Gas-to-Grid Anaerobic Digestion Plant

Tongue End, Deeping St. Nicholas

Flood Risk Assessment and Surface Water Drainage Strategy

SLR Ref: 408.03643.00033 April 2016 Version: 2 rsion JH Walter LLP i SLR Ref. 408.03643.00033 Tongue End AD Plant, Deeping St. Nicholas: FRA & SWDS April 2016

CONTENTS 1.0 INTRODUCTION ...... 1 1.1 Context ...... 1 1.2 Site Location and Features...... 1 1.3 Topography ...... 2 1.4 Hydrology and Surface Water Drainage ...... 3 1.5 Geological and Hydrogeological Features ...... 6 1.6 Development Proposals...... 6 1.7 Flood Zone Classification (Environment Agency) ...... 7 1.8 Flood Zone Classification (Strategic Flood Risk Assessment) ...... 9 1.9 Flood Zone Classification Requirements ...... 10 1.10 Flood Risk Vulnerability...... 10 1.11 Flood Risk Compatibility ...... 10 1.12 Sequential Test ...... 10 1.13 Exception Test ...... 12 2.0 SOURCES OF INFORMATION ...... 13 2.1 Topographical Survey ...... 13 2.2 Internal Drainage Board Watercourse Map ...... 13 2.3 Site Plans ...... 13 2.4 EA Mapping ...... 13 2.5 Strategic Flood Risk Assessment ...... 13 2.6 Preliminary Flood Risk Assessment ...... 13 2.7 Joint Lincolnshire Flood Risk and Drainage Management Strategy ...... 14 2.8 Historic Flooding ...... 14 3.0 FLOOD RISK ASSESSMENT ...... 15 3.1 Methodology & Best Practice ...... 15 3.2 National and Local Planning Policy ...... 15 3.3 Screening Study ...... 15 4.0 TECHNICAL ASSESSMENT OF FLOOD RISK ...... 16 4.1 Historic Flooding ...... 16 4.2 Flooding from Tidal and Fluvial Sources ...... 16 4.3 Flooding from Surface Water ...... 17 4.4 Flooding from Overland Flow ...... 21 4.5 Flooding from Groundwater ...... 21 4.6 Flooding from Sewers & Water Mains ...... 21 4.7 Flooding from Reservoirs and Canals ...... 22 4.8 Flooding from Infrastructure Failure ...... 23 4.9 Potential Flood Risk to Off-Site Areas ...... 23 5.0 CLIMATE CHANGE ...... 24 5.1 Anticipated Lifetime of Development ...... 24 5.2 Climate Change Allowances ...... 24 5.3 Impacts on Flood Risk ...... 26 5.4 Impacts on Drainage ...... 27 6.0 PROPOSED FLOOD MANAGEMENT MEASURES ...... 28 6.1 Flood Mitigation & Resilience Measures ...... 28 6.2 Residual Flood Risk Management ...... 29 6.3 Flood Defence Consent ...... 30 7.0 SURFACE WATER MANAGEMENT STATEMENT ...... 31 7.1 Key Principles ...... 31 7.2 Existing Surface Water Drainage Regime ...... 31 7.3 Sustainable Drainage ...... 32 7.4 Surface Water Treatment ...... 35 7.5 Surface Water Attenuation Storage Requirements ...... 36

SLR JH Walter LLP ii SLR Ref. 408.03643.00033 Tongue End AD Plant, Deeping St. Nicholas: FRA & SWDS April 2016

7.6 SuDS Maintenance Responsibilities ...... 37 8.0 PRINCIPAL OPERATION AND MAINTENANCE REQUIREMENTS ...... 38 8.1 Overview ...... 38 8.2 Piped Systems (including gullies and kerb drainage) ...... 38 8.3 Detention Basins and Lagoons ...... 39 8.4 Permeable Paving ...... 40 9.0 CONCLUSION ...... 41 10.0 CLOSURE ...... 43

FIGURES Figure 1-1 Site Location Plan ...... 1 Figure 1-2 View of Site from Counter Drain Drove (Looking South) ...... 2 Figure 1-3 River Glen and Flood Defence Embankment ...... 3 Figure 1-4 Counter Drain and Raised Southern Bank (Looking North East) ...... 4 Figure 1-5 Delph Drain from Site Access (Looking South West) ...... 4 Figure 1-6 Delph Drain Diversion (Looking South East Along SW Site Boundary) ...... 5 Figure 1-7 Extract of the Environment Agency Flood Map for Planning ...... 8 Figure 1-8 Extract of South Holland SFRA Figure 7 – Flood Zones ...... 9 Figure 4-1 EA Surface Water Depth Map - High Probability of Occurring ...... 18 Figure 4-2 EA Surface Water Depth Map - Medium Probability of Occurring ...... 19 Figure 4-3 EA Surface Water Depth Map - Low Probability of Occurring ...... 20 Figure 4-4 EA Reservoir Flood Risk ...... 22 Figure 5-1 SFRA ‘Actual Risk’ Predicted Flood Depth (Future with Climate Change) 26 Figure 7-1 Four Pillars of SuDS (after CIRIA Report C753) ...... 33

TABLES Table 1-1 Flood Risk Vulnerability and Flood Zone ‘Compatibility’ ...... 10 Table 3-1 Potential Risk Posed by Flooding Sources ...... 15 Table 5-1 National Precautionary Climate Change Sensitivity Ranges (2013) ...... 24 Table 5-2 Peak River Flow Allowances By River Basin District (2016) ...... 25 Table 5-3 National Precautionary Climate Change Sensitivity Ranges (2016) ...... 25 Table 7-1 Greenfield Runoff Analysis ...... 32 Table 7-2 Proposed Site Land Use ...... 35 Table 7-3 Summary of Post-Development Attenuation Storage Volumes ...... 37 Table 8-1 Typical Pipe System Maintenance Requirements ...... 38 Table 8-2 Typical Basin / Lagoon Maintenance Requirements ...... 39 Table 8-3 Typical Permeable Paving Maintenance Requirements ...... 40

APPENDIX

Appendix A Topographical Survey Appendix B Internal Drainage Board Watercourse Map Appendix C Development Proposals Appendix D South Holland District Council SFRA Extracts Appendix E Lincolnshire County Council PFRA Extracts Appendix F Joint Lincolnshire FRDMS Extracts Appendix G Surface Water Drainage Calculations Appendix H BS8533 Flowchart

SLR JH Walter LLP 1 SLR Ref. 408.03643.00033 Tongue End AD Plant, Deeping St. Nicholas: FRA & SWDS April 2016

1.0 INTRODUCTION

1.1 Context

SLR Consulting Limited has been commissioned by JH Walter LLP to prepare a Flood Risk Assessment (FRA) and Surface Waterr Drainage Strategy (SWDS) to support an outline planning application for development of land at Tongue End, Deeping St. Nicholas, Lincolnshire (“the Site”).

This FRA has been prepared under the direction of a Technical Dirreector of SLR who specialises in flood risk and associated planning matters.

The provisions of National Planning Policy Framework1 (NPPF) and its associated Planning Practice Guidance2 (PPG) have been considered in preparing this FRA. This report also takes into account local polices and other local and regional guidance documents (refer to Section 3.0).

1.2 Site Location and Features

The Site is located to the north west of Deeping St. Nicholas, centreed at National Grid Reference (NGR) 517401, 319044. The nearest postcode is PE11 3JJ. A site location plan is provided at Figure 1-1.

Figure 1-1 Site Location Plan

Approximate Site Location

1 National Planning Policy Framework: Department for Communities and Local Government (March 2012) 2 Planning Practice Guidance to the National Planning Policy Framework: Department for Communities and Local Government (March 2014)

SLR JH Walter LLP 2 SLR Ref. 408.03643.00033 Tongue End AD Plant, Deeping St. Nicholas: FRA & SWDS April 2016

The Site occupies a total area of approximately 3.5 hectares (ha) and is undeveloped ‘greenfield’ land, currently used for agricultural purposes.

Figure 1-2 View of Site from Counter Drain Drove (Looking South)

The Site is surrounded by undeveloped, agricultural fields. Residential properties are located to the north west of the Site. Land to the north east, south east and south west also comprises undeveloped, agricultural land.

1.3 Topography

Ordnance Survey mapping indicates that the general topography of the locale is very flat, low-lying fenland.

Topographical survey information has been provided for the Site (and additional land to the north west) above Ordnance Datum (AOD) in Appendix A.

The north western Site boundary lies at a typical level of 1.9m AOD. From this higher ground, the Site falls gradually in north easterly and south easterly directions towards the site corners; to circa 1.25m AOD at the eastern corner, and to circa 1.25m AOD at the southern corner.

Ground levels along the Site access fall in a north westerly direction from a level of circa 2.6m AOD adjacent to the existing access on the north eastern site boundary to a low point of 1.4m AOD before rising to 2.2m AOD on Counter Drain Drove to the north west of the Site.

Off-site carriageway levels along Counter Drain Drove are typically elevated at circa 2.2m AOD.

SLR JH Walter LLP 3 SLR Ref. 408.03643.00033 Tongue End AD Plant, Deeping St. Nicholas: FRA & SWDS April 2016

1.4 Hydrology and Surface Water Drainage

There are a number of hydrological features located within the locale, typical of the Fenland environment, however, there are no Main Rivers or significant watercourses located within the confines of the Site boundary.

1.4.1 Environment Agency Controlled

The River Glen (designated Main River) lies approximately 1km to the north west of the Site and flows in a north easterly direction towards its confluence with the River Welland at Surfleet Sluice, eventually flowing to The Wash near Fosdyke.

Figure 1-3 River Glen and Flood Defence Embankment

1.4.2 Welland and Deepings Internal Drainage Board Controlled

Details of the Welland and Deepings Internal Drainage Board (IDB) watercourses have been presented in Appendix B.

Counter Drain is routed along the northern side of Counter Drain Drove approximately 550m to the north west of the Site, and the Delph Drain is routed along the southern side of Counter Drain Drove approximately 520m to the north west of the Site.

Delph Drain Diversion abuts the south western Site boundary, and Pepper Hill Dyke abuts the south eastern Site boundary. North Drove Drain is routed along the northern side of North Drove approximately 1.6km to the south east of the Site.

The aforementioned Drains eventually outfall to Pode Hole Pumping Station, near Spalding, approximately 5km to the north east of the Site. Flows are lifted to Vernatt’s Drain which flows around Spalding before outfalling to the River Welland.

