OLD TIP MOUNTFIELD LANDFILL

PASSIVE LEACHATE TREATMENT SYSTEM

Flood Risk Assessment

Prepared for: Saint-Gobain Construction Products UK Limited

SLR Ref: 404.00195.00035 Version No: 2.1 May 2021

Saint-Gobain Construction Products UK Limited Old Tip Mountfield Landfill FRA Filename: 210511_404-01288-00019_Robertsbridge_FRA_v2.1

SLR Ref No:404.00195.00035 May 2021

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BASIS OF REPORT

This document has been prepared by SLR with reasonable skill, care and diligence, and taking account of the manpower, timescales and resources devoted to it by agreement with Saint-Gobain Construction Products UK Limited (the Client) as part or all of the services it has been appointed by the Client to carry out. It is subject to the terms and conditions of that appointment.

SLR shall not be liable for the use of or reliance on any information, advice, recommendations and opinions in this document for any purpose by any person other than the Client. Reliance may be granted to a third party only in the event that SLR and the third party have executed a reliance agreement or collateral warranty.

Information reported herein may be based on the interpretation of public domain data collected by SLR, and/or information supplied by the Client and/or its other advisors and associates. These data have been accepted in good faith as being accurate and valid.

The copyright and intellectual property in all drawings, reports, specifications, bills of quantities, calculations and other information set out in this report remain vested in SLR unless the terms of appointment state otherwise.

This document may contain information of a specialised and/or highly technical nature and the Client is advised to seek clarification on any elements which may be unclear to it.

Information, advice, recommendations and opinions in this document should only be relied upon in the context of the whole document and any documents referenced explicitly herein and should then only be used within the context of the appointment.

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CONTENTS

INTRODUCTION ............................................................................................................... 1

1.1 Administrative Context ............................................................................................................. 1

1.2 Site Location.............................................................................................................................. 1

PROJECT DESCRIPTION .................................................................................................... 2

SITE DETAILS ................................................................................................................... 3

3.1 Topography ............................................................................................................................... 3

3.2 Local Hydrology ......................................................................................................................... 4

3.2.1 River Line ........................................................................................................................................................................... 4

3.3 Geology and Hydrogeology ....................................................................................................... 4

3.3.1 Soils ................................................................................................................................................................................... 4

3.3.2 Geology ............................................................................................................................................................................. 5

3.3.3 Hydrogeology .................................................................................................................................................................... 5

POLICY STATUS FOR PROPOSED DEVELOPMENT ............................................................... 6

4.1 Development Proposals ............................................................................................................ 6

4.2 Flood Zone Classification........................................................................................................... 6

4.3 Planning Policy .......................................................................................................................... 6

4.3.1 Local Planning Policy ........................................................................................................................................................ 7

4.3.2 Flood Risk Compatibility ................................................................................................................................................... 7

4.3.3 Sequential Test ................................................................................................................................................................. 7

4.3.4 Exception Test ................................................................................................................................................................... 8

4.4 Climate Change ......................................................................................................................... 8

4.4.1 Anticipated Lifetime of Development ............................................................................................................................. 8

4.4.2 Climate Change Allowances ............................................................................................................................................. 8

4.4.3 Allowances for Extreme Rainfall ...................................................................................................................................... 8

POTENTIAL SOURCES OF FLOODING ................................................................................. 9

5.1 Methodology & Best Practice ................................................................................................... 9

5.2 Screening Study ........................................................................................................................ 9

5.2.1 Flooding from the Sea or Tidal Flooding ......................................................................................................................... 9

5.2.2 Flooding from Rivers or Fluvial Flooding ......................................................................................................................... 9

5.2.3 Flooding from Surface Water and Overland Flows ......................................................................................................... 9

5.2.4 Flooding from Groundwater .......................................................................................................................................... 11

5.2.5 Flooding from Sewers and Water Mains ....................................................................................................................... 11

5.2.6 Flooding from Reservoirs, Canals and other Artificial Sources .................................................................................... 11

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5.2.7 Flooding from Infrastructure Failure ............................................................................................................................. 11

5.3 Flood Summary ....................................................................................................................... 12

SURFACE WATER DRAINAGE STRATEGY ......................................................................... 13

6.1 Context.................................................................................................................................... 13

6.2 Key Principles of Surface Water Management ........................................................................ 13

6.2.1 Overview ......................................................................................................................................................................... 13

6.2.2 National Policy Context .................................................................................................................................................. 14

6.2.3 Local Policy Context ........................................................................................................................................................ 14

6.3 Existing Surface Water Drainage Regime ................................................................................ 14

6.3.1 Pre-Development Runoff Rates (Greenfield) ................................................................................................................ 14

6.4 Proposed Discharge Arrangements......................................................................................... 15

6.5 Conceptual Surface Water Drainage Strategy ......................................................................... 15

6.6 Proposed Area Schedule ......................................................................................................... 16

6.7 SuDS Attenuation Storage ....................................................................................................... 16

6.8 Water Quality .......................................................................................................................... 17

6.9 SuDS Operational Maintenance Requirements ....................................................................... 18

6.9.1 Swale ............................................................................................................................................................................... 18

6.10 Exceedance ............................................................................................................................. 19

CONCLUSIONS ............................................................................................................... 20

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DOCUMENT REFERENCES

TABLES

Table 4-1 Flood Risk Vulnerability and Flood Zone ‘Compatibility’ ...................................................... 7

Table 4-2 Peak rainfall intensity allowance in small and urban catchments ....................................... 8

Table 5-1 Potential Risk Posed by Flooding Sources ......................................................................... 12

Table 6-1 Estimation of ‘Greenfield’ Runoff Rates ............................................................................. 14

Table 6-2 Suitability of Surface Water Disposal Methods .................................................................. 15

Table 6-3 Proposed Contributing Catchment Areas ........................................................................... 16

Table 6-4 Attenuation Volumes ......................................................................................................... 17

Table 6-5 Pollution Hazard Potential for the Proposed Development ............................................... 17

Table 6-6 SuDS Mitigation Indices for Proposed Developments........................................................ 18

Table 6-7 SuDS Performance: Water Quality Indices Assessment - Swale ........................................ 18

Table 6-8 Typical Swale Maintenance Requirements ........................................................................ 19

FIGURES

Figure 3-1 Satellite Imagery of the Site ................................................................................................ 3

Figure 3-2 LiDAR Imagery of the Site ................................................................................................... 4

Figure 5-1 EA Surface Water Flood Map Extract ................................................................................ 10

Figure 6-1 Four Pillars of SuDS (after CIRIA Report C753) .................................................................. 13

APPENDICES

Appendix 01: Site location Plan

Appendix 02: Proposed Layout

Appendix 03: Local Watercourses Plan

Appendix 04: Concept Drainage Layout

Appendix 05: MicroDrainage Calculations

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Page 1

Introduction

SLR Consulting Limited (SLR) has been appointed by Saint-Gobain Construction Products UK Limited, trading as British Gypsum (SGCPUK) (the client) to prepare a Flood Risk Assessment (FRA) for a passive leachate treatment system primarily within the footprint of the Old Tip Mountfield Landfill at Robertsbridge, East Sussex, TN32 5LA (the site).

This FRA has been prepared by SLR Consulting Ltd (SLR), under the direction of a Technical Director Hydrologist of SLR who specialises in flood risk and associated planning matters. Reporting has been completed in accordance with guidance presented within the National Planning Policy Framework1 (NPPF) and its associated Planning Practice Guidance2 (PPG), taking due account of current best practice documents relating to assessment of flood risk published by the British Standards Institution BS85333.

1.1 Administrative Context

The proposed development falls entirely within the planning jurisdiction of the East Sussex County Council (ESCC) who act as the Lead Local Flood Authority (LLFA) however Rother District Council act as a Second-Tier authority for the area. The Romney Marshes Area Internal Drainage Board is located downstream of the site on the River Line and have a duty to co-operate with ESCC regarding local flood risk strategies.

1.2 Site Location

Old Tip Mountfield Landfill (the site) is situated in Robertsbridge approximately 4km north-west of the village of Battle and 1.5km west of the A2100 London Road. There are two landfills at the location adjacent to each other, the ‘Old Tip’ and the ‘New Tip’. Both landfills are operated by SGCPUK and both are in formal closure.

The Old Tip is accessed via Robertsbridge Gypsum Mine Access Road, which leads away from the site onto Eatenden Lane, approximately 1.2km to the east. The National Grid Reference (NGR) for the site is TQ 72834 19731.

The site location plan is shown in Appendix 01 (Drawing 001 Site Location Plan).

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1 National Planning Policy Framework: Communities and Local Government (Updated February 2019) 2 Planning Practice Guidance: Communities and Local Government (Updated October 2018) 3 BS8533:2017, Assessing and managing flood risk in development: Code of Practice (December 2017)

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Project Description

This FRA has been prepared in support of the proposed installation of a passive leachate treatment system (PTS), constructed on the Old Tip to treat leachate generated by both The Old Tip and New Tip landfills. The leachate would be treated and released to a nearby watercourse and would be supported by integrated renewable energy generation in the form of solar PV.

The proposed leachate treatment system is required to minimise the need for / target replacement of the current method of leachate management at the closed landfill site which requires leachate to be pumped into a road tanker and taken offsite to a suitable treatment works.

Leachate, destined for treatment at the PTS, will be collected in the existing 40,000 litre underground tank on site. Leachate will then be pumped into the first of four organic media treatment areas, following which it then flows through pipework at a controlled rate under gravity through the remaining treatment areas.

Leachate is then passed through a sand filter bed. Once the leachate has passed through the sand filter bed, it will flow under gravity to reed beds to re-aerate the anoxic discharge from the initial treatment areas. After passing through the reed bed, the water will be discharged to the River Line in accordance with the requirements of the Environmental Permit.

Whilst the system is designed to be a low energy user, there would be a small energy requirement to pump leachate around the system. The energy demand of the system would be powered by a private wire connection to an integral solar PV system. The solar panels would be set out in arrays facing south along the top of the landfill. The system would require pump house and switch house as part of the management and control system. Any surplus power generated would be diverted for reuse elsewhere on within the Works complex or exported to the grid.

The site layout is shown in Appendix 02 (Drawing 002 Proposed Layout).

