File 7 Floodrisk Drainage Report

8/13/2019 File 7 Floodrisk Drainage Report

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Shelford Road,

Radcliffe on Trent

Flood Risk Assessment and Drainage Strategy

for

William Davis


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BSP Consulting 12568/FRA/DS/Rev AShelford Road, Radcliffe on Trent Flood Risk Assessment and Drainage Strategy

Flood Risk Assessment and Drainage Strategy

Shelford Road, Radcliffe on Trent

Prepared By:

Tony Goddard BEng (Hons) CEng MICEAssociate Director

[email protected]

Checked By:

Matthew Viggars MEng (Hons) CEng MICE

Chartered Civil Engineer

[email protected]

Revision: - A

Contents

Executive Summary

1.0 Introduction

2.0 Background Information

3.0 Flood Risk Assessment and Drainage Strategy

4.0 Recommendations

Appendix A Detailed Site Location Plan
mailto:[email protected]:[email protected]:[email protected]:[email protected]:[email protected]:[email protected]


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Executive Summary

Introduction BSP Consulting has been commissioned by William Davis to undertake a Flood Risk

Assessment and Drainage Strategy for the development of land at Shelford Road,

Radcliffe on Trent, Nottinghamshire. This Flood Risk Assessment has been prepared

in accordance with the Department for Communities and Local Government (DCLG)

publication Technical Guidance to the National Planning Policy Framework

Existing Site

Conditions

The site is currently open fields and farm buildings. An unnamed watercourse,

Stream A, passes east to west along the southern edge of the site. Site levels vary

from over 49.5m AOD in the north east to 31m AOD at the outfall of Stream A in the

south west. There is a fall of 3m along Stream A at the site.Development

Description and

Planning Context

The development proposals are for the construction of residential dwellings,

attenuation ponds, adoptable roads and sewers, hardstandings and soft landscaping. In

accordance with the National Planning Policy Framework, the proposed residential

use falls under the more vulnerable category in terms of flood risk.

Definition of Flood

Hazard

The River Trent is the primary Main River in the Nottingham area. Land adjacent the

River Trent at the point where Stream A outfalls is at a level of approximately 20m

AOD. This is some 11m below the lowest level of Stream A on site. Stream A has the

potential to be the primary source of flood risk to the lower reaches of the site.

Probability The EA website indicative flood mapping confirms that site would not be at risk offlooding in a 0.1% (1:1000 year) probability flood event due to flooding from the

River Trent or other significant fluvial sources. A detailed modelling study of Stream

A has been undertaken to confirm the flood risk associated with this watercourse. The

modelling results show only the south west of the site is likely to be subject to

flooding in the 1:100 year plus climate change flood emanating from Stream A.

Climate Change The implications of climate change are taken into account in the flood modelling

exercise.

Detailed

DevelopmentProposals

The National Planning Policy Framework states that developments of a more

vulnerable category such as the proposed residential use are appropriate within FloodZone 1.

Flood Risk

Management

Measures

It is recommended that the finished floor levels are set at least 600mm above the

1:100 year plus climate change flood levels at the adjacent modelled watercourse

sections. SuDS techniques will be employed to provide a minimum of two treatment

trains of water quality improvement prior to the final discharge to Stream A. SuDS

features such as permeable paved private drives/parking courts and filter strips/filter

drains are proposed for use as source control and treatment features for surface water

runoff. Site control will be provided by two linked attenuation ponds that will balance

all surface water from the impermeable development areas back to the 1 in 1 yeargreenfield runoff rate. The ponds are indicated to be at the same invert level and are

to be linked by a pipe or narrow swale.

Off Site Impacts The proposed development surface water discharge rate will be limited to the existing

1 in 1 year greenfield runoff rate prior to entry to Stream A in a 1 in 100 year plus30% climate change rainfall event therefore the proposed development reduces

fluvial flooding problems adjacent to or downstream of the site for the proposed


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drawing 12568/100 and included in Appendix D.

Foul water from the proposed development will be drained to the existing adoptedfoul sewerage in Shelford Road to the north of the site.

1.0 INTRODUCTION

1.1 TERMS OF REFERENCE

1.1.1 BSP Consulting has been commissioned by William Davis to undertake a Flood

Risk Assessment and Drainage Strategy for the development of land at ShelfordRoad, Radcliffe on Trent, Nottinghamshire.

1.1.2 In the preparation of this report, consultations have been undertaken with the

Environment Agency (EA), Rushcliffe Borough Council (RBC) and Severn Trent

Water (STW). A site visit was made in November 2012, to walk the local

watercourse catchment, to assess the local topography and current site use. The

Greater Nottingham Strategic Flood Risk Assessment 2010 has also been referred

to.

1.1.3 This Flood Risk Assessment has been prepared in accordance with the Department

for Communities and Local Government (DCLG) publication Technical Guidance

to the National Planning Policy Framework while retaining the layout as

recommended in the superseded Planning Policy Statement 25 (PPS25)

Development and Flood Risk.

1.1.4 This report has been produced on behalf of the client, William Davis, and no

responsibility is accepted to any third party for all or any part. This report should

not be relied upon or transferred to any other parties without the express written

authorisation of BSP Consulting. If any unauthorised third party comes into

possession of this report, they rely on it at their own risk and the authors owe them

no duty of care or skill.

1.2 NATIONAL PLANNING POLICY FRAMEWORK

1.2.1 The National Planning Policy Framework was published on 27 March 2012. This

replaces Planning Policy Statement 25: Development and Flood Risk.