SLR JH Walter LLP 4 SLR Ref. 408.03643.00033 Tongue End AD Plant, Deeping St. Nicholas: FRA & SWDS April 2016

Figure 1-4 Counter Drain and Raised Southern Bank (Looking North East)

Figure 1-5 Delph Drain from Site Access (Looking South West)

SLR JH Walter LLP 5 SLR Ref. 408.03643.00033 Tongue End AD Plant, Deeping St. Nicholas: FRA & SWDS April 2016

Figure 1-6 Delph Drain Diversion (Looking South East Along SW Site Boundary)

1.4.3 Tidal Limits

Water levels across the Fenland area are predominantly controlled by sluices to retain sufficient water for irrigation and aquatic habitat, and prevent inland migration of tidal water. Pumping arrangements enable the release of surface water and land drainage during high tide and tidal flood conditions.

As a result, the tidal limit of the River Glen is at Surfleet Seas End near The Wash, while the tidal limit of the River Welland is at Fulney Lock to the north east of Spalding. Both locations are a significant distance downstream of the Site.

1.4.4 Surface Water Drainage

No formal on-site drainage system has been noted at the Site from the topographical survey or on-site observations.

SLR JH Walter LLP 6 SLR Ref. 408.03643.00033 Tongue End AD Plant, Deeping St. Nicholas: FRA & SWDS April 2016

1.5 Geological and Hydrogeological Features

1.5.1 Geology

British Geological Survey (BGS)3 records indicate that the underlying superficial geology consists of Tidal Flat Deposits (Clay and Silt), with an underlying solid geology of Oxford Clay (Mudstone).

The National Soils Resources Institute, Soilscapes website4 indicates that the Site is underlain by ‘Loamy and clayey soils of coastal flats with naturally high groundwater.

1.5.2 Hydrogeology

Mapping provided by the Environment Agency5 (EA) indicates that the Site does not lie within a Groundwater Source Protection Zone.

EA mapping indicates that the Site does not overlay a designated Aquifer.

EA Groundwater Vulnerability mapping identifies that the Site is located outside of all groundwater vulnerability zones.

1.6 Development Proposals

Planning consent is being sought for development of an anaerobic digestion plant and associated access. Refer to Appendix C for further details of the development proposals.

The proposed plant will supply biomethane to the national grid network and a proposed bio gas vehicle filling station.

The project will seek to produce biomethane from a combination of energy crop and a proportion of waste from the food processing industry. As well as the production of gas as a valuable source of fuel, the other output from the process is digestate; a naturally produced organic and environmentally friendly fertiliser to be recycled back to the land to promote the growth of future crops.

Energy crop feedstock (e.g. silage, maize and beet) will be produced from land farmed locally. Waste from the food preparation industry will be sourced from local businesses also within this area.

The material will be ensiled on the farm prior to being fed into the digestion system. The digester is an insulated concrete tank, covered by a double membrane roof which provides temporary storage for the biogas. Biogas is produced through the anaerobic digestion of organic matter, contained in the feedstock, and is directed to the strategic gas supply grid network.

After digestion, the processed digestate is stored in the gas-tight digestate storage tank before being applied back to the land as an organic fertiliser.

3 British Geological Society online viewer (http://mapapps.bgs.ac.uk/geologyofbritain/home.html 1:625,000 scale). 4 National Soil Resources Institute; http://www.landis.org.uk/soilscapes/ 5 http://maps.environment-agency.gov.uk/wiyby.

SLR JH Walter LLP 7 SLR Ref. 408.03643.00033 Tongue End AD Plant, Deeping St. Nicholas: FRA & SWDS April 2016

The proposed scheme will comprise the following key elements: • Feed Hoppers; • Liquid Storage Tanks (for liquid organic matter for mixing with feedstock); • Digester Tanks; • Digestate Storage Tank; • Combined Heat & Power Plant (to provide heat for heating the digesters and pasteurisation process, and electricity for plant operation); • Technical Building (for feedstock loading and preparation, offices and welfare facilities); • Electricity Substation (to provide import and export of power); • Gas Flare (for burning off excess gas); • Surface Water Storage Lagoons (for storing and re-use of surface water runoff from the site).

1.7 Flood Zone Classification (Environment Agency)

The definition of Environment Agency (EA) flood zones is provided in PPG Table 1: Flood Zones: • Zone 1 - low probability (Flood Zone 1) is defined as land which could be at risk of flooding from fluvial or tidal flood events with less than 0.1% (1:1,000 year) annual probability of occurrence i.e. considered to be at ‘low probability’ of flooding. • Zone 2 - medium probability (Flood Zone 2) is defined as land which could be at risk of flooding with an annual probability of occurrence between 1% (1:100 year) and 0.1% (1:1,000 year) from fluvial sources and between 0.5% (1:200 year) and 0.1% (1:1,000 year) from tidal sources i.e. considered to be at ‘medium probability of flooding. • Zone 3a - high probability (Flood Zone 3a) is defined as land which could be at risk of flooding with an annual probability of occurrence greater than 1% (1:100 year) from fluvial sources and greater than 0.5% (1:200 year) from tidal sources i.e. considered to be at ‘high probability’ of flooding. • Zone 3b - the functional floodplain (Flood Zone 3b) is defined as land where water has to flow or be stored in times of flood. Local planning authorities should identify in their Strategic Flood Risk Assessments areas of functional floodplain in agreement with the Environment Agency. However, in general it is defined as land that would flood with an annual probability of 5% (1:20 year) or greater.

SLR JH Walter LLP 8 SLR Ref. 408.03643.00033 Tongue End AD Plant, Deeping St. Nicholas: FRA & SWDS April 2016

With reference to the indicative Flood Map for Planning (Rivers and Sea)5 published on the Environment Agency (EA) website, the majority of the Site is shown to lie within ‘Zone 3 - High Probability’ (Flood Zone 3) flood risk area, with the northern corner of the Site shown to lie within ‘Zone 2 - Medium Probability’ (Flood Zone 2). An extract of the EA’s indicative flood map is provided at Figure 1-7.

Figure 1-7 Extract of the Environment Agency Flood Map for Planning

Approximate Site Location Main Rivers

Flood Zone 3 Flood Zone 2

Flood Defences Areas Benefitting from Flood Defences

SLR JH Walter LLP 9 SLR Ref. 408.03643.00033 Tongue End AD Plant, Deeping St. Nicholas: FRA & SWDS April 2016

1.8 Flood Zone Classification (Strategic Flood Risk Assessment)

South Holland District Council Update of Strategic Flood Risk Assessment (SFRA)6 contains detailed hydraulic mapping outputs for the District differentiating bettween Flood Zone extents. Refer to mapping extracts presented in Appendix D.

Based upon SFRA Figure 7 (refer to Figure 1-8) the Site is located within Flood Zones 1, 2 and 3a. Mapping shows that the Site is located outside of the functional floodplain (i.e. Flood Zone 3b) associated with the local hydrological features.

Figure 1-8 Extract of South Holland SFRA Figure 7 – Flood Zones

Approximate Site Locattion

6 South HHolland District Council: Update of Strategic Flood Risk Assessment: Final Report: Royal Haskoning (January 2010)

SLR JH Walter LLP 10 SLR Ref. 408.03643.00033 Tongue End AD Plant, Deeping St. Nicholas: FRA & SWDS April 2016

1.9 Flood Zone Classification Requirements

With reference to footnote 20 of the NPPF, any planning application for the Site, given the Site’s location within Flood Zone 3 and comprising an area of greater than 1ha, must be accompanied by a FRA.

1.10 Flood Risk Vulnerability

PPG Table 2: Flood Risk Vulnerability Classification identifies that the proposed land use (‘general industry’ and ‘waste treatment’) is considered as a ‘Less Vulnerable’ use in terms of flood risk vulnerability classification. The plant would not be classed as ‘essential infrastructure’ as it will be a privately owned and operated facility, supplementing the grid, and would not be relied upon as a strategic gas supply.

1.11 Flood Risk Compatibility

PPG Table 3: Flood risk vulnerability and flood zone ‘compatibility’ (replicated as Table 1-1) confirms that the Site is appropriate for ‘Less Vulnerable’ uses in Flood Zones 2 and 3a (refer to highlighted cells).

Therefore, the proposed development (and associated vulnerability classification) is considered appropriate within Flood Zone 1.

Table 1-1 Flood Risk Vulnerability and Flood Zone ‘Compatibility’

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

Zone 1 9 9 9 9 9

Exception Zone 2 9 Test 9 9 9 Required Exception Exception Zone 3a x Test 9 9 Test Required Required Zone 3b Exception (functional x x x 9 Flood Zone (PPG Table 1) Flood Zone Test Required floodplain) Key: 9 Development is appropriate x Development should not be permitted

1.12 Sequential Test

With reference to the NPPF the Sequential Test gives preference to locating new development in areas at lowest risk of flooding (i.e. Flood Zone 1). SFRAs are geared to providing the basis for applying this test.

The Sequential Test requires developers to:

“…..demonstrate that there are no reasonably available sites in areas with a lower probability of flooding that would be appropriate to the type of development or land use proposed.”

SLR JH Walter LLP 11 SLR Ref. 408.03643.00033 Tongue End AD Plant, Deeping St. Nicholas: FRA & SWDS April 2016

The Site does not lie within the lowest flood risk area, nor has the Site been allocated within a strategic development plan, both of which are mechanisms for automatically satisfying the NPPF Sequential Test. Therefore, based only upon flood zone classification or strategic planning status of the Site, the Sequential Test cannot be deemed to be automatically satisfied.

Based upon SFRA Flood Zone Mapping (refer to Figure 1-8), ignoring the presence of flood defence infrastructure, the Site is confirmed as being located within Flood Zone 1, 2 and 3a.

However, SFRA maps (refer to Appendix D) have been created based upon the ‘actual’ risk of flooding taking into account the presence and function of selected flood defence arrangements within the District where they are confirmed as offering a high standard of protection. Further SFRA maps (refer to Appendix D) have been created based upon the ‘residual’ risk of flooding taking less account of the presence and function of selected flood defence arrangements within the District, and allowing breaches of the defences where potential deficiencies have been established.

The ‘actual’ and relative degree of flood risk shown upon the SFRA maps, has been developed as a sound and reliable basis for South Holland District Council to make informed and confident decisions on planning issues, both at the strategic and site-specific levels.

Based upon the ‘actual’ flood risk maps presented in the SFRA, the entire Site is shown to be within the lowest flood probability band (effectively Flood Zone 1) for the ‘present day’ scenario (the appropriate scenario for determining the Sequential Test).

Based upon the ‘residual’ flood risk maps presented in the SFRA, the entire Site remains within the lowest flood probability band (effectively Flood Zone 1) for the ‘present day’ scenario.

Whilst the responsibility for validating the Sequential Test falls to the Local Planning Authority, the nature of the proposals (i.e. ‘Less Vulnerable’ in Flood Zone 1) appears to meet the requirements of the Sequential Test as set out in NPPF, subject to ratification by the Local Planning Authority.