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Site Details

The Old Tip is located within the existing British Gypsum complex. Adjacent to the Old Tip, on the southern edge of the permit boundary is the New Tip. The area immediately to the north of the Old Tip is industrial premises, while land immediately to the east and south comprises of woodland. There is open ground and woodland to the west. The closest residential dwellings are along Church Road, located to the north east. Figure 3-1 Satellite Imagery of the Site illustrates the local setting.

Figure 3-1 Satellite Imagery of the Site

‘Source: Esri, Maxar, GeoEye, Earthstar Geographics, CNES/Airbus DS, USDA, USGS, AeroGRID, IGN, and the GIS User Community’

3.1 Topography

LiDAR topographic data for the site and immediate locale has been downloaded from the Environment Agency (EA) open data website4 and a topographic survey has been undertaken and is illustrated in the drawing at Appendix 02.

These data sources highlight that the site covers a local topographic high with elevations ranging between 67m above ordnance datum (AOD) to circa 45m AOD. Higher elevations on the site are noted in the south and primarily fall to the north and west towards the River Line valley.

An extract of LiDAR data covering the site is illustrated in Figure 3-2.

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4 Environment Agency open data website, http://environment.data.gov.uk

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Figure 3-2 LiDAR Imagery of the Site

‘Source: Esri, Maxar, GeoEye, Earthstar Geographics, CNES/Airbus DS, USDA, USGS, AeroGRID, IGN, and the GIS User Community and Contains EA data © Environment Agency Copyright and Database Rights (2021).

3.2 Local Hydrology

3.2.1 River Line

The site lies entirely within the River Line catchment that rises to the west of site and flows east where it undergoes several phases of culverting beneath the site, emerging from culverted sections and continuing east downstream of the site. This is illustrated in the drawing shown at Appendix 03.

The River Line is a sub catchment of the River Brede that continues to flow eastward and ultimately discharges to the English Channel at Rye Bay.

Several ponds are identified within 500m of the site boundary, the closest of which lies approximately 270m to the north. Two further ponds are situated approximately 300m southeast and 380m south of the boundary.

3.3 Geology and Hydrogeology

3.3.1 Soils

The National Soils Resources Institute, Soilscapes website5 describes the soils at the site as ‘slightly acid loamy and clayey soils with impeded drainage”. The soils have slightly impeded drainage and the main land cover is generally arable and grassland.

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5 Soilscapes online soil map, Cranfield Soil and Agrifood Institute, available at http://www.landis.org.uk/soilscapes/

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3.3.2 Geology

British Geology Survey (BGS) mapping6 indicates that the site is underlain entirely by the Ashdown Formation of sandstone, siltstone and mudstone while an inferred fault is reported trending northwest to southeast to the west of the site. Superficial deposit are generally absent within the site with limited alluvium of clay, silt sand and gravel extending west from the River Line channel, illustrating the channel has been diverted from its original alignment that would have followed the alluvium.

Borehole record (BGS Reference: TQ71NW29 at NGR TQ 72890 19570) located immediately to the south of the site records the Ashdown Sandstone that lies above the Purbeck Beds (shales and limestones) and Portland Beds as follows:

• 0-10ft below ground level (BGL) – Yellow clay;

• 10-60ft BGL – Brown sandstone; and

• 60-64ft BGL – Grey sand.

To the east of the site, BGS borehole record TQ71NW23 (at NGR TQ 73010 19930) records the Ashdown Sandstone of sandstone and shales to a depth of 330ft BGL, on top of the Purbeck Beds (sandstone).

3.3.3 Hydrogeology

The bedrock underlying the permit boundary has been designated by the EA7 as a Secondary Aquifer A, described as permeable layers capable of supporting water supplies at a local rather than strategic scale, and in some cases forming an important source of base flow to rivers. These are generally aquifers formerly classified as minor aquifers.

The superficial deposits are not designated as an aquifer due to their general absence within the site boundary, a thin extent of Secondary A is recorded to bound the River Line channel to the east of the site.

Given the limited extent of the deposits across the site, evaluated from nearby borehole records, superficial deposits will not present any significant influence in impeding groundwater recharge. This is illustrated by the High groundwater vulnerability classification, highlighting that the absence of superficial cover provides no protected to the bedrock aquifer.

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6 BGS Onshore Geoindex, available at https://mapapps2.bgs.ac.uk/geoindex/home.html 7 DEFRA MagicMap, available at https://magic.defra.gov.uk/magicmap.aspx

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Policy Status for Proposed Development

4.1 Development Proposals

The proposed development will involve collecting and pumping leachate from the closed landfill and passing it through a series of organic media treatment areas prior to discharging it to a watercourse (River Line) via a reed bed filtration system. The organic media treatment areas will take the form of earth-bunded tanks / containers located within a series of terraces on the footprint of the restored landfill. The treatment areas will be no more than 3m high and cover an area of approximately 10,000m2. The reed bed system is expected to cover approximately 1,500m2. There will be a small pumping building, feed tank and control room located just east of the landfill. Given the nature of the development proposals, in that they are open ponding areas and wetlands, the leachate treatment aspect of the development is considered to be Water Compatible.

The proposed development also includes solar energy generation to provide the electricity required to pump leachate around the system, with excess energy exported to the grid. With reference to Table 2: Flood risk vulnerability classification at PPG Paragraph 066, ‘electricity generating power stations’ are classified as ‘Essential Infrastructure’.

4.2 Flood Zone Classification

The definition of 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% 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% and 0.1% from fluvial sources and between 0.5% and 0.1% 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% from fluvial sources and greater than 0.5% 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 EA. In the absence of definitive information, it is often defined as land that would flood with an annual probability of occurrence of 5% or greater.

Based upon the EA Flood Map for Planning8 the site lies in Flood Zone 1. Mapping contained in the Strategic Flood Risk Assessment Level 19 by Rother District Council confirms the Flood Zone 1 designation.

4.3 Planning Policy

This FRA report has been completed in accordance with the guidance presented in the NPPF1 and with reference to PPG2. The NPPF states that Local Plans should be supported by a Strategic Flood Risk Assessment (SFRA) and develop policies to manage flood risk from all sources taking account of advice from the EA. It is crucial that

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8 Flood Map for Planning, https://flood-map-for-planning.service.gov.uk/, accessed 13/10/2020 9 Strategic Flood Risk Assessment – Level 1, Rother District Council, August 2008, available at https://www.rother.gov.uk/wp-

content/uploads/2020/01/SFRA.pdf.

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Local Planning Authorities consider the risks posed by flooding within their boundary when determining planning applications.

4.3.1 Local Planning Policy

Core Policy 17: Environment: Flood Risk of the Rother District Local Plan 2014 states in Policy EN7:

“Development will be permitted providing the following criteria are met:

• Where development is proposed in an area identified as at flood risk, the applicant will be required to submit a site-specific Flood Risk Assessment which demonstrates that the development will be safe, will not increase flood risk elsewhere, and, where possible, will reduce flooding;

• When development is, exceptionally, acceptable in flood risk areas, consideration is paid to the layout and form of development to minimise flood risk;

• Drainage systems and sustainable drainage systems for all new development are in accordance with the Flood and Water Management Act 2010;

• Where it is appropriate, contributions will be sought for improvements to infrastructure to mitigate against flood risk.”

4.3.2 Flood Risk Compatibility

As discussed in Section 4.1, the proposed development is classified as Essential Infrastructure or Water Compatible and would be located within Flood Zone 1.

PPG Table 3: Flood risk vulnerability and Flood Zone ‘compatibility’ (reproduced as Table 4-1) confirms that this is acceptable.

Table 4-1 Flood Risk Vulnerability and Flood Zone ‘Compatibility’

Flood Risk Vulnerability Classification (PPG Table 2)

Essential Infrastructure

Highly Vulnerable

More Vulnerable

Less Vulnerable

Water Compatible

Flo

od

Zo

ne

(PP

G T

able

1) Zone 1 ✓ ✓ ✓ ✓ ✓

Zone 2 ✓ Exception Test

Required ✓ ✓ ✓

Zone 3a Exception Test

Required x

Exception Test Required

✓ ✓

Zone 3b (functional floodplain)

Exception Test Required

x x x ✓

Key: ✓ Development is appropriate x Development should not be permitted

4.3.3 Sequential Test

NPPF Paragraph 158 advises that the aim of the Sequential Test is to ‘steer new development to areas with the lowest probability of flooding’ and states:

‘Development should not be allocated or permitted if there are reasonably available Sites appropriate for the proposed development in areas with a lower risk of flooding.’

As the site is in Flood Zone 1 the Sequential Test is not required for development purposes.

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4.3.4 Exception Test

The Exception Test is required to show that the sustainability benefits of the proposed development to the community outweigh the flood risk. The sustainability benefits of the development are considered fully elsewhere in the planning application; however reduced tankering of leachate is clearly a key element in reducing carbon emissions. The Exception Test also must show that the development will be safe for its lifetime and will not increase the flood risk elsewhere.

As the proposed development is within Flood Zone 1 (Table 4-1), the Exception Test is not required. Development in this area is suitable.

4.4 Climate Change

PPG requires that consideration of future climate change is included in FRA reporting and should be considered over the project development lifetime.

4.4.1 Anticipated Lifetime of Development

PPG and best practice both recommend that for consideration of industrial development a 20-year development lifetime is assumed unless there is specific justification for considering a shorter period.

4.4.2 Climate Change Allowances

In February 2016 the EA issued updated guidance on the impacts of climate change on flood risk in the UK10 to support NPPF. This guidance sets out that peak rainfall intensity, sea level, peak river flow, offshore wind speed and extreme wave heights are all expected to increase in the future as a result of climate change.

The guidance acknowledges that in relation to certain factors there is considerable uncertainty with respect to the absolute level of change that is likely to occur. As such, in these instances, the guidance provides estimates of possible changes that reflect a range of different emission scenarios.

Concerns relating to offshore wind speed and wave height are only of relevance in contexts that are in direct proximity to the open coast or other large open bodies of water. Additionally, changes attributed to sea level and peak river flow allowances are only applicable to sites within proximity to fluvial and coastal bodies. This is not the case for this site and therefore potential changes in these are not considered further.

4.4.3 Allowances for Extreme Rainfall

For peak rainfall intensity the guidance states that flood risk assessments should assess both the ‘central’ and ‘upper end’ allowances to understand the range of impact. As detailed in Table 4-2, these equate to uplifts of 10% and 20% respectively.