1.2.2 Technical Guidance to the National Planning Policy Framework has been


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2.0 BACKGROUND INFORMATION

2.1 SITE LOCATION, DESCRIPTION AND DETAILS2.1.1 Figure 2.1 below indicates the location of the site; a more detailed site plan is

located in Appendix A. A site visit was made in November 2012, to walk the local

watercourse catchment, to assess the local topography and current site use.

Ordnance Survey Crown copyright 2010 All rights reserved. Licence number 100041272

Figure 2.1 Shelford Road, Radcliffe on Trent - Site Location Plan2.1.2 The approximate site boundary is outlined in red on Figure 2.1 above. The overall

site occupies an area of approximately 18.6 hectares and is located to the south of

Shelford Road, Radcliffe on Trent, Nottinghamshire at OSNGR 465600E340000N. The site is currently open fields and farm buildings. An unnamed

watercourse, Stream A, passes east to west along the southern edge of the site

indicated in Figure 2.1 above.

2 1 3 The topographical survey of the site in Appendix B indicates that all of the land

RiverTrent

Site

Unnamed

Watercourse

(Stream A)


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2.1.6 Site and Watercourse Photographs

Figure 2.2 Site frontage onto Shelford

Road. (Looking south west)

Figure 2.3 General site view across the

centre of the site. (Looking north east)

Figure 2.4 Culvert outlet to site from

under the railway. (Looking east)

Figure 2.5 View downstream at Section

18. (Looking west)


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Borough Council and Nottinghamshire County Council. This assessment seeks to

draw together the relevant information from these sources and to collate this withthe findings of our investigations, analysis and discussions to assess the flood risk

at this site.

3.0 FLOOD RISK ASSESSMENT AND DRAINAGE STRATEGY

3.1 DEVELOPMENT DESCRIPTION AND PLANNING CONTEXT

3.1.1 The development proposals are for the construction of residential dwellings,

attenuation ponds, adoptable roads and sewers, hardstandings and soft

landscaping. A proposed master planning layout is included in Appendix C.

3.1.2 The local area benefits from a Strategic Flood Risk Assessment. This assessment is

the Greater Nottingham Strategic Flood Risk Assessment October 2010. This

assessment was produced by Black & Veatch Limited for the Greater Nottingham

SFRA Partnership. The GNSFRA covered the River Trent but did not include any

modelling of Stream A.

3.1.3 In accordance with the National Planning Policy Framework, the proposed

residential use falls under the more vulnerable category in terms of flood risk.

3.2 DEFINITION OF THE FLOOD HAZARD

3.2.1 The potential sources of flooding in the vicinity of the site are as detailed below:

3.2.2 Fluvial Flood Risk

3.2.3 The River Trent is the primary Main River in the Nottingham area. Land adjacent

the River Trent at the point where Stream A outfalls is at a level of approximately

20m AOD. This is some 11m below the lowest level of Stream A on site.

3.2.4 Figure 3.1 below indicates the indicative floodplain associated with the River

Trent. The site can be seen to lie outside of the River Trent floodplain. This main

river can therefore be discounted as a significant source of flood risk to the site.

3 2 5 St A fl t t t l th th d f th it d h th


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Figure 3.1 Shelford Road, Radcliffe on TrentEnvironment Agency Flood Mapping

3.2.7 Tidal Flood Risk

3.2.8 The site is at a minimum level of approximately 31m above mean sea level. The

site is therefore not at risk of flooding from tidal sources.

3.2.9 Surface Water Flood Risk

3.2.10 The land to the North of the site falls towards the site but is separated from the site

by Shelford Road. The area to the north is insubstantial and does not have the

potential to generate any significant volume of surface water following majorrainfall events.

3.2.11 Any overland flow from the land to the north would be channelled away from the

site along Shelford road towards the west.

Site


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flowing across the site. The topographical survey does not indicate any notable

low spot at this location. This localised feature is therefore not of any significanceto the proposed development. The site is therefore not at risk of significant

flooding from surface water runoff from adjacent land.

3.2.14 Flood Risk from Ground Water

3.2.15 With regard to groundwater the phase 1 SI confirms the following. The data

indicates that there is a very high likelihood of persistent or seasonably shallow

groundwater across the southern part of the site which may impact on soakawaydrainage.

In addition, the data indicates that the bedrock deposits are likely to be poorly

draining below the site.

3.2.16 No springs were noted at the ground surface during our site walkover. It is

therefore confirmed that the site is therefore not at significant risk of flooding from

ground water.

3.2.17 Flood Risk from Sewers and Infrastructure

3.2.18 The site lies upstream of the local developed areas therefore any flooding from

sewerage or water utilities would be conveyed away from the site towards the

west. A 450mm diameter surface water sewer is noted to run along the western site

boundary. This is understood to be a highway drain that drains part of ShelfordRoad. This sewer would be maintained and incorporated into the development

proposals.

3.2.19 The site is not within close proximity of any reservoirs or wet process industrial

works. The sewers and infrastructure flood risk source can therefore be discounted

as a significant source of flood risk to the site.

