Land at Patford Bridge - Supporting Statement

Appendix 4 - Flood Risk Assessment, prepared by

Hafren Water (March 2013)

cemex Supportlng Statement A081776 24/05/2013

Hafren ~Wate r

Flood Risk Assessment

Proposed construction of a Pipeline Inspection Gauge compound

Patford Bridge, Great Brington, Northamptonshire

Final March 2013

Report prepared for:

CEMEX UK Cement Limited CEMEX House

Coldharbour Lane Thorpe EGHAM Surrey

TW208TD

Hafren % Water

BARKERS CHAMBERS. BARKER STREET. SHREWSBURY. UNITED KINGDOM. SY1 1SB

TEL : 01743 355770 FAX : 01743 357771 EMAIL : info@hafrenwaler.com

Flood Risk Assessment

Proposed construction of a Pipeline Inspection Gauge compound

Patford Bridge, Great Brington, Northamptonshire

Final March 2013

Prepared by:

I~~--=-=------S Gillson BSe, MSe, FGS

Checked by:

G Mayle BSe, MSe

CEMEX Flood Risk Assessment, Pafford Bridge Final

CONTENTS

1

1.1 Background 1 1.2 Scope of the assessment 1 1.3 Site location 1 1.4 Site description and elevations 1 1.5 Hydrology 1 1.6 Climate change 1 1.7 Ground conditions 1 1.8 Proposed development 2

2 FLOOD RISK TO THE SITE 3

2.1 Background 3 2.2 Fluvial flooding 3 2.2.1 Historical flood ing 3 2.2.2 Environment Agency Flood Map 3 2.2.3 Flood defences and structures 3 2.2.4 Modelled flood levels 3 2.2.5 Mitigation measures 3 2.2.6 Overall fluvial flood risk 4 2.3 Surface water run-off 4 2.4 Groundwater flooding 4 2.5 Flooding from water mains or sewers 4

3 FLOOD RISK TO THE SURROUNDING AREA 5

3.1 Background 5 3.2 Surface water run-off 5 3.2.1 Concrete areas 5 3.2.2 Lagoon 5 3.3 Floodplain storage and flow 5

4 SUMMARY AND CONCLUSIONS 7

INTRODUCTION 1

Figure 1 Figure 2

Appendix 1 Appendix 2 Appendix 3 Appendix 4

FIGURES

Site location Environment Agency Indicative Flood Zones

APPENDICES

Development plans Flood Risk Assessment Details J-FLOW flood depth outputs Surface water run-off calculations

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1 INTRODUCTION

1.1 Background

CEMEX UK Cement Limited is proposing to construct a compound to service a chalk slurry pipeline which connects Kensworth Chalk Quarry to Rugby Cement Plant at Patford Bridge, near Great Brington, Northamptonshire. The proposed compound consists of a Pipeline Inspection Gauge (PIG) launch station, vehicle turning area and lagoon.

The site is located within Flood Zone 3 on the Environment Agency Indicative Flood Map, which is defined as having an annual probability of fluvial flooding greater than 1 in 100 (>1%). The proposed development is classified as 'less vulnerable' in the National Planning Policy Framework (NPPF). 'Less vulnerable' development is permitted within Flood Zone 3 subject to the submission of a suitable Flood Risk Assessment (FRA) .

1.2 Scope of the assessment

The flood risk to and from the completed site has been assessed and quantified and potential mitigation measures outlined.

1.3 Site location

The Application Area is located some 2.5 km northwest of Great Brington, Northamptonshire. The site is located around National Grid Reference (NGR) SP 647 664 and is shown on Figure 1. Access is via Brington Road immediately north of the Application Area.

1.4 Site description and elevations

The Application Area is situated within a cropped field. It is bounded to the west by a track and footpath , to the north by Brington Road, to the south by railway embankments and to the east by fields .

The Application Area is broadly flat and situated some 105 metres Above Ordnance Datum (mAOD). There is a slight fall in elevation from westwards towards an adjacent river.

1.5 Hydrology

The Whilton Branch of the River Nene rises at Buckby Folly some 2.3 km north of the Application Area and flows to the west of the site in a southerly direction. The confluence of the Whilton Branch and an unnamed tributary is located immediately north of Patford Bridge. This watercourse rises some 1.5 km to the north-northwest of the Application Area at Long Buckby.

1.6 Climatechange

Within the UK projections of future climate change indicate that there will be more frequent, short duration, high intensity rainfall events and more frequent periods of long duration rainfall. The NPPF recommends that the effects of climate change are incorporated into Flood Risk Assessments and suggests precautionary sensitivity ranges for peak rainfall intensities and peak river flows.