Table 4-2 Peak rainfall intensity allowance in small and urban catchments

River Basin District

Allowance Category

Total potential change anticipated

for 2015 to 2039

Total potential change anticipated

for 2040 to 2069

Total potential change anticipated

for 2070 to 2115

Applies across all of England

Upper End 10% 20% 40%

Central 5% 10% 20%

In line with Table 4-2, the passive leachate treatment system has been developed to take into account increases in rainfall intensity catchments of 20% over the lifetime of the proposed development.

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10 Environment Agency, Flood Risk Assessments: Climate change allowances, February 2016 (last updated February 2019)

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Potential Sources of Flooding

5.1 Methodology & Best Practice

This report has 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)11, and BS85333.

A screening study has been completed to identify whether there are any potential sources of flooding at the site which may warrant further consideration. If required, any potential significant flooding issues identified in the screening study would then be considered in subsequent sections of the assessment.

5.2 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

• Flood from infrastructure failure.

The flood risk from each of these potential sources is discussed below.

5.2.1 Flooding from the Sea or Tidal Flooding

The site lies significantly above sea level (>40m AOD) and is not located in an area at risk of sea or tidal flooding. On this basis the risk associated with sea or tidal flooding is negligible and not considered further.

5.2.2 Flooding from Rivers or Fluvial Flooding

The site lies within Flood Zone 1 and given the elevated nature of the development proposals, is deemed a very low risk of flooding from fluvial sources. On this basis the risk associated with flooding from the rivers or fluvial flooding is not considered further.

5.2.3 Flooding from Surface Water and Overland Flows

Long Term Flood Risk Information (LTFRI)12 provided by the EA includes mapping of surface water flood risk. Surface water modelling has been undertaken by the EA in order to establish areas at risk of surface water flooding based upon latest hydrological techniques and surface terrain data.

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11 CIRIA Report C624, Development and flood risk: guidance for the construction industry 12 Environment Agency, Long Term Flood Risk Information Service: https://flood-warning-information.service.gov.uk/long-term-flood-

risk/map

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An extract of the map for the site and surrounding area is presented in Figure 5-1, where the EA define the surface water flood risk categories as:

• Very Low: less than 1 in 1,000 annual probability (0.1% AEP13) of flooding in any given year;

• Low: less than 1 in 100 annual probability (1% AEP) but greater than or equal to 1 in 1,000 annual probability (0.1% AEP) of flooding in any given year;

• Medium: between 1 in 100 annual probability (1% AEP) and 1 in 30 annual probability (3.33% AEP) of flooding in any given year; and

• High: greater than 1 in 30 annual probability (3.33% AEP) of flooding in any given year.

Figure 5-1 EA Surface Water Flood Map Extract

‘Source: Esri, Maxar, GeoEye, Earthstar Geographics, CNES/Airbus DS, USDA, USGS, AeroGRID, IGN, and the GIS User Community and Contains EA data © Environment Agency Copyright and Database Rights (2021).

The topography of the area illustrates potential for overland flow from the west following the River Line valley, converging on the western extent of the site. From this point, flows have the potential to pond beyond the site boundary or flow around the higher ground within the site to the north along the Robertsbridge Gypsum Mine Access Road, flowing east and away from the site. A smaller potential overland flow path is noted towards the east of the site, flowing from south to north. This feature would be along the toe of the landfill form and would not pass through any area of the proposed development.

The limited upgradient catchment and surrounding geology indicates potential for natural infiltration to ground.

On this basis the risk associated with flooding from surface water and overland flows is low and not considered further.

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13 Annual Exceedance Probability

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5.2.4 Flooding from Groundwater

The site is a managed landfill with a raised profile above the local topographical features. The River Line watercourse is evident to the west and east of the site and is known to be culverted beneath the site. Any shallow groundwater in surrounding local geology is likely to be in continuity with the River Line and would not be able manifest at surface on the site.

As a landfill and as part of the proposed development, leachate from the landfill is collected and managed such that it will not form a flood risk to the development or to down gradient offsite areas.

The risk of flooding at the site from groundwater sources is considered to be negligible.

5.2.5 Flooding from Sewers and Water Mains

There are no known public sewers running across the site. The landfill is raised in comparison to the adjacent access road which is generally the area where public or private sewers or water supply infrastructure would most likely to be located.

Any surface flooding from failure of sewers or water supply infrastructure would be limited to lower ground surrounding the site and would follow topographical gradients to the east and would flow away from the site.

On this basis the risk associated with flooding from sewers and water mains is assessed to be negligible and is not considered further.

5.2.6 Flooding from Reservoirs, Canals and other Artificial Sources

EA mapping12 shows that the site does not lie within the flood extent of a breach from any up gradient raised reservoir structures.

Following a review of Ordnance Survey mapping no other artificial waterbodies (canals, etc) have been identified in the vicinity of the site and therefore flooding from reservoirs, canals and other artificial sources is assessed to be negligible and is not considered further.

5.2.7 Flooding from Infrastructure Failure

The site is not protected by any formal flood defence infrastructure and there are no systems (such as drainage networks) reliant on pumping in the vicinity of the site.

The development proposals include a series of shallow bunded organic media treatment ponds and a tiered system of wetlands. The process for treating the landfill leachate will be a managed process that will be regularly checked and maintained. The risk of failure of any part of the proposed infrastructure is low and exceedance flow in the event of failure would result in shallow overland flow to the River line corridor to the east.

There is therefore low risk of flooding from infrastructure failure and this flood risk is not considered further.

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5.3 Flood Summary

A summary of the potential sources of flooding and the flood risk arising from them is presented in Table 5-1.

Table 5-1 Potential Risk Posed by Flooding Sources

Potential Source Potential Flood Risk at Site?

Sea or Tidal Flooding No

Rivers or Fluvial Flooding No

Surface Water and Overland Flow No

Groundwater No

Sewers and Water Mains No

Reservoirs, Canals and other Artificial Sources No

Infrastructure Failure No

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Surface Water Drainage Strategy

This surface water drainage strategy sets out high level principles for managing storm water on the site in line with best practice and the requirements of both East Sussex County Council (the LLFA) and Rother District Council. It has been produced in support of an outline planning application.

This strategy is intended to demonstrate that, given the nature and quantum of development proposed, it will be feasible to drain the site in line with planning requirements.

6.1 Context

Without mitigation, the proposed development of the site could lead to a small increase in the rate and volume of surface water runoff generated due to the small increase in impermeable coverage. To comply with current guidance and best practice, sustainable drainage systems (SuDS) will be required in order to manage quantum and quality of surface water runoff discharge off-site.

6.2 Key Principles of Surface Water Management

6.2.1 Overview

Current best practice guidance document: The SuDS Manual (CIRIA Report C753), promotes sustainable water management using sustainable drainage techniques (SuDS). There are for main categories of SuDS which are referred to as the ‘four pillars of SuDS design’ as depicted in Figure 6-1.

Figure 6-1 Four Pillars of SuDS (after CIRIA Report C753)

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

• 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 re-use, permeable paving and green roofs);

• Conveyance – routing of collected runoff from ‘Source Control’ features to ‘Site Control’ or ‘Regional Control’ measures;

• Site Control – management of water from several sub-catchments to one / several soakaways or attenuation ponds for the whole site; and

• Regional Control – management of runoff from several sites, typically in a retention pond or wetland.

6.2.2 National Policy Context

Current national planning policy guidance and best practice, namely NPPF and PPG, require development proposals in all Flood Zones to 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.

6.2.3 Local Policy Context

As discussed in Section 4.3.1 above, Rother District Council encourages the use of SuDS within the polices outlined in their local plan.

6.3 Existing Surface Water Drainage Regime

Incidental rainfall is considered to drain via a combination of evaporation, infiltration into the underlying strata and follow topographic gradients towards the River Line as described in Section 5.2.3 above.

6.3.1 Pre-Development Runoff Rates (Greenfield)

Greenfield runoff rates for the area equivalent to the proposed impermeable development were estimated through applications of the Revitalised Flood Hydrograph Model (ReFH2). ReFH2 is recommended by the EA as the methodology for estimating flood peaks and hydrographs for small catchments14.

The ReFH2 method is applied using software ‘The Revitalised Flood Hydrograph’ modelling tool. The FEH parameters obtained from FEH webservice for 1km grid15 were used in the assessment. Details of the greenfield runoff estimates are summarised within Table 6-3.

Table 6-1 Estimation of ‘Greenfield’ Runoff Rates

AEP (%) Estimated Greenfield Runoff Rate

l/s/ha l/s/0.003ha1

50 6.9 0.02

Notes: 1 Based on the proposed increase in impermeable area of 0.003ha, as discussed in Section 6.6 below

______________________

14 Environment Agency, Estimating flood peaks and hydrographs for small catchments: Phase 1, Project SC090031, May 2012 15 The FEH parameters have been reviewed and are considered to be appropriate for the known geology and soils at the site.

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6.4 Proposed Discharge Arrangements

With reference to the SuDS Manual, the hierarchy of preferred disposal options for surface water runoff from development sites in decreasing order of sustainability is as follows:

• Infiltration to Ground;

• Discharge to Surface Waters; or

• Discharge to Sewer.

Table 6-2 summarises the suitability of disposal methods suitability in the context of the site and the proposed development.

Table 6-2 Suitability of Surface Water Disposal Methods

Surface Water Disposal Method (in order of

preference)

Suitability Description Method Suitable? (Y/N)

Infiltration to Ground As discussed in Section 3.3, the site is underlain by the former capped landfill and by Ashdown Formation which according to the National Soils Resources Institute is ‘slightly impeded drainage’ and comprises ‘slightly acid loamy and clayey soils with impeded drainage’. It is therefore considered that infiltration is not suitable option for discharge at the site.

Groundwater is also expected to be near to surface which could prevent effective discharge from an infiltration SuDS feature.

N

Surface Water Discharge

As discussed in Section 3.2, the River Line is located in proximity to the proposed development. A small stream drains to the River Line alone the base of the eastern slope of the capped landfill, between the landfill and an access road. It is therefore proposed that surface water discharges into this stream which then drains to the River Line.

Y

Sewer Discharge None near and less desirable than disposable to surface watercourse.

N

6.5 Conceptual Surface Water Drainage Strategy

The proposed drainage strategy will manage surface water runoff as close to the source as possible.

The proposed solar panels would intercept precipitation and shed this onto the ground along the lower edge of each array (the ‘drip-line’). However, runoff from each solar panel would continue to infiltrate into the underlying soils locally, in much the same way as existing conditions.

