AMBER PLANNING Flood Risk Hydrology · 2017. 2. 14. · Flood Risk Assessment: Stonehill Quarry...

AMBER PLANNING Flood Risk & Hydrology

FLOOD RISK ASSESSMENT April 2016

Stonehill Quarry, Yarwell Northamptonshire

Version 2

This report has been prepared by Amber Planning within the terms of the contract with the client and taking account of the resources devoted to it by agreement with the client. We disclaim any responsibility to the client and others in respect of any matters outside of the scope agreed. This report is confidential to the client and we accept no responsibility of whatsoever nature to third parties to whom this report, or any part thereof, is made known. Any such party relies on the report at their own risk.

Email: [email protected] Website: www.amberplanning.co.uk

Flood Risk Assessment: Stonehill Quarry AMBER PLANNING April 2016 Flood Risk & Hydrology

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TABLE OF CONTENTS

EXECUTIVE SUMMARY III

1.0 INTRODUCTION 1

1.1 Background 1 1.2 Objectives 2 1.3 Confidentiality 2

2.0 SOURCES OF INFORMATION 3

2.1 General 3 2.2 National Planning Policy 3 2.3 Local Planning Policy 4

2.3.1 Core Spatial Strategy (June 2008) 4 2.3.2 Minerals and Waste Local Plan (October 2014) 4 2.3.3 Strategic Flood Risk Assessment (2015) 5

2.4 Environment Agency 5

3.0 BACKGROUND AND DATA REVIEW 6

3.1 Site Setting 6 3.2 Current Layout 6 3.3 Proposed Development 7 3.4 Topographical Survey 8 3.5 Surrounding Area 8 3.6 Hydrogeology 8 3.7 Hydrology 8

3.7.1 River Nene 8 3.7.2 Unnamed Watercourse 9 3.7.3 Flood Data 9 3.7.4 Flood Defences 10 3.7.5 Historic Flooding 10 3.7.6 Reservoir Flooding 10

3.8 Flood Zone Classification 10 3.9 Flood Risk Vulnerability 11 3.10 NPPF Sequential and Exception Tests 11 3.11 Surface Water Flooding 11 3.12 Sewers 12

4.0 FLOOD RISK ASSESSMENT 13

4.1 Screening Opinion 13 4.2 Fluvial Flood Risk 13

4.2.1 Flood Mitigation & Management 13 4.3 Summary of Flood Risk 13

5.0 SURFACE WATER 15

5.1 Introduction 15 5.2 Land Use 15 5.3 SuDS Options for Surface Water Disposal 15

5.3.1 Greenfield Runoff 15 5.4 Attenuation and Controlled Discharge 16

5.4.1 Results 16 5.5 Drainage Layout 17 5.6 Water Quality 17 5.7 Drainage Inspection and Maintenance Schedule 17


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6.0 CONCLUSIONS & RECOMMENDATIONS 19

7.0 CLOSURE 20

TABLES Table 001: Site Setting Table 002: Site Surrounds Table 003: Catchment Descriptor Information Table 004: PPG Table 3 – Flood Risk Vulnerability and Flood Zone Compatibility Table 005: Flood Risk Screening Opinion Table 006: Summary of Existing Runoff Rates Table 007: Surface Water Attenuation Requirements Table 008: Drainage Inspection and Maintenance Schedule FIGURES Figure 001: Environment Agency Fluvial Flood Map Figure 002: Site Location Plan Figure 003a: Existing Features Figure 003b: Restoration Plan Figure 004: EA Reservoir Flood Map Figure 005: EA Surface Water Flood Map DRAWINGS Drawing 001: Surface Water Management Plan APPENDICES Appendix I Workings Appendix II Environment Agency Data


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EXECUTIVE SUMMARY

Site Area 20.5ha

Existing / Historic Use Mineral working (Quarry)

Proposed Use Restored landform

Flood Zone Indicative:

Flood Zone 1 (Low Risk)

Flood Zone 2 (Medium Risk)

Flood Zone 3 (High Risk).

Assessed Fluvial Flood Risk:

Flood Zone 1 (Low)

Flood Zone 2 (Medium)

Flood Zone 3 (High)

NB: Flood Zones 2 & 3 restricted to northern margins and indicated not to impact the property. Overall flood hazard considered to be Low.

Groundwater Flooding Low

Reservoir Failure Low

Overland Flow - Flooding Low

Sewer Flooding Low

Change to Site Surface Finishings (Y/N) Yes

Infiltration Potential? Yes

Potential Receptor for Surface Water Discharges

Controlled discharge to Unnamed Watercourse on northern boundary.

Proposed Surface Water Attenuation 10,670m3

Climate Change Allowance 30% based a 100 year lifetime (restored landform).


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1.0 INTRODUCTION

1.1 Background

1.1.1 Stonehill Quarry is located to the north east of the County close to the boundary with Peterborough. The nearest settlements are Wansford and Yarwell villages some 700m east and 900m south, respectively. The property is accessed off Kings Cliffe Road.

1.1.2 Amber Planning Ltd has been commissioned by Mick George Ltd (the Client) to prepare a Flood Risk Assessment (FRA) in support of a planning application for proposed reprofiling and restoration works. The majority of the quarry is indicated to be located within Flood Zone 1 (Low Risk), with minor sections of the northern boundary located within Flood Zones 2 (Medium Risk) and 3a (High Risk), according to the Environment Agency (EA) Flood Map, Figure 001.

Figure 001: Environment Agency Fluvial Flood Map

1.1.3 This report has been prepared in accordance with the National Planning Policy Framework1 (NPPF) and its accompanying Planning Practice Guidance2 (PPG) document. The requirements of the Environment Agency, Lincolnshire and Northamptonshire Region and Northamptonshire County Council (NCC) have also been considered within this study.

1 Department for Communities and Local Government (2012). National Planning Policy Framework. 2 Department for Communities and Local Government (2014). Planning Practice Guidance.


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1.2 Objectives

1.2.1 The objectives of the Flood Risk Assessment are to:

Review national and local planning policy documents and identify the issues they raise and which need to be addressed in relation to flooding;

Review readily available information on flooding using data provided by the EA and, where available, the Strategic Flood Risk Assessment (SFRA);

Undertake an assessment of the risks from all sources of flooding, including fluvial;

Undertake an outline assessment of the surface water drainage requirements; and

Provide recommendations with regards to flood mitigation and management.

1.2.2 Local development framework documents, as well as strategic policy and technical studies, have been reviewed as part of this study.

1.2.3 The key issues that the report addresses are as those set out at para 103 of the NPPF:

Is the site at risk of flooding?

1.2.4 If yes, and following the sequential test:

Has the most vulnerable development been located in areas of lowest flood risk?

Is development appropriately flood resilient and resistant?

Can any residual risk be safely managed?

Has priority been given to the use of SUDS?

1.3 Confidentiality

1.3.1 Amber Planning has prepared this report solely for the use of the Client and those parties with whom a warranty agreement has been executed, or with whom an assignment has been agreed. Should any third party wish to use or rely upon the contents of the report, written approval must be sought from Amber Planning; a charge may be levied against such approval.


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2.0 SOURCES OF INFORMATION

2.1 General

2.1.1 In preparing this assessment background information has been sought from the following sources:

Communities and Local Government (2012). National Planning Policy Framework;

Communities and Local Government (2014). Planning Practice Guidance.

Northamptonshire County Council website, Planning Policy page3;

Northamptonshire County Council (Oct. 2014). Minerals and Waste Local Plan;

North Northamptonshire County Council (June 2008). Core Spatial Strategy;

East Northamptonshire Council (Aug. 2011). Level 1 Strategic Flood Risk Assessment Review and Update;

East Northamptonshire Council (Nov. 2012). Level 1 Strategic Flood Risk Assessment Review and Update;

Environment Agency website4 and site specific data request;

Topographical survey (Nov. 2015);

British Geological Survey online mapping5; and

Flood Estimation Handbook (FEH) CD ROM V3 catchment and rainfall data.

2.2 National Planning Policy

2.2.1 The National Planning Policy Framework (NPPF) Section 10: Meeting the Challenge of Climate Change, Flooding and Coastal Change, considers the implications of flooding within the planning process.