1.7 Groundconditions

The solid geology in the region of the Application Area comprises Jurassic age Upper Lias mudstones and Middle Lias ironstones, limestones and mudstones. Superficial deposits of alluvium are confined to the river channel west of the Application Area.

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CEMEX Flood Risk Assessment, Pafford Bridge Final

Soils within the vicinity of the site are identified as slowly permeable, seasonally wet, slightly acid but base-rich loamy and clayey (National Soils Resources Institute).

1.8 Proposed development

The proposed compound consists of a PIG launch station, vehicle turning area and lagoon. The site will be unmanned, therefore welfare facilities will not be required. Areas of landscape planting and installation of security fencing are also planned. The Application Area covers some 0.35 Hectares (Ha).

The site layout is presented in Appendix 1.

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CEMEX Flood Risk Assessment, Pafford Bridge Final

2 FLOOD RISK TO THE SITE

2.1 Background

The risk of flooding at the site has been assessed by examining the likelihood of flooding, the hazard caused if it were to flood and its vulnerability. The assessment has been undertaken for a variety of mechanisms using both quantitative and qualitative methods. Details of how these assessments were made are included within Appendix 2.

The Environment Agency has indicated that new development in the Upper Nene catchment should be assessed against the 1 in 200 (0.5%) annual probability event including an allowance for climate change. This is above the standard required within the NPPF and designed to afford greater protection from flooding to Northampton. Therefore the 1 in 200 (0.5%) annual probability rainfall flood event has been considered at this site.

2.2 Fluvial flooding

2.2.1 Historical flooding

The Environment Agency does not hold any data on historic flooding at this location.

2.2.2 Environment Agency Flood Map

The proposed development is classified as 'less vulnerable' in the NPPF and is situated within Flood Zone 3. This zone comprises land assessed as having a 1 in 100 or greater annual probability of river flooding (>1%) and 'less vulnerable' uses of land are appropriate in this zone.

2.2.3 Flood defences and structures

There are no flood defences in operation at the site.

2.2.4 Modelled flood levels

The Environment Agency does not hold any data on detailed modelled flood levels at this location, however flood depth information is available from generalised models (J-FLOW). Flood depth information is provided in Appendix 3, however this is based on generalised modelling data and is only provided as a guide to flood depths.

Water depths during a flood event with an annual probability of 1 in 100 (1 %), plus additional climate change, range from 0.25-0.5 m in small parts of the west of the Application Area to <0.25 m further east.

There are no modelled depth outputs for the 1 in 200 (0.5%) plus climate change annual probability event. Therefore the estimation of the flood depths has been based on the 1 in 1000 (0.1% annual probability flood event, excluding climate change). Water depths during this event range from between 0.25-0.5 m along the western fringes of the Application Area, decreasing to <0.25 m in the east. This is likely to provide a conservative estimation of flood depths during the 1 in 200 (0.5%) plus climate change annual probability event.

2.2.5 Mitigation measures

The site will be unmanned therefore welfare facilities will not be required, effectively limiting the number of structures vulnerable to flooding. However, it is recommended that any personnel accessing the site are made aware of flood risks when on-site and that suitable health and safety procedures are in place with clear egress routes indicated. The site access would be located in the northeast of the compound which is the area of the least flood risk. This would facilitate safe egress if any personnel were on-site during a flood event. Brington Road continues east away from the floodplain to Great Brington.

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CEMEX Flood Risk Assessment, Patford Bridge Final

2.2.6 Overall fluvial flood risk

Due to the site's proposed use the overall flood risk is considered to be 'moderate'. The mitigation measures outlined above are considered to be appropriate and will allow the flood risks to be managed.

2.3 Surface water run-off

The Application Area is situated on an area of generally flat agricultural land, therefore the majority of rainfall leaves the site via infiltration.

Due to the subdued topography there is very limited potential for surface water run-off to adversely affect the site. Therefore the overall risk from flooding from this source is considered to be 'very low'.

2.4 Groundwater flooding

Due to the proximity of the Application Area to the Whilton Branch of the River Nene, groundwater and fluvial flooding are likely to occur simultaneously. Therefore the overall risk of groundwater flooding in isolation is considered to be 'low'.

2.5 Flooding from water mains or sewers

Owing to the rural location of the proposed development, flooding from water mains or sewers is not considered to be a risk to the site. Therefore the overall risk of flooding from this source is 'negligible'.

