figure 4-2 Flood modelling extents

4.2.5 The updated flood modelling shows that for all modelled events some out of bank flooding occurs across the Site adjacent to Rawreth Brook. The modelled results were provided to Countryside Properties (UK) Ltd. to inform the master-planning of the Proposed Development, so that flood risk mitigation measures could be embedded into the design. The Proposed Development plans have been overlaid onto the modelled flood extents and are shown in Figure 4-3.

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Land Off Rawreth Lane, Rayleigh Essex Project number: 60469673

Figure 4-3 Flood Mapping with Proposed Development Plans (refer to Appendix C for landuse descriptions)

Flood Map Legend 1% AEP event including 65% climate change 0.1% AEP event

4.2.6 The Proposed Development has been planned so that all of the buildings, which includes residential (More Vulnerable receptors) and shops / restaurants (Less Vulnerable) are located outside of the flood extents for the 1% (1 in 100 year) AEP event including a 65% allowance for climate change and the 0.1% AEP events8. This is in keeping with the principles of the sequential approach advocated by the NPPF1. 4.2.7 The only part of the Site that is shown to be at risk of flooding from the Rawreth Brook is open space. In the event that these areas are flooded dry access and egress would still be possible without entering floodwaters using the primary road through the Site.

4.2.8 This assessment has identified that there is a source and pathway of fluvial flood risk to the Proposed Development, however, the More Vulnerable and Less Vulnerable receptors have been located outside of the flood extent and the overall flood risk to those is considered to be Very Low. No further mitigation is needed. 4.2.9 There is still a high probability (1% AEP event) that flooding will occur in the open spaces adjacent to the Rawreth Brook. It is understood that appropriate signage will be displayed on the development to raise awareness of the Rawreth Brook and that it is liable to flood. As the receptor is water compatible the overall flood risk is considered to be Low. 4.3 Tidal Flood Risk 4.3.1 Tidal sources of flooding include seas and estuaries and can occur through overtopping of defences, breaching of defences and wave action. Rochford is at risk of tidal flooding from the River Crouch Tidal Estuary, which is exposed to the North Sea.

4.3.2 The flood risk from the River Crouch was considered at a strategic scale as part of the South Essex Strategic Flood Risk Assessment (SFRA)9. As part of this SFRA, AECOM received modelled flood data from the River Crouch 2017 modelling carried out by the Environment Agency.

8 Note that the allotments will be located outside of the flood extent, to the north of where they are shown in this indicative land use plan. 9 AECOM (2018) ‘South Essex Level 1 Strategic Flood Risk Assessment’, AECOM Limited: Basingstoke.

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Land Off Rawreth Lane, Rayleigh Essex Project number: 60469673

4.3.3 As part of this dataset the peak flood levels from nodes located along the River Crouch are provided and the peak flood levels closest to the Site have been extracted and presented in Table 4-1. The node locations, present day flood extents and greatest climate change flood extent is presented in Figure 4-4.

Figure 4-4 River Crouch 2017 Modelled Tidal Extents (Contains Ordnance Survey data © Crown copyright and database right 2020)

4.3.4 This information shows that whilst there is a potential source of tidal flooding exists, the pathway to the Proposed Development is restricted by topography i.e. the ground levels on the Site are greater than the tide levels. Although the tidal extent does not reach the Site, there may be an effect on the discharge of fluvial water within the Rawreth Brook as a result of tide-locking. As part of the hydraulic modelling (Appendix E) a sensitivity test was carried out on the downstream boundary condition to determine the impact on varying the levels, this found there was found to be a negligible impact on the flood levels. This further confirms the tide-locking assessment carried out and agreed by the Environment Agency in 2015, which concluded there was a negligible impact on the Site as a result of tide-locking. 4.3.5 The overall risk of tidal flooding to the Proposed Development is assessed to be Very Low, and no further mitigation is required.

Table 4-1 Extracted Peak Water Levels from Environment Agency 2017 River Crouch Modelling (mAOD) Node 0.5% AEP (1 in 0.1% AEP (1 in 200 0.5% AEP (1 in 0.5% AEP (1 in 200 0.1% AEP (1 in 200 year) 200 year) AEP year) AEP event 200 year) AEP year) AEP event AEP event with 25% event present present day – event with 35% with 65% climate climate change day – Flood Flood Zone 2 climate change change Zone 3

CROU_05553d 4.98 5.50 5.24 5.43 5.75 CROU_05152 4.73 5.2 4.97 5.15 5.37 CROU_05152i2 4.69 5.2 4.94 5.12 5.35 CROU_05152i3 4.69 5.2 4.94 5.12 5.35 CROU_04211 4.66 5.15 4.92 5.1 5.32