Based upon the Site being within the lowest flood probability zone according to ‘actual’ and ‘residual’ risk designations, consideration of alternative sites is not necessary or appropriate in this instance.

In any case, as the majority of the South Holland District is protected by flood defence infrastructure to some degree, potential alternative sites at a lower probability of flooding are understandably few in number. Furthermore, the Site has been selected for its close proximity to an existing strategic gas grid connection, for its central location to sources of feedstock, and its proximity to customers for the digestate produced within the process. Sites satisfying this combination of criterion are extremely scarce and rarely commercially available.

For the purposes of this FRA, the Site is, therefore, deemed to satisfy the requirements of the NPPF ‘Flood Risk’ Sequential Test.

SLR JH Walter LLP 12 SLR Ref. 408.03643.00033 Tongue End AD Plant, Deeping St. Nicholas: FRA & SWDS April 2016

1.13 Exception Test

With reference to PPG Table 3: Flood risk vulnerability and flood zone ‘compatibility’ the flood risk vulnerability of the proposed development is deemed appropriate and compatible for the flood zone in which it sits in accordance with NPPF, and the Exception Test need not be applied.

In addition, this FRA considers flood risks from all sources and concludes that the proposed development site is appropriate, sustainable, and safe in flood risk terms. Readily deliverable flood management measures are outlined to ensure that the entire development will be safe from flooding over the anticipated lifetime of the development, and that the Site is afforded safe access and egress during flood conditions via the strategic highway network.

Based on the above information the proposed development meets the requirements of the Exception Test as set out in NPPF, were it to apply.

SLR JH Walter LLP 13 SLR Ref. 408.03643.00033 Tongue End AD Plant, Deeping St. Nicholas: FRA & SWDS April 2016

2.0 SOURCES OF INFORMATION

2.1 Topographical Survey

Topographical survey information for the Site was provided by NGH Construction Limited. Refer to Appendix A.

2.2 Internal Drainage Board Watercourse Map

Mapping information for the Site and local catchment was provided by Welland and Deepings IDB. Refer to Appendix B.

2.3 Site Plans

Baseline plans and development proposals have been provided by JH Walter LLP. Refer to Appendix C.

2.4 EA Mapping

Information regarding the current flood risk at the Site has been obtained from the EA website5.

EA flood mapping indicates areas at flood risk from rivers, the sea, surface water and reservoirs. It also highlights EA maintained flood defences and areas of land benefiting from flood defences.

2.5 Strategic Flood Risk Assessment

South Holland District Council SFRA6 assesses the flood risk from all types of flooding in the District, taking into account the existing climate and predicted changes in the climate and provides background evidence to the Local Development Framework.

Relevant SFRA extracts are included within Appendix D.

2.6 Preliminary Flood Risk Assessment

Lincolnshire County Council (LCC) Preliminary Flood Risk Assessment (PFRA)7, undertaken to fulfil LCC’s obligation as the Lead Local Flood Authority (LLFA), under the requirements of the Flood Risk Regulations 2009. The primary objective of the PFRA was to gather local data to identify past flooding events that have had harmful consequences for human health, economic activity, the environment and cultural heritage; and assesses possible harmful and adverse consequences of future floods.

Relevant PFRA extracts are included within Appendix E.

7 Lincolnshire County Council Lead Local Flood Authority: Preliminary Flood Risk Assessment: Preliminary Assessment Report: Final Report (June 2011)

SLR JH Walter LLP 14 SLR Ref. 408.03643.00033 Tongue End AD Plant, Deeping St. Nicholas: FRA & SWDS April 2016

2.7 Joint Lincolnshire Flood Risk and Drainage Management Strategy

The FRDMS8 for Lincolnshire was developed through public and stakeholder consultation and was implemented in December 2012. The Strategy, together with the accompanying Strategic Environmental Assessment, builds on the PFRA.

Relevant extracts are included within Appendix F.

2.8 Historic Flooding

A focussed internet search was undertaken to identify any significant flooding events within the vicinity of the Site. SFRA, PFRA and EA data has also been reviewed to identify historical flood events locally to the Site from all potential sources.

9 A search of the Chronology of British Hydrological Events database was also undertaken to identify any significant flooding events in the area.

8 Lincolnshire Flood Risk and Drainage Management Partnership Framework: Joint Lincolnshire Flood Risk and Drainage Management Strategy 2012-2025 (December 2012) 9 Chronology of British Hydrological Events database, available at: http://www.trp.dundee.ac.uk/cbhe

SLR JH Walter LLP 15 SLR Ref. 408.03643.00033 Tongue End AD Plant, Deeping St. Nicholas: FRA & SWDS April 2016

3.0 FLOOD RISK ASSESSMENT

3.1 Methodology & Best Practice

This report has also been prepared in accordance with the advice and requirements prescribed in current best practice documents relating to management of flood risk in development published by the Construction Industry Research and Information Association (CIRIA)10, the British Standards Institution BS853311, and the EA’s National Standing Advice on Development and Flood Risk12.

A screening study has initially been completed to identify whether there are any potential sources of flooding at the site which may warrant further consideration. Any potential flooding issues identified in the screening study have subsequently been considered in the technical assessment of flood risk.

3.2 National and Local Planning Policy

This FRA report has been completed in accordance with guidance presented within the NPPF and its associated PPG, and has taken account of local planning policies relating to flood risk and surface water management.

3.3 Screening Study

There are a number of potential sources of flooding and these include: • Flooding from the sea or tidal flooding; • Flooding from rivers or fluvial flooding; • Flooding from surface water and overland flow; • Flooding from groundwater; • Flooding from sewers; • Flooding from reservoirs, canals, and other artificial sources; and • Flooding from infrastructure failure.

All potential sources of flooding must be considered for any proposed development. A summary of the potential sources of flooding and a review of the potential risk posed by each source at the Site prior to formal assessment is presented in Table 3-1.

Table 3-1 Potential Risk Posed by Flooding Sources

Potential Source Potential Flood Risk at Site? Sea (or Tidal) Flooding Low Rivers (or Fluvial) Flooding Medium to High Flood Defence Breach Medium to High Surface Water / Overland Flow Low Rising / High Groundwater Low Sewers and Water Mains Low Reservoirs, Canals and other Artificial Sources High Infrastructure Failure Medium

10 CIRIA Report C624, Development and flood risk : guidance for the construction industry 11 BS8533:2011, Assessing and managing flood risk in development : Code of Practice (1st Ed. October 2011) 12 Environment Agency, April 2012, National Standing Advice to Local Planning Authorities for Planning Applications : Version 3.1 : Development and Flood Risk

SLR JH Walter LLP 16 SLR Ref. 408.03643.00033 Tongue End AD Plant, Deeping St. Nicholas: FRA & SWDS April 2016

4.0 TECHNICAL ASSESSMENT OF FLOOD RISK

4.1 Historic Flooding

From a focussed internet search, a review of SFRA and PFRA data, and a search of the Chronology of British Hydrological Events database the Site has not been historically affected by significant flooding from fluvial, surface water or groundwater sources despite the District being significantly affected by tidal flooding in January 1953, and pluvial and fluvial flooding in July 2007.

PFRA mapping extracts presented in Appendix E confirm that there have been no recorded incidents of local flooding at the Site or within the immediate locale.

4.2 Flooding from Tidal and Fluvial Sources

4.2.1 Tidal Flooding

Coastal hazard mapping presented on Map D2 within the FRDMS (refer to Appendix F) demonstrates that the Site lies several kilometres inland from the potential hazard zones in the event of tidal flood defence breach.

Due to its inland location, and prevention of tidal inundation by the presence of tidal flood defences and sluice arrangements on the River Glen and River Welland to the north east of Spalding, the Site is deemed to be at low risk of tidal flooding.

4.2.2 Combined Tidal and Fluvial Flooding (Main River)

Due to the presence of the aforementioned sluices the local rivers and fluvial watercourses upstream of the sluice arrangements can become ‘tide-locked’. For this reason, SFRA mapping presented in Appendix D is based upon modelled outputs from a combination of tidal and fluvial conditions.

Flood risk across the District at the ‘present day’ (taken as 2010 within the SFRA mapping) has been presented for two scenarios; ‘actual’ flood risk and ‘residual’ flood risk: • ‘Actual’ risk of flooding taking into account the presence and function of selected flood defence arrangements within the District where they are confirmed as offering a high standard of protection; and • ‘Residual’ risk of flooding taking less account of the presence and function of selected flood defence arrangements within the District, and allowing breaches of the defences where potential deficiencies have been established.

SFRA mapping for the ‘present day’ presented in Appendix D demonstrates that the entire Site and Counter Drain Drove is located outside of the combined 1% AEP fluvial / 0.5% AEP tidal ‘actual’ flood event.

SFRA mapping for the ‘present day’ presented in Appendix D demonstrates that the entire Site is located outside of the combined 1% AEP fluvial / 0.5% AEP tidal ‘residual’ flood event. Counter Drain Drove is predicted to be affected by shallow (< 0.5m depth), slow moving (velocity < 0.1 m/s) floodwater over a short distance immediately adjacent to the Site access.

4.2.3 Fluvial Flooding (IDB Drains)

Water levels are strictly regulated within the IDB drainage catchment for both irrigation and flood management.

SLR JH Walter LLP 17 SLR Ref. 408.03643.00033 Tongue End AD Plant, Deeping St. Nicholas: FRA & SWDS April 2016

During the summer months, retention levels of water within the Drains adjacent to the Site are maintained at circa -0.15m AOD.

During the winter months, retention levels of water within the Drains adjacent to the Site are maintained at circa -0.8m AOD.

Prior to the onset of extreme flood conditions, retention levels of water within the Drains adjacent to the Site are lowered to a ‘design level’ of circa -1.2m AOD to provide additional storage capacity.

Welland and Deepings IDB advised13 that predicted water levels within their Drain network adjacent to the Site for a 1% AEP (1:100 year) flood event are in the order of 0.31m AOD, i.e. a significant distance below general Site ground levels indicated in Appendix A.

The IDB also indicated that no flooding incidents had been recorded at the Site or locale, to their knowledge, further demonstrating the low risk of fluvial flooding anticipated at this location.

4.3 Flooding from Surface Water

4.3.1 FRDMS Mapping

Map D3d presented within the FRDMS (refer to Appendix F) demonstrates that the Site lies remote from areas requiring further investigation into potential surface water flooding.