3.3 PROBABILITY

3.3.1 The EA website indicative flood mapping confirms that site would not be at risk of

flooding in a 0.1% (1:1000 year) probability flood event due to flooding from the

River Trent or other significant fluvial sources. This map shows the indicative

t t f th t l fl d l i if th fl d d f t i th


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3.3.4 Watercourse Description

3.3.4.1 Stream A, as it exits the site, has a catchment area of about 3.24km2. The upstream

catchment is mainly arable land with some urban contribution. The bed and stream

channel are clearly defined. There is a hedge along both sides of Stream A but the

main channel is not heavily overgrown.

3.3.4.2 At the east of the site Stream A emerges from a brick culvert that conveys the

stream under the adjacent railway.

3.3.4.3 At the western site perimeter Stream A flows into a concrete culvert which flows

west, to the south of 87 Clumber Drive. The stream remains in culvert until it

emerges 320m to the west of the site.

3.3.5 Hydrology

3.3.5.1 No gauged flow data is available for Stream A.

3.3.5.2 In order to make an estimation of the likely flood flow rates from this un-gauged

catchment a hydrological analysis has been carried out using the FEH Revitalised

Rainfall Run-off method (ReFH). This analysis has been undertaken for the

watercourse as it exits the site towards Clumber Drive. The catchment area

includes for all of the upstream rural and urbanised areas to this point.

3.3.5.3 This methodology was selected on the basis that the catchment is un-gauged andthere are no local and suitable hydrologically similar sites available to act as a

donor for refining the Qmed estimate and growth curve. A summary of the peak

flow results are shown in Table 1 below with full calculations contained in

Appendix D.

Table 1Estimated Watercourse Flow Rates

Flood Return Period Flood Flow Rate (m3/s)1:2 Year 0.83

1:30 Year 1.72

1:100 year 2.29

1:100 year +20% 2.75

1:1000 4 19


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3.3.5.6 None of the catchment descriptors have been altered as all appear to be appropriatefor the catchment. These are listed in Appendix D.

3.3.5.7 We have queried the connectivity of the area of the Harlequin, to the south of the

A52, which is indicated as contributing to the catchment. This 0.21km2urbanised

area is remote from the site. It is separated from the site by both the A52 and the

railway. Severn Trent Water sewer records indicate only foul sewerage in this

area. Discussions with an experienced local Municipal Engineer have however

confirmed that the highways in this area are drained to a surface water sewer thatdischarges to Stream A just upstream of the culvert under the railway. This

arrangement has been verified during a second site visit.

3.3.5.8 The newer development at Hudson Way, to the north of the A52 is drained by a

surface water network that is noted to be constructed using oversized pipes to

attenuate flows.

3.3.5.9 As URBEXT is less than 0.125 the winter season has been used in accordance with

CEH guidance. All other ReFH design standards have been used in the

calculations.

3.3.6 Hydraulic Model

3.3.6.1 A steady state one dimensional mathematical hydraulic model of the watercourse

has been constructed using ISIS version 3.6. This modelling software has beenchosen as it is accepted by the Environment Agency and is widely used within the

industry.

3.3.6.2 Cross sections of Stream A have been surveyed by BluePlan. The model extends

from the culvert outlet to site from under the railway in the east to 53m

downstream of the western edge of the site. Sections and the section locations are

illustrated on drawing 1627Sectionsand drawing 1627Topographical Survey

included within Appendix B.

3.3.6.3 The farm access bridge downstream of Section 11 has only been modelled as a

structure in the 1:1000 year event (with no culvert downstream for model stability

reasons) as the bridge soffit is above all other modelled flood levels at this point.

Th t t h j t t f S ti 2 h t b d ll d th


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3.3.6.5 Mannings n values for the circular concrete culvert has been taken as 0.010 in

accordance with the CIRIA Culvert Design and Operation Guide 2010.

3.3.6.6 A ReFH hydrograph was introduced as the upstream boundary and flows were

generated by the ISIS software for the peak outflow at the required return periods.

The flow plots were checked for each return period and these all correlated with

the CEH ReFH Spreadsheet results.

3.3.6.7 The downstream culvert was initially included in the model at a length of 320m

but the model was very unstable. The culvert operates under entry controltherefore the culvert has been shortened to 53m. This should not affect the

accuracy of the final results. Four arbitrary river sections at the outfall of the

model and replicated sections have been added in line with ISIS guidance.

3.3.6.8 A Round Nosed Broad Crested Weir with a crest level of 33.150m was introduced

in parallel with the downstream culvert to represent the potential overland flood

flow route that exists in the more onerous flood flow events between the culvert

entry and Clumber Drive.

3.3.6.9 The downstream boundary has been taken as the normal flow depth for the

gradient of the culvert (1:122). As the culvert is laid at an average gradient of

1:122 for the following 267m downstream this is a reasonable assumption.

3.3.7 Modelling Results

3.3.7.1 The ISIS model has been run under steady state conditions to generate water levels

for the 1:2year(Qmed), 1:30year, 1:100year, 1:100year+20% climate change and

1:1000 year floods. Full results for these model runs are included within Appendix

D. Figure 3.2 below shows the results for the long section along the watercourse

adjacent to the site for the 1:100year+20% climate change flood.

Table 2Estimated Watercourse Flood Levels at Section 1

Flood Return Period Peak Flood Level

(mAOD)

1:2 year 31.876

1: 30 year 32.622

1:100 year 33.342


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Figure 3.2- Modelling Results Long Section1:100year+20% climate change Peak Stage

3.3.7.3 The model was unstable when the bridge unit was added at Section 11 so this was

modelled separately for the 1:1000 year event without the downstream culvert.