2.2.2 According to the NPPF:

2.2.3 ‘A site-specific flood risk assessment is required:

1. For proposals of 1ha or greater in Flood Zone 1;

2. All proposals for new development (including minor development and change of use) in Flood Zones 2 and 3, or in an area within Flood Zone 1 which has critical drainage problems (as notified by the Environment Agency); and

3. Where proposed development or change of use to a more vulnerable class may be subject to other sources of flooding.’

2.2.4 Paragraph 103 of the NPPF states the following regarding the consideration of flood risk within the planning application process:

2.2.5 ‘When determining planning applications, local planning authorities should ensure flood risk is not increased elsewhere and only consider development appropriate in areas at risk of flooding, where, informed by a site-specific flood risk assessment following the Sequential Test, and if required the Exception Test, it can be demonstrated that:

Within the site, the most vulnerable development is located in areas of lowest flood risk

3 http://www.northamptonshire.gov.uk/en/councilservices/Environ/planning/policy/Pages/default.aspx 4 http://www.environment-agency.gov.uk 5 http://mapapps.bgs.ac.uk/geologyofbritain/home.html


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unless there are overriding reasons to prefer a different location; and

Development is appropriately flood resilient and resistant, including safe access and escape routes where required, and that any residual risk can be safely managed, including by emergency planning; and it gives priority to the use of sustainable drainage systems.’

2.3 Local Planning Policy

2.3.1 Core Spatial Strategy (June 2008)

2.3.1 The North Northamptonshire Joint Planning Committee formally adopted the Core Spatial Strategy on 12 June 2008. This document forms part of the Development Plan for East Northamptonshire.

2.3.2 The Development Plan forms the basis for decisions about the use and development of land in the area and includes a separate Proposals Map, which identifies the sites and policies on a detailed OS map of the county.

2.3.3 The Core Spatial Strategy and Proposals Maps have been reviewed as part of this assessment. Policies relevant to the consideration of flood risk are as follows:

Policy 13: General Sustainable Development Principles

2.3.4 This policy, item ‘q’ states:

2.3.5 ‘Development should:

2.3.6 ‘Not cause a risk to (and where possible enhance) the quality of the underlying groundwater or surface water, or increase the risk of flooding on the site or elsewhere, and where possible incorporate Sustainable Drainage Systems (SuDS) and lead to a reduction in flood risk.’

2.3.2 Minerals and Waste Local Plan (October 2014)

2.3.7 The Local Plan identifies what minerals and waste related development should go where, why it should go there, and how by doing so, it can make other land use and infrastructure systems function better. It considers the impact and design of new minerals and waste development, and focuses on how this development can best relate to the surrounding land use and link with the wider community. The plan period for the Local Plan is 2011 to 2031. The Local Plan includes a separate Policies Map which identifies the sites and policies on a detailed OS map of the county.

2.3.8 The Local Plan and Policies Maps have been reviewed as part of this assessment. Key Policies relevant to the consideration of flood risk and drainage are as follows:

Policy 28: Restoration and after-use

2.3.9 ‘All minerals and waste related development of a temporary nature must ensure that the site is progressively restored to an acceptable condition and stable landform.

2.3.10 ‘The after-use of a site will be determined in relation to its land use context, the surrounding environmental character and any specific local requirements, but on the basis that it:

Enhances biodiversity, the local environment and amenity, and

Benefits the local community and / or economy.


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2.3.11 ‘The restoration of minerals and waste sites should meet the following requirements (where appropriate):

Sites previously comprising high-grade agricultural land or good-quality forestry use should be restored to the original land use and coupled with a secondary after-use objective,

Precedence should be given to the establishment of Biodiversity Action Plan habitat, strategic biodiversity networks, promotion of geodiversity and enhancement of the historic environment and heritage assets where the specific conditions occur that favour such after-use objectives,

Sites connecting or adjacent to identified habitat areas should be restored in a manner which promotes habitat enhancement in line with Biodiversity Action Plan targets and green infrastructure plans,

Sites located near to areas identified as lacking recreational facilities should be restored in a manner that promotes such opportunities,

Sites located within river corridors should be restored to support water catchment conservation and incorporate flood attenuation measures, and

In specific instances, and where fully in accordance with policies in other local plans in Northamptonshire, sites may be restored in a manner that promotes economic opportunities.

2.3.12 ‘Sites for mineral extraction in river valleys should not be restored to a predominantly open water based form. Restoration of mineral sites elsewhere in the county to a lower level form will be acceptable if it is able to retain the integrity of the local landscape character and minimises overall traffic movements associated with extraction and restoration of the site.’

2.3.3 Strategic Flood Risk Assessment (2015)

2.3.13 A Strategic Flood Risk Assessment (SFRA) Level 1 report was produced for East Northamptonshire Council in August 2011. This was followed by a Level 2 SFRA in November 2012. Both documents have been reviewed as part of this study.

2.4 Environment Agency

2.4.1 A detailed flood data request was submitted to the Environment Agency as part of this assessment. The following information was requested:

Fluvial flood data:

o Flood levels

o Flood flows

o Detailed flood outlines

Historic flood outlines

Flood defence data

Surface water flood maps

Groundwater data


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3.0 BACKGROUND AND DATA REVIEW

3.1 Site Setting

Property Address Stonehill Quarry, Kings Cliffe Road, Near Yarwell, Northamptonshire PE8 6NU

National Grid Reference 506158, 298790

Area 20.5ha

Table 001: Site Setting

3.1.1 Refer to Drawings S22/15/01 Site Location Plan & S22/15/02 Existing Features (including topographical survey) within the main application.

3.2 Current Layout

Figure 002: Site Location Plan

3.2.1 The property comprises an existing quarry. Access is via the north eastern corner, which leads onto a haul road to the north and consequently connects into Kings Cliffe Road further north. Surface finishings at the quarry currently comprise a mixture of soft landscaping, and bare earth. The northern boundary is located in close proximity to a minor unnamed watercourse, which convenes with the River Nene 1km to the east.

3.2.2 The land ownership boundary, represented by the blue line in Figure 002 (above) extends to the watercourse on the northern boundary, where the client benefits from riparian ownership.

3.2.3 The site contains a total of four ponds, the three ponds in the north east intercept surface waters, while a fourth, located in the south west of the site is a standalone water body, and is not related to flood storage.


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3.3 Proposed Development

3.3.1 Planning permission is sought for restoration of the former mineral workings at Stonehill Quarry using imported inert materials and to provide enhancement to its biodiversity value.

3.3.2 This may have a slight impact on the rates and volumes of surface water runoff generated within the plot, mainly through a reduced soil permeability.

3.3.3 The existing ponds are to be retained to provide surface water attenuation storage for the restored landform.

3.3.4 Drawings S22/15/02 (Existing Features) and S22/15/04 (Restoration Plan) are summarised in Figures 003a & 003b; more detailed copies are located within the main application.

Figure 003b: Restoration Plan

Figure 003a: Existing Features


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3.4 Topographical Survey

3.4.1 Topographical survey was obtained in November 2015 is presented within the main application as Drawing S22/15/02. This shows ground elevations between 32.00m AOD and 46.00m AOD, reducing in a north easterly direction, with the lowest levels adjacent to the ponds in the north eastern corner, and greatest elevations in the south west.

3.4.2 The overall topographical relief will remain largely unchanged within the restored site.

3.5 Surrounding Area

3.5.1 The area surrounding the property is described in Table 002, below:

Direction Description

North Access road off Kings Cliffe Road, Unnamed watercourse, agricultural land and depot buildings beyond

East Agricultural land

West Agricultural land

South Old Sulehay Forest

Table 002: Site Surrounds

3.6 Hydrogeology

3.6.1 Regional geological mapping6 shows the bedrock within the catchment to be comprised of the Lower Lincolnshire Limestone and Rutland Formation Argillaceous rocks with subordinate Sandstone and Limestone. The nature of the underlying geology suggests the use of infiltration to be suitable for the disposal of surface water runoff.

3.6.2 Mapping downloaded from the EA website indicates the property to be located external to Groundwater Source Protection Zones.