Additionally, the grass vegetation that would be maintained between and beneath the solar panel arrays would also ensure that the runoff generated from the panels would continue to drain diffusely across the site following the general topography.

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Page 16

The scheme would result in a small increase in impermeable surface area due to the construction of the pump house and switch house, which contributes to 28.8m2 of the site area.

This surface water drainage strategy will seek to mimic the existing runoff regime for this land (towards the River Line to the east, via an existing stream along the toe of the eastern landfill slope) and ensure that there is no increase in peak discharge from the impermeable areas on site. This will be achieved by the introduction of a swale to collect, attenuate, and then discharge runoff to the adjacent stream, for up to and including the 1% AEP + 20% CC.

The proposed swale is to be located to the west of the existing track and adjacent to the stream, within the eastern extent of the proposed development. Runoff from the buildings will be directed to the proposed swale, prior to controlled discharge to the adjacent stream.

The conceptual drainage strategy is shown on the proposed development plan in Appendix 04.

6.6 Proposed Area Schedule

For the purposes of the drainage calculations, the proposed impermeable areas ‘contributing’ runoff to the drainage network, and permeable runoff to the drainage network, were assessed from the development proposals plan (refer to Appendix 01). A breakdown of the proposed surface types (and associated contributing catchment areas) is presented in Table 6-3.

Table 6-3 Proposed Contributing Catchment Areas

Proposed Land Use Area (ha)

Pump House 0.0014

Switch House 0.0014

Total Impermeable Coverage 0.003

Permeable Coverage 3.997

Total Catchment 4.0

6.7 SuDS Attenuation Storage

Using the MicroDrainage ‘Source Control’ module, the attenuation volume required to accommodate the runoff from the proposed impermeable areas in response to a range of AEP rainfall events up to and including the 1% AEP + 20% rainfall event has been estimated, as shown in Table 6-4. Full details of the analysis are enclosed at Appendix 05.

Due to the small impermeable area proposed, it will not be possible to limit outflow to the equivalent pre-development runoff rates.

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Table 6-4 Attenuation Volumes

AEP (%) Maximum Allowable Discharge (l/s)1

Maximum Proposed Discharge (l/s)2

Maximum Water Depth (mm)

Maximum Storage Required (m3)

Half Drain Time (minutes)

50

0.02

0.0 0.358 0.7 476

3.3 0.1 0.420 0.9 212

1 0.1 0.456 1.0 163

1 + 20% 0.1 0.491 1.2 134

Notes: 1 Equivalent to the greenfield runoff calculation discussed in Section 6.3.1. 2 Lowest discharge available on Source Control module.

A maximum attenuation volume of approximately 1.2m3 will be required to manage runoff from the proposed buildings, assuming a depth of 0.5m, a base width of 0.5m, length of 1.2m and a side slope of 1:3.

6.8 Water Quality

The simple index method, as outlined within the SuDS Manual, provides a way of quantifying the benefit to water quality of the SuDS Management Train. The pollution hazard from the land use and the mitigation from the SUDS component are each assigned an index. The total mitigation index must be greater than the pollution hazard index for adequate treatment to be delivered.

Total SuDS mitigation index ≥ pollution hazard index (for each contaminant type) (for each containment type)

The total SUDS mitigation is the summation of the first components mitigation index and half the mitigation index of any subsequent component.

With reference to the SuDS Manual, post-development surface water runoff generated from is considered to have a ‘Low’ Pollution Hazard Level respectively as presented in Table 6-5.

Table 6-5 Pollution Hazard Potential for the Proposed Development

Land Use Pollution Hazard Level

Pollution Hazard Indices

Total Suspended Solids (TSS)

Metals Hydro-Carbons

Other Roofs (typically commercial/industrial roofs)

Low 0.3 0.2 0.05

Low Traffic Roads Low 0.5 0.4 0.4

The proposed SWDS is required to demonstrate sufficient treatment capability to manage the specified Pollution Hazard Indices.

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Page 18

Table 6-6 SuDS Mitigation Indices for Proposed Developments

SuDS Component

Mitigation Indices

Total Suspended Solids (TSS)

Metals Hydro-Carbons

Swale 0.5 0.6 0.6

Table 6-7 compares the SuDS Mitigation Indices, provided by the proposed ‘Source Control’, ‘Conveyance’ and ‘Site Control’ measures against the Pollution Hazard Indices.

Table 6-7 SuDS Performance: Water Quality Indices Assessment - Swale

Land Use Pollution Hazard Level

Pollution Hazard and SuDS Mitigation Indices Comparison

Total Suspended Solids (TSS)

Metals Hydro-Carbons

Pollution Index

SuDs Mitigation

Index

Pollution Index

SuDs Mitigation

Index

Pollution Index

SuDs Mitigation

Index

Industrial Roof Low 0.3 0.5 0.2 0.6 0.05 0.6

Substation Platform

(Individual property driveway

parameters)

Low 0.5 0.5 0.4 0.6 0.4 0.6

As the SuDS Mitigation Index provided by the proposed SuDS measures are ≥ Pollution Hazard Index the water quality assessment criteria are satisfied for all Land Use criteria.

6.9 SuDS Operational Maintenance Requirements

A full SuDS maintenance plan would be produced as part of the detailed drainage design post-development and the precise requirement would depend on manufacture specification of the final design. At this time, it is considered that the responsibility for the swale would pass to British Gypsum.

An outline of the typical maintenance requirements of each proposed SuDS feature is outlined below.

6.9.1 Swale

The proposed drainage scheme will utilise a swale as a mechanism for treatment, attenuation and infiltration of surface water runoff.

The anticipated maintenance and management for swales associated with the surface water drainage system is outlined in Table 6-8.

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Table 6-8 Typical Swale Maintenance Requirements

Maintenance Schedule

Required Action Minimum Frequency

Regular Maintenance Remove litter and debris. Monthly, or as required.

Cut grass- to retain grass height within specified design range. Monthly (during growing season), or as required.

Manage other vegetation and remove nuisance plants. Monthly at start, then as required.

Inspect inlets and overflows for blockages, and clear if required.

Monthly.

Inspect infiltration surfaces for ponding, compaction, silt accumulation, record areas where water is ponding >48 hours.

Monthly or when required.

Inspect vegetation coverage. Monthly for 6 months, quarterly for 2 years and then half yearly.

Inspect inlets and facility surface for silt accumulation, establish appropriate slit removal frequencies.

As required or if bare soil is exposed over 10% or more of the swale treatment area.

Occasional Maintenance Reseed area of poor vegetation growth, alter plant types to better suit conditions, if required.

Annually

Remedial Actions Repair erosion or other damage by re-turfing or reseeding. As required.

Relevel uneven surfaces and reinstate design levels. As required.

Scarify and spike topsoil layer to improve infiltration performance, break up silt deposits and prevent compaction of the soil surface.

As required.

Remove build-up of sediment on upstream gravel trench, flow spreader or at top of filter strip.

As required.

Remove and dispose of oils or petrol residues using safe standard practices.

As required.

Repair erosion or other damage by re-turfing or reseeding. As required.

6.10 Exceedance

In the low probability event of an exceedance within the swale, water would overtop the swale and follow the topographic gradient towards the adjacent stream before passing to the River Line to the east. This is following the existing route of overland flow from the site.

This would not increase the risk of flooding on the downslope areas. No adverse flooding would be anticipated as a result of surcharging from the surface water network.

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Page 20

Conclusions

SLR Consulting Limited (SLR) has been appointed by Saint-Gobain Construction Products UK Limited, trading as British Gypsum (the client) to produce a Flood Risk Assessment (FRA) for a proposed passive leachate treatment system.

Flood risk has been assessed in line with British Standards3, taking account of national and local planning policy and guidance, and all potential sources of flooding to the site have been considered.

The perimeter of the site is indicated to show a low risk of shallow surface water flooding through adjacent watercourses and access tracks; however, this would not be significant to the proposed development. The surface flow pathways would not be altered by the development proposals.

A screening assessment has reviewed the flood risk posed by other sources including, tidal, fluvial, groundwater, sewer and water mains, reservoirs, canals and infrastructure failure. This concluded that there was no significant risk of flooding at the site.

An outline surface water drainage strategy is proposed for the minor increase in impermeable areas proposed at the site. A singular swale is proposed in order to mitigate impacts of changes in storm water runoff from the site, including impacts to water quality.

The swale is to be located to the west of the existing track and adjacent to an existing stream that drains to the River Line, within the eastern extent of the development. Runoff from the buildings will be directed to the proposed swale, prior to controlled discharge to the adjacent stream. Modelling indicates that the swale is sufficient to accommodate up to and including the 1% AEP with a 20% uplift for climate change.

The proposed Surface Water Drainage Strategy will ensure that proposed development will not increase the flood risk elsewhere and the runoff will have no adverse impact on the water quality at the point of discharge.

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Page 21

APPENDICES

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Appendix 01: Site Location Plan

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Appendix 02: Site Layout

SOLAR ARRAYS

PUMP HOUSE

UNDERGROUND STORAGE TANK

REED BED

SAND FILTER BED

ORGANIC MEDIA TREATMENT AREA

PARKING

SWITCH HOUSE

SITE ACCESS

TARMAC AREA

INTERNAL ACCESS TRACKS

WOODEN PEDESTRIAN

ACCESS STOPS

1. DRAWING IS BASED ON JC WHITE

TOPOGRAPHICAL SURVEY, DRAWING REF:

17/08/035 DWG 1, DATED: APRIL 2018.

