addendum to flood risk assessment november 2017 land … · 1.5.1 the surface water storage...

AMBERPLANNING FloodRisk&Hydrology

ADDENDUMTOFLOODRISKASSESSMENT

November2017

LandoffGipsyLane,IrchesterNorthampton

ThisreporthasbeenpreparedbyAmberPlanningwithinthetermsofthecontractwiththeclientandtakingaccountoftheresourcesdevotedtoitbyagreementwiththeclient.Wedisclaimanyresponsibilitytotheclientandothersinrespectofanymattersoutsideofthescopeagreed.Thisreportisconfidentialtotheclientandweacceptnoresponsibilityofwhatsoevernaturetothirdpartiestowhomthisreport,oranypartthereof,ismadeknown.Anysuchpartyreliesonthereportattheirownrisk.

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

Flood Risk Assessment: Land off Gipsy Lane, Irchester AMBERPLANNING November 2017 FloodRisk&Hydrology

i Job No. H8109

TABLE OF CONTENTS

1.0 INTRODUCTION 11.1 Background 11.2 Land Use 11.3 SuDS Options for Surface Water Disposal 1

1.3.1 Greenfield Runoff 11.4 Climate Change 21.5 Attenuation and Controlled Discharge 2

1.5.1 Results 21.6 Drainage Layout 3

1.6.1 Discharge 31.6.2 Swales 3

1.7 Blockage / Surcharge 41.8 Water Quality 4

1.8.1 Restoration Phase 41.8.2 Restored Landform 4

1.9 Surface Water Management – Operation and Maintenance Regime 51.10Summary and Conclusions 6

2.0 CLOSURE 7 TABLES Table 001: Greenfield Runoff Rates Table 002: Summary of Surface Water Attenuation Requirements Table 003: Drainage Inspection and Maintenance Schedule DRAWINGS Updated Drg No H8109-001 Surface Water Drainage Summary APPENDICES Appendix I Workings

Updated National Coalboard Nomogram

Updated WinDes Calculations

Peak Runoff Calculations

Manning’s Discharge Calculations


1 Job No. H8109

1.0 INTRODUCTION

1.1 Background

1.1.1 A Flood Risk Assessment report was submitted in February 2017 in support of a planning application for the importation of suitable inert materials to create an ecologically rich and diverse range of habitats, incorporating species rich grassland (Lowland Meadow), the planting of scrub and species rich hedgerows and the creation of new wetland habitats (including purpose built wildlife ponds).

1.1.2 Further to review of this FRA Northamptonshire County Council in its capacity as the Lead Local Flood Authority, has requested that additional detail be supplied in respect of the proposed surface water management networks serving the proposed final landform, letter dated 23rd August 2017 (ref. 17/00040/WASFUL).

1.1.3 Following review of the NCC correspondence, and subsequent telephone conversation with Pankit Shah, please accept this this report as an addendum to the February 2017 FRA. The updated calculations and drainage layout supersede the information contained within Section 5.0 Surface Water of the FRA.

1.1.4 The NPPF and its PPG require that existing runoff rates must be maintained, taking account of climate change and that wherever possible a degree of betterment is provided. This assessment considers the potential impacts of development proposals on the rates and volumes of surface water runoff generated to ensure that no increase in flooding arises. The use of Sustainable Drainage Systems (SuDS) has been considered, wherever possible.

1.2 Land Use 1.2.1 The surface finishings currently comprise rough grassland which drains via overland flow to north west

and west, discharging into local watercourses via the drainage channel present on the western boundary. This will remain the case for the restored landform, with an increase in the gradient across central areas, and consequent elevation in the rate and volume of surface runoff generated.

1.3 SuDS Options for Surface Water Disposal

1.3.1 The application area is understood to be underlain by permeable soils including interbedded limestone and sandstone, the former associated with the Blisworth Formation and Wellingborough Member. It is likely that historic mineral workings have altered the subsurface geology at a local scale, with the limestone replaced with less permeable infill material.

1.3.2 The site currently drains via overland flow to the north west and west, discharging to local watercourses (to the south) via the drainage channel on the western boundary. It is proposed to continue to discharge runoff in this manner. This is in accordance with the SuDS hierarchy as outlined within Section 3.2.3 of the SuDS Manual, and summarised below:

SuDS Discharge Hierarchy: § Infiltration

§ Discharge to surface waters

§ Discharge to surface water sewer

§ Discharge to combined sewer (Last Resort).

1.3.1 Greenfield Runoff

1.3.3 Greenfield runoff rates have been estimated using the WinDes Micro drainage ICPSUDS function, with input data from the Flood Estimation Handbook CD ROM (V3). These are based on a linear interpolation from a 50ha catchment, in accordance with SUDS Manual guidance. Table 001 summarises the results of this analysis. Full copies of these calculations are appended.