4.3.2 EA Mapping

Surface water modelling has been undertaken by the EA in order to seek to establish areas at risk of surface water flooding based upon latest hydrological techniques and surface terrain data. Extracts of the Surface Water Flood Map are presented in Figures 4-1 to 4-3 where the EA define the surface water flood risk categories as:

• Very Low: less than 1 in 1,000 (0.1% AEP) chance of flooding in any given year; • Low: less than 1 in 100 (1% AEP) but greater than or equal to 1 in 1,000 (0.1% AEP) chance of flooding in any given year; • Medium: between 1 in 100 (1% AEP) and 1 in 30 (3.3% AEP) chance of flooding in any given year; and • High: greater than 1 in 30 (3.3% AEP) chance of flooding in any given year.

13 Correspondence with Welland and Deepings IDB Assistant Engineer and Operations Engineer: 15/03/16)

SLR JH Walter LLP 18 SLR Ref. 408.03643.00033 Tongue End AD Plant, Deeping St. Nicholas: FRA & SWDS April 2016

Surface Water and Overland Flows - High Probability

Based upon EA mapping (refer to extract of the EA’s Surface Water Depth mapping in Figure 4-1), the entire Site and Counter Drain Drove lies outside of land indicated at ’High’ probability of flooding from surface water for rainfall events with a high probability of occurrence (i.e. 3.3% AEP / 1 in 30 year events).

Surface water flows remain ‘in-bank’ along the local land drainage network for the high probability event.

Figure 4-1 EA Surface Water Depth Map - High Probability of Occurring

SLR JH Walter LLP 19 SLR Ref. 408.03643.00033 Tongue End AD Plant, Deeping St. Nicholas: FRA & SWDS April 2016

Surface Water and Overland Flows - Medium Probability

Based upon EA mapping (refer to extract of the EA’s Surface Water Depth mapping in Figure 4-2), the entire Site and Counter Drain Drove lies outside of land indicated at ‘Medium’ probability of flooding from surface water for rainfall events with a medium probability of occurrence i.e. between the 3.3% AEP (1 in 30 year) and 1% AEP (1 in 100 year) events.

Surface water flows remain ‘in-bank’ along the local land drainage network for the medium probability event.

Figure 4-2 EA Surface Water Depth Map - Medium Probability of Occurring

SLR JH Walter LLP 20 SLR Ref. 408.03643.00033 Tongue End AD Plant, Deeping St. Nicholas: FRA & SWDS April 2016

Surface Water and Overland Flows - Low Probability

Based upon EA mapping (refer to extract of the EA’s Surface Water Depth mapping in Figure 4-3), the vast majority of the Site and Counter Drain Drove lies outside of land indicated at ‘Low’ probability of flooding from surface water for rainfall events with a low probability of occurrence i.e. between the 1% AEP (1 in 100 year) and 0.1% AEP (1 in 1,000 year) events. Only very minor isolated and localised ‘spots’ ponding of floodwater are predicted at the Site.

The corresponding depth of flooding associated with these identified ‘Low’ probability flood zones within the Site boundary is below 300mm.

Figure 4-3 EA Surface Water Depth Map - Low Probability of Occurring

4.3.3 Summary

Based upon EA Mapping5 set out in Figures 4-1 to 4-3, the Site is located outside of the modelled areas at elevated risk of surface water flooding.

Risk to the proposed routes of vehicular / pedestrian access and egress to and from the Site is ‘Very Low’.

Taking the above into consideration, the associated risk of surface water flooding to the proposed built development and Site access is considered to be ‘Very Low’.

SLR JH Walter LLP 21 SLR Ref. 408.03643.00033 Tongue End AD Plant, Deeping St. Nicholas: FRA & SWDS April 2016

4.4 Flooding from Overland Flow

Due to the flat, gently sloping terrain surrounding the Site, very limited potential exists for surface water from higher ground to progress overland towards the Site.

Taking the above into consideration, risk of flooding from this source is considered ‘very low’.

4.5 Flooding from Groundwater

Groundwater flooding can be defined as flooding caused by the emergence of water originating from subsurface strata. Groundwater flooding can occur where sites are located on permeable ground. After a prolonged period of rainfall and groundwater recharge, a considerable rise in the water table can results in inundation for extended periods of time.

Whilst the local geology has a naturally high groundwater table, the risk of groundwater flooding to the Site is ‘low’ due to the presence of Drains around the perimeter of the Site which will regulate and control groundwater levels.

Map D4 presented within the FRDMS (refer to Appendix F) demonstrates that the Site lies remote from areas deemed to be susceptible to groundwater flooding.

Notwithstanding the above, the potential risk to the proposed development is very low due to the raised elevation of the development platform and availability of flow pathways around the built development.

It is anticipated that the identified level of flood risk is manageable via the implementation of appropriate mitigation and management considered further in Section 6.0.

4.6 Flooding from Sewers & Water Mains

The Site is largely undeveloped and, therefore, there is no formal drainage regime at the Site.

There are no public sewers routed beneath the Site, and there are no public surface water sewer assets identified in the local area.

Asset records indicate a network of public foul water sewers located beneath Counter Drain Drove located to the north-west of the Site, which drain to a small Sewage Treatment Works located to the rear of properties along Counter Drain Drove.

Any excess flood flows arising from surcharging of sewers beneath Counter Drain Drove would tend to be of a minor quantum due to the limited upstream drainage catchment, and would tend to be detained on off-site land at a lower elevation than the developed areas of the Site, over 300m to the north-west of the Site.

Burst public or private water mains, or failure of highway drainage infrastructure could inherently pose a residual risk to any site. However, the flood risk from this source is likely to be very similar to that from the overland flow and therefore would not tend to be directed towards the Site.

Taking the above into consideration, risk of flooding from this source is considered ‘low’. It is anticipated that the identified level of flood risk is manageable via the implementation of appropriate mitigation and management considered further in Section 6.0.

SLR JH Walter LLP 22 SLR Ref. 408.03643.00033 Tongue End AD Plant, Deeping St. Nicholas: FRA & SWDS April 2016

4.7 Flooding from Reservoirs and Canals

4.7.1 Reservoirs

EA mapping5 shows that the Site lies within an area denoted as being at risk of flooding attributed to the failure (breach) of raised embankments of raised large reservoirs (in this instance, Rutland Water). Refer to Figure 4-4.

In any case, reservoir flood maps are typically used for strategic emergency planning purposes rather than for consideration at site level.

Flood risk from reservoirs is considered to be ‘very low’ due to the ‘less vulnerable’ nature of the proposed land use, and the extremely low probability of occurrence of a reservoir breach.

Figure 4-4 EA Reservoir Flood Risk

4.7.2 Canals

Flood risk from canals is considered to be ‘near zero’ as the Site lies remote from such waterways.

SLR JH Walter LLP 23 SLR Ref. 408.03643.00033 Tongue End AD Plant, Deeping St. Nicholas: FRA & SWDS April 2016

4.8 Flooding from Infrastructure Failure

4.8.1 Drainage Infrastructure

The Site is not deemed to be at significant risk of flooding attributed to the failure of drainage infrastructure such as pumped drainage outfalls or automated sluices due to the significant distance of strategic features from the Site, and the vast expanse of naturally low-lying land within the catchment that would provide buffer storage capacity to accommodate excess floodwater.

Flood risk from drainage infrastructure is considered to be ‘very low’.

4.8.2 Other Infrastructure

Breach (failure) of flood defence infrastructure has been considered as part of the residual risk assessment in Section 4.2.

4.9 Potential Flood Risk to Off-Site Areas

4.9.1 Off-Site Impact: Regrading of Existing Levels

Site levels will generally remain at, or close, to existing levels. As a result, there will be no material off-site impacts arising from elevation of on-site areas.

4.9.2 Off-Site Impact: Floodplain Storage Displacement

The Site and locale benefit from the presence and function of raised flood defences, therefore, no ‘active’ floodplain storage or flood conveyance capacity will be displaced as a result of the proposals over the anticipated lifetime of the development.

4.9.3 Off-Site Impact: Surface Water Runoff

There will be a net increase in overall impermeable area as a result of the proposed development when compared to the baseline ‘greenfield’ Site conditions, with a potential associated increase in the rate and volume of off-site runoff post-development. Without mitigation, the proposed development could result in an increase in run-off generated from the Site which would have a minor off-site impact upon surface water and fluvial flood risk.

Whilst impermeable area coverage across the Site will increase, it is proposed that surface water runoff will be managed at sources within the confines of the Site such that the existing off-site rates and volume are not exceeded.

Sustainable drainage techniques and features (SuDS) will be used where possible to control; and manage surface water runoff generated by the proposed development thus providing additional benefit to the received sewer system and downstream catchment. Refer to Section 7.0.

SLR JH Walter LLP 24 SLR Ref. 408.03643.00033 Tongue End AD Plant, Deeping St. Nicholas: FRA & SWDS April 2016

5.0 CLIMATE CHANGE

5.1 Anticipated Lifetime of Development

In line with PPG and best practice guidance (BS8533), a conservative 75 year lifetime of development has been assumed for this commercial (non-residential) development.

5.2 Climate Change Allowances

Technical Work Stage

At the time of undertaking the technical assessment (prior to February 2016), and through the pre-application stage, advice on climate change was reported in EA guidance to support NPPF14, namely the ‘Climate change allowance for planners, September 2013 Table 2: Recommended national precautionary sensitivity ranges for peak rainfall intensities, peak river flows, offshore wind speeds and wave heights’ (replicated as Table 5-1 below). This advice confirms that the above parameters are all expected to increase in the future. PPG recommends that considerations for future climate change are included in FRAs for proposed developments.

Table 5-1 National Precautionary Climate Change Sensitivity Ranges (2013)

Parameter 1990 to 2025 2025 to 2055 2055 to 2085 2085 to 2115 Peak rainfall intensity +5% +10% +20% +30% Peak river flow +10% +20% +20% +20% Offshore wind speed +5% +5% +10% +10% Extreme wave height +5% +5% +10% +10%

During the latter stages of this project, updated guidance on climate change allowances to be used in FRAs was released by the EA on 19th February 201615.

New Guidance

In line with the new guidance, advice on climate change has been provided for:

• Peak river flow allowances by river basin district; • Peak rainfall intensity allowance; • Sea level allowances; and • Offshore wind speed and extreme wave height allowance.

Advice on peak river flow allowances is provided by Table 1: Peak river flow allowances by river basin district (replicated as Table 5-1 below).

14 Environment Agency, Climate change allowances for planners. September 2013. 15 Environment Agency, Flood Risk Assessments: Climate change allowances. February 2016

SLR JH Walter LLP 25 SLR Ref. 408.03643.00033 Tongue End AD Plant, Deeping St. Nicholas: FRA & SWDS April 2016

Table 5-2 Peak River Flow Allowances By River Basin District (2016)

Total potential Total potential Total potential change change River Basin District Allowance Category change anticipated anticipated for anticipated for for 2015 to 2039 2040 to 2059 2060 to 2115 Upper End 25% 35% 65% Anglian Higher Central 15% 20% 35% Central 10% 15% 25%

Latest guidance sets out that for Less Vulnerable development in Flood Zone 3a, the Central and Higher Central categories should be used to assess a range of allowances. For Less Vulnerable development in Flood Zone 2, the Central category should be used. Allowance ranges do not apply to sites in Flood Zone 1.