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CEMEX Flood Risk Assessment, Patford Bridge Final

3 FLOOD RISK TO THE SURROUNDING AREA

3.1 Background

The proposed development has the potential to increase flooding to the surrounding area through changes to the surface water run-off regime and to floodplain storage. The proposals have been assessed against these criteria to ensure that there is no detrimental impact on flood risk in the surrounding area.

The development is classified as 'less vulnerable' in the NPPF.

3.2 Surface water run-off

3.2.1 Concrete areas

The only impermeable surfaces proposed will be a concrete arron at the site entrance and an area around the pigging station which amounts to some 350 m . The concrete apron at the site entrance is proposed to drain to the adjacent grass where it will be allowed to infiltrate to ground. Surface water within the area around the pigging station will flow by gravity to a pit where it will be pumped into the lagoon from where it will be periodically injected into the pipeline . The pit will have a capacity of some 30 m3 and the lagoon will have a capacity of some 2,000 m3

. The lagoon is proposed to be kept empty the majority of the time and will therefore have capacity to hold storm rainfall events.

Run-off rates from the development have been calculated to determine the volume of storage required to attenuate flows, including the increase attributed to climate change. This has been undertaken to ensure there is no increase in flood risk downstream of the site from increased future run-off rates. Further details on these calculations can be found in Appendix 4.

The peak run-off rates (Op) for the post-completion site have been estimated for a range of storm durations using the Rational Method, which is of the form:

o,=2.78 CiA

Where: C = run-off co-efficient (dimensionless) i = rainfall intensity (mm/hr) A = catchment area (Ha)

The co-efficient of run-off, C, varies for different surfaces. The value of C used for the concrete areas has been taken as 0.9 as the majority of rainfall will run-off. The volume of storage required for the 1 in 200-year event for the 6-hour storm (which is the recommended duration for small catchments - HR Wallingford 2004, 'Drainage of development sites') is some 34 m3

.

It is recommended that a volume of 34 m3 is available at all times to accommodate the 1 in 200­year plus climate change rainfall event.

3.2.2 Lagoon

The lagoon covers a surface area of some 784 m2• Rainfall from this area will not have the

potential to reach the adjacent river and therefore this will further reduce the impact of the development on flood risk to the surrounding area.

3.3 Floodplain storage and flow

The proposed development is situated partially in the floodplain of the Whilton Branch of the River Nene. However, the site will contain minimal structures and will therefore allow flood water

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CEMEX Flood Risk Assessment. Patford Bridge Final

to pass through it with no effect on the flood levels in the surrounding area. Similarly, as there are only minor buildings proposed there is considered to be no potential for detrimental impact on floodplain storage.

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CEMEX Flood Risk Assessment, Pafford Bridge Final

4 SUMMARYAND CONCLUSIONS

4.1 The proposed development is classified as 'less vulnerable' in the NPPF and is situated within Flood Zone 3.

4.2 Fluvial flooding from the Whilton Branch is considered to be the main source of flood risk in the vicinity of the Application Area.

4.3 The site will be unmanned but personnel on-site should be made aware of flood risk and egress routes maintained and kept clear.

4.4 Due to the site's proposed use the overall flood risk is considered to be 'moderate'. The mitigation measures outlined above are considered to be sufficient to allow the flood risks to be managed.

4.5 There is not considered to be a significant flood risk to the site of flooding from surface water, groundwater or water mains and sewers sources.

4.6 The volume of storage required for the 1 in 200-year event for the 6-hour storm is some 34 rrr'.

4.7 Due to the relatively small footprint of the development there is not considered to be an increased flood risk on land downstream of the Application Area.

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CEMEX Flood Risk Assessment, Pafford Bridge Final

FIGURES

March 2013

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lienl: CEMEX UK Cement Limited CEMEX House Coldharbour Lane. Thorpe EGHAM Surrey TW20 8TD

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Indicative Flood Risk Map

Project: Patford Bridae Date: Aug-2012 Figure: 2 Scale: as shown

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CEMEX Flood Risk Assessment, Pafford Bddge Final

APPENDIX 1

Development plans

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CEMEX Flood Risk Assessment, Pafford Bridge Final

APPENDIX 2

Flood Risk Assessment details

March 2013

Hafren P:\Projects \Pafford Bridge\ReportslPafford Bridge FRA (Mar-2013) .doc '%.Water

Assessment of Flood Risk Assessment of flood risk is undertaken following the requirements outlined in the National Planning Policy Framework (NPPF). Although each assessment is specific to the site and mechanism of flooding in question a general method is followed when making all assessments. This method is outlined below.