2 Job No. H8109

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

QBAR 1.510

30 3.634

100 5.382

Table 001: Greenfield Runoff Rates

1.4 Climate Change

1.4.1 Climate change has been applied to the surface water storage calculations at 40%.

1.5 Attenuation and Controlled Discharge

1.5.1 The surface water storage calculations have been updated to include a total of 5 drainage catchments throughout the site, labelled A-E in the attached drawing (H8109-001 Surface Water Drainage Summary).

1.5.2 Runoff coefficients for the final landform have been derived using the National Coal Board Nomogram, a technique used for estimating runoff from spoil heaps and man-made landforms, taking account of the topographical relief (average gradient); changes to soil type (clay / loam assumed) and nature of surface finishing (rough grassland).

1.5.3 The WinDes Micro Drainage software package assumes all surfaces to be impermeable. The total catchment areas have therefore been multiplied by the established runoff coefficients to produce Effective Impermeable Areas for assessment.

1.5.4 The established catchments drain to 3 ponds, which have been considered separately within the WinDes Micro drainage calculations, as follows:

Pond 1: Drains Catchment A only.

Pond 2: Drains Catchments B, C & D – discharges from pond A also route via this pond at greenfield rates, although no further flood storage is required.

Pond 3: Drains Catchment E only.

1.5.1 Results

1.5.5 The WinDes Micro Drainage software suite has been re-run with the updated catchment and land use data, to estimate the surface water storage requirements for each of the catchments within the proposed development. Storm scenarios have been run for both winter and summer profiles, for a range of durations between 15-10,080 minutes, with existing Greenfield runoff rates as input. Climate change allowance has been applied at 40% for the restored landform, based on a 100 year lifetime. Copies of these calculations are appended and are summarised in Table 002 below.


3 Job No. H8109

* Includes discharge from catchments B,C & D. Catchment A will route discharges via a separate outfall at greenfield rates.

Table 002: Summary of Surface Water Attenuation Requirements

1.6 Drainage Layout

1.6.1 A maximum surface water attenuation requirement of up to 16,241m3 has been calculated, which will be provided within ponds 1, 2 and 3. In line with best practice the ponds include attenuation storage for return period events up to and including 100 years with climate change consideration at 40%.

1.6.2 An updated Surface Water Management Plan drawing (H8109-001: Surface Water Drainage Summary) is appended, which indicates the drainage layout and which includes upstream and downstream invert levels and cross sectional profiles through the drainage channels and Pond 2; the latter including details of the flow control structures.

1.6.3 All ponds include bank slopes at 1:3 and 300mm freeboard between the maximum water level and top of bank, to account for successive rainfall events, variations in flood flows / volumes and bank settlement.

1.6.1 Discharge Pond 1

1.6.4 Discharges from pond 1 are restricted to greenfield rates using an orifice plate fitted with flow control slots for the 2 year storm, while an overflow weir is proposed for discharges between 2 and 100 years.

Pond 2

1.6.5 Pond 2 is designed to discharge at greenfield rates via a Hydrobrake to the drainage channel present on the western boundary for events up to and including 2 years, with outflow via an overflow weir for events between 2 and 100 years.

1.6.6 A separate outfall will be input at the upper section of the pond which will discharge water at greenfield rates from pond 1, which routes through the upper section of pond 2, via an orifice plate and flow control slot (2 year flows) with overflow weir (2 year – 100 year flows).

Pond 3

1.6.7 Pond 3 is set to discharge via an orifice plate and overflow weir at greenfield rates via a minor channel and diffuse out of bank flow into the surrounding wet woodland, with a boundary channel proposed around the lower perimeter of the wet woodland area to pick up any residual flows and link them into the existing pond present on the eastern boundary.

1.6.2 Swales

1.6.8 Water will be conveyed to the storage areas via perimeter drainage swales. The cross-sectional profile of the swales is trapezoidal in nature, with banks set at 1:3. They have been designed to retain Q100 flows without surcharge, including climate change at 40%, based on rainfall data downloaded for the catchment from the FEH CD ROM, Depth Duration Frequency (DDF) modelling function, for a 60 minute

Pond 1 Pond 2 Pond 3

Return Period (Yrs.)

Greenfield Runoff Rate

(l/s) Max Volume

(m3) Greenfield

Runoff Rate (l/s)*

Max Volume (m3)

Greenfield Runoff Rate

(l/s)

Max Volume (m3)

QBAR 14.060 1548 34.345 3501 10.485 1137

30 33.838 2993 82.655 6985 25.233 2189

100+CC 50.114 3980 122.414 9356 37.370 2905


4 Job No. H8109

duration rainfall event.

1.6.9 The drainage channel between ponds 1 and 2 has been designed to accept peak runoff from Catchment B as well as greenfield discharges from Pond 1.

1.6.10 All drainage channels include a 300mm freeboard above the maximum modelled water levels to allow for successive rainfall events, variations in flood flows / volumes and bank settlement. The outer banks (off-site side) of the swales are elevated relative to the inboard banks, to form preferential flowpaths for floodwater into the centre of the site.