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Land Off Rawreth Lane, Rayleigh Essex Project number: 60469673

4.4 Surface Water Flood Risk and Overland Flow 4.4.1 Surface water flooding results from rainfall that fails to infiltrate the surface and travels over the ground surface. This is exacerbated by low permeability urban development or low permeability soils and geology (such as clayey soils). Developments located on or adjacent to sites with steep slopes are often at greater risk. 4.4.2 As the Proposed Development will include hardstanding areas and the soils on the Site have limited infiltration potential, during intense rainfall events there is anticipated to be a potential source of surface water / overland flow flooding. Additionally, the surrounding land may generate overland flow which could be directed onto the Site. 4.4.3 The Environment Agency’s Risk of Flooding from Surface Water (RoFSW) mapping10 is strategic mapping used to indicate whether an area is likely to suffer from surface water flooding. The RoFSW mapping indicates the Proposed Development to be at high risk of surface water flooding in the centre of the Site, along the Rawreth Brook. There is also a medium risk of surface water flooding north of the Rawreth Brook, as well as areas slightly south. The majority of the Proposed Development in the north and the south are shown to be at very low risk of surface water flooding. There are some small areas isolated patches of surface water where there are depressions in the land, such as the pond.

4.4.4 The South Essex Surface Water Management Plan (SWMP)11 undertook analysis of surface water flooding and identified Critical Drainage Areas (CDAs). The Site itself is not within a CDA, however to the east of the Site, the urban area of Rayleigh is within a CDA (ROC1) and to the north west of the Site Watery Lane is a CDA (ROC2). Of importance to this Site are the surface water flow paths that are shown to flow within ROC1. The SWMP shows that these flow from across the urban extent of Rayleigh towards the west of the urban area (i.e. towards the Site). The surface water flow paths tend towards the channel of the Rawreth Brook which then flows into the Site. Flows from the CDA ROC2 flow away from the Site in a northerly direction. 4.4.5 Analysis of the topography of the area suggests that surface water is likely to discharge towards the Site from the Rayleigh Urban area to the west along the channel of the Rawreth Brook, and drainage ditches to the north of Grosvenor Road and the south of Victoria Road. Surface water entering the Site from the Rayleigh urban area will largely be contained within the channel of the Rawreth Brook. 4.4.6 Consultation with Countryside Properties Ltd. and Essex County Council carried out as part of the original outline planning application confirmed that a number of surface water flooding incidents have occurred within the vicinity of the Site. These include: • 20th July 2014: Heavy rainfall across the area resulted in flooding at Salem Walk, Fairmead, Maine Crescent, Laburnum Way, Victoria Avenue and London Road; • 30th January 2014: 1 property was recorded to flood at Parkhurst Drive; • 24th August 2013: Extensive surface water flooding following heavy rainfall. Record of property flooding within the areas of Laburnum Way, Victoria Avenue, Salem Walks and Fairmead; • 9th July 2013: Flooding at Laburnum Way; • 3rd December 2012: Properties flooding at Laburnum Way; and, • Pre 2010 (exact dates are unknown): Frequent flooding of Road and roundabout, thought to be due to runoff from surrounding areas. 4.4.7 Flooding at Salem Walk, Fairmead, Maine Crescent and Victoria Avenue is likely to be due to a combination of surface water runoff following heavy rainfall, coinciding within high flows within the river channel. Within the residential area, there is a network of drainage ditches and small watercourses that are thought to drain the area towards the Rawreth Brook. During heavy rainfall events, these channels are likely to be become overwhelmed resulting in localised

10 Environment Agency’s ‘Long-Term Flood Risk Map’ available at https://flood-warning-information.service.gov.uk/long-term- flood-risk/map accessed July 2020. 11 URS Scott Wilson (2012) South Essex Surface Water Management Plan Phases II, III and IV.

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flooding. Details of the recent flooding on the 20th of July 2014, recorded by residents, indicates that in this instance, flooding was a result of a blocked sluice gate within the channel behind the properties. 4.4.8 Anecdotal evidence (discussions with Countryside Properties (UK) Ltd. during preparation of the original planning application) suggests that flooding in this area on the 24th of August 2013 may have been exacerbated by the infilling of drainage ditches associated with the new development to the west of Boston Avenue and south of Cheapside West. 4.4.9 In relation to the Proposed Development, surface water runoff and the resulting high river flows are likely to propagate downstream along the Rawreth Brook towards the Site, potentially increasing the flood risk to the Proposed Development. 4.4.10 Flooding recorded within the Parkhurst Drive and Laburnum Way is likely to be a result of intense rainfall overwhelming the drainage system within the area. At the junction of Laburnum Way and Rawreth Lane, there is a small drainage ditch which will have limited capacity for draining surface water runoff. The flooding recorded at Parkhurst Drive and Laburnum Way would be unlikely to affect the Site, as there is an area of raised elevation between the flooding locations and the Site.