Section 11 is sufficiently remote that it is unaffected by the backing up of flows at

the culvert entry. The 1:1000 year model run indicated minor afflux at theupstream bridge face but no overtopping. A long section indicating this portion of

the watercourse in the 1:1000 year modelled event is indicated below in Figure

3.3.


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3.3.7.4 No flooding is modelled to occur on site other than at the extreme south west of

the site.

3.3.7.5 The modelled flood contours are included on the modelled flood extents plan

included in Appendix D.

3.3.8 Sensitivity Analysis

3.3.8.1 Unfortunately no historical data is available to calibrate the model. The only

reference to potential flooding of Stream A is contained in the GNSFRA at Table6.1 where under a reference to Clumber Drive, Radcliffe on Trent it states Thedyke on the field side of Clumber Drive overflowed into the fields and up to the

properties but did not affect them. This entry is referenced to the Planning

Department at Rushcliffe Borough Council. No entry has been made by Radcliffe

on Trent Parish Council regarding this issue. We have therefore performed a

sensitivity analysis on the model variables.

3.3.8.2 Mannings n has been estimated for the channel based upon recommendations in

technical literature. We have therefore carried out a sensitivity analysis on the

value of n by +/-20%, the results are shown within Table 3 below for the 1:100

year flood, full results can be found in Appendix D.

3.3.8.3 The results of this sensitivity analysis show that a 20% change in the value of ndoes not cause a change in the water level at the critical culvert entry section and

does not cause any significant change in modelled flood extents along the model.

It is therefore considered that the hydraulic model is not sensitive to changes in

mannings n and that the estimated values provide a robust assessment. This is

t lik l d t th d i f th d t l t th h d li t

Table 3Mannings n Sensitivity Analysis

Water Level (m AOD) 1:100 yr flood

Cross Section n -20% Existing n n +20%

1 33.342 33.342 33.342


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Table 4Downstream Boundary Sensitivity Analysis

3.4 CLIMATE CHANGE

3.4.1 Climate change is recognised as a factor for consideration in terms of its effects on

flood risk. This issue affects the local catchment from fluvial sources in as much as

fluvial flood flows are estimated to increase by up to 20% over the next 100 years.

3.4.2 The implications of climate change have been taken into account in the modelling

work that has been carried out in the discussions on probability above.

3.4.3 The proposed surface water drainage system should be designed to accommodate

the 1 in 30 year rainfall event without any surface water flooding and should be

capable of retaining the 1 in 100 year plus climate change storm event on site

without flooding any buildings. Climate change should be allowed for in the

detailed surface water design calculations as an additional 30% on the modelled

rainfall intensity.

3.5 DETAILED DEVELOPMENT PROPOSALS

3.5.1 The proposed development and vulnerability classification are discussed in Section

3.1 above. A draft master planning layout plan is included in Appendix C.

3.5.2 The National Planning Policy Framework states that developments of a more

vulnerable category such as the proposed residential use are appropriate withinFlood Zone 1.

3.6 FLOOD RISK MANAGEMENT MEASURES

3 6 1 E i ti Fl d D f d St t

Water Level

(m AOD) 1:100 yr flood

Cross Section Existing DS Boundary 1:1000

1 33.342 33.342


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site in its present form and it is intended that the development proposals will

enhance the ecological value of this watercourse by developing the woodland

buffer and landscaping as noted on the proposed masterplan in Appendix C.

3.6.2 Proposed Site Development and Finished Floor Levels

3.6.2.1 The development proposals are for the construction of residential dwellings,

adoptable roads and sewers, hardstandings and soft landscaping. It is

recommended that the finished floor levels are set at least 600mm above the 1:100

year plus climate change flood levels at the adjacent modelled watercoursesections. As the fields fall relatively steeply towards the south of the site it is likely

that floor levels will be set higher than these levels for other practical reasons.

3.6.3 Sustainable Site Drainage Systems

3.6.3.1 The existing site can be seen to be almost entirely farm land. The current runoff

regime is therefore that of a greenfield site. The Phase 1site investigation suggests

that the superficial soils will be head deposits (mixed clays, silts, sands andgravels) with red brown clays, mudstones, siltstone and sandstone beds with some

gypsum veins.

3.6.3.2 No intrusive investigations have been undertaken however on the basis of the

available information the Phase 1 site investigation concludes that Preliminary

assessment indicates the soils generally present below the site are unlikely to

prove suitable for soakaway drainage.

3.6.3.3 The existing runoff regime from the 18.6 ha site has been evaluated in accordance

with the ICOP for SUDS. The 1 in 1 year greenfield site peak runoff rate for this

site area is 43.9 l/s. A copy of the greenfield runoff calculations are included in

Appendix F. An approximate evaluation of the likely site drainage area has been

carried out at an estimated level of impermeability of 60% of the total site area.

This equates to an impermeable area of 11.16 ha.

3.6.3.4 At this stage it is proposed that surface water runoff from the proposed

development will be drained from the proposed impermeable areas utilising, where

possible, SuDS techniques but not employing infiltration techniques unless this

proves to be viable following further investigation. SuDS techniques will be

l d t id i i f t t t t t i f t lit


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A. The preliminary design calculations associated with these ponds are included in

Appendix F. These calculations indicate that the ponds have sufficient capacity to

attenuate the 1 in 100 year plus 30% climate change rainfall event.