1.7 Blockage / Surcharge

1.7.1 The use of overflow weirs provides flow control measures which would restrict discharges back to greenfield rates in the event of a blockage or surcharge of the main outfall. Emergency flood storage would be provided by the freeboard within the ponds and by preferential flow paths to on-site overbank areas (drainage channels).

1.8 Water Quality 1.8.1 Restoration Phase

1.8.1 The restoration phase comprises an industrial use. It is therefore proposed to install substantive mitigation measures to remove potential contaminants, suspended sediments and to aid water quality polishing. These include:

§ Drainage sump, sized to accommodate a 2 year rainfall event and aid sedimentation;

§ All water to pass to the surface water storage area via a silt buster;

§ Reed bed area within / upstream of the main surface water storage areas (where possible) to aid water quality polishing;

§ Water to be appropriately aerated ahead of discharge;

§ All fuel / chemicals to be stored within double skinned tanks located within an impermeable bunded area, in accordance with EA regulations for the storage of fuel oils, to enable containment of accidental spillages;

§ Emergency spillage kits to be present within the site to enable clear up of accidental spills of stored fuel oils or chemicals;

§ All trafficked areas to be subject to one-way routing to reduce the potential for accidents leading to accidental spills;

§ Manual isolation of outfalls to watercourse using penstocks / pump switches to contain surface water in the event of contamination;

§ Regular hydrometric testing to ensure the quality of surface water discharges;

§ Background water quality data to be obtained for the ordinary watercourse adjacent to the southern boundary, with ongoing monitoring throughout quarry operations to ensure no detrimental impacts on water quality of receptors.

1.8.2 The inclusion of the above water quality treatment measures will ensure that only clean water is discharged.

1.8.2 Restored Landform

1.8.3 The restored landform will incorporate grassland with wetland and scrub habitats. Measures are included within the wetland habitat and linked swales to aid the settlement of silts and sediments, with no further potential contaminant sources present within the site and no further water quality mitigation


5 Job No. H8109

proposed.

1.8.4 It is recommended that all surface water attenuation facilities be de-silted once the restoration phase is complete, to ensure the continued efficiency of the surface water management system.

1.9 Surface Water Management – Operation and Maintenance Regime

1.9.1 The following programme of inspection and maintenance (Table 003) is proposed, to ensure the continued efficiency of the system over time. This will be executed by the applicant either themselves or using an appointed management company / drainage contractor in accordance with the schedule outlined below and following significant rainfall events and / or storm activity. A photographic record of inspections is recommended to pick up long term changes that may not be apparent within a single inspection. Inspections should comply with all relevant Health and Safety legislation.

1.9.2 This maintenance schedule applies for the lifetime of the development. Please also refer to the notes section beneath the table.

Table 003: Drainage Inspection and Maintenance Schedule

Notes

1.9.3 Where silt removal is proposed, this should be undertaken in an environmentally sensitive manner. For example, reeds should be removed and replaced to encourage rapid recovery of habitats which may have become reliant on the drainage feature.

1.9.4 All waste arisings should be collected by an approved contractor and should be subject to appropriate treatment and disposal.

Element Frequency Notes

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

Annually (Sept./Oct.)

§ Visual inspection for siltation and reduced efficiency / storage volume.

§ Where excessive siltation is seen, remedial works should be undertaken within 1 month.

§ Replanting of reeds where die off is seen, accumulated silt is removed.

§ Remove accumulated vegetation, weeds, debris etc. § Reed cutting to stimulate regrowth and prevent die back.

Drainage Channels

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

Annually

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

§ Mowing / cutting of vegetation to prevent eutrophication and debris build up.

Inlets / Outfalls

Twice annually and following significant storm events

§ Visual inspection for accumulated debris or blockage, at both upstream and downstream faces.

§ Check every orifice / inlet / outlet / structure for blockage or siltation, pour water into each to verify through flow.

§ Remove any debris and rod where required.

Vegetation Annually (October) § Regular grass cutting and maintenance of shrubs / trees will be key in reducing the presence of debris which could cause blockage of the drainage network. Grass should be cut annually, at the end of the growing season (March – October) and leaves and other debris cleared from soft landscaped areas.

§ Shrubs / trees should be pruned to reduce accumulated vegetation within the site / reservoirs.


6 Job No. H8109

1.10 Summary and Conclusions

1.10.1 The surface water attenuation requirements for the development have been assessed with a total surface water storage requirement of 16,241m3 proposed to ensure that existing surface water discharge rates are maintained. Climate change consideration at 40% has been accounted for within these calculations.

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

1.10.3 It is proposed to continue to discharge surface water runoff to the drainage channel on the western boundary, which in turn discharges to a larger watercourse present to the south. The western drainage channel is situated within land which is under the control of the applicant and currently accepts runoff from the site at greenfield rates.

1.10.4 A surface water management system is proposed at the site, which includes attenuation storage and controlled discharge at greenfield rates, to ensure no detrimental impacts to pluvial flooding arise throughout the development lifetime, as required by the National Planning Policy Framework.

1.10.5 All new outfalls for discharge(s) to watercourse will be subject to ratification by the EA via discharge consent and flood risk activities consent (or exemption).