4.4.11 In addition, Countryside Properties (UK) Ltd. are also aware of flooding having occurred along London Road, to the southwest of the Site, on frequent occasions following heavy rainfall. This is thought to be due to runoff from the adjacent land to the south which comprises extensive hardstanding areas with little formal surface water drainage. This area is below the southern elevation of the Site; therefore, it is unlikely that surface water generated from this source would flow beyond London Road onto the Site. 4.4.12 Considering this information there is a potential source and pathway of surface water flooding to parts of the Site, however, these parts are planned to be open spaces. As part of the detailed design of the surface water drainage strategy the existing potential surface water pathways will be taken into consideration in the design of the SuDS. The SuDS proposed will be maintained for the lifetime of the development and therefore the surface water flood risk to the Proposed Development is assessed to be Low; no further mitigation is needed. 4.5 Groundwater Flood Risk 4.5.1 Groundwater flooding usually occurs in low lying areas underlain by permeable rock and aquifers that allow groundwater to rise to the surface through the permeable subsoil following long periods of wet weather. Low lying areas may be more susceptible to groundwater flooding because the water table is usually at a much shallower depth and groundwater paths tend to travel from high to low ground. 4.5.2 The hydrogeology at the Site is described in Section 2.5. This information indicates that the solid geology beneath the Site is London Clay and would not present a source of groundwater flooding to the Proposed Development. The superficial deposits of Alluvium and Head Deposits may present a source of groundwater flooding.

4.5.3 The Proposed Development does not include any major excavations such as for the construction of deep foundations or basements although as groundwater may be present in the superficial deposits, during construction there could be a pathway to the construction workers to any excavations. 4.5.4 If groundwater flooding occurs once the Site is developed the quantities of water are likely to be minimal and be in hydraulic connectivity with Rawreth Brook, so the flood extents would be similar to fluvial flooding and the embedded mitigation of locating the More Vulnerable and Less Vulnerable receptors outside of the areas at risk of fluvial flooding will also mitigate the risk of groundwater flooding. 4.5.5 The risk of groundwater flooding to the Proposed Development is considered to be Low, the risk of groundwater flooding during construction is considered to be Moderate; further mitigation is recommended in Section 6.

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4.6 Sewer Flood Risk 4.6.1 Sewer flooding occurs when the sewer capacity becomes exceeded or where a blockage occurs causing the sewer to surcharge and flood. 4.6.2 An asset location plan has been provided by Anglian Water which shows the sewer network in and around the Site. The sewer systems within the Site and the surrounding area are separate systems, that is, foul water and surface water are drained separately. There is a 675mm diameter public foul sewer that passes through the Site and drains to the Rayleigh West Sewage Treatment Works. This flows from Rayleigh in a north westerly direction and exits the Site just to the east of Rawreth Hall. There are several manholes located along the length of the sewer at approximately 90m intervals. In addition, there are smaller foul sewers that run along Rawreth Lane from the west and east to join the trunk sewer in Rawreth Lane. The Anglian Water sewer plans show the closest surface water sewers to be within the residential developments to the east of the Site. 4.6.3 Providing that there are no misconnections to the foul sewer, the flows within the pipes will remain relatively constant and will not be affected by surface water resulting from rainfall events. In the unlikely event that the foul sewers exceed their capacity, there is the potential for the foul water to surcharge manholes and to flow, following the topography of the land, across the Site towards the low point of the Rawreth Brook channel.

4.6.4 The SWMP11 indicates that there have been several DG5 records of sewer flooding within the Rayleigh Urban area in the last 10 years. There are no records associated with this Site.

4.6.5 The risk of sewer flooding to the Proposed Development is considered to be Low. 4.7 Artificial Sources 4.7.1 Artificial flood sources include raised channels such as canals or storage features such as ponds and reservoirs. The Environment Agency’s Long-Term flood risk information map10 indicates the Proposed Development is not at risk of flooding from artificial sources.