The assessment of flood risk is undertaken by considering the likelihood of flooding and the consequence of flooding as outlined in Table 1

Likelihood of Conseauence of flooding Flooding NeQIiQibie Low Medium High Low Very Low Very Low Low Medium Medium Very Low Low Medium Hiqh Hiqh Low Medium Hiqh Hiqh

Table 1: Assessment of Flood Risk

Likelihood of Flooding Likelihood of flooding is outlined in Table 1 of the NPPF Technical Guide. For some fluvial sources ie main watercourses the Environment Agency's flood maps are used to determine the likelihood of flooding. For other mechanisms of flooding assessment is made using other sources of data such as historical information, flow data etc. In some situations it may be necessary to undertake monitoring or modelling to determine likelihood of flooding. In others a more qualitative approach can be taken.

Consequence of Flooding The assessment of flood consequence is undertaken by considering the Vulnerability of the site and the hazard of flooding at the site as outlined in Table 2.

Flood Vulnerabilitv of Site Hazard Water Compatible Less Vulnerable More Vulnerable Highly Vulnerable Neolioible Neqliq lble Neqlluible Neuliqible Necllolble Low Neoliolble Low Low Medium Medium Low Medium Medium HiQh Hloh Medium Medium Hiqh Hiqh Very Hiah Medium High High High

Table 2: Assessment of Flood Consequence

Flood Hazard Assessment of flood hazard is undertaken for each possible flooding mechanism and specific to the site in question. An outline of the considerations taken into account when determining the hazard categories used within this report are outlined below:

Very high High depths of inundation (>600 mm). High velocities of floodwater entering the site (>0.15 m/sec for residential, >0.3 m/sec for commercial). Restricted access/ egress to the site.

Depths of inundation up to 600 mm. Floodwater flowing across site at speeds of >0.15 m/s. Access/egress possible but may be through floodwaters.

P:lLegislation & GuidanceIFlood riskINPPFIRisk Assessment NPPF.doc Page 1

Medium Inundation of the site below 600 mm. Slack floodwaters with either very low velocities or on the edge of the floodplain. Easy access and egress.

Some flooding on-site. Not affecting buildings. Dry access/egress routes.

Negligible flood flows.

Negligible No flooding on-site.

Vulnerability of Site Vulnerability of the site is determined using classifications outlined in Table 2 of the NPPF Technical Guide.

P:v..egislation & GuidancelFlood risklNPPARisk Assessment NPPF.doc Page 2

CEMEX Flood Risk Assessment, Pafford Bridge Final

APPENDIX 3

J-FLOW flood depth outputs

March 2013

Hafren P:\Projects\Pafford BridgelReportslPatford Bridge FRA (Mar-2013).doc ~Water

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CEMEX Flood Risk Assessment, Pafford Bridge Final

APPENDIX 4

Surface water run-off calculations

March 2013

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Patford Bridge - Surface water run-off - Proposed - Impermeable surfaces

Parameters Max height 106 mAOD Min height 105 mAOD Flow path 80 m Slope 0.01 C 0.9 Area 0.035 ha

Climate change (% rainfall 20 % increase)

The Rational Method to give peak flow Qp is in the form:

Qp = 2.78 CiA

Where:

C co-efficient of run-off(dimensionless) i rainfall intensity (mm/hr) A catchment area (Ha)

Rainfall .1 Rainfall intensity Flow·2 Flow Volume

Duration 200 yr event 200 yr event 200 yr event 200 yr event

hours mm mm/hr lIs I/s/Ha m 3

0.25 40.94 163.76 17.21 491.67 15 0.5 49 98.00 10.30 294.24 19 1 58.25 58.25 6.12 174.89 22 2 68.87 34.44 3.62 103.39 26 4 81.13 20.28 2.13 60.90 31 6 89.17 14.86 1.56 44.62 34 8 95.3 11.91 1.25 35.77 36 12 104.59 8.72 0.92 26.17 40 16 109.41 6.84 0.72 20.53 41 20 113.27 5.66 0.60 17.00 43 24 116.51 4.85 0.51 14.58 44 28 119.32 4.26 0.45 12.79 45 32 121.8 3.81 0.40 11.43 46 36 124.02 3.45 0.36 10.34 47 40 126.04 3.15 0.33 9.46 48 44 127.9 2.91 0.31 8.73 48 48 129.61 2.70 0.28 8.11 49

•1 Obtained from FEH CD-ROM version 3

.2 Climate change factored into rainfall intensity at this stage

P:lProjectslPatford BridgelDatalSurface water runoff PatfordlProposed - Imperm without dis.

Land at Patford Bridge - Supporting Statement •

Appendix 5 - Essential requirements for a suitable

site for cleaning activities and

summary analysis of alternative sites

considered

cemex Supporting Statement A081776 24/05/2013