1.10.6 The updated layout of the surface water management system(s) is detailed within Drawing H8109-001, which is appended to this addendum report.

1.10.7 A plan for the ongoing management and maintenance of the proposed drainage elements is outlined to ensure the continued efficiency of the proposed surface water management systems over time.


7 Job No. H8109

2.0 CLOSURE

2.1 This report has been prepared by Amber Planning Ltd with all reasonable skill, care and diligence, and taking account of the manpower and resources devoted to it by agreement with the client. Information reported herein is based on the interpretation of data collected and has been accepted in good faith as being accurate and valid.

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

2.3 This report is for the exclusive use of the client; no warranties or guarantees are expressed or should be inferred by any third parties. This report may not be relied upon by other parties without written consent from Amber Planning.

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

DRAWINGS

Section CA-CA' : Scale 1:200

max water

level 0.45m

Channel A

Off Site

Site

1

3

1

3

4.50m

0.75m

0.30m 0.40m

Section CB-CB' : Scale 1:200

Channel B

1

3

1

3

4.68m

max water

level 0.48m

Off SiteSite

0.78m

0.30m 0.40m

Section CC-CC' : Scale 1:200

Channel C

1

3

1

3

3.48m

Off SiteSite

0.58m

max water

level 0.28m

0.40m0.30m

Section CD-CD' : Scale 1:200

Channel D

1

3

1

3

4.20m

0.70m

max water

level 0.40m

Off Site

Site

0.40m0.30m

Section CE-CE' : Scale 1:200

Channel E

1

3

1

3

4.86m

0.81m

max water

level 0.51m

Off SiteSite

0.40m0.30m

Lowland Meadow

A

B

C D

E

Pond 1

Pond 3

Orifice plate

Orifice plate

Orifice plate

Overflow Weir

Overflow Weir

Overflow Weir

C

h

a

n

n

e

l

B

Channel D

Channel E

Pond 2 Section

Sec CA

5

0

5

2

54

56

54

5

8

6

0

6

2

6

4

66

5

4

56

58

7

0

6

8

72

7

4

6

4

6

8

7

0

76

7

2

7

4

7

6

Gate

Existing

gate

33kV underground

power cable

Access &

easement

area

Existing pond

retained

70

6

8

7

2

7

4

7

5

7

4

6

0

6

2 6

4

6

6

74

7

0

5

4

7

4

Sec P2-P2': Scale 1:500

0.00

54.00

Level

Chainage

Datum

50.00mAOD

5.79

54.00

14.02

56.00

Orifice Plate

IL 54.0mAOD

29.63

56.00

34.34

54.89

38.13

54.00

75.44

54.00

84.61

56.00

101.94

58.31

1

4

Off Site

Site

Overflow Weir

IL 54.892mAOD

max water level

Existing

Watercourse

1

4

Headwall & Hydrobrake

IL 54.00mAOD

5

6

Pond 1:

Depth 2m

Top of Bank – 63m AOD

Base – 61m AOD

Freeboard: 300mm

Side Slope: 1:4

Inlet: 63m AOD (Invert level)

Outfall: 61m AOD (invert level of orifice)

Outfall: 61.818m AOD (overflow weir)

Top of bank area = 3,600m²

Basal area = 1,456m²

Pond 2:

Depth 2m

Top of Bank – 56m AOD

Base – 54m AOD

Freeboard: 300mm

Side Slope: 1:4

Inlet: 56m AOD



Upper Outfall: 54m AOD Invert level (orifice)

Upper Outfall: 54.818m AOD (invert level at

overflow weir)



Pond 3:

Depth 1.9m

Top of Bank 66.9m AOD

Base – 65m AOD

Freeboard: 300mm

Side Slope: 1:4

Inlet:66.9m AOD





Channel A

Sec CA'

C

h

a

n

n

e

l

C

Sec CC'

Sec CC

Pond 2

Sec P2

Sec CA'

Sec CA

Sec CA'

Sec CA

Sec P2'

68

5

8

6

8

5

6

Sec CB'

Sec CB

160m 80m 0 160m

SCALE: 20mm = 80m (1:4,000 @ A3)

© Crown Copyright 2017. All rights reserved. Licence number 100048891

Restoration contours70

Existing contours

60

New wetland area

(attenuation ponds)

Scrub habitat areas

Surface water drainage

channel with flow direction

New fencing (with gate)

Existing retained hedgerows

Tussocky grassland

Trees

New hibernacula

New hedgerows with trees

Lowland meadow

Ephemeral wetland areas

(attenuation ponds)

Application boundary

PROJECT

DRAWING TITLE

CLIENT

SCALE PROJECT NO.

DATE DRAWING NO.