4.7.2 As part of the entire Proposed Development, five ponds will be constructed to attenuate surface water runoff. These will hold varying volumes from approximately 700m³ to 6000m³ and will finally discharge into the Rawreth Brook. These ponds will be bunded with slopes of 1 in 3 and will be maintained by Anglian Water (pond 2 and 3) and the Management Company (pond 5)12. The water levels within the ponds will be designed so that under normal circumstances they are not elevated above the surrounding ground level, during flood events the water levels may rise partially up the bund, so they are elevated above the adjacent ground level. A 300mm freeboard has been allowed for in the design. If the water within the ponds were to exceed the bank level or breach, the water would flow in accordance with the topography towards the channel of the Rawreth Brook within the areas that are proposed to be open space. 4.7.3 The ponds will be maintained for the lifetime of the Proposed Development and are therefore designed to manage flood flows up to the 1% AEP event including the effects of climate change. The likelihood of them failing and / or being exceeded is low. As there are no receptors in the pathway, should floodwater escape from the ponds the risk of flooding from these features to the Proposed Development is considered to be Very Low. 4.8 Summary of Flood Risk to the Proposed Development 4.8.1 Table 4-2 summarises the sources of flooding and their impact to the Proposed Development. It also identifies whether mitigation is required.

12 Ponds 1 and 4 fall outside of this planning application but will be managed by Anglian Water.

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Table 4-2 Summary of Flood Risk to the Proposed Development

Type of Source of Flooding Overall Flood Risk to the Is Further Mitigation Required? Flooding Proposed Development

Tidal River Crouch Estuary Very Low No.

Fluvial Rawreth Brook and tributaries Very Low – buildings (residential No. and commercial) Low – open spaces and allotments

Surface Runoff from surrounding land and the Low – existing surface water flow No. Water Proposed Development itself paths will be considered as part of the drainage strategy detailed design

Sewers Surrounding public/private drainage systems Low No.

Groundwater Low – to the permanent Underlying geology and groundwater development Yes - see Section 6. levels Moderate – during construction

Ponds within the Proposed Artificial Development and previously consented Very Low No. development

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5. Flood Risk from the Proposed Development 5.1 Overview 5.1.1 The NPPF1 advises that a FRA should consider potential risk of flooding arising as a result of a proposed development. This section of the FRA summarises the flood risk from the Proposed Development in accordance with the requirements of the NPPF1 and identifies where further mitigation is recommended. 5.2 Tidal Flood Risk 5.2.1 As discussed in Section 4.3 there is no pathway of tidal flooding to the Proposed Development and therefore there is no risk of tidal flooding from the Proposed Development. 5.3 Fluvial Flood Risk 5.3.1 Development within a floodplain can result in loss of storage or an obstruction to a fluvial flood flow pathway which can lead to an increase in flood risk elsewhere. It has been identified that parts of the Site lie within the floodplain of the Rawreth Brook and therefore have the potential to increase flood risk elsewhere. 5.3.2 As part of the Proposed Development, to mitigate the risk to the Proposed Development from fluvial flood sources and to mitigate the risk of the Proposed Development exacerbating fluvial flood risk through floodplain volume displacement, all of development parcels and buildings (residential / commercial) development are located in Flood Zone 1 (i.e. outside of 0.1% AEP or 1 in 1000 year floodplain) as shown in Figure 4-3. 5.3.3 The only part of the Proposed Development, as part of this application that is shown to be located in the floodplain of the Rawreth Brook is open space and the surrounding earthworks of three surface water attenuation ponds. The attenuation ponds are proposed to be bunded to ensure they are not flooded from the Rawreth Brook and available for surface water storage. This bunding means that there is a small loss in floodplain storage which could potentially increase flood risk elsewhere. 5.3.4 To assess whether the Proposed Development will increase flood risk elsewhere, hydraulic modelling has been carried out; the details of this are included in Appendix E. The model was updated to incorporate the key features of the Proposed Development, key features including the new bridge, land raising on the Site and five surface water attenuation ponds.

5.3.5 The 1D results show that the peak river levels for the 1%, 0.1% AEP and 1% plus 65% climate change flood events have not changed significantly as a consequence of the developed design. There is a slight decrease in river stage upstream of the new bridge in both events followed by a slight increase in river level downstream of the new bridge during both flood events. The greatest change in river level is at BENF2_3141i1 upstream of the proposed bridge. At this node there is an increase in river level of 0.13m during the 0.1% AEP event, though this increase is contained within the Site and there is no increase in fluvial flood risk as a result of the Proposed Development to the housing estate to the east. 5.3.6 The proposed earthworks result in a more constrained floodplain close to the proposed bridge, however, due to the shallow flood depths in the overbank area, the displaced volume is minimal. 5.3.7 The maximum flood levels and flows upstream and downstream of the Site have been extracted from the model for the “developed” and “baseline” scenarios for the 5%, 1%, 0.1% and 1% + 35% climate changes events; these are included in the hydraulic modelling report (Appendix D). There is a negligible impact on maximum flood levels further downstream and upstream of the Site, in all AEP events.

