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Shelford Road,
Radcliffe on Trent
Flood Risk Assessment and Drainage Strategy
for
William Davis
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Flood Risk Assessment and Drainage Strategy
Shelford Road, Radcliffe on Trent
Prepared By:
Tony Goddard BEng (Hons) CEng MICEAssociate Director
Checked By:
Matthew Viggars MEng (Hons) CEng MICE
Chartered Civil Engineer
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
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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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Radcliffe on TrentShelford Road SCA Sewer Capacity Assessment Severn Trent Water
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
Radcliffe on TrentShelford Road SCA Sewer Capacity Assessment Severn Trent Water
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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Mouchel 6 April 2013
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.
Radcliffe on TrentShelford Road SCA Sewer Capacity Assessment Severn Trent Water
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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Mouchel 7 April 2013
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
Radcliffe on TrentShelford Road SCA Sewer Capacity Assessment Severn Trent Water
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.
Radcliffe on TrentShelford Road SCA Sewer Capacity Assessment Severn Trent Water
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.
Radcliffe on TrentShelford Road SCA Sewer Capacity Assessment Severn Trent Water
Appendix A: Site and Development Information
Figure A-1: Site location plan
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Mouchel April 2013
Radcliffe on TrentShelford Road SCA Sewer Capacity Assessment Severn Trent Water
Figure A-2: Local sewerage network and critical assets
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Mouchel April 2013
Radcliffe on TrentShelford Road SCA Sewer Capacity Assessment Severn Trent Water
Figure A-3: Known flooding locations
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Mouchel April 2013
Radcliffe on TrentShelford Road SCA Sewer Capacity Assessment Severn Trent Water
Figure A-4: Modelled flooding nodes
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Mouchel April 2013
Radcliffe on TrentShelford Road SCA Sewer Capacity Assessment Severn Trent Water
Figure A-5: Location plan from developer
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Mouchel April 2013
Radcliffe on TrentShelford Road SCA Sewer Capacity Assessment Severn Trent Water
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
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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
BSP Consulting Ltd Page 1
12 Oxford Street Shelford Road
i h d liff
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Nottingham Radcliffe on Trent
NG1 5BG Single Pond
Date March 2013 Designed by AG
File 12568 Linked Twi... Checked by
Micro Drainage Source Control 2013.1
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
BSP Consulting Ltd Page 2
12 Oxford Street Shelford Road
Nottingham Radcliffe on Trent
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Nottingham Radcliffe on Trent
NG1 5BG Single Pond
Date March 2013 Designed by AG
File 12568 Linked Twi... Checked by
Micro Drainage Source Control 2013.1
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
BSP Consulting Ltd Page 3
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Nottingham Radcliffe on Trent
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Nottingham Radcliffe on Trent
NG1 5BG Single Pond
Date March 2013 Designed by AG
File 12568 Linked Twi... Checked by
Micro Drainage Source Control 2013.1
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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