DRAWN CHECKED

Land off Gipsy Lane

Surface Water Drainage Summary

Mick George Ltd

1:4,000 @ A3

December 2017

KR

H8109

H8109-001

KS

www.amberplanning.co.uk

Tel. 07930 877447

KEY

Surface water

catchment area

B

Surface water catchment area

reference

AutoCAD SHX Text

Station

AutoCAD SHX Text

Pumping

AutoCAD SHX Text

GIPSY LANE

AutoCAD SHX Text

89

AutoCAD SHX Text

87a

AutoCAD SHX Text

Car

AutoCAD SHX Text

Park

AutoCAD SHX Text

B 570

AutoCAD SHX Text

Drain

AutoCAD SHX Text

Travellers Site

AutoCAD SHX Text

Animals In Need

AutoCAD SHX Text

(Animal Welfare Centre)

AutoCAD SHX Text

MP

AutoCAD SHX Text

GIPSY LANE

AutoCAD SHX Text

GP

AutoCAD SHX Text

A 509

AutoCAD SHX Text

B 570

AutoCAD SHX Text

El Sub Sta

AutoCAD SHX Text

Def

AutoCAD SHX Text

Pond

AutoCAD SHX Text

Issues

AutoCAD SHX Text

N

APPENDIXI-WORKINGS

ReturnPeriod(Yrs.) RunoffRate(l/s/ha)QBAR 1.51030 3.634100 5.382

CatchmentA EIA ActualArea(ha) QBAR 30 10052144 93115 14.060 33.838 50.114

ClimateChange 1.4 AverageSlope 0.030ReturnPeriod Time(s) Rainfall(mm) Volume(l) Runoffrate(l/s) Flow(m3/s)30(60min) 3600 33.12 2417832 672 0.672100(60min) 3600 48.48 3539145 983 0.983

CatchmentB EIA ActualArea(ha) QBAR 30 10045392 82530 12.462 29.991 44.418


CatchmentC EIA ActualArea(m2) QBAR 30 10039732 72240 10.908 26.252 38.880


CatchmentD EIA ActualArea(m2) QBAR 30 10039974 72680 10.975 26.412 39.116


CatchmentE EIA ActualArea(m2) QBAR 30 10038189 69435 10.485 25.233 37.370


CatchmentsB,C,D EIA ActualArea(m2) QBAR 30 100125098 227450 34.345 82.655 122.414

EIA

Only1/3catchmentdrainsviadrainagechannel-theremainderdischargesintothepondviaoverlandflow.CATCHMENTBIncludescapacitytodrainPondAatGreenfieldRates

PEAKRUNOFFCALCULATIONS

RunoffRatel/s

EffectiveImpermeableAreaGLOSSARY

NOTESCATCHMENTC

GreenfieldRunoffRates

RunoffRatel/s

RunoffRatel/s

RunoffRatel/s

RunoffRatel/s

RunoffRatel/s

Flow (Q) m3/s 1.015Manning's Value (n) 0.03Area (A) 0.61Hydraulic Radius - R 0.21Perimeter (P) 2.85Slope (S) 0.020





Catchment E Bankfull 0.51m: Width 3.06m: Bank Slope 1:3

Manning's Normal Depth EquationCatchment A: Bankfull 0.45m: Width 2.70m: Bank Slope 1:3

Catchment B Bankfull 0.48m: Width 2.88m: Bank Slope 1:3

Catchment C Bankfull 0.28m: Width 1.68m: Bank Slope 1:3

Catchment D Bankfull 0.40m: Width 2.40m: Bank Slope 1:3

Only 1/3 catchment drains via drainage channel - the remainder discharges into the pond via overland flow.

NOTESCATCHMENT BDrainage channel includes discharge capacity for Pond A at Greenfield RatesCATCHMENT C

Amber Planning Flood Risk & Hydrology Page 146 Ash Lane

WellsSomerset BA5 2LSDate 07/12/2016 18:34 Designed by kirsten.d...

File Checked byMicro Drainage Source Control W.12.6

ICP SUDS Mean Annual Flood

©1982-2011 Micro Drainage Ltd

Input

Return Period (years) 100 Soil 0.300Area (ha) 50.000 Urban 0.001SAAR (mm) 596 Region Number Region 5

Results l/s

QBAR Rural 75.5QBAR Urban 75.7

Q100 years 269.1

Q1 year 65.8Q30 years 181.7

Q100 years 269.1

Amber Planning Flood Risk & Hydrology Page 146 Ash Lane H8109

Wells Irchester QuarrySomerset BA5 2LS Catchment ADate October 2017 Designed by K de Savary

File 171030-H8109-Cat... Checked byMicro Drainage Source Control W.12.6

Summary of Results for 2 year Return Period (+40%)


StormEvent

MaxLevel(m)

MaxDepth(m)

MaxControl(l/s)

MaxOverflow(l/s)

MaxΣ Outflow(l/s)

MaxVolume(m³)

Status

15 min Summer 0.327 0.327 8.4 0.0 8.4 533.0 O K30 min Summer 0.391 0.391 9.3 0.0 9.3 651.0 O K60 min Summer 0.464 0.464 10.2 0.0 10.2 791.0 O K