In light of the SFRA flood zones, the type of development, and lifetime of development being less than 75 years, a 20% uplift in peak river flow (as used to generate SFRA mapping in Appendix D and IDB flood levels) is deemed appropriate and sufficient to understand the range of climate change effects based upon both sets of guidance. Proposed flood management measures (set out in Section 7.0) have been considered in relation to a 20% uplift in peak river flow.

Advice on peak rainfall intensity allowances is provided by Table 2: Peak rainfall intensity allowance in small and urban catchments (replicated as Table 5-3 below).

Table 5-3 National Precautionary Climate Change Sensitivity Ranges (2016)

Allowance Total potential change Total potential change Total potential change anticipated for 2010 to anticipated for 2040 to anticipated for 2060 to Category 2039 2059 2115 Upper End 10% 20% 40% Central 5% 10% 20%

In light of the rural catchment area, the type of development, and lifetime of development, a 30% uplift in peak rainfall intensity is deemed appropriate and sufficient to understand the range of climate change effects based upon both sets of guidance. Proposed surface water management measures (set out in Section 7.0) have been considered in relation to a 30% uplift in peak rainfall intensity.

Proposed flood management measures (set out in Section 6.0) and surface water management measures have been considered in relation to climate change impacts based on the September 2013 advice. Design performance checks have been undertaken in accordance with the latest climate change guidance.

SLR JH Walter LLP 26 SLR Ref. 408.03643.00033 Tongue End AD Plant, Deeping St. Nicholas: FRA & SWDS April 2016

5.3 Impacts on Flood Risk

5.3.1 Combined Tidal and Fluvial Sources

SFRA mapping for the ‘future’ (to 2115 beyond the anticipated lifetime of the development) presented in Appendix D demonstrates that the entire Site is located outside of the combined 1% AEP fluvial / 0.5% AEP tidal ‘actual’ flood event taking into account the effects of climate change beyond the anticipated lifetime of the development. Refer to SFRA mapping extract provided in Figure 5-1.

Figure 5-1 SFRA ‘Actual Risk’ Predicted Flood Depth (Future with Climate Change)

Counter Drain Drove is predicted to be affected by shallow (< 0.5m depth), slow moving (velocity < 0.1 m/s) floodwater over a short distance immediately adjacent to the Site access.

SFRA mapping for the ‘future’ (to 2115 beyond the anticipated lifetime of the development) presented in Appendix D demonstrates that the entire Site is located outside of the combined 1% AEP fluvial / 0.5% AEP tidal ‘residual’ flood event taking into account the effects of climate change beyond the anticipated lifetime of the development.

Counter Drain Drove is predicted to be affected by shallow (< 0.5m depth), slow moving (velocity < 0.1 m/s) floodwater over a short distance immediately adjacent to the Site access.

As demonstrated above, climate change effects upon tidal and fluvial flood risk at the Site are deemed to be negligible and readily manageable.

5.3.2 Other Sources

The potential advent of climate change over the anticipated lifetime of development will not materially increase the risk of flooding to the Site from the other sources of flooding considered in Section 4.0.

As there will be no material change in the topography of the Site existing flow paths will be maintained or managed over the lifetime of development.

SLR JH Walter LLP 27 SLR Ref. 408.03643.00033 Tongue End AD Plant, Deeping St. Nicholas: FRA & SWDS April 2016

5.4 Impacts on Drainage

Climate change impacts over the anticipated lifetime of development will be duly taken into consideration within the assessment of post-development surface water runoff.

In line with PPG (as replicated in Table 5-1), climate change impacts upon the surface water runoff generated by the proposed development have been applied as a 30% uplift in peak rainfall intensity. Proposed attenuation storage arrangement has been ‘performance tested’ against new climate change guidance. The new guidance does not specially require climate change allowance to be used for ‘design’ purposes, therefore, this is an appropriate approach for the proposed outline planning application.

Post development, impermeable area coverage will increase as a result of the development. Appropriately sized drainage and sustainable drainage systems (SuDS) measures will be incorporated into the development to manage surface water generated on the Site to mitigate potential effects upon off-site areas.

Surface water management is discussed further in Section 7.0.

SLR JH Walter LLP 28 SLR Ref. 408.03643.00033 Tongue End AD Plant, Deeping St. Nicholas: FRA & SWDS April 2016

6.0 PROPOSED FLOOD MANAGEMENT MEASURES

6.1 Flood Mitigation & Resilience Measures

6.1.1 Siting of Built Development

Within the proposed layout, a sequential approach to land use management has been adopted whereby the proposed built development has been steered towards the central portion of the Site extents with significant buffer zones maintained between the development area and existing Drains around the south western and south eastern perimeter of the Site.

6.1.2 Finished Floor Levels

Due to the low flood risks identified, the proposed development platform will be elevated at, or above, existing external ground levels; no ground lowering is proposed. Finished floor levels of the proposed buildings and plant will be elevated at, or above, 1.9m AOD (the highest existing on-site ground level).

Due to the significant freeboard (factor of safety) inherently provided between existing (and proposed) ground levels and local fluvial flood levels and post-breach tidal / fluvial flood levels, even climate change effects predicted by new EA guidance can be readily mitigated at the Site.

6.1.3 Level Differentials

A minimum level differential of 150mm will be maintained below the finished ground floor slab level above immediately adjacent external ground levels in accordance with Building Regulations.

This minimum ‘step’ in levels provides a degree of ‘freeboard’ to prevent the ingress of any overland flow from surface water, or fluvial floodwater from perimeter Drains, into the proposed buildings and plant over the lifetime of the development by providing a level differential above shallow overland flood flow routes.

6.1.4 Flood Resistance & Resilience Measures

Due to the low residual risk of flooding from an event exceeding the proposed design criteria no specific flood resilience measures are necessary. However, whilst not mandatory, based on the recommendations within guidance document ‘Improving the Flood Performance of New Buildings: Flood Resilient Construction’, consideration could be given to the following “flood repairable” options and preferences to be integrated into the ground floor of the proposed development:

• Flood resilient building materials across ground floors such as concrete flooring; • Plastic surfaced materials to reduce damage and replacement costs in the event of a flood (welfare area); and • Raising electrical supply boxes, wall sockets, air vents etc 450mm – 1200mm above ground floor level (in line with Building Regulations).

6.1.5 Flood Storage Compensation

No compensatory flood storage is required as there will be no loss of ‘active’ or ‘passive’ fluvial floodplain storage as a result of the proposed development.

SLR JH Walter LLP 29 SLR Ref. 408.03643.00033 Tongue End AD Plant, Deeping St. Nicholas: FRA & SWDS April 2016

6.1.6 Flood Conveyance Compensation

No compensatory flood conveyance capacity is required as there will be no loss of ‘active’ or ‘passive’ fluvial flood conveyance capacity as a result of the proposed development.

6.1.7 Surface Water (Overland) Flood Flow Mitigation

Existing natural overland flow paths are to be retained within the proposed layout, wherever practical to do so, in order that progress of any overland flows through the Site remains unhindered.

Proposed access arrangements and drainage will be designed in accordance with latest Building Regulations and / or Sewers for Adoption criteria, incorporating overland flood flow routes for the conveyance of excess floodwater towards areas of low vulnerability land use (i.e. areas of external hardstanding, or buffer zones around the Site perimeter).

6.2 Residual Flood Risk Management

6.2.1 Safe Route of Access and Egress

Safe, dry access and egress for users and vehicles is readily available in all directions via the strategic highway network for up to and including the present day 1% AEP fluvial / 0.5% AEP tidal flood events.

Safe access and egress for users and vehicles is readily available in all directions via the strategic highway network during future 1% AEP fluvial / 0.5% AEP tidal flood events incorporating climate change effects beyond the anticipated lifetime of the development. Depths of flooding are predicted to remain well below 500mm, with negligible velocity (< 0.1 m/s) and would, therefore, be negotiable via high wheel base vehicles that would typically frequent the Site post-development.

6.2.2 Site Flood Warning Strategy

The Site lies within an area covered by the EA’s Flood Warning System which means that future users of the Site would be able to receive official flood warnings and be informed of the onset of flooding.

Whilst the Site is considered ‘safe’ in flood risk terms, the aim will be to seek to ensure that future Site users will have significant advance warning and notice prior to the onset of significant tidal conditions along the East Coast and major fluvial flood events on the River Glen (which could lead to a breach of the defences). The proposed mitigation put forward is as follows.

• It is proposed that the Site operator sign up to the EA Flood Warnings Direct Service. This will help to act as an early warning system. These proposals are in line with the Defra / EA document entitled “Flood Warning Dissemination Technologies”.

• As a minimum, linkage to the flood warning system should be provided to the Site (land-line), Site manager (mobile telephone), an appropriate senior representative of operating company (mobile) and Head Office of the operating company (land-line) throughout the lifetime of the development.

By signing up to the EA ‘Flood Warning’ and ‘Flood Alert’ system, Site users would receive sufficient prior notice to an impending fluvial flood event and thus would be able to take necessary precautions and evacuate the Site if deemed appropriate.

SLR JH Walter LLP 30 SLR Ref. 408.03643.00033 Tongue End AD Plant, Deeping St. Nicholas: FRA & SWDS April 2016

6.2.3 Site Flood Response & Evacuation Plan

The EA issue three types of flood warning that help prepare the general public for flooding and appropriate action. These are tabulated below along with an outline action plan for consideration by future Site management.

Flood What it When it’s What to Do? Warning Means? Used?

Monitor River Glen (fluvial) and The Wash (tidal) flood Flooding is 2 hours to 2 days forecast on EA website. possible. Be in advance of Assemble emergency kit (torches, battery-powered radio, prepared. flooding. fully charged mobile phone, emergency food supply etc).

Move any critical or high value plant to higher ground on- Flooding is 0.5 hours to 1 day site, or off-site premises (as appropriate). expected. in advance of Continually monitor the flood forecast on EA website, inform Immediate flooding. Site users, and consider cancellation of scheduled next-day action required. deliveries of feedstock.

When flooding Consider evacuation of the Site and ensure high wheel base Severe danger. poses a vehicle(s) are available on-site for means of escape. Danger to life. significant threat Co-operate with the Emergency Services. to life. Call 999 if in immediate danger.