3.6.3.6 As indicated on drawing 12568/100 the ponds are located in an elevated location

adjacent to Stream A. The proposed ponds lie outside of the modelled flood

extents associated with Stream A. The precise detailing of the ponds is not fixed at

this stage but they are to be set out as linear features to give enhanced water

quality benefits in line with CIRIA recommendations.

3.6.4 Foul Water Drainage

3.6.4.1 The site is green field in its predevelopment state therefore there is no current

discharge of foul water from the site.

3.6.4.2 Severn Trent Water (STW) have been consulted and have provided a preliminary

developer enquiry response that confirmed that sufficient foul water capacity may

exist within the existing network and waste water treatment works but that thiswould need to be verified by further detailed modelling. A copy of this response is

included in Appendix E.

3.6.4.3 STW were subsequently engaged to model the impact of the proposed

development. This study concluded that the proposed development presents a low

risk to the existing adopted sewer network. A copy of the STW Sewer Capacity

Assessment is included in Appendix E.

3.6.4.4 Foul water from the proposed development will therefore be drained under gravity

to an adoptable pumping station at the south of the site. From here it will be

pumped to the existing adopted foul sewerage in Shelford Road to the north of the

site.

3.7 OFF SITE IMPACTS

3.7.1 The proposed development surface water discharge rate will be limited to the

existing 1 in 1 year greenfield runoff rate prior to entry to Stream A in a 1 in 100

year plus 30% climate change rainfall event therefore the proposed development

reduces fluvial flooding problems adjacent to or downstream of the site for the

d lif ti f th d l t


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4.0 RECOMMENDATIONS

4.1 The following recommendations are made to reduce flood risk and promote a

sustainable and practicable drainage strategy at the proposed development:

Finished floor levels are to be set at least 600mm above the 1:100 year plusclimate change flood levels at the adjacent modelled watercourse sections.

SuDS techniques will be employed to provide a minimum of two treatmenttrains of water quality improvement prior to the final discharge to Stream A.

The SuDS features will be a combination of source control and site controlfeatures.

Two linked attenuation ponds shall be utilised to provide two treatment trainsfor water quality and attenuate surface water runoff from the impermeable

development area back to greenfield runoff rates. A preliminary attenuation

strategy is outlined on drawing 12568/100 and included in Appendix D.

Foul water from the proposed development will be drained to the existingadopted foul sewerage in Shelford Road to the north of the site.

Disclaimer

We would note that all comments made in this report are based on the sources stated in

Section 1.1. This report and its recommendations are intended for the use of William Davis

for the above site only.


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Appendix A

Detailed Site Location Plan


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Appendix B

Topographical Survey


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Appendix CDevelopment Proposals


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VERSION FEHCDROM Version 3 exportedat 08:10:39 GMT Mon 12Nov12

CATCHMENT GB 465550 339650 SK6555039650

AREA 3.24

ALTBAR 52

ASPBAR 203ASPVAR 0.22

BFIHOST 0.465

DPLBAR 1.29

DPSBAR 31.8

FARL 1

LDP 2.53

PROPWET 0.27

RMED1H 10

RMED1D 28.9

RMED2D 37.4

SAAR 597

SAAR4170 592

SPRHOST 47.12

URBCONC1990 0.679

URBEXT1990 0.0409

URBLOC1990 0.555URBCONC2000 0.774

URBEXT2000 0.0444

URBLOC2000 0.491

C 0.02349

D1 0.33135

D2 0.33982

D3 0.25521

E 0.30769F 2.33395

C(1km) 0.024

D1(1km) 0.338

D2(1km) 0.334

D3(1km) 0.261

E(1km) 0.308

F(1km) 2.331


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Revitalised FSR/FEH rainfall runoff methodSpreadsheet application report

Rainfall

Recommended season is Winter, as URBEXT < 0.125

ReFH design standard Seasonal Correction Factor of 0.63 applied

ReFH design standard Areal Reduction Factor of 0.97 applied

Loss Model

CMaxderived from catchment descriptors

ReFH design standard Ciniused

ReFH design standard factor used

Routing Model

Tpderived from catchment descriptors

ReFH design standard used for Up

ReFH design standard used for Uk

Baseflow Model

BL derived from catchment descriptors

BR derived from catchment descriptors

ReFH design standard BF0used


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12568 WCM NO CULVERT FILE=12568 WCM NO CUL ISIS VER= 6.6.0.81

results from the direct method at time 5.0000 hourslabel12 ? flow stage froude velocity umode ustate z

SECTION_1 y 4.194 32.231 0.415 1.329 0.000 0.000 31.160SECTION_2 y 4.194 32.344 0.273 0.867 0.000 0.000 31.192SECTION_3 y 4.194 32.416 0.465 1.258 0.000 0.000 31.384SECTION_4 y 4.194 32.607 0.513 1.356 0.000 0.000 31.619SECTION_5 y 4.194 32.850 0.594 1.554 0.000 0.000 31.898SECTION_6 y 4.194 33.151 0.574 1.490 0.000 0.000 32.179SECTION_7 y 4.194 33.439 0.589 1.500 0.000 0.000 32.461SECTION_8 y 4.194 33.691 0.456 1.238 0.000 0.000 32.550SECTION_9 y 4.194 33.843 0.347 1.033 0.000 0.000 32.550SECTION_10 y 4.194 33.828 0.413 1.282 0.000 0.000 32.550SECTION_11 y 4.194 33.942 0.412 1.310 1.000 0.000 32.555