NOTES

PLANNING APPLICATION

BOUNDARY

NOTESLEGEND

Scale Date

TREENWOOD HOUSE

ROWDEN LANE

BRADFORD-ON-AVON

WILTS. BA15 2AU

T: 01225 309400

F: 01225 309401

3RD FLOOR THE BREW HOUSEJACOB STREETBRISTOL, BS2 0EQT: 01179 064280

FULMAR HOUSE BEIGNON CLOSEOCEAN WAYCARDIFF. CF24 5PBT: 0292 049 1010F: 029 2048 7903

4 WOODSIDE PLACE CHARING CROSSGLASGOWG3 7QFT: 0141 353 5037F: 0141 353 50384/5 LOCHSIDE VIEWEDINBURGH PARKEDINBURGHEH12 9DHT: +44 (0)131 335 6830

8 STOW COURT STOW-CUM-QUYCAMBRIDGECAMBRIDGESHIRE. CB25 9AST: 01223 813805F: 01223 81378365 WOODBRIDGE ROADGUILDFORDSURREYGU1 4RDT:+44 (0)1483 889800

SUITE 1,JASON HOUSEKERRY HILLHORSFORTHLEEDS. LS18 4JRT: 0113 2580650F: 0113 2818832 MILL BARN28 HOLLINGWORTH COURTTURKEY MILLMAIDSTONE, ME14 5PPT: 01622 609242F: 01622 695872

SAILORS BETHEL HORATIO STREETNEWCASTLE UPON TYNETYNE AND WEAR. NE1 2PET: 0191 261 1966F: 0191 230 2346

ASPECT HOUSE ASPECT BUSINESS PARKBENNERLEY ROADNOTTINGHAM. NG6 8WRT: 01159 647280F: 01159 751576

7 WORNAL PARK MENMARSH ROADWORMINGHALL, AYLESBURYBUCKS. HP18 9PHT: 01844 337380F: 01844 337381 2ND FLOORHERMES HOUSEHOLSWORTH PARKOXON BUSINESS PARKSHREWSBURY, SY3 5HJT: 01743 239250

8TH FLOOR, QUAY WESTMEDIACITYUKTRAFFORD WHARF ROADMANCHESTERM17 1HH, UKT:+44 (0)161 872 7564

LEGEND

69 POLSLOE ROADEXETERDEVONEX1 2NFT: +44 (0)1392 490152F: +44(0)1392 495572WATERHOUSE BUSINESS CENTREUNIT 77, 2 CROMAR WAYCHELMSFORDESSEX CM1 2QET: 01245 392170F: 01245 392171SLR CONSULTING IRELAND7 DUNDRUM BUSINESS PARKWINDY ARBOURDUBLIN 14T: +353-1-2964667F: +353-1-2964676 8 PARKER COURTSTAFFORDSHIRE TECHNOLOGYPARK, BEACONSIDE,STAFFORD ST18 OWPT: 01785 241755F: 01785 241780SUITE 1 POTTERS QUAY5 RAVENHILL ROADBELFASTBT6 8DNNORTHERN IRELANDT: +44 (0)28 9073 2493

00

19

5.0

00

35

.1

6.L

TS

03

.1

_S

IT

E_

LA

YO

UT

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wg

UNIT 2, NEWTON BUSINESS CENTRETHORNCLIFFE PARK ESTATENEWTON CHAMBERS ROADCHAPELTOWNSHEFFIELD, S35 2PWT:+44 (0)114 2455153SUITE 5, BRINDLEY COURTGRESLEY ROADSHIRE BUSINESS PARKWORCESTER WR4 9FDT: +44 (0)1905 751310F: +44 (0)1905 7513112 LINCOLN STREETLANE COVENEW SOUTH WALES 2066AUSTRALIAT: 61 2 9427 8100F: 61 2 9427 820083 VICTORIA STREETLONDONSW1H 0HWT: 44 (0)203 691 58102

NContains OS data © Crown copyright [and database rights] (2015) 0100031673.Contains public sector information licensed under Open government Licence v3.0© Crown copyright [and database rights] 0100031673 Expires

214 UNION STREETABERDEENAB10 1TLT: +44 (0)1224 517405NO. 68 STIRLING BUSINESS CENTREWELLGREENSTIRLINGFK8 2DZT: +44 (0)1786 239900

BUROCLUB157/155 COURS BERRIAT38028 GRENOBLE CEDEX 1FRANCET: + 33 4 76 70 93 41

www.slrconsulting.com

© This drawing and its content are the copyright of SLR Consulting Ltd and may not be reproduced or amended except by prior writ ten permission.SLR Consult ing Ltd accepts no liabi lity for any amendments made by other persons.

© This drawing and its content are the copyright of SLR Consulting Ltd and may not be reproduced or amended except by prior written permission. SLR Consulting Ltd accepts no liability for any amendments made by other persons.

LTS/3

1:1000 @ A3 APRIL 2021

SITE LAYOUT

DRAWING_TITLE_3

PLANNING APPLICATION

LEACHATE TREATMENT SYSTEM

PROJECT_TITLE_3

ROBERTSBRIDGE

SITE_NAME_2

[02/11/21]2020

0 10 20 30 40m 60 80 100

Metres 1:1000

LEGEND

BRITISH GYPSUM

Saint-Gobain Construction Products UK Limited Old Tip Mountfield Landfill FRA Filename: 210511_404-01288-00019_Robertsbridge_FRA_v2.1

SLR Ref No:404.00195.00035 May 2021

Appendix 03: Local Watercourses Plan

Saint-Gobain Construction Products UK Limited Old Tip Mountfield Landfill FRA Filename: 210511_404-01288-00019_Robertsbridge_FRA_v2.1

SLR Ref No:404.00195.00035 May 2021

Appendix 04: Conceptual Drainage Layout

SOLAR ARRAYS

PUMP HOUSE

UNDERGROUND STORAGE TANK

REED BED

SAND FILTER BED

ORGANIC MEDIA TREATMENT AREA

PARKING

SWITCH HOUSE

SITE ACCESS

TARMAC AREA

INTERNAL ACCESS TRACKS

WOODEN PEDESTRIAN

ACCESS STOPS

1. DRAWING IS BASED ON JC WHITE

TOPOGRAPHICAL SURVEY, DRAWING REF:

17/08/035 DWG 1, DATED: APRIL 2018.

NOTES

PLANNING APPLICATION

BOUNDARY

NOTESLEGEND

Scale Date

TREENWOOD HOUSE

ROWDEN LANE

BRADFORD-ON-AVON

WILTS. BA15 2AU

T: 01225 309400

F: 01225 309401

3RD FLOOR THE BREW HOUSEJACOB STREETBRISTOL, BS2 0EQT: 01179 064280

FULMAR HOUSE BEIGNON CLOSEOCEAN WAYCARDIFF. CF24 5PBT: 0292 049 1010F: 029 2048 7903

4 WOODSIDE PLACE CHARING CROSSGLASGOWG3 7QFT: 0141 353 5037F: 0141 353 50384/5 LOCHSIDE VIEWEDINBURGH PARKEDINBURGHEH12 9DHT: +44 (0)131 335 6830

8 STOW COURT STOW-CUM-QUYCAMBRIDGECAMBRIDGESHIRE. CB25 9AST: 01223 813805F: 01223 81378365 WOODBRIDGE ROADGUILDFORDSURREYGU1 4RDT:+44 (0)1483 889800

SUITE 1,JASON HOUSEKERRY HILLHORSFORTHLEEDS. LS18 4JRT: 0113 2580650F: 0113 2818832 MILL BARN28 HOLLINGWORTH COURTTURKEY MILLMAIDSTONE, ME14 5PPT: 01622 609242F: 01622 695872

SAILORS BETHEL HORATIO STREETNEWCASTLE UPON TYNETYNE AND WEAR. NE1 2PET: 0191 261 1966F: 0191 230 2346

ASPECT HOUSE ASPECT BUSINESS PARKBENNERLEY ROADNOTTINGHAM. NG6 8WRT: 01159 647280F: 01159 751576

7 WORNAL PARK MENMARSH ROADWORMINGHALL, AYLESBURYBUCKS. HP18 9PHT: 01844 337380F: 01844 337381 2ND FLOORHERMES HOUSEHOLSWORTH PARKOXON BUSINESS PARKSHREWSBURY, SY3 5HJT: 01743 239250

8TH FLOOR, QUAY WESTMEDIACITYUKTRAFFORD WHARF ROADMANCHESTERM17 1HH, UKT:+44 (0)161 872 7564

LEGEND

69 POLSLOE ROADEXETERDEVONEX1 2NFT: +44 (0)1392 490152F: +44(0)1392 495572WATERHOUSE BUSINESS CENTREUNIT 77, 2 CROMAR WAYCHELMSFORDESSEX CM1 2QET: 01245 392170F: 01245 392171SLR CONSULTING IRELAND7 DUNDRUM BUSINESS PARKWINDY ARBOURDUBLIN 14T: +353-1-2964667F: +353-1-2964676 8 PARKER COURTSTAFFORDSHIRE TECHNOLOGYPARK, BEACONSIDE,STAFFORD ST18 OWPT: 01785 241755F: 01785 241780SUITE 1 POTTERS QUAY5 RAVENHILL ROADBELFASTBT6 8DNNORTHERN IRELANDT: +44 (0)28 9073 2493

00

19

5.0

00

35

.1

6.L

TS

03

.1

_S

IT

E_

LA

YO

UT

.d

wg

UNIT 2, NEWTON BUSINESS CENTRETHORNCLIFFE PARK ESTATENEWTON CHAMBERS ROADCHAPELTOWNSHEFFIELD, S35 2PWT:+44 (0)114 2455153SUITE 5, BRINDLEY COURTGRESLEY ROADSHIRE BUSINESS PARKWORCESTER WR4 9FDT: +44 (0)1905 751310F: +44 (0)1905 7513112 LINCOLN STREETLANE COVENEW SOUTH WALES 2066AUSTRALIAT: 61 2 9427 8100F: 61 2 9427 820083 VICTORIA STREETLONDONSW1H 0HWT: 44 (0)203 691 58102

NContains OS data © Crown copyright [and database rights] (2015) 0100031673.Contains public sector information licensed under Open government Licence v3.0© Crown copyright [and database rights] 0100031673 Expires

214 UNION STREETABERDEENAB10 1TLT: +44 (0)1224 517405NO. 68 STIRLING BUSINESS CENTREWELLGREENSTIRLINGFK8 2DZT: +44 (0)1786 239900

BUROCLUB157/155 COURS BERRIAT38028 GRENOBLE CEDEX 1FRANCET: + 33 4 76 70 93 41

www.slrconsulting.com

© This drawing and its content are the copyright of SLR Consulting Ltd and may not be reproduced or amended except by prior writ ten permission.SLR Consult ing Ltd accepts no liabi lity for any amendments made by other persons.

© This drawing and its content are the copyright of SLR Consulting Ltd and may not be reproduced or amended except by prior written permission. SLR Consulting Ltd accepts no liability for any amendments made by other persons.