3.6.3 No BGS borehole log data is available for the area.

3.6.4 Based on the above information the steep nature of the local topography, and lower land present in the eastern catchment downstream, would lead a reduced likelihood of groundwater flooding at the site. Groundwater flooding will therefore not be considered further.

3.7 Hydrology

3.7.1 The property is located in the vicinity of two watercourses:

River Nene 1km east

Unnamed Watercourse on the northern boundary

3.7.2 These watercourses represent the principal fluvial flood risk.

3.7.1 River Nene

3.7.3 The River Nene is located approximately 1km to the east of the application area, with no flooding indicated to reach the quarry.

6 http://mapapps.bgs.ac.uk/geologyofbritain/home.html


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3.7.2 Unnamed Watercourse

3.7.4 The Unnamed Watercourse is located on the northern boundary of the quarry. It has its headwaters located 400m west of the quarry boundary, upstream of Sulehay Road. From here it flows within a well incised, steep, natural, open channel in an easterly direction for c. 2.5km where it discharges into the River Nene.

3.7.5 The steep nature of the surrounding catchment and difference in level between the site and the Nene suggests that this river is unlikely to influence water levels in the adjacent Unnamed Watercourse.

Catchment Details

3.7.6 Catchment descriptor information for the Unnamed Watercourse has been downloaded from the Flood Estimation Handbook CD ROM V37, and is summarised in Table 003, above. This indicates a small, entirely rural, catchment with moderate to highly permeable geology.

3.7.7 Based on consideration of the underlying geology and the hydrological data outlined in Table 003, the catchment response to incident rainfall is likely to be low to moderate, with flows predominated by baseflow (i.e. water entering the watercourse via infiltration rather than overland flow). There is likely to be a lag between incident rainfall and consequent flows within the watercourse, as water percolates through the ground to reach the channel.

Catchment Descriptor Value

AREA 3.6km2

BFIHOST 0.702

SPRHOST 23.30

DPLBAR 2.36

DPSBAR 20.30

FARL 1.00

PROPWET 0.21

SAAR 597

URBEXT (2000) 0.000

Table 003: Catchment Descriptor Information

3.7.3 Flood Data

3.7.8 The EA was consulted as part of this project to obtain flood risk data for the catchment. Detailed Flood Mapping for the Unnamed Watercourse and immediate environs has been supplied.

3.7.9 The flood risk posed to the restored landform by the Unnamed Watercourse is considered in greater detail in Section 4.0.

7 Centre for Ecology and Hydrology (2009). Flood Estimation Handbook CD ROM. Version 3.


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3.7.4 Flood Defences

3.7.10 The site is not indicated to benefit from the presence of flood defences.

3.7.5 Historic Flooding

3.7.11 There are no records of historic flooding in the area, although this may arise from a lack of recorded incidents due to the current and historic land uses (i.e. mineral workings and agricultural activity).

3.7.6 Reservoir Flooding

Figure 004: EA Reservoir Flood Map

3.7.12 The entire property is indicated to be unaffected by reservoir flooding according to National Reservoir Maps provided by the EA.

3.7.13 The flood risk from reservoirs therefore requires no further consideration.

3.8 Flood Zone Classification

3.8.1 Whilst discrete sections adjacent to the northern boundary are shown to be partially affected by Flood Zones 2 (Medium Risk) and 3a (High Risk), development is only proposed within Flood Zone 1 (Low Risk.


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3.9 Flood Risk Vulnerability

Flood Risk Vulnerability Class’n (PPG Table 2)

Essential Infrastructure

Highly Vulnerable

More Vulnerable

Less Vulnerable

Water Compatible

Floo

d Zo

ne (P

PG 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

Table 004: PPG Table 3 – Flood Risk Vulnerability and Flood Zone Compatibility

3.9.1 It is proposed to restore the existing quarry to its pre-developed landform using imported soils. This development is defined as ‘land and buildings used for agriculture and industry’. Table 2 of the PPG classifies this as a ‘Less Vulnerable’ use. According to Table 3 of the PPG this is considered appropriate within Flood Zone 1.

3.10 NPPF Sequential and Exception Tests

3.10.1 The Sequential Test steers development preferentially towards Flood Zone 1 (Low Risk), considering Flood Zone 2 (Medium Risk) and then Flood Zone 3 (High Risk) only if land cannot be identified as available for development in zones at lower risk from flooding.

3.10.2 The Sequential Test is generally carried out at a strategic level by the Local Planning Authority with input from the Environment Agency, as part of the Local Plan process and should be informed by a Strategic Flood Risk Assessment.

3.10.3 Given the nature of the development proposed and its location within Flood Zone 1 the Sequential and Exception Tests need not be applied. Nevertheless element two of the Exception Test is addressed within this FRA.

3.11 Surface Water Flooding

3.11.1 EA mapping indicates Stonehill Quarry to be at very low risk from surface water flooding. A number of discrete points within the site are indicated to be at low risk from surface water flooding, although these correspond with the location of the ponds in the north east and south west.

3.11.2 The plot is elevated above land to the north and east and therefore surface water flooding via overland from these areas is considered unlikely.

3.11.3 Land to the south and west is elevated relative to the quarry. The catchment area of the land to the west is limited, with Sulehay Road likely intercepting the majority of runoff further west, and with only a small field located between this and the site’s western boundary. This field comprises calcareous grassland which grades to the north and east and which likely discharges the majority of runoff via infiltration to ground and overland flow to the Unnamed Watercourse on its northern boundary. A small proportion of flows generated within this field may progress towards its eastern boundary, which it shares with the site, but this would likely


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be intercepted by field drains or blocked topographically by hedges and associated banking. It is therefore considered unlikely that significant overland flows would be generated by land to the west.

Figure 005: EA Surface Water Flood Map

3.11.4 Land to the south, which is elevated relative to the site comprises woodland, which with the combination of infiltration to calcareous soils and interception of incident rainfall by arboriculture would lead to a minimal surface water runoff to the development.

3.11.5 The risks posed to the restored landform by surface water flooding are considered to be low and will therefore not be assessed further.

3.12 Sewers

3.12.1 The plot is located remote to sewerage infrastructure, with the nearest sewer likely to be located on Kings Cliffe Road to the north. This road is separated from the development by an Unnamed Watercourse, which would intercept any overland flow and convey it away to the east. The risks posed to the restored landform from sewer flooding are therefore considered to be low and will not be assessed further.


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4.0 FLOOD RISK ASSESSMENT

4.1 Screening Opinion

4.1.1 In accordance with the NPPF Section 10 it is necessary to consider all forms of flood risk. A flood risk scoping exercise has therefore been completed for the site, the results of which are outlined in Table 005, below.

Nature of Flood Risk Flood Risk to Site?

Fluvial Potentially. Area of development is located entirely within Flood Zone 1, but in close proximity to Flood Zones 2 & 3.

Tidal No. Due to inland location.

Surface Water Drainage (on site) Yes. Proposed change in land form and surface geology of top soil.

Groundwater No. Nature of use, coupled with steep topography indicates a low risk.

Infrastructure Failure (Reservoirs, Canals and Other Artificial Sources)

No. EA website indicates no flood risk from reservoirs, with no further infrastructure located in the vicinity.

Overland Flow (surface water from off-site sources)

No

Sewers No

Table 005: Flood Risk Screening Opinion

4.2 Fluvial Flood Risk

4.2.1 The site is located in close proximity to an Unnamed Watercourse, which represents the principal fluvial flood risk. This watercourse flows within a steep, well incised, channel at this location, with land levels falling from 44m AOD to 32m AOD over a 1km distance adjacent to the development. No significant flow constrictions exist downstream of the site, and the steep nature of the catchment suggests water levels in the River Nene downstream are unlikely to have a significant influence on flooding at this location.

4.2.2 EA detailed Flood Maps, (Appendix II), confirm flooding to be restricted to minor and discrete areas on the northern boundary and not to ingress the zones of proposed reprofiling or affect the main attenuation ponds. These factors along with the proposed nature of use (agricultural) and flood vulnerability classification (less vulnerable) lead to a Low fluvial flood risk.