SECTION_12 y 4.194 34.071 0.368 1.153 0.000 0.000 32.666SECTION_13 y 4.194 34.201 0.395 1.196 0.000 0.000 32.820SECTION_14 y 4.194 34.339 0.344 1.054 0.000 0.000 32.929SECTION_15 y 4.194 34.450 0.337 0.913 0.000 0.000 33.083SECTION_16 y 4.194 34.609 0.850 1.953 0.000 0.000 33.832SECTION_17 y 4.194 35.074 0.810 1.801 0.000 0.000 33.992SECTION_18 y 4.194 35.479 0.554 1.706 0.000 0.000 34.110

Page 1


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BSP Consulting 12568/FRA/DS/Rev AShelford Road Radcliffe on Trent Flood Risk Assessment and Drainage Strategy


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Shelford Road, Radcliffe on Trent Flood Risk Assessment and Drainage Strategy

Appendix ESevern Trent Water Correspondence


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Sewer Capacity Assessment

Shelford RoadRadcliffe On Trent, Nottinghamshire

DE-1210-072 (WT26939)

Version 1

Date: 02/May/13

Radcliffe on TrentShelford Road SCA Sewer Capacity Assessment Severn Trent Water


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Sewer Capacity Assessment Summary

Sewer Capacity

Assessment prepared for

William Davis Ltd.

Forest Field, Forest Road, Loughborough, Leics. LE11 3NS

Development location and

existing use

Land at Shelford Road Farm, Shelford Road, Radcliffe on Trent, Nottingham

NG12 1BA. Greenfield with associated farm dwelling and out buildings.

Development proposals

Development includes building 350 mixed residential dwellings. Foul

effluent is proposed to be pumped into the existing Severn Trent Water

network. Storm flows are proposed to flow to the watercourse south of

development site and have not been assessed as part of this assessment.

Planning application was not submitted as of 17/04/13. There is no knownphasing or construction programme at this stage.

Study aimThe aim of the study is to identify the potential impact of foul flows only

from the proposed development on the existing sewerage system.

Impact of proposed

development on public

sewer network

Sewer flooding LOW

Combined Sewer Overflows LOW

Sewage Pumping Stations LOW

Requirement for Capacity

Improvements

Capacity improvements are not required to accommodate flows from the

proposed development.

Sewage Treatment Works

capacity

The site drains to Radcliffe on Trent sewage treatment work. There is not

sufficient capacity at the STW to accommodate flows from this

development



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Table of Contents

1 Introduction _______________________________________________________________________ 12 Sewer Capacity Assessment ___________________________________________________________ 33 Conclusions and Recommendations _____________________________________________________ 94 Appendicies_______________________________________________________________________ 13



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1 Introduction1.1 Site LocationDevelopment site is located on the south side of Shelford Road in north-east Radcliffe on Trent.

Easting: 465559

Northing: 340049

Existing land use is a rural Greenfield site with farm buildings and residential dwelling. The proposed

development site is bounded to the north by Shelford Road, to the west by residential properties, to the

south by a watercourse and railway line and to the east by greenfield. Adjacent land uses include residential,

farmland and railway.

The site location is shown in Figure A-1, Appendix A.

1.2 Local Sewerage NetworkFlows from the Shelford Road area cross under a railway line to Bingham Road, then along Main Road to

Sydney Grove sewerage pumping station (SPS). From here effluent is pumped 1.4 km to Radcliffe on Trent

sewage treatment works (STW) via a 300mm diameter rising main. Between the development and Sydney

Grove SPS there are two combined sewer overflows (CSOs), with a third CSO located inside the SPS

compound. Spills from these sites drain to a local ditch that flows to the River Trent at Radcliffe Park.

Sydney Grove SPS was upgraded as part of a Capital scheme in 2006 and surveyed in 2013. It has two

variable speed pumps arranged duty/standby which can discharge between 29-79 litres per second. There is

a combined sewer overflow to a storm wet wet well. Spills from this site are pumped to the surface water

system to the same outfall as the two previously mentioned CSOs .

The local sewerage network and the location of critical sewer assets are shown in Figure A-2, Appendix A.

1.3 Proposed DevelopmentThe proposed development covers 18.7ha on an existing farm site and consists of 350 mixed residential

dwellings. Foul flows are proposed to gravitate to the south end of the site and pumped to the existing

225mm diameter foul sewer on Shelford Road at MH SK65404201.



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Development Type Units

Mixed Residential 350 dwellings

1.4 Study Aims and ObjectivesThe aim of the study is to identify the potential impact of flows from the proposed development on the

public sewer network. This will be achieved through undertaking hydraulic computer modelling of the

proposed development and assessing the impact at key points on the sewer network.



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2 Sewer Capacity Assessment2.1 MethodologyHydraulic modelling has been used to assess the impacts of the proposed development. The methodology is

summarised below:

The best available model for the area was used as the baseline model. A review of the model wasundertaken to ensure that it is suitable to inform the assessment.

The base model used for the study was taken from the current live Rushcliffe Residual SMP (523-136). The network 523-136 Rushcliffe Residual#26 was verified in 2003.The model was re-verified

and upgraded to asset management period (AMP) 5 specifications. This network includes a new

asset survey of six relevant manholes in Radcliffe on Trent, Bingham Road CSO and Sydney Grove

SPS. The master database has been compiled in InfoWorks CS version 9.5.

o To update the model with the proposed development, local 150mm sewers were modelledto serve the development draining to the south end of the site. From here a pumping station

was modelled to return flow to the 225mm sewer at MH SK65404201 on Shelford Road. The

wet well storage volume of 35.44m3and pump rate of 5 l/s were calculated using the Severn

Trent design standards and Sewers for Adoption design guide. Cover and invert levels for the

network were estimated from surrounding manholes.