120 min Summer 0.545 0.545 11.2 0.0 11.2 951.7 O K180 min Summer 0.593 0.593 11.7 0.0 11.7 1052.4 O K240 min Summer 0.627 0.627 12.1 0.0 12.1 1124.4 O K360 min Summer 0.673 0.673 12.5 0.0 12.5 1222.1 O K480 min Summer 0.701 0.701 12.8 0.0 12.8 1284.2 O K600 min Summer 0.719 0.719 13.0 0.0 13.0 1324.9 O K720 min Summer 0.731 0.731 13.1 0.0 13.1 1351.1 O K960 min Summer 0.734 0.734 13.1 0.0 13.1 1357.4 O K

1440 min Summer 0.733 0.733 13.1 0.0 13.1 1355.3 O K2160 min Summer 0.721 0.721 13.0 0.0 13.0 1328.5 O K2880 min Summer 0.702 0.702 12.8 0.0 12.8 1286.9 O K4320 min Summer 0.661 0.661 12.4 0.0 12.4 1195.8 O K5760 min Summer 0.618 0.618 12.0 0.0 12.0 1105.3 O K7200 min Summer 0.579 0.579 11.6 0.0 11.6 1022.3 O K8640 min Summer 0.543 0.543 11.2 0.0 11.2 947.7 O K

10080 min Summer 0.509 0.509 10.8 0.0 10.8 880.7 O K15 min Winter 0.362 0.362 8.9 0.0 8.9 597.5 O K30 min Winter 0.433 0.433 9.9 0.0 9.9 730.2 O K60 min Winter 0.513 0.513 10.8 0.0 10.8 887.9 O K

120 min Winter 0.602 0.602 11.8 0.0 11.8 1069.8 O K

StormEvent

Rain(mm/hr)

OverflowVolume(m³)

Time-Peak(mins)

15 min Summer 55.501 0.0 3430 min Summer 34.070 0.0 4860 min Summer 20.914 0.0 78

120 min Summer 12.838 0.0 136180 min Summer 9.650 0.0 194240 min Summer 7.881 0.0 252360 min Summer 5.924 0.0 368480 min Summer 4.838 0.0 486600 min Summer 4.134 0.0 602720 min Summer 3.636 0.0 714960 min Summer 2.912 0.0 816

1440 min Summer 2.129 0.0 10642160 min Summer 1.557 0.0 14722880 min Summer 1.247 0.0 18844320 min Summer 0.914 0.0 26965760 min Summer 0.734 0.0 35127200 min Summer 0.619 0.0 42648640 min Summer 0.538 0.0 5032

10080 min Summer 0.478 0.0 584015 min Winter 55.501 0.0 3430 min Winter 34.070 0.0 4860 min Winter 20.914 0.0 76

120 min Winter 12.838 0.0 134






StormEvent

MaxLevel(m)

MaxDepth(m)

MaxControl(l/s)

MaxOverflow(l/s)

MaxΣ Outflow(l/s)

MaxVolume(m³)

Status

180 min Winter 0.656 0.656 12.4 0.0 12.4 1184.7 O K240 min Winter 0.694 0.694 12.7 0.0 12.7 1267.6 O K360 min Winter 0.745 0.745 13.2 0.0 13.2 1381.9 O K480 min Winter 0.778 0.778 13.5 0.0 13.5 1456.4 O K600 min Winter 0.800 0.800 13.7 0.0 13.7 1507.3 O K720 min Winter 0.815 0.815 13.9 0.0 13.9 1542.5 O K960 min Winter 0.817 0.817 13.9 0.0 13.9 1548.0 O K


10080 min Winter 0.483 0.483 10.5 0.0 10.5 828.2 O K

StormEvent

Rain(mm/hr)

OverflowVolume(m³)

Time-Peak(mins)

180 min Winter 9.650 0.0 190240 min Winter 7.881 0.0 248360 min Winter 5.924 0.0 362480 min Winter 4.838 0.0 476600 min Winter 4.134 0.0 588720 min Winter 3.636 0.0 698960 min Winter 2.912 0.0 906


10080 min Winter 0.478 0.0 6064




Rainfall Details


Rainfall Model FEH D3 (1km) 0.253 Cv (Winter) 0.840Return Period (years) 2 E (1km) 0.313 Shortest Storm (mins) 15

Site Location F (1km) 2.487 Longest Storm (mins) 10080C (1km) -0.026 Summer Storms Yes Climate Change % +40

D1 (1km) 0.314 Winter Storms YesD2 (1km) 0.246 Cv (Summer) 0.750

Time / Area Diagram

Total Area (ha) 5.214

Time(mins)

Area(ha)

Time(mins)

Area(ha)

Time(mins)

Area(ha)

Time(mins)

Area(ha)

Time(mins)

Area(ha)

0-4 1.043 4-8 1.043 8-12 1.043 12-16 1.043 16-20 1.042




Model Details


Storage is Online Cover Level (m) 2.000

Tank or Pond Structure

Invert Level (m) 0.000

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

0.000 1456.0 2.000 3600.0

Orifice Outflow Control

Diameter (m) 0.087 Discharge Coefficient 0.600 Invert Level (m) 0.000

Weir Overflow Control

Discharge Coef 0.544 Width (m) 0.021 Invert Level (m) 0.818






StormEvent

MaxLevel(m)