4.2.3 No loss in fluvial flood storage arises from development proposals, since the land is to be restored back to its pre-developed form.

4.2.1 Flood Mitigation & Management

4.2.4 No flood mitigation or management measures are proposed.

4.3 Summary of Flood Risk

4.3.1 In accordance with the requirements of the NPPF all potential flood risks posed to and by the development have been assessed. It has been demonstrated that the land will be safe from flooding throughout its lifetime and will not detrimentally impact flood risk elsewhere. The sequential approach has also been applied at the site level, with all proposed development located in the areas at least risk from flooding.


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4.3.2 The development is therefore considered appropriate within the context of the Core Spatial Strategy (Policy 13), the Minerals and Waste Local Plan (Policy 28) and the NPPF paragraph 103:

Is the site at risk of flooding?

4.3.3 If yes and following the Sequential Test:

Has the most vulnerable development been located in areas of lowest flood risk?

Is development appropriately flood resilient and resistant?

Can any residual risk be safely managed?


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5.0 SURFACE WATER

5.1 Introduction

5.1.1 The site is approximately 20.5ha in area and comprises an existing quarry with associated bare earth floor and soft landscaping. The quarry currently drains surface water to 3 ponds in the north east, which then discharge via infiltration. These attenuate surface water through direct interception of incident rainfall and receipt of overland flows generated within the site.

5.1.2 As part of development proposals a 20.5ha area is to be restored to its pre-developed form. Surface finishings will comprise imported inert soil with a planted grass sward.

5.1.3 The NPPF and its PPG require that existing runoff rates must be maintained, taking account of climate change. This assessment considers the potential impacts of development proposals on the rate and volume of surface water runoff generated by the restored landform in order to ensure that no increase in flooding arises. The use of Sustainable Drainage Systems (SuDS) has been considered, where possible.

5.2 Land Use

5.2.1 The existing quarry is to be restored using inert fill. This will result in a slight change in the runoff coefficient. It is anticipated that the previously undeveloped grassland would have had a runoff coefficient of c. 0.30, based on consideration of SPRHOST Class and topography, while the restored site will likely have a runoff coefficient of c. 0.54, refer to Appendix I - Workings.

5.2.2 It is therefore seen that the proposals will result in an increase in the runoff coefficient, mainly owing to the reduced permeability of imported fill material. This, coupled with potential increased rainfall and storminess associated with climate change, could lead to detrimental impacts on surface water flood risk at the site and to third party land.

5.3 SuDS Options for Surface Water Disposal

5.3.1 Desk based investigation has been undertaken which indicates the presence of permeable soils beneath the site, and which suggests the potential for the use of infiltration measures.

5.3.2 The property is located adjacent to an Unnamed Watercourse which forms the northern boundary. Historically this would have accepted surface water generated by the pre-developed site and likely still accepts a proportion of overland flow. The option therefore exists for this watercourse to accept attenuated surface water discharges at controlled (greenfield) rates.

5.3.3 The site currently drains via a combination of infiltration to ground and overland flow to the ponds in the north eastern corner, which provide attenuation and settlement of any sediment load from the water. Discharge of surface water is currently via infiltration to ground, with the potential for some overland flow to enter the watercourse on the northern boundary.

5.3.4 It is proposed to release attenuated surface water at controlled rates to the watercourse on the northern boundary. This will likely require a discharge consent from the EA; where new outfalls are proposed Flood Defence Consent will also be required.

5.3.1 Greenfield Runoff

5.3.5 Greenfield runoff rates have been estimated using the WinDes Micro drainage IH124 function, with input data from the Flood Estimation Handbook CD ROM (V3). These are based on a linear interpolation from a 50ha catchment, in accordance with the SUDS manual. Table 006


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summarises the results of this analysis.

Return Period (yrs.) Runoff Rate (l/s/ha) Runoff Rate (l/s)

QBAR 0.34 7.27

30 0.81 17.46

100 1.20 25.89

Table 006: Summary of Existing Runoff Rates

5.4 Attenuation and Controlled Discharge

5.4.1 The WinDes Micro Drainage software suite has been used to estimate the surface water attenuation requirements, to limit surface water discharges to existing rates outlined above. Storm scenarios were run for both winter and summer profiles, for a range of durations between 15-10,080 minutes, with the existing Greenfield runoff rates (outlined above) as input. A 30% uplift in peak rainfall intensity was applied to account for climate change.

5.4.2 The WinDes Micro Drainage package assumes all areas to be impervious, therefore an aerial reduction factor has been applied to the total restoration area (20.5ha) based on the calculated runoff coefficient (0.54) for the restored landform.

5.4.3 Water will be discharged into ponds 2 and 3, which will be linked. Pond 2 will then discharge via a controlled outfall to pond 1, which will in turn release into the stream on the northern boundary, again via a controlled outfall.

5.4.4 The pond dimensions have been measured from the topographical survey and input into the model, with the storage areas defined as the depth available above the standing water level. The bank profiles are taken as trapezoidal with a 1:4 slope. Whilst additional storage is available within pond 1 this has been disregarded as this feature will largely accept flows ahead of discharge to the stream and is the most likely to be full (being at the topographically lowest point). This represents a conservative estimation of the likely maximum water levels in the upper ponds, since it incorporates a degree of redundancy within the system. This also reduces the potential for impacts from fluvial flooding to the storage within Pond 1.

5.4.5 Copies of the WinDes calculations are located at Appendix I – Workings, with the results summarised below.

5.4.1 Results

5.4.5 Based on the above calculations the following surface water storage requirements are proposed:

Return Period Rainfall Event (Yrs.) Runoff Rate (l/s) Estimated Storage Volume (m3) Ponds 2 & 3

30 16.61 8,380

100 24.60 10,670

Table 007: Surface Water Attenuation Requirements


17 Job No. H8100

5.5 Drainage Layout

6.7.1 A maximum surface water attenuation requirement of up to 10,670m3 has been calculated. This will be provided within ponds 2 and 3. From here water will be discharged into pond 1 at controlled rates for eventual release to the stream on the northern boundary, again at controlled rates, refer to Drawing H8100-001: Surface Water Management Plan. Discharge restriction will be achieved by the diameter of the outfall pipe.

5.5.1 In this way it is proposed to attenuate surface water runoff back to existing rates. It is considered that sufficient storage is available within the upper two ponds (2 & 3).

5.5.2 In line with best practice the ponds will provide below ground storage for return period events up to and including 100 years with climate change consideration at 30%. Water will be conveyed to the storage area via a combination of perimeter drainage swales sized to convey flows during a 30 year storm, without surcharge. Flows to the ponds during a 100 year return period storm be achieved via a combination of swales and overland flow. Where overland flowpaths are not possible without flooding of off-site areas the swales have been sized to accommodate runoff for rainfall events of up to 100 years.

5.5.3 The cross sectional profile of the swales are designed to retain Q100 flows within site, with the outer bank (off site side) elevated relative to the inboard (site side) banks, to form preferential flowpaths for floodwater into the centre of the site.

5.5.4 All calculations have used the storage available above the standing water levels in the ponds with an additional freeboard of 300mm above the maximum modelled water levels to allow for fluctuation in groundwater levels, successive rainfall events, variations in flood flows / volumes and for bank settlement. Pond 1 will provide additional attenuation, which will likely reduce water levels in ponds 2 and 3, but this has not been accounted for within the drainage calculations. It is calculated that a total increase in water level of 0.88m and 1.1m will occur within the ponds during Q30 and Q100 rainfall events, respectively.

5.5.5 All surface water storage should incorporate freeboard above groundwater to maximise efficiency.

5.5.6 Where discharge to watercourse is proposed this will be subject to ratification by the EA. A discharge consent and flood defence consent will need to be obtained where new surface water outfalls are proposed.

5.6 Water Quality

5.6.1 Given the nature of the proposed use – restored grassland – it is not considered necessary to provide specific water quality treatment measures. The ponds will encourage the sedimentation of any suspended solids and it is anticipated that no further treatment will be required, since no contaminant source is present upstream.