Details of proposed development flows used in the assessment are included in Section2.2. The baseline model and proposed model were run for dry weather flow analysis and the 20 and

40 year return period events for a suite of storm durations. The results for the critical storm duration

(20 year 240 minute and 40 year 240 minute) are reported throughout this report. The models were

also run for the 1 year 60 minute and 5 year 90 minute storms, to enable an assessment of CSO

performance.

The model results were analysed to determine the impact of the additional flows on networkperformance and identify whether capacity improvements are required.

2.2 Proposed Development Flows


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Table 2-1: Predicted impact on sewer flooding >1m3for modelled scenarios (baseline and post-development)


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Mouchel 5 April 2013

Location Baseline performance Post-development impactImpact

Risk Level

Road DWF 20 year event 40 year event DWF 20 year event 40 year event

Shelford Rd No surcharge 143.2m3 196.4m3 No surcharge 150.8m3(+5%) 204.3m3(+4%) Low

Addington Court No surcharge 111.1m3 896.1m3 No surcharge 112.6m3(+1%)898.7m

3

(+/-0%)Low

Bingham Road No surcharge 52.0m3 240.9m

3 No surcharge 58.3m

3(+12%) 244.3m

3(+1%) Low

Berkeley Crescent No surcharge 28.6m3 260.7m3 No surcharge 31.7m

3(+11%) 262.7m3(+1%) Low


Table 2-2: Predicted Combined Sewer Overflow performance for modelled scenarios (baseline and post-development)

C bi d S O fl

Receiving watercourse Baseline spill volume (m3) Post-development spill volume (m

3)

Impact


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Combined Sewer OverflowRisk LevelName

Special

designation?*

1year 60 minute

event

5 year 90 minute

event

1year 60 minute

event

5 year 90 minute

event

CSO Radcliffe on Trent -

Bingham Road (SOQ-948-99-53) River Trent No 1057.3m

3

1767.8m

3

1066.3m

3

(+1%)

1780.2m3 (+/-

0%) Low

EO Radcliffe on Trent - Main

Road (SOQ-948-99-52)River Trent No 372.7m

3 610.2m

3 371.2m

3(+/-0%) 615.0m3(+1%) Low

CSO Radcliffe on Trent - Sydney

Grove SPS (SOQ-948-99-56)River Trent No 711.4m

3 1047.6m

3 720.7m

3(+1%)

1052.5m3(+/-

0%)Low

* Special designation refers to environmental designations such as Special Areas of Conservation (SAC) and Sites of Special Scientific Interest (SSSI). The special

designation may be at the location of the overflow or in downstream reaches of the receiving watercourse.


Table 2-3: Predicted Sewage Pumping Station performance for modelled scenarios (baseline and post -development)

Sewage Pumping Station

Emergency overflow Baseline performance (m3) Post-development performance (m

3)

Impact


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Sewage Pumping StationRisk Level

Receiving

watercourse

Special

designation?DWF

20 year

event

40 year

eventDWF

20 year

event

40 year

event

Radcliffe on Trent -

Sydney Grove SPSRiver Trent No

Pump

operates 0.79times/hr;

Storage for

2hrs @

3DWF=

330.07m3;

Meets

storage

requirement -

has 363.65m3

Spills

1724.3m3

Spills

1881.7m3

Pump

operates 0.79times/hr;

Storage for

2hrs @

3DWF=

346.41m3;

Meets

storage

requirement -

has 363.65m3

Spills

1742.2m3

(+1%)

Spills

1892.1m3

(+1%)

Low


2 4 C it I t R i t


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2.4 Capacity Improvement RequirementsThe overall impact of the development is LOW based on the analysis in Tables 2-1 to 2-3. Impact of the

proposed development based on flooding is LOW due to predicted flood volume increases being less than

20m3 per manhole and predicted flooding locations are not near any reported flooding. Impact from the

proposed development based on CSO performance is LOW due to predicted overflow volumes increasing

less than 10% and outfalls do not drain to specially designated watercourses. Impact of the proposed

development based on SPS performance is LOW due to current sufficient storage capacity and minimal

increase in overflow operation as well as the age and condition of Sydney Grove SPS. Sewer network

capacity improvements are not likely to be required to accommodate flows from the proposed

development.


3 C l i d R d ti


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3 Conclusions and Recommendations3.1 Conclusions

The impact of foul flows arising from the proposed development at Shelford Road on the sewernetwork has been assessed using hydraulic modelling.