MaxDepth(m)

MaxControl(l/s)

MaxOverflow(l/s)

MaxΣ Outflow(l/s)

MaxVolume(m³)

Status





120 min Winter 1.152 1.152 16.6 6.9 23.6 2389.0 O K

StormEvent

Rain(mm/hr)

OverflowVolume(m³)

Time-Peak(mins)





120 min Winter 28.397 135.9 134






StormEvent

MaxLevel(m)

MaxDepth(m)

MaxControl(l/s)

MaxOverflow(l/s)

MaxΣ Outflow(l/s)

MaxVolume(m³)

Status



10080 min Winter 0.880 0.880 14.5 0.6 15.0 1696.4 O K

StormEvent

Rain(mm/hr)

OverflowVolume(m³)

Time-Peak(mins)



10080 min Winter 0.776 28.9 6272




Rainfall Details





Time / Area Diagram


Time(mins)

Area(ha)

Time(mins)

Area(ha)

Time(mins)

Area(ha)

Time(mins)

Area(ha)

Time(mins)

Area(ha)

0-4 1.043 4-8 1.043 8-12 1.043 12-16 1.043 16-20 1.042




Model Details






0.000 1456.0 2.000 3600.0










StormEvent

MaxLevel(m)

MaxDepth(m)

MaxControl(l/s)

MaxOverflow(l/s)

MaxΣ Outflow(l/s)

MaxVolume(m³)

Status





120 min Winter 1.506 1.506 19.1 20.4 39.5 3407.0 O K

StormEvent

Rain(mm/hr)

OverflowVolume(m³)

Time-Peak(mins)





120 min Winter 40.647 603.1 132






StormEvent

MaxLevel(m)

MaxDepth(m)

MaxControl(l/s)

MaxOverflow(l/s)

MaxΣ Outflow(l/s)

MaxVolume(m³)

Status



10080 min Winter 1.064 1.064 16.0 4.4 20.3 2154.8 O K

StormEvent

Rain(mm/hr)

OverflowVolume(m³)

Time-Peak(mins)



10080 min Winter 0.965 434.3 6160




Rainfall Details





Time / Area Diagram


Time(mins)

Area(ha)

Time(mins)

Area(ha)

Time(mins)

Area(ha)

Time(mins)

Area(ha)

Time(mins)

Area(ha)

0-4 1.043 4-8 1.043 8-12 1.043 12-16 1.043 16-20 1.042




Model Details






0.000 1456.0 2.000 3600.0






Wells Irchester QuarrySomerset BA5 2LS Catchment B,C,D Hyrdo...Date October 2017 Designed by K de Savary




StormEvent

MaxLevel(m)

MaxDepth(m)

MaxControl(l/s)

MaxOverflow(l/s)

MaxΣ Outflow(l/s)

MaxVolume(m³)

Status





120 min Winter 0.711 0.711 34.0 0.0 34.0 2515.3 O K

StormEvent

Rain(mm/hr)

OverflowVolume(m³)

Time-Peak(mins)





120 min Winter 12.838 0.0 132






StormEvent

MaxLevel(m)

MaxDepth(m)

MaxControl(l/s)

MaxOverflow(l/s)

MaxΣ Outflow(l/s)

MaxVolume(m³)

Status



10080 min Winter 0.336 0.336 31.2 0.0 31.2 915.2 O K

StormEvent

Rain(mm/hr)

OverflowVolume(m³)

Time-Peak(mins)



10080 min Winter 0.478 0.0 5640




Rainfall Details





Time / Area Diagram


Time(mins)

Area(ha)

Time(mins)

Area(ha)

Time(mins)

Area(ha)

Time(mins)

Area(ha)

Time(mins)

Area(ha)

0-4 2.502 4-8 2.502 8-12 2.502 12-16 2.502 16-20 2.502




Model Details






0.000 2000.0 2.000 10670.0

Hydro-Brake® Outflow Control

Design Head (m) 0.891 Hydro-Brake® Type Md5 SW Only Invert Level (m) 0.000Design Flow (l/s) 34.3 Diameter (mm) 236

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

0.100 8.5 1.200 37.4 3.000 58.1 7.000 88.70.200 20.8 1.400 39.9 3.500 62.7 7.500 91.80.300 29.6 1.600 42.5 4.000 67.0 8.000 94.80.400 33.1 1.800 45.0 4.500 71.1 8.500 97.70.500 34.0 2.000 47.4 5.000 75.0 9.000 100.60.600 33.7 2.200 49.7 5.500 78.6 9.500 103.30.800 33.7 2.400 51.9 6.000 82.11.000 35.1 2.600 54.1 6.500 85.5








StormEvent

MaxLevel(m)

MaxDepth(m)

MaxControl(l/s)

MaxOverflow(l/s)

MaxΣ Outflow(l/s)

MaxVolume(m³)