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5.3.8 Given the evidence from the hydraulic modelling exercise carried out, the risk of fluvial flooding from the Proposed Development is considered to be Negligible. 5.4 Surface Water Flood Risk and Overland Flow 5.4.1 Undeveloped greenfield sites rely on natural drainage to convey or absorb rainfall. In general, development reduces the permeability of sites, increasing the volume and rate of water running off the site to nearby watercourses, potentially increasing flood risk to downstream areas. Therefore, appropriate drainage arrangements are required for new developments to ensure that flood risk is not increased offsite. 5.4.2 An outline surface water strategy (Appendix D) has been developed in order to manage surface water to ensure that flood risk is not increased elsewhere. In order to prevent increased flows offsite, surface water control features and storage facilities are installed prior to any discharge to Rawreth Brook. The drainage strategy can be summarised as: • Surface water runoff is restricted to the 1 in 1 year greenfield rate from Pond 2, 3 and 5 for all storm events, including the 1% AEP event; • Attenuation ponds 2, 3 and 5 are designed to attenuate the surface water runoff for the 1% AEP including 40% climate change event; and, • Incorporation of SuDS drainage features include the pond and roadside swales provides source control, improves water quality, reduces flood risk and provide amenity. 5.4.3 The risk of surface water flooding and overland flow is considered to be Low, as long as the SuDS are maintained. 5.5 Groundwater Flood Risk 5.5.1 Where a new development is located in an area of high groundwater levels, the underlying groundwater regime may be interrupted temporarily during construction or permanently through the installation of deep foundations and can subsequently increase the risk of groundwater flooding. 5.5.2 As identified in Section 2 the superficial deposits are classified as secondary aquifers and are likely to only transmit water on a local scale. There are no infiltration SuDS planned as part of the development and no additional water will be directed to ground.

5.5.3 The risk of impact on the local groundwater level is considered to be Low. 5.6 Sewer Flood Risk 5.6.1 New developments can increase the risk of flooding from sewers by overloading the network. 5.6.2 As described in Section 5.4, surface water will be managed on the Site. The foul water from the Proposed Development is proposed to be connected to the existing Anglian Water sewer that passes through the Site. A Pre-Planning Assessment Report for the Proposed Development completed by Anglian Water (Appendix F) states that it is acceptable to connect to the foul sewer that passes through the Site as there is the capacity available. The report also states that the Rayleigh West Sewage Treatment Works has the capacity to treat the foul flows from the Site. A new pre-planning enquiry is being progressed to support this application. 5.6.3 The proposed connection will be at two points along the 675 mm public foul sewer at nodes 2501 and 3902. These are located to the western side of area proposed for residential development, and to the north just before Rawreth Lane, respectively.

5.6.4 The risk of sewer flooding as a result of the Proposed Development is therefore considered to be Low.

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5.7 Artificial Sources 5.7.1 As part of the Proposed Development three of the previously approved ponds will be used to attenuate surface water. As discussed in Section 4, these are very unlikely to be exceeded or breach. In the unlikely event they do, the floodwaters will flow, in accordance with topography towards the Rawreth Brook in areas that will be open space. 5.7.2 The risk of flooding elsewhere from the artificial sources proposed as part of this development is considered to be Very Low. 5.8 Summary of Flood Risk from the Proposed Development 5.8.1 Table 5-1 summarises the assessment of flood risk from the Proposed Development and whether further mitigation is required.

Table 5-1 Summary of Flood Risk from the Proposed Development

Type of Flooding Source of Flooding Overall Flood Risk to the Is Further Mitigation Proposed Development Required?

Negligible – No loss of Tidal River Crouch Estuary floodplain caused by No development

Fluvial Rawreth Brook Very Low No

Surface Water Runoff from surrounding land Low No

Surrounding public/private Sewers drainage systems Low No

Underlying geology and Groundwater groundwater levels Low No

Ponds within the Proposed Artificial Development Very Low No

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6. Mitigation Measures 6.1 Overview 6.1.1 It has been identified that additional mitigation measures are recommended to reduce flood risk to the Proposed Development for groundwater sources. This Section discusses the mitigation measures that are recommended to incorporated into the Proposed Development, in order to mitigate the risk of these to a safe level. 6.2 Mitigation of Groundwater Flood Risk 6.2.1 It has been identified that during construction there is a potential impact to the construction workers as any excavations could potentially encounter groundwater. 6.2.2 It is recommended that groundwater levels are monitored during construction to determine the risk of flooding and inform appropriate mitigation during construction.