Appendix 04

1:1000 @ A3 May 2021

DRAINAGE LAYOUT

DRAWING_TITLE_3

PLANNING APPLICATION

LEACHATE TREATMENT SYSTEM

PROJECT_TITLE_3

ROBERTSBRIDGE

SITE_NAME_2

[02/11/21]2020

0 10 20 30 40m 60 80 100

Metres 1:1000

LEGEND

BRITISH GYPSUM

Saint-Gobain Construction Products UK Limited Old Tip Mountfield Landfill FRA Filename: 210511_404-01288-00019_Robertsbridge_FRA_v2.1

SLR Ref No:404.00195.00035 May 2021

Appendix 05: MicroDrainage Calculations

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Summary of Results for 2 year Return Period

©1982-2018 Innovyze

Half Drain Time : 476 minutes.

StormEvent

MaxLevel(m)

MaxDepth(m)

MaxInfiltration

(l/s)

MaxControl(l/s)

MaxΣ Outflow(l/s)

MaxVolume(m³)

Status

15 min Summer 45.171 0.171 0.0 0.0 0.0 0.2 O K30 min Summer 45.204 0.204 0.0 0.0 0.0 0.3 O K60 min Summer 45.237 0.237 0.0 0.0 0.0 0.3 O K120 min Summer 45.283 0.283 0.0 0.0 0.0 0.5 O K180 min Summer 45.312 0.312 0.0 0.0 0.0 0.5 O K240 min Summer 45.326 0.326 0.0 0.0 0.0 0.6 O K360 min Summer 45.335 0.335 0.0 0.0 0.0 0.6 O K480 min Summer 45.340 0.340 0.0 0.0 0.0 0.6 O K600 min Summer 45.343 0.343 0.0 0.0 0.0 0.6 O K720 min Summer 45.346 0.346 0.0 0.0 0.0 0.6 O K960 min Summer 45.349 0.349 0.0 0.0 0.0 0.6 O K1440 min Summer 45.351 0.351 0.0 0.0 0.0 0.7 O K2160 min Summer 45.352 0.352 0.0 0.0 0.0 0.7 O K2880 min Summer 45.351 0.351 0.0 0.0 0.0 0.7 O K4320 min Summer 45.349 0.349 0.0 0.0 0.0 0.6 O K5760 min Summer 45.346 0.346 0.0 0.0 0.0 0.6 O K7200 min Summer 45.344 0.344 0.0 0.0 0.0 0.6 O K8640 min Summer 45.342 0.342 0.0 0.0 0.0 0.6 O K10080 min Summer 45.340 0.340 0.0 0.0 0.0 0.6 O K

15 min Winter 45.184 0.184 0.0 0.0 0.0 0.2 O K

StormEvent

Rain(mm/hr)

FloodedVolume(m³)

DischargeVolume(m³)

Time-Peak(mins)

15 min Summer 36.828 0.0 0.0 2730 min Summer 24.155 0.0 0.0 4260 min Summer 15.256 0.0 0.0 72120 min Summer 10.195 0.0 0.0 132180 min Summer 7.982 0.0 0.0 190240 min Summer 6.660 0.0 0.1 246360 min Summer 5.080 0.0 0.2 340480 min Summer 4.146 0.0 0.2 370600 min Summer 3.527 0.0 0.3 420720 min Summer 3.086 0.0 0.3 482960 min Summer 2.495 0.0 0.4 6081440 min Summer 1.848 0.0 0.5 8622160 min Summer 1.387 0.0 0.6 12202880 min Summer 1.143 0.0 0.7 15684320 min Summer 0.884 0.0 0.9 22565760 min Summer 0.747 0.0 1.1 29527200 min Summer 0.663 0.0 1.3 36808640 min Summer 0.606 0.0 1.5 440810080 min Summer 0.565 0.0 1.6 5144

15 min Winter 36.828 0.0 0.0 27

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Summary of Results for 2 year Return Period

©1982-2018 Innovyze

StormEvent

MaxLevel(m)

MaxDepth(m)

MaxInfiltration

(l/s)

MaxControl(l/s)

MaxΣ Outflow(l/s)

MaxVolume(m³)

Status

30 min Winter 45.219 0.219 0.0 0.0 0.0 0.3 O K60 min Winter 45.254 0.254 0.0 0.0 0.0 0.4 O K120 min Winter 45.303 0.303 0.0 0.0 0.0 0.5 O K180 min Winter 45.329 0.329 0.0 0.0 0.0 0.6 O K240 min Winter 45.340 0.340 0.0 0.0 0.0 0.6 O K360 min Winter 45.349 0.349 0.0 0.0 0.0 0.6 O K480 min Winter 45.354 0.354 0.0 0.0 0.0 0.7 O K600 min Winter 45.357 0.357 0.0 0.0 0.0 0.7 O K720 min Winter 45.358 0.358 0.0 0.0 0.0 0.7 O K960 min Winter 45.358 0.358 0.0 0.0 0.0 0.7 O K1440 min Winter 45.356 0.356 0.0 0.0 0.0 0.7 O K2160 min Winter 45.352 0.352 0.0 0.0 0.0 0.7 O K2880 min Winter 45.348 0.348 0.0 0.0 0.0 0.6 O K4320 min Winter 45.343 0.343 0.0 0.0 0.0 0.6 O K5760 min Winter 45.339 0.339 0.0 0.0 0.0 0.6 O K7200 min Winter 45.336 0.336 0.0 0.0 0.0 0.6 O K8640 min Winter 45.334 0.334 0.0 0.0 0.0 0.6 O K10080 min Winter 45.333 0.333 0.0 0.0 0.0 0.6 O K

StormEvent

Rain(mm/hr)

FloodedVolume(m³)

DischargeVolume(m³)

Time-Peak(mins)

30 min Winter 24.155 0.0 0.0 4260 min Winter 15.256 0.0 0.0 72120 min Winter 10.195 0.0 0.0 132180 min Winter 7.982 0.0 0.1 182240 min Winter 6.660 0.0 0.2 236360 min Winter 5.080 0.0 0.3 288480 min Winter 4.146 0.0 0.3 356600 min Winter 3.527 0.0 0.4 424720 min Winter 3.086 0.0 0.4 494960 min Winter 2.495 0.0 0.5 6261440 min Winter 1.848 0.0 0.6 8842160 min Winter 1.387 0.0 0.8 12522880 min Winter 1.143 0.0 0.9 15924320 min Winter 0.884 0.0 1.1 22925760 min Winter 0.747 0.0 1.3 30007200 min Winter 0.663 0.0 1.5 37368640 min Winter 0.606 0.0 1.7 444810080 min Winter 0.565 0.0 1.9 5136

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Rainfall Details

©1982-2018 Innovyze

Rainfall Model FEHReturn Period (years) 2FEH Rainfall Version 2013

Site Location GB 573000 119750 TQ 73000 19750Data Type Catchment

Summer Storms YesWinter Storms YesCv (Summer) 0.750Cv (Winter) 0.840

Shortest Storm (mins) 15Longest Storm (mins) 10080

Climate Change % +0

Time Area Diagram

Total Area (ha) 0.003

TimeFrom:

(mins)To:

Area(ha)

TimeFrom:

(mins)To:

Area(ha)

TimeFrom:

(mins)To:

Area(ha)

0 4 0.001 4 8 0.001 8 12 0.001

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Model Details

©1982-2018 Innovyze

Storage is Online Cover Level (m) 45.500

Swale Structure

Infiltration Coefficient Base (m/hr) 0.00000Infiltration Coefficient Side (m/hr) 0.00000

Safety Factor 2.0Porosity 1.00

Invert Level (m) 45.000Base Width (m) 0.5

Length (m) 1.2Side Slope (1:X) 3.0

Slope (1:X) 100000.0Cap Volume Depth (m) 0.000

Cap Infiltration Depth (m) 0.000

Weir Outflow Control

Discharge Coef 0.544 Width (m) 0.001 Invert Level (m) 45.300

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Summary of Results for 30 year Return Period

©1982-2018 Innovyze

Half Drain Time : 212 minutes.

StormEvent

MaxLevel(m)

MaxDepth(m)

MaxInfiltration

(l/s)

MaxControl(l/s)

MaxΣ Outflow(l/s)

MaxVolume(m³)

Status

15 min Summer 45.278 0.278 0.0 0.0 0.0 0.4 O K30 min Summer 45.328 0.328 0.0 0.0 0.0 0.6 O K60 min Summer 45.369 0.369 0.0 0.0 0.0 0.7 O K120 min Summer 45.387 0.387 0.0 0.0 0.0 0.8 O K180 min Summer 45.394 0.394 0.0 0.0 0.0 0.8 O K240 min Summer 45.400 0.400 0.0 0.1 0.1 0.8 O K360 min Summer 45.406 0.406 0.0 0.1 0.1 0.8 O K480 min Summer 45.407 0.407 0.0 0.1 0.1 0.8 O K600 min Summer 45.406 0.406 0.0 0.1 0.1 0.8 O K720 min Summer 45.405 0.405 0.0 0.1 0.1 0.8 O K960 min Summer 45.402 0.402 0.0 0.1 0.1 0.8 O K1440 min Summer 45.394 0.394 0.0 0.0 0.0 0.8 O K2160 min Summer 45.385 0.385 0.0 0.0 0.0 0.8 O K2880 min Summer 45.378 0.378 0.0 0.0 0.0 0.7 O K4320 min Summer 45.368 0.368 0.0 0.0 0.0 0.7 O K5760 min Summer 45.361 0.361 0.0 0.0 0.0 0.7 O K7200 min Summer 45.356 0.356 0.0 0.0 0.0 0.7 O K8640 min Summer 45.352 0.352 0.0 0.0 0.0 0.7 O K10080 min Summer 45.350 0.350 0.0 0.0 0.0 0.7 O K

15 min Winter 45.298 0.298 0.0 0.0 0.0 0.5 O K

StormEvent

Rain(mm/hr)

FloodedVolume(m³)

DischargeVolume(m³)

Time-Peak(mins)

15 min Summer 79.073 0.0 0.0 2730 min Summer 52.424 0.0 0.1 4160 min Summer 33.356 0.0 0.2 66120 min Summer 19.871 0.0 0.4 118180 min Summer 14.672 0.0 0.5 140240 min Summer 11.830 0.0 0.6 170360 min Summer 8.734 0.0 0.7 236480 min Summer 6.992 0.0 0.8 302600 min Summer 5.872 0.0 0.8 366720 min Summer 5.088 0.0 0.9 430960 min Summer 4.059 0.0 1.0 5541440 min Summer 2.963 0.0 1.1 7962160 min Summer 2.176 0.0 1.3 11522880 min Summer 1.760 0.0 1.4 15044320 min Summer 1.323 0.0 1.6 22125760 min Summer 1.093 0.0 1.9 29447200 min Summer 0.951 0.0 2.1 36728640 min Summer 0.854 0.0 2.3 440810080 min Summer 0.784 0.0 2.5 5144