5.7 Drainage Inspection and Maintenance Schedule

5.7.1 It is proposed that the following programme of inspection and maintenance (Table 008) be undertaken at the site. This will be executed by an appointed management company or drainage contractor. This should be undertaken in accordance with the schedule outlined below and following significant rainfall events and / or storm activity. A photographic record of inspections should be undertaken to pick up long term changes that may not be apparent within a single inspection. Inspections should comply with all relevant Health and Safety legislation.

5.7.2 The maintenance schedule applies for the lifetime of the development.


18 Job No. H8100

Element Frequency Notes

Drainage Channels

Twice annually (March / Sept.) and following large storm events

Visual inspection and removal of any accumulated debris, siltation or blockage.

Mowing of vegetation.

Attenuation Ponds

Annually and following large storm events

Visual inspection for accumulated silt / sediment. Where significant siltation is seen remedial works should be undertaken.

Annual cutting of vegetation surrounding the pond to prevent eutrophication and debris build up.

Debris removal.

Outfalls Twice annually (March / Sept.) and following large storm events

Visual inspection of outfall(s) to check for accumulated debris or blockage, at both upstream and downstream faces. Remove grill (where present).

Check every orifice / pipe / structure for blockage / siltation, pour water into each to verify through flow.

Remove any debris and rod where required. Any silt traps present should be cleansed before and after rodding being undertaken.

Silt Traps

(where present)

Twice annually (March / Sept.) and following large storm events

Visual inspection, removal of accumulated silt. Where rodding is proposed silt traps should be cleansed

before and after.

Table 008: Drainage Inspection and Maintenance Schedule


19 Job No. H8100

6.0 CONCLUSIONS & RECOMMENDATIONS

6.1 This Flood Risk Assessment has been completed in accordance with the guidance set out in the NPPF, Section 10, and it’s accompanying PPG, for a change of use within Flood Zone 1. The requirements of Local Planning Policy, as well as the SFRA, have also been accounted for within the assessment of flood risk.

6.2 The proposed development includes the restoration of an existing quarry to its pre-developed landform, using imported topsoil. This is considered a ‘Less Vulnerable’ use within the context of the NPPF. No change in floodplain storage arises from the application.

6.3 A scoping exercise has been completed which considers the flood risks to the site. Each of the identified risks have been fully assessed as part of this study.

6.4 Review of EA indicative fluvial flood mapping has been undertaken, with the risks from fluvial flooding at the site concluded to be low, now and in the future.

6.5 The surface water attenuation requirements for the development have been assessed with a total surface water storage requirement of 10,670m3 proposed to ensure that existing surface water discharge rates are maintained. Climate change consideration at 30% has been accounted for within these calculations.

6.6 It is proposed to discharge surface water runoff to the watercourse on the northern boundary at controlled rates.

6.7 All drainage networks have been designed to account for industry best practise with regards system capacity.

6.8 It is anticipated that the provision of a formal Surface Water Management System, including on site attenuation storage, will ensure that potential detrimental impacts on flood risk to third party property are suitably mitigated throughout the development lifetime, as required by the National Planning Policy Framework.

6.9 The mitigation solutions noted within this report are subject to agreement with the EA and Northamptonshire County Council as part of the application process.

6.10 A schedule for the inspection and maintenance of the proposed drainage systems has been prepared, which should be executed throughout the lifetime of the development.

6.11 In accordance with the requirements of the NPPF, Core Spatial Strategy (Policy 13), and the Minerals and Waste Local Plan (Policy 28) the impact to / from the development from all potential forms of flooding has been assessed and concluded to be low.

6.12 It is duly presented that the proposed development is appropriate within the context of the National Planning Policy Framework (Section 10) and local planning policy concerning flood risk and drainage.


20 Job No. H8100

7.0 CLOSURE

This report has been prepared by Amber Planning Ltd 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.

Reliance has been placed on factual and anecdotal data obtained from the sources identified. Amber Planning Ltd cannot be held responsible for the scope of work, or any omissions, misrepresentation, errors or inaccuracies with the supplied information. New information, revised practices or changes in legislation may necessitate the re-interpretation of the report, in whole or in part in the event of delay between the writing of the report and submission of the planning application.

This report is for the exclusive use of the client; 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 Amber Planning.

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

DRAWINGS

Access

road

Pond № 4

Broadleaf

woodland

planting

Pond

№ 3

Pond

№ 2

Pond

№ 1

Proposed

wetland

Retained area of

natural regeneration

Scrub habitat

retained

Scrub habitat

retained

Existing quarry

face retained

Retained

"Hollow"

Retained

stream

Pond № 4 and

"Hollow" to the

north retained

Vegetation retained

at northern end of

remnant hedgerow

4

6

4

2

4

0

3

8

3

6

3

6

3

4

4

4

4

3

3

9

3

7

3

5

4

5

4

1

Controlled

outfall to

Watercourse at

Greenfield rates

Controlled outfall

at Greenfield

rates

Watercourse

1:3 side slope

0.5m x 4.5m

1:3 side slope

0.62m x 5.3m

1:3 side slope

0.5m x 4.5m

1:3 side slope

0.5m x 4.5m

1:3 side slope

0.5m x 4.5m

4.50

0.78

0.72

off sitesite

0.48

off site

site

5.30

0.62

0.84

0.92

4.50

0.78

0.72

off site site

0.48

max water level

max water level

max water level

PROJECT

DRAWING TITLE

CLIENT

SCALE PROJECT NO.

DATE DRAWING NO.

DRAWN CHECKED

Stonehill Quarry

Surface Water Management Plan

Mick George Ltd

1:5000 @ A3

March 2016

KR

H8100

H8100-001

KS

www.amberplanning.co.uk

Tel. 07930 877447

KEY

Application Boundary

Proposed Restoration Contours

Drainage Swales - (1:3 side slope 0.5m x 4.5m)

© Crown Copyright 2015. All rights reserved. Licence number 0100031673

Drainage Swales - (1:3 side slope 0.62m x 5.3m)

AutoCAD SHX Text

48.2m

AutoCAD SHX Text

Track

AutoCAD SHX Text

51.8m

AutoCAD SHX Text

ROMAN ROAD

AutoCAD SHX Text

Stone Quarry

AutoCAD SHX Text

RH

AutoCAD SHX Text

EER & Co Const Bdy

AutoCAD SHX Text

Tk H

AutoCAD SHX Text

UA Bdy

AutoCAD SHX Text

Nightingale Farm

AutoCAD SHX Text

Und

AutoCAD SHX Text

Track

AutoCAD SHX Text

56.7m

AutoCAD SHX Text

Tanks

AutoCAD SHX Text

31.7m

AutoCAD SHX Text

Stone Quarry

AutoCAD SHX Text

36.0m

AutoCAD SHX Text

ROMAN ROAD

AutoCAD SHX Text

44.2m

AutoCAD SHX Text

Pond

AutoCAD SHX Text

Depot

AutoCAD SHX Text

Tk H

AutoCAD SHX Text

RH

AutoCAD SHX Text

EER & Co Const Bdy

AutoCAD SHX Text

UA Bdy

AutoCAD SHX Text

Path (um)