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7. Planning Policy 7.1 National Planning Policy Framework: 7.1.1 The NPPF1 and the associated PPG2 details current policy in respect to flood risk in England. Site-Specific Flood Risk Assessment 7.1.2 Paragraph 163 states that ‘When determining any planning applications, local planning authorities should ensure that flood risk is not increased elsewhere. Where appropriate, applications should be supported by a site-specific flood-risk assessment50. Development should only be allowed in areas at risk of flooding where, in the light of this assessment (and the sequential and exception tests, as applicable) it can be demonstrated that:

a) within the site, the most vulnerable development is located in areas of lowest flood risk, unless there are overriding reasons to prefer a different location;

b) the development is appropriately flood resistant and resilient; c) it incorporates sustainable drainage systems, unless there is clear evidence that this would be inappropriate;

d) any residual risk can be safely managed; and

e) safe access and escape routes are included where appropriate, as part of an agreed emergency plan. 7.1.3 Paragraph 163 (footnote 50) of the NPPF states that “a site-specific flood risk assessment is required for all development in Flood Zone 2 and 3”. The Site is shown to be located within Flood Zone 3 in the Environment Agency Flood Map for Planning. 7.1.4 This report fulfils the requirements of the NPPF1 as a site-specific FRA has been prepared which addresses the points under Paragraph 163. Vulnerability Classification 7.1.5 Table 3 of the PPG2 illustrates a matrix that identifies which vulnerability classifications are appropriate within each Flood Zone (reproduced in Table 7-1).

Table 7-1 PPG (Table 3) Flood risk vulnerability and flood zone ‘compatibility’

Flood Risk Vulnerability Essential Water Highly More Less Classification Infrastructure Compatible Vulnerable Vulnerable Vulnerable (Table 2 NPFF) 1 ✓ ✓ ✓ ✓ ✓

2 ✓ ✓ Exception Test ✓ ✓ required 3a Exception Test ✓ X Exception Test ✓

required required FloodZone 3b Exception Test ✓ X X X required 7.1.6 More Vulnerable developments are considered to be appropriate within Flood Zone 1 and 2. The Exception Test would need to be passed to locate More Vulnerable development within Flood Zone 3a and More Vulnerable Development is not compatible with Flood Zone 3b. As discussed in Section 4 the sequential approach has been applied to the masterplanning of the development and all vulnerability types are compatible with the flood zones they are in.

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Sequential Test and Exception Test 7.1.7 The Sequential and Exception Tests are strategic tools used in planning to steer new development to areas with the lowest risk of flooding, and where this may not be possible, to make them safe. Local planning authorities should apply the Sequential Test and Exception Test at a strategic scale when allocating development. The Site is allocated for residential development, in accordance with Policy SER1 of the Rochford Local Development Framework13. 7.1.8 This indicates that the Sequential Test and Exception Test has been passed by the local planning authority and that no other reasonably available sites appropriate for the Proposed Development in areas at a lower risk of flooding were found. Impact of Climate Change 7.1.9 In accordance with the PPG2, it is recommended that the potential effects of Climate Change should be considered realistically for the lifetime of a Proposed Development and that “…developers, the local planning authority and Environment Agency should discuss and agree what allowances are acceptable”. 7.1.10 In February 2016 the Environment Agency updated its guidance on climate change allowance to be applied within FRAs14. Considering that the life span of the development is 100 years, increases in peak rainfall intensity to allow for the impacts of climate change should be between 20% and 40% in order to understand the potential range of impacts on peak rainfall from climate change2. Similarly, the river flow increases to allow the impacts of climate change should be between 35% and 65% in order to understand the potential range of impacts of peak river flows resulting from climate change (Table 7-2).

Table 7-2 Peak river flow allowances by river basin district (Ref: Flood risk assessments: climate change allowances Guidance by Environment Agency, February 2016)

River basin district Total potential change Total potential change Total potential change Allowance category anticipated for the anticipated for the anticipated for the ‘2020s’ (2015 to 2039) ‘2050s’ (2040 to 2069) ‘2080s’ (2070 to 2115) Upper end 25% 35% 65% Anglian Higher central 15% 20% 35% Central 10% 15% 25%

7.1.11 These climate change allowances have been used in the SuDS design, hydraulic modelling and FRA. 7.2 Local Planning Policy: Rochford District Council Local Development Framework Core Strategy 7.2.1 Rochford District Council Local Development Framework: Core Strategy Adopted Version 201115 forms the main document for Rochford District Councils Local Development Framework. The Local Development Framework has replaced the Rochford Local Plan. None of the policies relating to flooding or surface water management (NR11 and NR12) were saved when the Local Plan expired in 2009.