15 min Winter 79.073 0.0 0.0 27

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Summary of Results for 30 year Return Period

©1982-2018 Innovyze

StormEvent

MaxLevel(m)

MaxDepth(m)

MaxInfiltration

(l/s)

MaxControl(l/s)

MaxΣ Outflow(l/s)

MaxVolume(m³)

Status

30 min Winter 45.349 0.349 0.0 0.0 0.0 0.6 O K60 min Winter 45.390 0.390 0.0 0.0 0.0 0.8 O K120 min Winter 45.408 0.408 0.0 0.1 0.1 0.8 O K180 min Winter 45.415 0.415 0.0 0.1 0.1 0.9 O K240 min Winter 45.419 0.419 0.0 0.1 0.1 0.9 O K360 min Winter 45.420 0.420 0.0 0.1 0.1 0.9 O K480 min Winter 45.417 0.417 0.0 0.1 0.1 0.9 O K600 min Winter 45.413 0.413 0.0 0.1 0.1 0.9 O K720 min Winter 45.409 0.409 0.0 0.1 0.1 0.8 O K960 min Winter 45.401 0.401 0.0 0.1 0.1 0.8 O K1440 min Winter 45.389 0.389 0.0 0.0 0.0 0.8 O K2160 min Winter 45.376 0.376 0.0 0.0 0.0 0.7 O K2880 min Winter 45.368 0.368 0.0 0.0 0.0 0.7 O K4320 min Winter 45.357 0.357 0.0 0.0 0.0 0.7 O K5760 min Winter 45.350 0.350 0.0 0.0 0.0 0.7 O K7200 min Winter 45.346 0.346 0.0 0.0 0.0 0.6 O K8640 min Winter 45.343 0.343 0.0 0.0 0.0 0.6 O K10080 min Winter 45.340 0.340 0.0 0.0 0.0 0.6 O K

StormEvent

Rain(mm/hr)

FloodedVolume(m³)

DischargeVolume(m³)

Time-Peak(mins)

30 min Winter 52.424 0.0 0.2 4060 min Winter 33.356 0.0 0.3 64120 min Winter 19.871 0.0 0.5 112180 min Winter 14.672 0.0 0.6 140240 min Winter 11.830 0.0 0.7 176360 min Winter 8.734 0.0 0.8 248480 min Winter 6.992 0.0 0.9 314600 min Winter 5.872 0.0 1.0 382720 min Winter 5.088 0.0 1.0 446960 min Winter 4.059 0.0 1.1 5721440 min Winter 2.963 0.0 1.3 8142160 min Winter 2.176 0.0 1.5 11722880 min Winter 1.760 0.0 1.6 15284320 min Winter 1.323 0.0 1.9 22485760 min Winter 1.093 0.0 2.1 29447200 min Winter 0.951 0.0 2.4 36808640 min Winter 0.854 0.0 2.6 440810080 min Winter 0.784 0.0 2.8 5152

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Rainfall Details

©1982-2018 Innovyze

Rainfall Model FEHReturn Period (years) 30FEH Rainfall Version 2013

Site Location GB 573000 119750 TQ 73000 19750Data Type Catchment

Summer Storms YesWinter Storms YesCv (Summer) 0.750Cv (Winter) 0.840

Shortest Storm (mins) 15Longest Storm (mins) 10080

Climate Change % +0

Time Area Diagram

Total Area (ha) 0.003

TimeFrom:

(mins)To:

Area(ha)

TimeFrom:

(mins)To:

Area(ha)

TimeFrom:

(mins)To:

Area(ha)

0 4 0.001 4 8 0.001 8 12 0.001

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Model Details

©1982-2018 Innovyze

Storage is Online Cover Level (m) 45.500

Swale Structure

Infiltration Coefficient Base (m/hr) 0.00000Infiltration Coefficient Side (m/hr) 0.00000

Safety Factor 2.0Porosity 1.00

Invert Level (m) 45.000Base Width (m) 0.5

Length (m) 1.2Side Slope (1:X) 3.0

Slope (1:X) 100000.0Cap Volume Depth (m) 0.000

Cap Infiltration Depth (m) 0.000

Weir Outflow Control

Discharge Coef 0.544 Width (m) 0.001 Invert Level (m) 45.300

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Summary of Results for 100 year Return Period

©1982-2018 Innovyze

Half Drain Time : 163 minutes.

StormEvent

MaxLevel(m)

MaxDepth(m)

MaxInfiltration

(l/s)

MaxControl(l/s)

MaxΣ Outflow(l/s)

MaxVolume(m³)

Status

15 min Summer 45.319 0.319 0.0 0.0 0.0 0.6 O K30 min Summer 45.373 0.373 0.0 0.0 0.0 0.7 O K60 min Summer 45.414 0.414 0.0 0.1 0.1 0.9 O K120 min Summer 45.426 0.426 0.0 0.1 0.1 0.9 O K180 min Summer 45.433 0.433 0.0 0.1 0.1 0.9 O K240 min Summer 45.438 0.438 0.0 0.1 0.1 1.0 O K360 min Summer 45.441 0.441 0.0 0.1 0.1 1.0 O K480 min Summer 45.440 0.440 0.0 0.1 0.1 1.0 O K600 min Summer 45.437 0.437 0.0 0.1 0.1 1.0 O K720 min Summer 45.434 0.434 0.0 0.1 0.1 0.9 O K960 min Summer 45.428 0.428 0.0 0.1 0.1 0.9 O K1440 min Summer 45.416 0.416 0.0 0.1 0.1 0.9 O K2160 min Summer 45.402 0.402 0.0 0.1 0.1 0.8 O K2880 min Summer 45.392 0.392 0.0 0.0 0.0 0.8 O K4320 min Summer 45.378 0.378 0.0 0.0 0.0 0.7 O K5760 min Summer 45.369 0.369 0.0 0.0 0.0 0.7 O K7200 min Summer 45.363 0.363 0.0 0.0 0.0 0.7 O K8640 min Summer 45.359 0.359 0.0 0.0 0.0 0.7 O K10080 min Summer 45.355 0.355 0.0 0.0 0.0 0.7 O K

15 min Winter 45.340 0.340 0.0 0.0 0.0 0.6 O K

StormEvent

Rain(mm/hr)

FloodedVolume(m³)

DischargeVolume(m³)

Time-Peak(mins)

15 min Summer 99.200 0.0 0.1 2730 min Summer 66.600 0.0 0.2 3960 min Summer 42.700 0.0 0.5 64120 min Summer 24.950 0.0 0.6 100180 min Summer 18.297 0.0 0.7 130240 min Summer 14.700 0.0 0.8 162360 min Summer 10.800 0.0 1.0 228480 min Summer 8.663 0.0 1.1 294600 min Summer 7.294 0.0 1.1 356720 min Summer 6.333 0.0 1.2 418960 min Summer 5.061 0.0 1.3 5401440 min Summer 3.692 0.0 1.5 7802160 min Summer 2.704 0.0 1.7 11362880 min Summer 2.177 0.0 1.8 15004320 min Summer 1.617 0.0 2.1 22125760 min Summer 1.320 0.0 2.3 29447200 min Summer 1.136 0.0 2.6 36728640 min Summer 1.010 0.0 2.8 440810080 min Summer 0.919 0.0 3.0 5144

15 min Winter 99.200 0.0 0.1 26

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Summary of Results for 100 year Return Period

©1982-2018 Innovyze

StormEvent

MaxLevel(m)

MaxDepth(m)

MaxInfiltration

(l/s)

MaxControl(l/s)

MaxΣ Outflow(l/s)

MaxVolume(m³)

Status

30 min Winter 45.396 0.396 0.0 0.1 0.1 0.8 O K60 min Winter 45.439 0.439 0.0 0.1 0.1 1.0 O K120 min Winter 45.450 0.450 0.0 0.1 0.1 1.0 O K180 min Winter 45.455 0.455 0.0 0.1 0.1 1.0 O K240 min Winter 45.456 0.456 0.0 0.1 0.1 1.0 O K360 min Winter 45.452 0.452 0.0 0.1 0.1 1.0 O K480 min Winter 45.446 0.446 0.0 0.1 0.1 1.0 O K600 min Winter 45.440 0.440 0.0 0.1 0.1 1.0 O K720 min Winter 45.434 0.434 0.0 0.1 0.1 0.9 O K960 min Winter 45.423 0.423 0.0 0.1 0.1 0.9 O K1440 min Winter 45.406 0.406 0.0 0.1 0.1 0.8 O K2160 min Winter 45.389 0.389 0.0 0.0 0.0 0.8 O K2880 min Winter 45.378 0.378 0.0 0.0 0.0 0.7 O K4320 min Winter 45.365 0.365 0.0 0.0 0.0 0.7 O K5760 min Winter 45.357 0.357 0.0 0.0 0.0 0.7 O K7200 min Winter 45.352 0.352 0.0 0.0 0.0 0.7 O K8640 min Winter 45.348 0.348 0.0 0.0 0.0 0.6 O K10080 min Winter 45.345 0.345 0.0 0.0 0.0 0.6 O K

StormEvent

Rain(mm/hr)

FloodedVolume(m³)

DischargeVolume(m³)

Time-Peak(mins)

30 min Winter 66.600 0.0 0.3 3860 min Winter 42.700 0.0 0.6 62120 min Winter 24.950 0.0 0.8 98180 min Winter 18.297 0.0 0.9 136240 min Winter 14.700 0.0 1.0 170360 min Winter 10.800 0.0 1.1 240480 min Winter 8.663 0.0 1.2 306600 min Winter 7.294 0.0 1.3 370720 min Winter 6.333 0.0 1.4 434960 min Winter 5.061 0.0 1.5 5581440 min Winter 3.692 0.0 1.7 7982160 min Winter 2.704 0.0 1.9 11562880 min Winter 2.177 0.0 2.1 15124320 min Winter 1.617 0.0 2.4 22485760 min Winter 1.320 0.0 2.7 29927200 min Winter 1.136 0.0 2.9 36728640 min Winter 1.010 0.0 3.2 440810080 min Winter 0.919 0.0 3.4 5152

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Rainfall Details

©1982-2018 Innovyze

Rainfall Model FEHReturn Period (years) 100FEH Rainfall Version 2013

Site Location GB 573000 119750 TQ 73000 19750Data Type Catchment

Summer Storms YesWinter Storms YesCv (Summer) 0.750Cv (Winter) 0.840

Shortest Storm (mins) 15Longest Storm (mins) 10080

Climate Change % +0

Time Area Diagram

Total Area (ha) 0.003

TimeFrom:

(mins)To:

Area(ha)

TimeFrom:

(mins)To:

Area(ha)

TimeFrom:

(mins)To:

Area(ha)

0 4 0.001 4 8 0.001 8 12 0.001

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Model Details

©1982-2018 Innovyze

Storage is Online Cover Level (m) 45.500

Swale Structure

Infiltration Coefficient Base (m/hr) 0.00000Infiltration Coefficient Side (m/hr) 0.00000

Safety Factor 2.0Porosity 1.00

Invert Level (m) 45.000Base Width (m) 0.5

Length (m) 1.2Side Slope (1:X) 3.0

Slope (1:X) 100000.0Cap Volume Depth (m) 0.000

Cap Infiltration Depth (m) 0.000

Weir Outflow Control

Discharge Coef 0.544 Width (m) 0.001 Invert Level (m) 45.300

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Summary of Results for 100 year Return Period (+20%)

©1982-2018 Innovyze

Half Drain Time : 134 minutes.