AutoCAD SHX Text

Foot Bridge

AutoCAD SHX Text

RH

AutoCAD SHX Text

SS

AutoCAD SHX Text

Und

AutoCAD SHX Text

Hill House

AutoCAD SHX Text

30.5m

AutoCAD SHX Text

36.0m

AutoCAD SHX Text

Wansford Quarter

AutoCAD SHX Text

Track

AutoCAD SHX Text

King's Oaks

AutoCAD SHX Text

WANSFORD ROAD

AutoCAD SHX Text

Track

AutoCAD SHX Text

Old Sulehay Forest

AutoCAD SHX Text

Mortar Pits

AutoCAD SHX Text

37.2m

AutoCAD SHX Text

Track

AutoCAD SHX Text

Track

AutoCAD SHX Text

36.9m

AutoCAD SHX Text

Linley

AutoCAD SHX Text

Cottage

AutoCAD SHX Text

YARWELL ROAD

AutoCAD SHX Text

Sulehay Cottages

AutoCAD SHX Text

44.8m

AutoCAD SHX Text

Sluice

AutoCAD SHX Text

Pond

AutoCAD SHX Text

FB

AutoCAD SHX Text

51.8m

AutoCAD SHX Text

Track

AutoCAD SHX Text

Drain

AutoCAD SHX Text

Issues

AutoCAD SHX Text

Drain

AutoCAD SHX Text

GP

AutoCAD SHX Text

54.6m

AutoCAD SHX Text

Old Sulehay Lodge

AutoCAD SHX Text

Sl

AutoCAD SHX Text

SULEHAY ROAD

AutoCAD SHX Text

44.5m

AutoCAD SHX Text

Pond

AutoCAD SHX Text

51.8m

AutoCAD SHX Text

Cow Wood

AutoCAD SHX Text

CR

AutoCAD SHX Text

Und

AutoCAD SHX Text

FW

AutoCAD SHX Text

Und

AutoCAD SHX Text

FW

AutoCAD SHX Text

EER & Co Const Bdy

AutoCAD SHX Text

UA Bdy

APPENDIX I ‐ WORKINGS

Amber Planning Flood Risk & Hydrology Page 146 Ash Lane Stonehill Quarry

Wells H8100Somerset BA5 2LS Ponds 2&3 GRDate November 2015 Designed by KdS

File 160308-H8100-WIN... Checked byMicro Drainage Source Control W.12.6

Summary of Results for 100 year Return Period (+30%)

©1982-2011 Micro Drainage Ltd

StormEvent

MaxLevel(m)

MaxDepth(m)

MaxControl(l/s)

MaxOverflow(l/s)

MaxΣ Outflow

(l/s)

MaxVolume(m³)

Status

15 min Summer 33.036 0.436 13.1 0.0 13.1 3957.7 O K30 min Summer 33.103 0.503 13.1 0.0 13.1 4603.2 O K60 min Summer 33.180 0.580 13.0 0.0 13.0 5348.6 O K

120 min Summer 33.267 0.667 13.1 0.0 13.1 6202.8 O K180 min Summer 33.322 0.722 13.1 0.0 13.1 6754.6 O K240 min Summer 33.363 0.763 13.1 0.0 13.1 7168.6 O K360 min Summer 33.423 0.823 13.1 0.5 13.2 7779.7 O K480 min Summer 33.466 0.866 13.1 2.3 15.3 8222.6 O K600 min Summer 33.499 0.899 13.3 4.1 17.3 8562.7 O K720 min Summer 33.525 0.925 13.5 5.5 19.0 8832.7 O K960 min Summer 33.549 0.949 13.6 6.3 19.9 9089.2 O K


15 min Winter 33.086 0.486 13.1 0.0 13.1 4434.4 O K30 min Winter 33.160 0.560 13.1 0.0 13.1 5157.8 O K60 min Winter 33.246 0.646 13.1 0.0 13.1 5992.9 O K

120 min Winter 33.341 0.741 13.1 0.0 13.1 6951.4 O K

StormEvent

Rain(mm/hr)

OverflowVolume(m³)

Time-Peak(mins)

15 min Summer 191.428 0.0 3530 min Summer 111.404 0.0 5060 min Summer 64.833 0.0 80

120 min Summer 37.730 0.0 140180 min Summer 27.489 0.0 198240 min Summer 21.958 0.0 258360 min Summer 15.998 5.2 378480 min Summer 12.778 54.5 496600 min Summer 10.735 135.9 616720 min Summer 9.310 229.9 734960 min Summer 7.311 349.3 972

1440 min Summer 5.201 519.9 14502160 min Summer 3.700 710.7 21642880 min Summer 2.905 828.5 28804320 min Summer 2.028 851.3 35885760 min Summer 1.571 789.6 43287200 min Summer 1.289 646.0 51928640 min Summer 1.097 475.5 6056

10080 min Summer 0.956 304.8 696815 min Winter 191.428 0.0 3530 min Winter 111.404 0.0 4960 min Winter 64.833 0.0 80

120 min Winter 37.730 0.0 138






StormEvent

MaxLevel(m)

MaxDepth(m)

MaxControl(l/s)

MaxOverflow(l/s)

MaxΣ Outflow(l/s)

MaxVolume(m³)

Status

180 min Winter 33.402 0.802 13.1 0.1 13.1 7571.1 O K240 min Winter 33.448 0.848 13.1 1.5 14.4 8034.3 O K360 min Winter 33.513 0.913 13.4 4.9 18.2 8708.7 O K480 min Winter 33.559 0.959 13.7 6.6 20.3 9194.0 O K600 min Winter 33.595 0.995 14.0 7.5 21.4 9570.8 O K720 min Winter 33.624 1.024 14.2 8.1 22.3 9875.5 O K960 min Winter 33.651 1.051 14.3 8.7 23.1 10168.6 O K


10080 min Winter 33.546 0.946 13.6 6.2 19.8 9051.9 O K

StormEvent

Rain(mm/hr)

OverflowVolume(m³)

Time-Peak(mins)

180 min Winter 27.489 0.3 196240 min Winter 21.958 24.6 254360 min Winter 15.998 166.8 372480 min Winter 12.778 338.0 488600 min Winter 10.735 492.4 606720 min Winter 9.310 629.3 722960 min Winter 7.311 773.4 956


10080 min Winter 0.956 1087.5 7264




Rainfall Details


Rainfall Model FEH D3 (1km) 0.228 Cv (Winter) 0.840Return Period (years) 100 E (1km) 0.309 Shortest Storm (mins) 15

Site Location F (1km) 2.488 Longest Storm (mins) 10080C (1km) -0.025 Summer Storms Yes Climate Change % +30

D1 (1km) 0.334 Winter Storms YesD2 (1km) 0.275 Cv (Summer) 0.750

Time / Area Diagram

Total Area (ha) 11.070

Time(mins)

Area(ha)

Time(mins)

Area(ha)

Time(mins)

Area(ha)

Time(mins)

Area(ha)

Time(mins)

Area(ha)

0-4 2.214 4-8 2.214 8-12 2.214 12-16 2.214 16-20 2.214




Model Details


Storage is Online Cover Level (m) 34.000

Tank or Pond Structure

Invert Level (m) 32.600

Depth (m) Area (m²) Depth (m) Area (m²)

0.000 8665.0 1.400 11350.0

Hydro-Brake® Outflow Control

Design Head (m) 1.400 Hydro-Brake® Type Md4 Invert Level (m) 32.600Design Flow (l/s) 16.6 Diameter (mm) 134

Depth (m) Flow (l/s) Depth (m) Flow (l/s) Depth (m) Flow (l/s) Depth (m) Flow (l/s)

0.100 3.6 1.200 15.3 3.000 24.2 7.000 37.00.200 10.9 1.400 16.6 3.500 26.2 7.500 38.30.300 13.0 1.600 17.7 4.000 28.0 8.000 39.60.400 11.5 1.800 18.8 4.500 29.7 8.500 40.80.500 10.8 2.000 19.8 5.000 31.3 9.000 42.00.600 11.1 2.200 20.8 5.500 32.8 9.500 43.10.800 12.5 2.400 21.7 6.000 34.31.000 14.0 2.600 22.6 6.500 35.7

Orifice Overflow Control

Diameter (m) 0.095 Discharge Coefficient 0.600 Invert Level (m) 33.390






StormEvent

MaxLevel(m)

MaxDepth(m)

MaxControl(l/s)

MaxOverflow(l/s)

MaxΣ Outflow

(l/s)

MaxVolume(m³)

Status

15 min Summer 32.891 0.291 13.1 0.0 13.1 2602.0 O K30 min Summer 32.943 0.343 13.1 0.0 13.1 3088.9 O K60 min Summer 33.005 0.405 13.1 0.0 13.1 3663.5 O K



15 min Winter 32.925 0.325 13.1 0.0 13.1 2915.3 O K30 min Winter 32.983 0.383 13.1 0.0 13.1 3462.2 O K60 min Winter 33.051 0.451 13.1 0.0 13.1 4107.2 O K

120 min Winter 33.130 0.530 13.1 0.0 13.1 4863.0 O K

StormEvent

Rain(mm/hr)