13 Rochford District Council (2014) ‘Local Development Framework: Allocations Plan’, available at https://www.rochford.gov.uk/sites/default/files/documents/files/planning_all_allplan.pdf accessed July 2020. 14 Environment Agency (February 2016) Flood risk assessments: climate change allowances. https://www.gov.uk/guidance/flood-risk-assessments-climate-change-allowances Accessed: October 2019 15 Rochford District Council Local Development Framework: Core Strategy Adopted Versions 2011. Available online at: http://fs- drupal-rochford.s3.amazonaws.com/pdf/planningpolicy_cs_adoptedstrategy.pdf

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7.2.2 The policies within the Core Strategy that relate to the flood risk of the Proposed Development are presented below. Policy ENV 3 – Flood Risk 7.2.3 “The Council will direct development away from areas at risk of flooding by applying the sequential test and, where necessary, the exceptions test, as per PPS25 (sic). The vast majority of development will be accommodated within Flood Zone 1. However, considering the very limited supply of previously developed land in the District, proposed development on previously developed land within Flood Zone 3 will be permitted if it enables a contribution towards the District’s housing requirement that would otherwise require the reallocation of Green Belt land, providing that it passes the exceptions tests and is able to accommodate the necessary flood defence infrastructure. 7.2.4 The Council will continue to work with the Environment Agency to manage flood risk in a sustainable manner through capitalising on opportunities to make space for water wherever possible and through the continued provision of flood defences where necessary.” 7.2.5 This policy is commensurate with that of the NPPF which the Proposed Development is considered to have met and the Proposed Development is considered to pass the Exception Test. Policy 4 – Sustainable Drainage Systems (SuDS) 7.2.6 “All residential development over 10 units will be required to incorporate runoff control via SuDS to ensure runoff and infiltration rates do not increase the likelihood of flooding. 7.2.7 The requirement for SuDS will only be relaxed where there is conclusive evidence demonstrating that the system is not viable on a particular site.”

7.2.8 An outline drainage strategy including the provision of SuDS is proposed (as outlined in Appendix D), therefore it is considered that this policy is met. 7.3 Rochford District Council Local Development Framework Allocations Plan 7.3.1 The Rochford District Council Allocation Document16, developed as part of the Local Development Framework, was adopted on the 25th of February 2014. 7.3.2 Policy SER1 outlines the requirements of the allocated land associated with the Proposed Development. In relation to flood risk, the policy outlines the need to accommodate sustainable drainage systems as part of the development. 7.3.3 It is outlined that ‘the 3.1 ha of the site associated within Flood Zone 2 and 3 should be set aside for public open space and natural/semi-natural greenspace.

7.3.4 Attenuation and source control SuDS should be utilised and incorporated into the green space on or adjacent to, the development. Appropriate SuDS should be determined in consultation with Essex County Council and the Environment Agency. A site specific Flood Risk Assessment, incorporating a surface water drainage strategy should be prepared for the site.’ 7.3.5 As the Proposed Development incorporates SuDS techniques to manage surface water on the Site, and this document is the site-specific FRA. This policy is considered to be met.

16 Rochford District Council – Local Development Framework Allocations Document Adopted on the 25 th of February 2014. Available online at: http://www.rochford.gov.uk/sites/rochford.gov.uk/files/documents/files/planning_all_allplan.pdf?bcsi_scan_E956BCBE8ADBC8 9F=0&bcsi_scan_filename=planning_all_allplan.pdf

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8. Residual Flood Risk 8.1 Overview 8.1.1 Residual risk is the risk that remains after flood risk management and mitigation measures have been put in place. Residual risks often have a low probability of occurrence, although the impacts can be severe. This Section identifies the residual risks for the Site and further recommendations on how they can be managed so that the Proposed Development is safe over its lifetime. 8.2 Blockages at structures along Rawreth Brook 8.2.1 Blockages along a watercourse typically cause the water levels upstream to rise above the predicted water levels and potentially increase flood risk upstream. Structures along watercourses are more prone to blockages, by either accumulating debris or collapse. 8.2.2 The Rawreth Brook is an Environment Agency Main River and thus will be inspected and maintained which reduces the likelihood of blockages. Although, the maintenance regime is not known and blockages of these structures may occur. 8.2.3 The structures along the Rawreth Brook that could pose a risk to the Proposed Development are:

• Bridge consented on the Site as part of the 2016 Outline Application and currently in the process of gaining planning and highway approvals. This bridge is a clear span bridge with the soffit level set above the 0.1% AEP flood level including a freeboard. Given the freeboard associated with this structure the risk of blockage is greatly reduced as debris is more likely to be able to flow through the structure on the water surface. • Existing 750mm diameter culvert (node BENF2753c) – this is located where the Rawreth Brook exits the Site. A blockage at this structure may occur but through a review of the results in the hydraulic model in the 1% AEP + 65% climate change this structure surcharged and the majority of the water is spilling over the top of the deck, therefore the impact of a blockage within the culvert pipe itself is likely to be small. • Existing 700mm diameter culvert (node BENF2_2469c) – this is located approximately 350m downstream of the Site boundary. A blockage at this structure may occur but through a review of the results in the hydraulic model in the 1% AEP + 65% climate change this structure surcharged and the majority of the water is spilling over the top of the deck, therefore the impact of a blockage within the culvert pipe itself is likely to be small. 8.2.4 The buildings on the Proposed Development will be raised to a typical threshold height, which would further restrict a pathway of flooding to any receptors. 8.2.5 Using the information stated above the overall risk of a blockage in these structures causing an increased flood risk to the Proposed Development is considered to be very low. 8.3 Failure or Exceedance of Sewer Network 8.3.1 If a sewer network becomes surcharged and floods through a blockage, failure of a pumping station or exceedance flows unexpected flooding may occur.

8.3.2 A foul water network proposed as part of the wider Site includes the provision of a pumping station. The pumping station has been designed to provide emergency storage for 4 hours and is bunded on three downhill sides. 8.3.3 The outline drainage strategy (Appendix D) states that ‘The strategic drainage network consists of pipes, swales and ponds. These are designed such that in an event exceeding the design event the excess flows will be diverted from the properties. The excess flows from pipes and

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roadside swales will be diverted from properties via the strategic road. The excess flows from swales and ponds will be distributed across the surrounding landscape areas, which are all at a lower level than the surrounding properties.’ 8.3.4 There is assessed to be a very low residual risk from failure or exceedance of the sewer network.

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9. Summary 9.1 Overview 9.1.1 AECOM has been commissioned by Countryside Properties (UK) Limited to prepare a flood risk assessment (FRA) to support a new outline planning application which re-plans part of a previously consented planning application for a residential mixed-used development at a site “Land off Rawreth Lane”, Rayleigh, Essex (hereinafter referred to as the ‘Site’). Hereinafter the subject of this application is referred to as the ‘Proposed Development’.

9.1.2 This FRA has been prepared in accordance with the National Planning Policy Framework (NPPF)1 and supporting Planning Practice Guidance (PPG)2. 9.1.3 This FRA has been undertaken based on the available information, including updated hydraulic modelling. A summary of the main outcomes of the FRA in relation to the objectives are summarised below. 9.2 Flood Risk – To the Proposed Development 9.2.1 This FRA has assessed that:

• Modelled flood extents from the tidal River Crouch do not extend onto the Site and therefore the Proposed Development is at a Very Low risk of tidal flooding; • The proposed attenuation ponds present a possible artificial source of flooding. These will be maintained, and should they flood there are no downstream receptors, therefore the overall flood risk is considered to be Very Low; • The Proposed Development is at a Low risk of flooding from sewers or surface water sources; • The Proposed Development is at a Low risk of flooding from groundwater, although during construction there is a Moderate risk to the construction works when excavating into the superficial deposits; and, • The Proposed Development has been planned so that all of the buildings, which includes residential (More Vulnerable receptors) and shops / restaurants (Less Vulnerable) are located outside of the 1% (1 in 100 year) AEP event including a 65% allowance for climate change and the 0.1% AEP event flood extents. Therefore, the majority of the Proposed Development is at a Very Low risk of fluvial flooding. There is a high probability of flooding to the open spaces near the Rawreth Brook but as these are water-compatible uses the overall risk from flooding to these areas is Low. 9.3 Flood Risk – From the Proposed Development 9.3.1 This FRA has assessed that there the risk of flooding from the Proposed Development to elsewhere is Very Low. 9.4 Planning Policy 9.4.1 The sequential approach has been applied to the master-planning of the development and all vulnerability types are compatible with the flood zones they are in, in accordance with Table 2 of the PPG2. 9.5 Recommended Mitigation 9.5.1 It is recommended that groundwater levels are monitored during construction to determine the risk of flooding and inform appropriate mitigation during construction

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Appendix A Redline Boundary

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Appendix B Topographic Survey

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Appendix C Proposed Development Plans

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Appendix D Outline Drainage Strategy

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Appendix E Model Build Report

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Appendix F Anglian Water Correspondence

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