StormEvent

MaxLevel(m)

MaxDepth(m)

MaxInfiltration

(l/s)

MaxControl(l/s)

MaxΣ Outflow(l/s)

MaxVolume(m³)

Status

15 min Summer 45.353 0.353 0.0 0.0 0.0 0.7 O K30 min Summer 45.410 0.410 0.0 0.1 0.1 0.9 O K60 min Summer 45.451 0.451 0.0 0.1 0.1 1.0 O K120 min Summer 45.463 0.463 0.0 0.1 0.1 1.0 O K180 min Summer 45.469 0.469 0.0 0.1 0.1 1.1 O K240 min Summer 45.473 0.473 0.0 0.1 0.1 1.1 O K360 min Summer 45.473 0.473 0.0 0.1 0.1 1.1 O K480 min Summer 45.470 0.470 0.0 0.1 0.1 1.1 O K600 min Summer 45.466 0.466 0.0 0.1 0.1 1.1 O K720 min Summer 45.461 0.461 0.0 0.1 0.1 1.0 O K960 min Summer 45.451 0.451 0.0 0.1 0.1 1.0 O K1440 min Summer 45.435 0.435 0.0 0.1 0.1 0.9 O K2160 min Summer 45.417 0.417 0.0 0.1 0.1 0.9 O K2880 min Summer 45.404 0.404 0.0 0.1 0.1 0.8 O K4320 min Summer 45.388 0.388 0.0 0.0 0.0 0.8 O K5760 min Summer 45.378 0.378 0.0 0.0 0.0 0.7 O K7200 min Summer 45.371 0.371 0.0 0.0 0.0 0.7 O K8640 min Summer 45.366 0.366 0.0 0.0 0.0 0.7 O K10080 min Summer 45.363 0.363 0.0 0.0 0.0 0.7 O K

15 min Winter 45.376 0.376 0.0 0.0 0.0 0.7 O K

StormEvent

Rain(mm/hr)

FloodedVolume(m³)

DischargeVolume(m³)

Time-Peak(mins)

15 min Summer 119.040 0.0 0.2 2630 min Summer 79.920 0.0 0.4 3860 min Summer 51.240 0.0 0.6 62120 min Summer 29.940 0.0 0.8 94180 min Summer 21.956 0.0 1.0 126240 min Summer 17.640 0.0 1.1 158360 min Summer 12.960 0.0 1.2 224480 min Summer 10.396 0.0 1.4 288600 min Summer 8.753 0.0 1.5 350720 min Summer 7.600 0.0 1.5 412960 min Summer 6.073 0.0 1.7 5321440 min Summer 4.430 0.0 1.9 7742160 min Summer 3.245 0.0 2.1 11322880 min Summer 2.613 0.0 2.3 15004320 min Summer 1.940 0.0 2.6 22125760 min Summer 1.584 0.0 2.9 29447200 min Summer 1.363 0.0 3.2 36808640 min Summer 1.212 0.0 3.4 440810080 min Summer 1.102 0.0 3.7 5136

15 min Winter 119.040 0.0 0.2 25

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Summary of Results for 100 year Return Period (+20%)

©1982-2018 Innovyze

StormEvent

MaxLevel(m)

MaxDepth(m)

MaxInfiltration

(l/s)

MaxControl(l/s)

MaxΣ Outflow(l/s)

MaxVolume(m³)

Status

30 min Winter 45.435 0.435 0.0 0.1 0.1 0.9 O K60 min Winter 45.478 0.478 0.0 0.1 0.1 1.1 O K120 min Winter 45.488 0.488 0.0 0.1 0.1 1.2 O K180 min Winter 45.491 0.491 0.0 0.1 0.1 1.2 O K240 min Winter 45.489 0.489 0.0 0.1 0.1 1.2 O K360 min Winter 45.482 0.482 0.0 0.1 0.1 1.1 O K480 min Winter 45.473 0.473 0.0 0.1 0.1 1.1 O K600 min Winter 45.465 0.465 0.0 0.1 0.1 1.1 O K720 min Winter 45.456 0.456 0.0 0.1 0.1 1.0 O K960 min Winter 45.442 0.442 0.0 0.1 0.1 1.0 O K1440 min Winter 45.421 0.421 0.0 0.1 0.1 0.9 O K2160 min Winter 45.401 0.401 0.0 0.1 0.1 0.8 O K2880 min Winter 45.389 0.389 0.0 0.0 0.0 0.8 O K4320 min Winter 45.373 0.373 0.0 0.0 0.0 0.7 O K5760 min Winter 45.364 0.364 0.0 0.0 0.0 0.7 O K7200 min Winter 45.358 0.358 0.0 0.0 0.0 0.7 O K8640 min Winter 45.354 0.354 0.0 0.0 0.0 0.7 O K10080 min Winter 45.351 0.351 0.0 0.0 0.0 0.7 O K

StormEvent

Rain(mm/hr)

FloodedVolume(m³)

DischargeVolume(m³)

Time-Peak(mins)

30 min Winter 79.920 0.0 0.5 3760 min Winter 51.240 0.0 0.8 60120 min Winter 29.940 0.0 1.0 96180 min Winter 21.956 0.0 1.2 132240 min Winter 17.640 0.0 1.3 168360 min Winter 12.960 0.0 1.5 236480 min Winter 10.396 0.0 1.6 300600 min Winter 8.753 0.0 1.7 364720 min Winter 7.600 0.0 1.8 426960 min Winter 6.073 0.0 1.9 5501440 min Winter 4.430 0.0 2.2 7902160 min Winter 3.245 0.0 2.4 11522880 min Winter 2.613 0.0 2.7 15044320 min Winter 1.940 0.0 3.0 22485760 min Winter 1.584 0.0 3.3 29527200 min Winter 1.363 0.0 3.6 36808640 min Winter 1.212 0.0 3.9 440010080 min Winter 1.102 0.0 4.2 5136

SLR Consulting Ltd Page 34/5 Lockside ViewEdinburgh ParkEdinburgh, EH12 9DHDate 06/05/2021 14:24 Designed by krainfordFile 210506_Swale+weir_1-100... Checked byInnovyze Source Control 2018.1

Rainfall Details

©1982-2018 Innovyze

Rainfall Model FEHReturn Period (years) 100FEH Rainfall Version 2013

Site Location GB 573000 119750 TQ 73000 19750Data Type Catchment

Summer Storms YesWinter Storms YesCv (Summer) 0.750Cv (Winter) 0.840

Shortest Storm (mins) 15Longest Storm (mins) 10080

Climate Change % +20

Time Area Diagram

Total Area (ha) 0.003

TimeFrom:

(mins)To:

Area(ha)

TimeFrom:

(mins)To:

Area(ha)

TimeFrom:

(mins)To:

Area(ha)

0 4 0.001 4 8 0.001 8 12 0.001

SLR Consulting Ltd Page 44/5 Lockside ViewEdinburgh ParkEdinburgh, EH12 9DHDate 06/05/2021 14:24 Designed by krainfordFile 210506_Swale+weir_1-100... Checked byInnovyze Source Control 2018.1

Model Details

©1982-2018 Innovyze

Storage is Online Cover Level (m) 45.500

Swale Structure

Infiltration Coefficient Base (m/hr) 0.00000Infiltration Coefficient Side (m/hr) 0.00000

Safety Factor 2.0Porosity 1.00

Invert Level (m) 45.000Base Width (m) 0.5

Length (m) 1.2Side Slope (1:X) 3.0

Slope (1:X) 100000.0Cap Volume Depth (m) 0.000

Cap Infiltration Depth (m) 0.000

Weir Outflow Control

Discharge Coef 0.544 Width (m) 0.001 Invert Level (m) 45.300

EUROPEAN OFFICES United Kingdom

AYLESBURY T: +44 (0)1844 337380 BELFAST T: +44 (0)28 9073 2493 BRADFORD-ON-AVON T: +44 (0)1225 309400 BRISTOL T: +44 (0)117 906 4280 CARDIFF T: +44 (0)29 2049 1010 CHELMSFORD T: +44 (0)1245 392170 EDINBURGH T: +44 (0)131 335 6830 EXETER T: + 44 (0)1392 490152 GLASGOW T: +44 (0)141 353 5037 GUILDFORD T: +44 (0)1483 889800

Ireland

DUBLIN T: + 353 (0)1 296 4667

.

LONDON T: +44 (0)203 805 6418 MAIDSTONE T: +44 (0)1622 609242 MANCHESTER T: +44 (0)161 872 7564 NEWCASTLE UPON TYNE T: +44 (0)191 261 1966 NOTTINGHAM T: +44 (0)115 964 7280 SHEFFIELD T: +44 (0)114 245 5153 SHREWSBURY T: +44 (0)1743 23 9250 STIRLING T: +44 (0)1786 239900 WORCESTER T: +44 (0)1905 751310 WORCESTER T: +44 (0)1905 751310

France

GRENOBLE T: +33 (0)6 23 37 14 14