6.2.4 Safe Refuge

Due to the low vulnerability of the Site and its users (i.e. no sleeping accommodation) there is no formal requirement for safe refuge to be provided within the building. However, if an upper floor level, or mezzanine could be provided as part of the development proposals this would provide a further safety measure at the Site.

6.3 Flood Defence Consent

Any works required within the Byelaw distance associated with IDB Drains will require prior Flood Defence Consent (FDC) to be granted by Welland and Deepings IDB. Applications for FDC would be made at an appropriate time, post-determination of the scheme.

SLR JH Walter LLP 31 SLR Ref. 408.03643.00033 Tongue End AD Plant, Deeping St. Nicholas: FRA & SWDS April 2016

7.0 SURFACE WATER MANAGEMENT STATEMENT

7.1 Key Principles

The surface water drainage strategy for the development seeks to provide a sustainable and integrated surface water management scheme for the Site as a whole and aims to ensure no increase in downstream flood risk by managing discharges from the development to the local water environment in a controlled manner.

To comply with current guidance and best practice, Sustainable Drainage Systems (SuDS) will be required to be implemented in order to manage the quantum and quality of surface water runoff discharged off-site from any proposed development at the Site.

Provision of surface water attenuation capacity and implementation of SuDS techniques ensure that post-development discharges are restricted to those rates generated by the ‘pre- developed’ (greenfield) Site, or less, for up to and including the critical 1% AEP / 1 in 100 year storm event incorporating an allowance for climate change (applied as a 30% uplift in peak rainfall intensity) over the lifetime of the development (considered as 75 years in this instance) in line with NPPF guidelines1. Discharge from the Site will outfall to IDB maintained and managed drainage channels. Water levels within the drainage channels are controlled by the IDB.

Whilst pollutant sources are limited, the surface water drainage strategy aims to ensure no detrimental impact in downstream water quality providing robust surface water treatment via use of a management train incorporating SuDS.

7.2 Existing Surface Water Drainage Regime

Under current conditions, there is no formal drainage system in place to serve the undeveloped Site. Precipitation falling onto the Site currently disperses through a combination of evaporation, transpiration and overland flow to the network of drainage ditches of the locale. Infiltration to the ground is considered unlikely based on the local geology and low-lying nature of the Site.

Based upon the topographical survey data, excess runoff not lost through evaporation and/or transpiration drains diffusely across the undeveloped surface of the Site towards the south- east/south-west towards the drainage channels, under the influence of the topographic gradients following the topography of the Site.

7.2.1 Pre-Development Runoff Rates

Pre-Development / Greenfield

Greenfield runoff rates for the Site were estimated through application of the methodology outlined in IH R12416 as set out within the Interim Code of Practice for SuDS (ICP) for catchment areas of 50 hectares or less. IH R124 is widely recognised as current best practice for estimation of catchment release rates for small rural catchments.

The IH R124 method can be used to estimate greenfield runoff release rates for a range of annual probability events, or return periods, by applying regional growth curve factors to the mean annual peak runoff.

16 Institute of Hydrology Report No. 124 (1994) (IH R124). Flood estimation for small catchments.

SLR JH Walter LLP 32 SLR Ref. 408.03643.00033 Tongue End AD Plant, Deeping St. Nicholas: FRA & SWDS April 2016

The UK hydrological region for Deeping St. Nicholas is Region 5 therefore appropriate growth curve factors for this region have been incorporated into the analysis undertaken in the MicroDrainage (2014) software suite17. Results are presented in Appendix G and are summarised in Table 7-1 for a range of AEP storm events.

The following parameters have been incorporated into the runoff modelling.

• Total Developable Site Area: 3.5 hectares (from site plans provided); • Average Annual Rainfall (SAAR): 577mm/year (as taken from WinDes) • Soil Index: 0.3 (as taken from WinDes);

Table 7-1 Greenfield Runoff Analysis Return Site Greenfield Runoff Site Greenfield Runoff Annual Probability Period Rate* Rate (1 in X Years) (l/s/ha) (l/s) 100% 1 1.3 4.4 QBar 2.3 1.4 5.1 3.3% 30 3.5 12.2 1% 100 5.2 18.1 *Total Site Area = 3.50 hectares.

7.3 Sustainable Drainage

7.3.1 Design Statement

Current best practice SuDS guidance states:

“The rate of discharge of the urban runoff to the receiving water should be limited to the equivalent greenfield runoff rate for the site via the provision of storage (Attenuation Storage) and flow constraints (Downstream Flow Controls).

In the case of brownfield sites, drainage discharges should preferably still aim to achieve greenfield runoff characteristics, but minimum requirements are based on the existing drainage conditions and ensuring discharge rates are not increased.”

In line with the PPG, development proposals in all flood zones should seek opportunities to reduce the overall level of flood risk in the area and beyond through the layout and form of the development, and the appropriate application of SuDS.

7.3.2 Background

Current best practice guidance18 promotes sustainable water management through the use of SuDS.

There are four main categories of SuDS which are referred to as the ‘four pillars of SuDS design’ as depicted in Figure 7-1.

17 MicroDrainage (2014). WinDes Drainage Design and Modelling Software (Version 2014.1.1) 18 CIRIA (2015). Report C753, The SuDS Manual

SLR JH Walter LLP 33 SLR Ref. 408.03643.00033 Tongue End AD Plant, Deeping St. Nicholas: FRA & SWDS April 2016

Figure 7-1 Four Pillars of SuDS (after CIRIA Report C753)

The SuDS Manual identifies a hierarchy of SuDS for managing runoff, which is commonly referred to as a ‘management train’:

• Prevention – the use of good site design and housekeeping measures on individual sites to prevent runoff and pollution (e.g. minimise areas of hard standing). • Source Control – control of runoff at or very near its source (such as the use of rainwater harvesting). • Site Control – management of water from several sub-catchments (including routing water from roofs and car parks to one/several large soakaways for the whole site). • Regional Control – management of runoff from several sites, typically in a retention pond or wetland.

It is generally accepted that the implementation of SuDS as opposed to conventional drainage systems, provides several benefits by:

• reducing peak flows to watercourses or sewers and potentially reducing the risk of flooding downstream; • reducing the volumes and frequency of water flowing directly to watercourses or sewers from developed sites; • improving water quality over conventional surface water sewers by removing pollutants from diffuse pollutant sources; • reducing potable water demand through rainwater harvesting; • improving amenity through the provision of public open spaces and wildlife habitat; and replicating natural drainage patterns, including the recharge of groundwater so that base flows are maintained.

7.3.3 Constraints to the use of SuDS

Based upon the regional and local geology and groundwater, traditional SuDS infiltration techniques (e.g. infiltration basins and soakaways, etc) are considered unviable for the strategic disposal of surface water runoff at this location.

SLR JH Walter LLP 34 SLR Ref. 408.03643.00033 Tongue End AD Plant, Deeping St. Nicholas: FRA & SWDS April 2016

The shallow groundwater table will also need to be taken into account within the design of the proposed detention basins and lagoons to be provided for treatment and attenuation of runoff.

Adequate on-site land would appear to be available for the provision of SuDS, located down- gradient of the proposed built facilities.

Subject to development preference, there may be the opportunity for simple rainwater harvesting systems to be used and incorporated into the development (subject to demand and developer preference). Their use will largely be restricted to ‘non-potable’ external uses such as vehicle washing, irrigation of soft landscaping etc.

For the purposes of the surface water drainage strategy the precautionary principle has been adopted whereby no (beneficial) allowance for rainwater re-use has been factored into the calculations or design, at this stage.

No other significant constraints to the use of SuDS were identified.

7.3.4 Proposed Surface Water Disposal

The rate and volume of runoff from the proposed development will be controlled to those generated by the ‘pre-developed’ (greenfield) site, or less, for up to and including the critical 1% AEP (1 in 100 year return period) storm event incorporating the impacts of climate change allowances (applied as a 30% uplift in peak rainfall intensity – refer to Section 5.1) for the lifetime of the development (assessed as being 75 years – refer to Section 5.2).

Further provision of ‘in-parcel’ SuDS, in the form of filter trenches, and pervious surfaces across selected external areas, may also be provided onsite to control and manage additional surface water runoff generated by the proposed development. The integration of SuDS is in line with NPPF guidelines.

7.3.5 Welland and Deepings IDB Criteria

Liaison with Welland and Deepings IDB (WDIDB) confirmed that:

• The IDB greenfield runoff rate for discharge into its systems is 1.4 litres per second per hectare (l/s/ha); • Discharge rates greater than the greenfield rate require a commuted sum. The current charge is £52,000 per impermeable hectare (up to March 2017); • The charge is calculated on a pro rata basis depending on the proposed litres/sec discharge; and • All new discharges into the District, require the prior consent of the Board.

Therefore, adopting the precautionary principle, the rate and volume of runoff from the proposed development will be controlled to the IDB drainage network at the advised greenfield rate (i.e. 1.4 l/sec/ha), or less, for up to and including the critical 1% AEP (1 in 100 year return period) storm event incorporating climate change allowances over the lifetime of the development (applied as a 30% uplift in peak rainfall intensity).

Welland and Deepings IDB indicated that, in principle, their drainage network could accept a direct unrestricted discharge from the Site. This connection would be subject to payment of a full-rate commuted sum.

SLR JH Walter LLP 35 SLR Ref. 408.03643.00033 Tongue End AD Plant, Deeping St. Nicholas: FRA & SWDS April 2016

The commuted sum is currently applied at the rate of £52,000 per impervious hectare of area that contributes to the IDB drainage network, however, where an attenuated discharge is provided, the commuted sum is pro-rata’d according to the degree of attenuation provided.

7.3.6 Proposed Contributing Catchment Area Schedule

For the purposes of the drainage calculations, the impermeable area coverage of the proposed development was assessed as a percentage of the total Site area based on technical experience and assessment of development densities associated with other recent Gas-to-Grid AD sites. Table 7-2 provides a summary of the proposed development impermeable area coverage.

Table 7-2 Proposed Site Land Use

Total Site Proposed Net Effective Net Effective Site Area Area Impermeable Impermeable Impermeable Descriptor (m2) Coverage (%) Area (m2) Area (ha)

Whole Site 35,000 55 19,250 1.93

7.4 Surface Water Treatment

In accordance with the CIRIA C753 surface water runoff from the proposed development will undergo robust treatment through a SuDS management train.

To provide a “management train” at the Site a range of SuDS methods (refer to Section 3.4) will be implemented. CIRIA C753 identifies a hierarchy approach to SuDS which should be linked together to form a surface water “management train”:

The proposed surface water management regime will provide at least two stages of the SuDS ‘management train’ (in line with SuDS Manual guidance) by implementing appropriate proprietary pollution control measures, in-parcel SuDS measures, strategic SuDS facilities within and immediately adjacent to the development areas.