The proposed development is predicted to have the following impacts:o Sewer Flooding: LOWo Combined Sewer Overflows: LOWo Sewage Pumping Stations: LOW

3.2 Recommendations Based on current model, there are no recommendations to further network capacity investigations.


Appendix A: Site and Development Information

Figure A-1: Site location plan


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Mouchel April 2013


Figure A-2: Local sewerage network and critical assets


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Mouchel April 2013


Figure A-3: Known flooding locations


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Mouchel April 2013


Figure A-4: Modelled flooding nodes


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Mouchel April 2013


Figure A-5: Location plan from developer


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Mouchel April 2013


Appendix B: Model Review Proforma


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Appendix B: Model Review Proforma

This appendix is for internal use only and has been removed prior to external distribution

Information contained within this appendix must notbe referred to elsewhere within this report


Appendix C: Supplementary Information


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This appendix is for internal use only and has been removed prior to external distribution

Information contained within this appendix must notbe referred to elsewhere within this report



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Appendix F

Surface Water Drainage Proposals

BSP Consulting Ltd Page 1

12 Oxford Street Shelford Road


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Nottingham Radcliffe on Trent

NG1 5BG William Davis

Date March 2013 Designed by AG

File Checked by

Micro Drainage Source Control 2013.1

ICP SUDS Mean Annual Flood

Input

Return Period (years) 100 Soil 0.400Area (ha) 18.600 Urban 0.000

SAAR (mm) 600 Region Number Region 4

Results l/s

QBAR Rural 52.8

QBAR Urban 52.8

Q100 years 135.8

Q1 year 43.9

Q30 years 103.5

Q100 years 135.8



i h d liff


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NG1 5BG Single Pond


File 12568 Linked Twi... Checked by


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

Storm

Event

Max

Level

(m)

Max

Depth

(m)

Max

Control

(l/s)

Max

Overflow

(l/s)

Max

Outflow

(l/s)

Max

Volume

(m)

Status

480 min Summer 33.148 1.148 39.1 0.0 39.1 5990.8 O K

600 min Summer 33.167 1.167 39.3 0.0 39.3 6108.7 O K

720 min Summer 33.177 1.177 39.5 0.0 39.5 6175.0 O K

960 min Summer 33.182 1.182 39.5 0.0 39.5 6208.1 O K

1440 min Summer 33.166 1.166 39.3 0.0 39.3 6103.7 O K

2160 min Summer 33.134 1.134 38.9 0.0 38.9 5900.4 O K

2880 min Summer 33.098 1.098 38.5 0.0 38.5 5671.5 O K

480 min Winter 33.270 1.270 40.7 0.0 40.7 6779.7 O K

600 min Winter 33.292 1.292 41.0 0.0 41.0 6930.3 O K720 min Winter 33.306 1.306 41.1 0.0 41.1 7023.6 O K

960 min Winter 33.318 1.318 41.3 0.0 41.3 7101.2 O K

1440 min Winter 33.306 1.306 41.1 0.0 41.1 7021.2 O K

2160 min Winter 33.262 1.262 40.6 0.0 40.6 6731.4 O K

2880 min Winter 33.216 1.216 40.0 0.0 40.0 6428.0 O K

Storm

Event

Rain

(mm/hr)

Flooded

Volume

(m)

Discharge

Volume

(m)

Overflow

Volume

(m)

Time-Peak

(mins)

480 min Summer 10.143 0.0 5888.9 0.0 486

600 min Summer 8.503 0.0 5951.3 0.0 604

720 min Summer 7.359 0.0 5951.7 0.0 724

960 min Summer 5.854 0.0 5874.3 0.0 962

1440 min Summer 4.234 0.0 5637.6 0.0 1238

2160 min Summer 3.057 0.0 9032.5 0.0 1604

2880 min Summer 2.424 0.0 9468.6 0.0 2000

480 min Winter 10.143 0.0 6155.1 0.0 476

600 min Winter 8.503 0.0 6151.1 0.0 592

720 min Winter 7.359 0.0 6122.8 0.0 708

960 min Winter 5.854 0.0 6045.3 0.0 932

1440 min Winter 4.234 0.0 5862.4 0.0 13622160 min Winter 3.057 0.0 10065.7 0.0 1700

2880 min Winter 2.424 0.0 10491.5 0.0 2164





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NG1 5BG Single Pond




Rainfall Details

Rainfall Model FSR Winter Storms Yes

Return Period (years) 100 Cv (Summer) 0.750

Region England and Wales Cv (Winter) 0.840M5-60 (mm) 18.600 Shortest Storm (mins) 480

Ratio R 0.400 Longest Storm (mins) 2880

Summer Storms Yes Climate Change % +30

Time Area Diagram

Total Area (ha) 11.160

Time

From:

(mins)

To:

Area

(ha)

Time

From:

(mins)

To:

Area

(ha)

Time

From:

(mins)

To:

Area

(ha)

0 4 3.720 4 8 3.720 8 12 3.720





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NG1 5BG Single Pond




Model Details

Storage is Online Cover Level (m) 34.000

Tank or Pond Structure

Invert Level (m) 32.000

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

0.000 4122.0 0.750 5563.0 1.500 7116.0 2.000 8000.0

Hydro-Brake Outflow Control

Design Head (m) 1.500 Hydro-Brake Type Md5 SW Only Invert Level (m) 32.000

Design Flow (l/s) 43.9 Diameter (mm) 243

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

0.100 8.7 1.200 39.8 3.000 61.6 7.000 94.0

0.200 21.7 1.400 42.4 3.500 66.5 7.500 97.3

0.300 31.3 1.600 45.1 4.000 71.1 8.000 100.5

0.400 35.4 1.800 47.7 4.500 75.4 8.500 103.6

0.500 36.5 2.000 50.3 5.000 79.5 9.000 106.6

0.600 36.3 2.200 52.7 5.500 83.3 9.500 109.50.800 36.1 2.400 55.1 6.000 87.1

1.000 37.5 2.600 57.3 6.500 90.6

Weir Overflow Control

Discharge Coef 0.544 Width (m) 10.000 Invert Level (m) 34.000


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Documents

File 7 Floodrisk Drainage Report