OverflowVolume(m³)

Time-Peak(mins)

15 min Summer 126.049 0.0 3530 min Summer 74.918 0.0 5060 min Summer 44.528 0.0 80

120 min Summer 26.465 0.0 138180 min Summer 19.521 0.0 198240 min Summer 15.730 0.0 258360 min Summer 11.602 0.0 378480 min Summer 9.349 0.0 496600 min Summer 7.907 0.0 616720 min Summer 6.896 0.0 736960 min Summer 5.463 0.0 974

1440 min Summer 3.934 0.0 14522160 min Summer 2.833 0.0 21682880 min Summer 2.245 0.0 28844320 min Summer 1.586 0.0 41965760 min Summer 1.240 0.0 47927200 min Summer 1.024 0.0 55448640 min Summer 0.876 0.0 6240

10080 min Summer 0.768 0.0 706415 min Winter 126.049 0.0 3530 min Winter 74.918 0.0 4960 min Winter 44.528 0.0 78

120 min Winter 26.465 0.0 138






StormEvent

MaxLevel(m)

MaxDepth(m)

MaxControl(l/s)

MaxOverflow(l/s)

MaxΣ Outflow

(l/s)

MaxVolume(m³)

Status


1440 min Winter 33.446 0.846 13.1 1.5 14.4 8017.1 O K2160 min Winter 33.472 0.872 13.1 2.6 15.7 8286.3 O K2880 min Winter 33.481 0.881 13.1 3.1 16.2 8379.3 O K4320 min Winter 33.464 0.864 13.1 2.2 15.2 8202.0 O K5760 min Winter 33.440 0.840 13.1 1.2 14.0 7956.9 O K7200 min Winter 33.418 0.818 13.1 0.4 13.1 7734.0 O K8640 min Winter 33.395 0.795 13.1 0.0 13.1 7495.2 O K10080 min Winter 33.370 0.770 13.1 0.0 13.1 7239.7 O K

StormEvent

Rain(mm/hr)

OverflowVolume(m³)

Time-Peak(mins)



10080 min Winter 0.768 0.0 7576

Amber Planning Flood Risk & Hydrology 6 Ash Lane Stonehill Quarry



Rainfall Details


Rainfall Model FEH D3 (1km) 0.228 Cv (Winter) 0.840Return Period (years) 30 E (1km) 0.309 Shortest Storm (mins) 15

Site Location F (1km) 2.488 Longest Storm (mins) 10080C (1km) -0.025 Summer Storms Yes Climate Change % +30

D1 (1km) 0.334 Winter Storms YesD2 (1km) 0.275 Cv (Summer) 0.750

Time / Area Diagram

Total Area (ha) 11.070

Time(mins)

Area(ha)

Time(mins)

Area(ha)

Time(mins)

Area(ha)

Time(mins)

Area(ha)

Time(mins)

Area(ha)

0-4 2.214 4-8 2.214 8-12 2.214 12-16 2.214 16-20 2.214




Model Details


Storage is Online Cover Level (m) 34.000

Tank or Pond Structure

Invert Level (m) 32.600

Depth (m) Area (m²) Depth (m) Area (m²)

0.000 8665.0 1.400 11350.0

Hydro-Brake® Outflow Control

Design Head (m) 1.400 Hydro-Brake® Type Md4 Invert Level (m) 32.600Design Flow (l/s) 16.6 Diameter (mm) 134

Depth (m) Flow (l/s) Depth (m) Flow (l/s) Depth (m) Flow (l/s) Depth (m) Flow (l/s)

0.100 3.6 1.200 15.3 3.000 24.2 7.000 37.00.200 10.9 1.400 16.6 3.500 26.2 7.500 38.30.300 13.0 1.600 17.7 4.000 28.0 8.000 39.60.400 11.5 1.800 18.8 4.500 29.7 8.500 40.80.500 10.8 2.000 19.8 5.000 31.3 9.000 42.00.600 11.1 2.200 20.8 5.500 32.8 9.500 43.10.800 12.5 2.400 21.7 6.000 34.31.000 14.0 2.600 22.6 6.500 35.7

Orifice Overflow Control

Diameter (m) 0.095 Discharge Coefficient 0.600 Invert Level (m) 33.390

APPENDIX II – ENVIRONMENT AGENCY DATA

Nene House Pytchley Lodge Road Kettering NN15 6JQ. Customer services line: 08708 506 506 Email: [email protected] www.gov.uk/environment-agency

Kirsten de Savary [email protected]

Our ref: CCN-2015-40306 Date: 3 December 2015

Dear Kirsten Basic Flood Risk Assessment Data Request for Stonehill Quarry, Wansford, PE8 6PL NGR: TL 06327 98875 Thank you for your request of 6 November 2015 to use Environment Agency data, Product 3, in the development of the Flood Risk Assessment (FRA) for the above site. The information is attached. If you have requested this information to help inform a development proposal, then you should note the detail in the attached advisory text on the use of Environment Agency Information for Flood Risk Assessments. Flood Map The attached map includes the current Flood Map for your area. The Flood Map indicates the area at risk of flooding, assuming no flood defences exist, for a flood event with a 0.5% chance of occurring in any year for flooding from the sea, or a 1% chance of occurring for fluvial (river) flooding. It also shows the extent of the Extreme Flood Outline which represents the extent of a flood event with a 0.1% chance of occurring in any year, or the highest recorded historic extent if greater. The Flood Map only indicates the extent and likelihood of flooding from rivers or the sea. It should also be remembered that flooding may occur from other sources such as surface water sewers, road drainage, etc. JFLOW Depth Maps Our first release of the flood zones in 2004 were produced using national generalised flood modelling of all catchments greater than 3km2. Since that time we have worked hard to continually improve the flood zones using detailed surveys and models. These detailed updates have been prioritised on flooding associated with Main Rivers. The flood zones in the area of your site have not been updated based on detailed modelling and therefore we are unable to provide modelled flood levels or flows. From the national generalised modelling we are able to provide the flood depths, averaged over a 100m grid, that have been used in the production of the flood zones. These are shown on the enclosed plans. Please read the attached guidance note for further information relating to this data.

http://www.gov.uk/environment-agency

mailto:[email protected]


Fluvial Defence Information There are no formal flood defences protecting this site. The watercourse is a non main river please contact the Local Authority (Northamptonshire County Council) as may hold information regarding the watercourse. History of Flooding With regards to the history of flooding I can advise that we do not have any records of flooding in this area. It is possible that other flooding may have occurred that we do not have records for, and other organisations, such as the Local Authority or Internal Drainage Boards, may have records. Further details about the Environment Agency information supplied can be found on the GOV.UK website: https://www.gov.uk/browse/environment-countryside/flooding-extreme-weather If you have requested this information to help inform a development proposal, then you should note the information on GOV.UK on the use of Environment Agency Information for Flood Risk Assessments https://www.gov.uk/planning-applications-assessing-flood-risk https://www.gov.uk/government/publications/pre-planning-application-enquiry-form-preliminary-opinion Supporting Information This information is provided subject to the enclosed notice which you should read. I hope that we have correctly interpreted your request. Please see the attached Standard Notice or licence for details of permitted use. We respond to requests for recorded information that we hold under the Freedom of Information Act 2000 (FOIA) and the associated Environmental Information Regulations 2004 (EIR). If you are not satisfied with our response to your request for information you can contact us within 2 calendar months to ask for our decision to be reviewed. If you have any queries or would like to discuss the content of this letter further please contact Rosemary Thirumalareddy at the Environment Agency.


https://www.gov.uk/browse/environment-countryside/flooding-extreme-weather

https://www.gov.uk/planning-applications-assessing-flood-risk

https://www.gov.uk/government/publications/pre-planning-application-enquiry-form-preliminary-opinion

https://www.gov.uk/government/publications/pre-planning-application-enquiry-form-preliminary-opinion


Yours sincerely

Rosemary Thirumalareddy FOR Alastair Windler Partnership and Strategic Overview Team Leader Lincolnshire & Northamptonshire Area Direct dial 01536 385120 e-mail [email protected]

Awarded to Lincolnshire & Northamptonshire Area Enc. FRA Advisory Text Basic FRA Map JFLOW Depth Maps JFLOW Guidance Note Standard Notice


mailto:[email protected]

Contact Us: National Customer Contact Centre, PO Box 544, Rotherham, S60 1BY. Tel: 03708 506 506 (Mon-Fri 8-6). Email: [email protected]© Environment Agency copyright and / or database rights 2015. All rights reserved. © Crown Copyright and database right. All rights reserved. Environment Agency, 100026380, 2015.