The Site drainage system is expected to incorporate two treatment basins and one attenuation lagoon to reduce the risk of pollution to receiving watercourses. Surface water will initially be drained to one of the two lined detention basins where the water quality will be tested. Runoff of an appropriate water quality will be released to the Delph Drain Diversion or Pepper Hill Dyke at controlled rates. In the event that water quality testing identifies elevated levels of pollutants, runoff will be diverted to the other detention basin for re-use within on-site processes, or tankered off-site for disposal at an appropriate licensed facility.

Each detention basin will be sized to accommodate a 10% AEP (1 in 10 year return period), 24 hour duration, rainfall event incorporating an allowance for climate change (applied as a 30% uplift in rainfall intensity). Drainage calculations presented in Appendix G indicate that the minimum storage capacity of each detention basin will be 1,139 m3.

To prevent ingress of groundwater and leaching of pollutants, it is anticipated that each detention basin will be lined and weighted.

Manually operated penstock valves will be installed at the outlets from the detention basins to allow controlled shutdown of each facility as necessary for pollution control and routine maintenance.

SLR JH Walter LLP 36 SLR Ref. 408.03643.00033 Tongue End AD Plant, Deeping St. Nicholas: FRA & SWDS April 2016

The following proprietary pollution control measures will also be included within the proposed drainage scheme:

• Hydrocarbon Interceptors / Separators etc; • Trapped Gullies; • Silt Traps / Catchpit Manholes.

SuDS source control measures will be incorporated within the Site where practical, including:

• Permeable Pavements (Lined) – a permeable surface suitable for pedestrian and/or light vehicular traffic that allow surface water to infiltrate through the pavement into the underlying sub-base layers. Permeable pavements provide informal attenuation within void space, and robust surface water treatment as water filtrates through the surface and underlying sub-base layers. Treatment potential can be increased further by incorporating a geotextile layer as a filtration component near the top of the structure.

• Filter Trenches (Lined) – a shallow excavation filled with stone that allows temporary surface water storage and facilitates informal attenuation and treatment of surface water runoff as flows filtrate through the stone. Filter trenches can either be surface or subsurface features. Surface filter trenches accept linear inflow from adjacent hardstanding areas. Subsurface filter trenches are an enclosed below ground structure which accept point source inflows.

The development is served by a robust SuDS management train which utilises a range of source control and site control SuDS measures. This management train ensures that surface water runoff discharged from the Site to the receiving water environment will not have an adverse impact on water quality in the downstream catchment.

7.5 Surface Water Attenuation Storage Requirements

To demonstrate the performance of the proposed drainage system under storms of varying annual probability and duration, holistic hydraulic modelling was undertaken using the Source Control function in the WinDes software suite, an appropriate methodology for masterplanning purposes.

The Flood Estimation Handbook (FEH) rainfall model was used.

Surface water runoff generated by rainfall events that exceed the capacity of the ‘treatment’ detention basins, up to and including the 1% AEP (1 in 100 year) incorporating an allowance for climate change (applied as a 30% uplift in rainfall intensity), will be accommodated within an attenuation lagoon.

A full suite of drainage calculations has been provided within Appendix G and Table 7-3 provides a summary of the required attenuation storage volume.

SLR JH Walter LLP 37 SLR Ref. 408.03643.00033 Tongue End AD Plant, Deeping St. Nicholas: FRA & SWDS April 2016

Table 7-3 Summary of Post-Development Attenuation Storage Volumes 1% Annual Exceedance Probability + 30% Allowance for Climate Change Contributing Functional Post Modelled Indicative Catchment Attenuation Development Storage Outlet Commuted Sum Storage Volume Peak Outflow Method Control Type Payment (£)* (m3) (l/s) Whole Site Orifice Plate Lagoon 0.00 (Contributing (or Similar) 1,838 4.9 Impermeable Area)

Whole Site None None Required 0 Unrestricted £100,100 (Contributing Required Impermeable Area) * In line with IDB Byelaws a sliding scale of commuted sum would be payable, subject to discharge rate. The table provides the maximum commuted sum based an unrestricted discharge.

Key Assumptions

The attenuation storage calculation assumes a ‘worst case’ scenario whereby the two ‘treatment’ detention basins are already full at the start of the design rainfall event.

No allowance has been provided within the drainage strategy or calculations for outlying areas as the ‘status quo’ is being maintained and runoff will continue to be managed as per the existing ‘greenfield’ site.

7.5.1 ‘In-Parcel’ SuDS

Subject to developer preference, further provision of ‘in-parcel’ SuDS may also be implemented in the development layout, where practical considerations allow, in order to manage runoff at source and to provide water quality improvements. The informal attenuation credentials of such measures will further offset against peak flow increases induced by climate change prior to discharge into the receiving IDB drainage network. These are likely to take the form of:

Shallow permeable surfaces (e.g. permeable paving – lined and under-drained)

Grassed filter trenches

Rainwater Harvesting techniques (including water butts)

Adopting the precautionary principle, no (beneficial) allowance has been factored into the calculations or design for the impact of further ‘in-parcel’ SuDS at this stage.

7.6 SuDS Maintenance Responsibilities

For the purposes of this FRA and SWDS, it is anticipated that a client-funded management company will be set up to manage and maintain the long-term integrity and function of the proposed SuDS facilities that will fall under private ownership. This can be secured by way of an appropriately worded planning condition, if required by the Local Planning Authority.

Operation and maintenance of the Site will, in any case, be strictly regulated in line with the requirements of the terms of its Environmental Permit, which falls outside the remit of a planning application.

SLR JH Walter LLP 38 SLR Ref. 408.03643.00033 Tongue End AD Plant, Deeping St. Nicholas: FRA & SWDS April 2016

8.0 PRINCIPAL OPERATION AND MAINTENANCE REQUIREMENTS

8.1 Overview

All surface water drainage features associated with the development will remain under private ownership and will be maintained by the Site operator under the terms of the Site’s Environmental Permit.

The following sections outline recommended maintenance requirement for the various aspects of the surface water drainage system for the development. If necessary these outline maintenance and management proposals will be refined by the Site operator once the Site is in operation to suit specific conditions.

8.2 Piped Systems (including gullies and kerb drainage)

The anticipated maintenance and management plan for piped systems associated with the surface water drainage system is outlined in Table 8-1.

Table 8-1 Typical Pipe System Maintenance Requirements Maintenance Required Action Minimum Frequency Schedule

Regular Ensuring drainage intakes are clear of debris / silt. Monthly (or as required). maintenance Clear gully pots. Six monthly. Occasional Jet clean sewer lines, gully tails and kerb channels to remove maintenance grease, grit, sediment and other debris to ensure conveyance Every 2 years. capacity is not compromised. CCTV survey of sewer lines to identify any defects/signs of performance degradation such as: • Cracked/deteriorating pipes; Intermittent • Leaking joints/seals at manholes; Every 5 years. maintenance • High water lines showing regular high stage in pipes (sign of lack of capacity or downstream constraint); and • Suspected infiltration or exfiltration. Repair defects using suitable methods. Effective temporary repairs Remedial actions may be sufficient in short term until scheduled / capital As required. improvements can be made. Record areas of surface ponding / intake bypassing / surcharging Monitoring (photos, inundated areas, depths) during extreme storm events and As required. investigate the reasoning for this post-storm.

SLR JH Walter LLP 39 SLR Ref. 408.03643.00033 Tongue End AD Plant, Deeping St. Nicholas: FRA & SWDS April 2016

8.3 Detention Basins and Lagoons

The proposed drainage scheme will utilise detention basins or lagoons as a mechanism for treatment and attenuation of surface water runoff.

The anticipated maintenance and management plan for such basins or lagoons at the Site is outlined in Table 8-2.

Table 8-2 Typical Basin / Lagoon Maintenance Requirements

Maintenance Required Action Minimum Frequency Schedule Remove litter and debris removal. Monthly. Half yearly (spring – Cut grass in and around basin / lagoon. before nesting season, and autumn). Manage other vegetation and remove nuisance plants. Monthly (or as required). Inspect inlets, outlets and overflows for blockages, and Monthly. clear if required. Regular Inspect banksides, liner, structures, pipework etc for Monthly. Maintenance evidence of physical damage. Monthly (for first year), Inspect inlets and facility surface for silt accumulation. then annually or as Establish appropriate silt removal frequencies. required. Check any penstocks and other mechanical devices. Annually. Tidy all dead growth before start of growing season. Annually. Remove sediment from inlet, outlets and forebay. Annually (or as required). Manage wetland plants in outlet pool – where provided. Annually. Re-seed areas of poor vegetation growth. As required. Every 2 years, or as Prune and trim any trees and remove cuttings. Occasional required. Maintenance Remove sediment from inlets, outlets, forebay and main Every 5 years, or as basin when required. required.

Repair erosion or other damage by reseeding or re-turfing. As required. Realignment of rip-rap. As required. Remedial actions Repair/rehabilitation of inlets, outlets and overflows. As required.

Relevel uneven surfaces and reinstate design levels. As required.

SLR JH Walter LLP 40 SLR Ref. 408.03643.00033 Tongue End AD Plant, Deeping St. Nicholas: FRA & SWDS April 2016

8.4 Permeable Paving

The anticipated maintenance and management plan for the pervious paving associated with the surface water drainage system is outlined in Table 8-3.

Table 8-3 Typical Permeable Paving Maintenance Requirements

Maintenance Required Action Minimum Frequency Schedule 4 Monthly (or as Regular Brushing and vacuuming. maintenance required). Occasional Stabilise and maintain contributing and adjacent areas. As required. maintenance Removal of weed. As required. Remediate any landscaping which, through vegetation maintenance or soil slip, has been raised to within As required. 50mm of the level of the paving. Remedial work to any depressions, rutting and cracked Remedial or broken blocks considered detrimental to the structural As required. actions performance or a hazard to users. As required (if infiltration performance is reduced Rehabilitation of surface and upper sub-structure. as a result of significant clogging). Monthly (for 3 months Initial inspection. after installation). Inspect for evidence of poor operation and/or weed 3 monthly. Monitoring growth. If required take remedial action. Inspect silt accumulation rates and establish appropriate Annually. brushing frequencies. Monitor inspections chambers. Annually.

SLR JH Walter LLP 41 SLR Ref. 408.03643.00033 Tongue End AD Plant, Deeping St. Nicholas: FRA & SWDS April 2016

9.0 CONCLUSION

SLR Consulting Limited has been commissioned by JH Walter LLP to prepare a Flood Risk Assessment (FRA) and Surface Water Drainage Strategy (SWDS) to support an outline planning application for a gas-to-grid anaerobic digestion plant on land at Tongue End, Deeping St. Nicholas, Lincolnshire (“the Site”).

Flood risk has been assessed in line with BS8533 as demonstrated by the flowchart provided in Appendix H. Taking account of national planning policy and guidance, all potential sources of flooding to the Site have been considered.

SFRA Flood Zone Mapping (refer to Figure 1-8), ignoring the presence of flood defence infrastructure, the Site is confirmed as being located within Flood Zone 1, 2 and 3a.

However, based upon the best available information presented upon SFRA ‘actual’ risk maps (refer to Appendix D), which take due account of the extensive strategic flood defence infrastructure in the locale, the entire Site is shown to be within the lowest flood probability band (effectively Flood Zone 1) taking into account climate change effects beyond the anticipated lifetime of the proposed development.

The primary residual flood risk to the Site is from significant failure (breach) of local flood defences coinciding with significant fluvial and tidal flood conditions. However, based upon the best available information presented upon SFRA ‘residual’ risk maps (refer to Appendix D), the entire Site is shown to be within the lowest flood probability band (effectively Flood Zone 1) taking into account climate change effects beyond the anticipated lifetime of the proposed development, and a significant distance outside of any Rapid Inundation Zones.

Flood risk to the Site from other potential sources, such as local Drains, surface water, groundwater, sewer systems and infrastructure failure is considered ‘low’.

The Site has no recorded history of fluvial flooding. No history of ‘local’ flooding at the Site from other sources has been established based upon research and stakeholder liaison.

For the purposes of this FRA, the Site is deemed to satisfy the requirements of the NPPF ‘Flood Risk’ Sequential Test.

Based upon the Site being within the lowest flood probability zone according to ‘actual’ and ‘residual’ risk designations, consideration of alternative sites is not necessary or appropriate in this instance.

In any case, as the majority of the South Holland District is protected by flood defence infrastructure to some degree, potential alternative sites at a lower probability of flooding are understandably few in number. Furthermore, the Site has been selected for its close proximity to an existing strategic gas grid connection, for its central location to sources of feedstock, and its proximity to customers for the digestate produced within the process. Sites satisfying this combination of criterion are extremely scarce and rarely commercially available.

The proposed ‘Less Vulnerable’ land use is deemed an appropriate and compatible land use for this Site and there is no requirement for the development proposals to be subject to the Exception Test.

A suite of readily deliverable flood mitigation and management measures will be integrated within the development proposals and layout to further reduce the probability and consequence of flooding at the Site.

SLR JH Walter LLP 42 SLR Ref. 408.03643.00033 Tongue End AD Plant, Deeping St. Nicholas: FRA & SWDS April 2016

Safe access and egress for users and vehicles is readily available in all directions via the strategic highway network during future 1% AEP fluvial / 0.5% AEP tidal flood events incorporating climate change effects beyond the anticipated lifetime of the development. Depths of flooding are predicted to remain well below 500mm, with negligible velocity (< 0.1 m/s) and would, therefore, be negotiable via high wheel base vehicles that would typically frequent the Site post-development.

The technical assessment of flood risk presented within this FRA demonstrates that flood risks and residual flood risks are manageable over the lifetime of the development and the development proposals are deemed to be ‘safe’ and sustainable in flood risk terms.

As a result of the proposed development, post development impermeable surfaces will result in an overall increase compared to the former use; however, additional runoff generated by climate change impacts and the uplift in impermeable surfaces over the lifetime of the development will be negated by the incorporation of sustainable drainage systems (SuDS) through a combination of appropriate methods across selected areas of the Site.

The Site drainage system is expected to incorporate two treatment basins and one attenuation lagoon to reduce the risk of pollution to receiving watercourses. Surface water will initially be drained to one of the two lined detention basins where the water quality will be tested. Runoff of an appropriate water quality will be released to the Delph Drain Diversion or Pepper Hill Dyke at controlled rates. In the event that water quality testing identifies elevated levels of pollutants, runoff will be diverted to the other detention basin for re-use within on-site processes, or tankered off-site for disposal at an appropriate licensed facility.

Surface water runoff generated by rainfall events that exceed the capacity of the ‘treatment’ detention basins, up to and including the 1% AEP (1 in 100 year) incorporating an allowance for climate change (applied as a 30% uplift in rainfall intensity), will be accommodated within an attenuation lagoon.

Off-site surface water discharge rates to the local watercourse network are to be agreed, post-determination, with the Welland and Deepings IDB as part of a future Discharge Consent application. Either:

• Surface water runoff will be discharged off-site at rates exceeding the pre-developed ‘greenfield’ runoff rate in return for full or pro-rata payment of a commuted sum to the IDB; or • Surface water runoff will be managed at source within an on-site attenuation lagoon for up to and including the critical 1% AEP (1 in 100 year return period) storm event incorporating climate change allowances over the anticipated lifetime of the development and released off-site at the pre-developed ‘greenfield’ runoff rate (circa 5 l/s).

Technical information provided within this SWDS seeks to demonstrate that viable solutions are available for management of quantum and quality of surface water runoff from the Site post-development, and that the proposed surface water management strategy and recommended SuDS provisions are robust, deliverable and sustainable in terms of the requirements of local and national planning policy.

SLR JH Walter LLP 43 SLR Ref. 408.03643.00033 Tongue End AD Plant, Deeping St. Nicholas: FRA & SWDS April 2016

10.0 CLOSURE

This report has been prepared by SLR Consulting Limited with all reasonable skill, care and diligence, and taking account of the manpower and resources devoted to it by agreement with the client. Information reported herein is based on the interpretation of data collected and has been accepted in good faith as being accurate and valid.

This report is for the exclusive use of JH Walter LLP; no warranties or guarantees are expressed or should be inferred by any third parties. This report may not be relied upon by other parties without written consent from SLR.

SLR disclaims any responsibility to the client and others in respect of any matters outside the agreed scope of the work.

SLR JH Walter LLP SLR Ref. 408.03643.00033 Tongue End AD Plant, Deeping St. Nicholas: FRA & SWDS April 2016

APPENDIX

SLR JH Walter LLP SLR Ref. 408.03643.00033 Tongue End AD Plant, Deeping St. Nicholas: FRA & SWDS April 2016

APPENDIX A

Topographical Survey

SLR

JH Walter LLP SLR Ref. 408.03643.00033 Tongue End AD Plant, Deeping St. Nicholas: FRA & SWDS April 2016

APPENDIX B

Internal Drainage Board Watercourse Map

SLR 172-P03

144-P13 172-P04Ironbar Drove Dyke

172-P05 129-P03Delph144-P14 Drain-144 Shoals Drain 144-P15

144-P16 Ironbar172-P06 Drove Dyke-172 140-P07

172-P07 Decoy Drain-140

140-P06

144-P17

129-P04144-P18

140-P05 Counter Drain-129 144-P19

Pepper Hill Dyke 129-P05 144-P20 140-P04 Counter Drain Washes Soke Dyke-131 Delph Drain Decoy Drain Counter Drain Washes Outfall 129-P06 144-P21

144-P22 144-P24144-P23 144-P25 140-P03 Owens Farm Dyke 130-P01 144-P27144-P26 144-P28 142-P02 144-P31144-P30144-P29 144-P32 140-P02 144-P37144-P35144-P34144-P33 144-P36 Pepper Hill Dyke-194 144-P38 144-P39 140-P01 North Drove Drain Counter Drain Washes Soke Dyke 144-P40

144-P41 Grays Farm Delph Diversion

129-P07 Grays Farm-155 Green Lane Drain-157

125-P06

Delph Diversion-142 Worths Farm Dyke-232 144-P42

144-P44144-P43 Chimney Farm Dyke Counter144-P45 Drain Green Lane Drain 144-P46191-P04 125-P05 144-P47 144-P48 129-P08 191-P03

Parrs Farm Dyke 125-P04 129-P09 Chimney Farm Dyke-125 North Drove Drain-185 Worths Farm Dyke 142-P01

Wards Farm Dyke 125-P03

224-P03 1,000 500 0 Meters µ 198-P01 JH Walter LLP SLR Ref. 408.03643.00033 Tongue End AD Plant, Deeping St. Nicholas: FRA & SWDS April 2016

APPENDIX C

Development Proposals

SLR

JH Walter LLP SLR Ref. 408.03643.00033 Tongue End AD Plant, Deeping St. Nicholas: FRA & SWDS April 2016

APPENDIX D

South Holland District Council Strategic Flood Risk Assessment Extracts

SLR JH Walter LLP SLR Ref. 408.03643.00033 Tongue End AD Plant, Deeping St. Nicholas: FRA & SWDS April 2016

Actual Flood Risk

Present Day Scenario

SLR NOTES

1. The potential flooding consequences shown on this map relate to flooding from the sea, main rivers and Internal Drainage Board systems taking into account the presence of current flood risk management measures such as flood defences. 2. In addition to the potential flood extents shown on this map, there may be shallow flooding in low-lying rural areas 3. The consequences designated as being an Actual Risk arise from direct overtopping of defences, where this would occur, together with assumed breach failure of some defences. Breach failure has been assumed to occur in places where the freeboard between peak sea or river water level and the defence crest level is less than the minimum desirable for structural security of the defence. 4. The consequences designated as being a Residual Risk arise from direct overtopping of defences, where this would occur, together with breach failure which is assumed could occur at any point along the defences. 5. The potential flooding consequences relate to flood probability bandings as follows:

Annual probability of Flooding The Wash Probability Band from a river (fluvial) from the sea (tidal)

Low <0.1% <0.1%

Medium 1%-0.1% 0.5%-0.1%

High >1% >0.5%

6. Functional Floodplain encompasses areas where water is intended to flow or be stored in times of flood. 7. Land outside South Holland District is not considered. 8. This map shows the extents only of the flooding probability bands relevent to the map Title

Map Legend

Flooding Probability bands :

High

Low or medium, but reliant on protection by flood defences for this standard

Functional Floodplain

South Holland District Boundary

REV DATE REMARKS This map is reproduced from the Ordnance Survey map with the permission of the Controller of HM Stationery Office, © Crown Copyright . Unathorised reproduction infringes Crown Copyright and may lead to prosecution or civil proceddings Licence No: 100018215, 2009

ROYAL HASKONING RIGHTWELL HOUSE BRETTON PETERBOROUGH PE3 8DW TEL +44 (0)1733 334455 FAX +44 (0)1733 262243

SOUTH HOLLAND DISTRICT COUNCIL COUNCIL OFFICES PRIORY ROAD SPALDING LINCOLNSHIRE PE11 2XE

UPDATE OF STRATEGIC FLOOD RISK ASSESSMENT Actual Risk Extent District - 2055 1% Fluvial / 0.5% Tidal Event Probability

DATE OF ISSUE: January 2010 REV NO:

SCALE: MAP NO: 1 : 60,000 @ A1