Basic FRA MapMap centred on TL 06327 98875 created December 2015 [Ref: CCN-2015-40306]

-1:10,000Scale

Created by the Partnerships & Strategic Overview Team, Kettering

Dark blue shows the area that could be affected by flooding,either from rivers or the sea, if there were no flood defences. This area could be flooded: - from the sea by a flood that has a 0.5% (1 in 200) or greater chance of happening each year.- or from a river by a flood that has a 1% (1 in 100) or greaterchance of happening each year. Light blue shows the extent of the Extreme Flood Outline,which represents the extent of a flood event with a 0.1% chance of occurring in any year, or the highest recorded historic extent if greater.These two colours show the extent of the natural floodplain if there were no flood defences or certain other manmade structures and channel improvements. Sites outside the twoextents, but behind raised defences, may be affected byflooding if the defences are overtopped or fail.

Main RiverArea at Risk of Flooding from Rivers or The SeaExtreme Flood Outline

LegendJFLOW Max Depth (m)1%

0 - 0.0250.025 - 0.50.5 - 11 - 22 - 8

1:5,000

JFLOW Depth Map - 1% (1 in 100) Scenario Map centred on TL 06327 98875 - created December 2015 [Ref: CCN-2015-40306]

Scale

Please refer to the enclosed guidance note for more information

Created by the Partnerships and Strategic Overview Team, Kettering


-

LegendJFLOW Max Depth (m)1% Plus Climate Change

0 - 0.0250.025 - 0.50.5 - 11 - 22 - 8

1:5,000

JFLOW Depth Map - 1% (1 in 100) Scenario including Climate ChangeMap centred on TL 06327 98875 - created December 2015 [Ref: CCN-2015-40306]

Scale




-

LegendJFLOW Max Depth (m)0.1%

0 - 0.0250.025 - 0.50.5 - 11 - 22 - 8

1:5,000

JFLOW Depth Map - 0.1% (1 in 1000) Scenario Map centred on TL 06327 98875 - created December 2015 [Ref: CCN-2015-40306]

Scale




-

LegendJFLOW Max Depth (m)0.1% Plus Climate Change

0 - 0.0250.025 - 0.50.5 - 11 - 22 - 8

1:5,000

JFLOW Depth Map - 0.1% (1 in 1000) Scenario including Climate ChangeMap centred on TL 06327 98875 - created December 2015 [Ref: CCN-2015-40306]

Scale




-

Waterside House, Waterside North, Lincoln, LN2 5HA. Customer services line: 08708 506 506 Email: [email protected] www.environment-agency.gov.uk

Weekday Daytime calls cost 8p plus up to 6ppm from BT Weekend Unlimited. Mobile and other providers’ charges may vary

Explanatory Note on the use of J-FLOW Generalised Depth Data Our first release of the flood zones in 2004 were produced using J-Flow as part of a national generalised flood modelling programme, covering all catchments greater than 3km2. Since that time we have worked hard to continually improve the flood zones using detailed surveys and models. These detailed updates have been prioritised on flooding associated with Main Rivers. If an area has not been updated based on detailed modelling we are unable to provide modelled flood levels or flows. However from the national generalised modelling we are able to provide the flood depths, averaged over a 100m grid, that have been used in the production of the flood zones. Although water levels or depths were not part of the specified outputs of our national generalised modelling a 'by-product' of the process was the production of water depth information. However since J-Flow was developed and tested for the production on flood extents only we currently have no information on the accuracy of the water depth data. Where this depth data is used for site specific Flood Risk Assessments it must only be done so as a guide to flood depths and not for any detailed design. In using this data the user must verify that the data is fit for purpose and appropriate bearing in mind the conclusions the user wishes to draw from them and this use must be agreed by the local Environment Agency staff. If any agreement is given by the Environment Agency in pursuance of the above, the User accepts and agrees that such agreement by the Environment Agency that the National Generalised Modelling outputs are suitable for a particular use and does not imply agreement that the proposals are appropriate or that the Environment Agency has no further comment on flood risk, rather that following verification that the User has proven that the outputs are suitable to help assess the flood risk in the particular circumstances. Any assessment of Flood Risk undertaken must be appropriate for the decisions that need to be based upon it, consider the risks and also take into account any limitations of the data used. Please read the enclosed Notice and be aware that the Environment Agency does not guarantee that this data is suitable for your purposes.

Use of Environment Agency Information for Flood Risk / Flood Consequence Assessments Important If you have requested this information to help inform a development proposal, then we recommend that you undertake a formal pre-application enquiry using the form available from our website:- http://www.environment-agency.gov.uk/research/planning/33580.aspx Depending on the enquiry, we may also provide advice on other issues related to our responsibilities including flooding, waste, land contamination, water quality, biodiversity, navigation, pollution, water resources, foul drainage or Environmental Impact Assessment. In England, you should refer to the Environment Agency’s Flood Risk Standing Advice, the technical guidance to the National Planning Policy Framework and the existing PPS25 Practice Guide for information about what flood risk assessment is needed for new development in the different Flood Zones. These documents can be accessed via:

http://www.environment-agency.gov.uk/research/planning/82587.aspx http://www.communities.gov.uk/publications/planningandbuilding/nppftechnicalguidance http://www.communities.gov.uk/publications/planningandbuilding/pps25guideupdate You should also consult the Strategic Flood Risk Assessment produced by your local planning authority. In Wales, you should refer to TAN15 for information about what flood consequence assessment is needed for new development in the different flood zones http://new.wales.gov.uk/splash;jsessionid=8ylGTfGZthmB0t2vhp6hS1GcB1LXvZzB3Ylczf20Xn7LK3zK0nMk!981825250?orig=/topics/planning/policy/tans/tan15/ You should also consult the Strategic Flood Consequence Assessment if one has been produced by your local planning authority.

http://www.environment-agency.gov.uk/research/planning/33580.aspx

http://www.environment-agency.gov.uk/research/planning/82587.aspx

http://www.communities.gov.uk/publications/planningandbuilding/nppftechnicalguidance

http://www.communities.gov.uk/publications/planningandbuilding/nppftechnicalguidance

http://www.communities.gov.uk/publications/planningandbuilding/pps25guideupdate

http://www.communities.gov.uk/publications/planningandbuilding/pps25guideupdate

http://new.wales.gov.uk/splash;jsessionid=8ylGTfGZthmB0t2vhp6hS1GcB1LXvZzB3Ylczf20Xn7LK3zK0nMk!981825250?orig=/topics/planning/policy/tans/tan15/

http://new.wales.gov.uk/splash;jsessionid=8ylGTfGZthmB0t2vhp6hS1GcB1LXvZzB3Ylczf20Xn7LK3zK0nMk!981825250?orig=/topics/planning/policy/tans/tan15/

In both England and Wales you should note that:

1. Information supplied by the Environment Agency may be used to assist in producing a Flood Risk / Consequence Assessment (FRA / FCA) where one is required, but does not constitute such an assessment on its own.

2. This information covers flood risk from main rivers and the sea, and you

will need to consider other potential sources of flooding, such as groundwater or overland runoff. The information produced by the local planning authority referred to above may assist here.

3. Where a planning application requires a FRA / FCA and this is not

submitted or deficient, the Environment Agency may well raise an objection.

4. For more significant proposals in higher flood risk areas, we would be

pleased to discuss details with you ahead of making any planning application, and you should also discuss the matter with your local planning authority.

89_07_SD02, Version 6

Contact: [email protected] 03708 506506

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AMBER PLANNING Flood Risk Hydrology · 2017. 2. 14. · Flood Risk Assessment: Stonehill Quarry...

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