Status





120 min Winter 1.224 1.224 37.7 22.1 59.8 5692.4 O K

StormEvent

Rain(mm/hr)

OverflowVolume(m³)

Time-Peak(mins)





120 min Winter 28.397 460.7 134






StormEvent

MaxLevel(m)

MaxDepth(m)

MaxControl(l/s)

MaxOverflow(l/s)

MaxΣ Outflow(l/s)

MaxVolume(m³)

Status



10080 min Winter 0.810 0.810 34.0 0.0 34.0 3040.7 O K

StormEvent

Rain(mm/hr)

OverflowVolume(m³)

Time-Peak(mins)



10080 min Winter 0.776 0.0 6376




Rainfall Details





Time / Area Diagram


Time(mins)

Area(ha)

Time(mins)

Area(ha)

Time(mins)

Area(ha)

Time(mins)

Area(ha)

Time(mins)

Area(ha)

0-4 2.502 4-8 2.502 8-12 2.502 12-16 2.502 16-20 2.502




Model Details






0.000 2000.0 2.000 10670.0




0.100 8.5 1.200 37.4 3.000 58.1 7.000 88.70.200 20.8 1.400 39.9 3.500 62.7 7.500 91.80.300 29.6 1.600 42.5 4.000 67.0 8.000 94.80.400 33.1 1.800 45.0 4.500 71.1 8.500 97.70.500 34.0 2.000 47.4 5.000 75.0 9.000 100.60.600 33.7 2.200 49.7 5.500 78.6 9.500 103.30.800 33.7 2.400 51.9 6.000 82.11.000 35.1 2.600 54.1 6.500 85.5








StormEvent

MaxLevel(m)

MaxDepth(m)

MaxControl(l/s)

MaxOverflow(l/s)

MaxΣ Outflow(l/s)

MaxVolume(m³)

Status





120 min Winter 1.529 1.529 41.6 58.9 100.5 8128.7 O K

StormEvent

Rain(mm/hr)

OverflowVolume(m³)

Time-Peak(mins)





120 min Winter 40.647 1778.0 132






StormEvent

MaxLevel(m)

MaxDepth(m)

MaxControl(l/s)

MaxOverflow(l/s)

MaxΣ Outflow(l/s)

MaxVolume(m³)

Status



10080 min Winter 1.060 1.060 35.7 8.0 43.7 4558.5 O K

StormEvent

Rain(mm/hr)

OverflowVolume(m³)

Time-Peak(mins)



10080 min Winter 0.965 674.3 6360




Rainfall Details





Time / Area Diagram


Time(mins)

Area(ha)

Time(mins)

Area(ha)

Time(mins)

Area(ha)

Time(mins)

Area(ha)

Time(mins)

Area(ha)

0-4 2.502 4-8 2.502 8-12 2.502 12-16 2.502 16-20 2.502

Amber Planning Flood Risk & Hydrology 6 Ash Lane H8109



Model Details






0.000 2000.0 2.000 10670.0




0.100 8.5 1.200 37.4 3.000 58.1 7.000 88.70.200 20.8 1.400 39.9 3.500 62.7 7.500 91.80.300 29.6 1.600 42.5 4.000 67.0 8.000 94.80.400 33.1 1.800 45.0 4.500 71.1 8.500 97.70.500 34.0 2.000 47.4 5.000 75.0 9.000 100.60.600 33.7 2.200 49.7 5.500 78.6 9.500 103.30.800 33.7 2.400 51.9 6.000 82.11.000 35.1 2.600 54.1 6.500 85.5




Wells Irchester QuarrySomerset BA5 2LS Catchment EDate October 2017 Designed by K de Savary




StormEvent

MaxLevel(m)

MaxDepth(m)

MaxControl(l/s)

MaxOverflow(l/s)

MaxΣ Outflow(l/s)

MaxVolume(m³)

Status





120 min Winter 0.520 0.520 8.6 0.0 8.6 784.4 O K

StormEvent

Rain(mm/hr)

OverflowVolume(m³)

Time-Peak(mins)





120 min Winter 12.838 0.0 134






StormEvent

MaxLevel(m)

MaxDepth(m)

MaxControl(l/s)

MaxOverflow(l/s)

MaxΣ Outflow(l/s)

MaxVolume(m³)

Status



10080 min Winter 0.422 0.422 7.7 0.0 7.7 622.9 O K

StormEvent

Rain(mm/hr)

OverflowVolume(m³)

Time-Peak(mins)



10080 min Winter 0.478 0.0 6064




Rainfall Details





Time / Area Diagram


Time(mins)

Area(ha)

Time(mins)

Area(ha)

Time(mins)

Area(ha)

Time(mins)

Area(ha)

Time(mins)

Area(ha)

0-4 0.764 4-8 0.764 8-12 0.763 12-16 0.764 16-20 0.764




Model Details






0.000 1345.0 1.900 2528.0










StormEvent

MaxLevel(m)

MaxDepth(m)

MaxControl(l/s)

MaxOverflow(l/s)

MaxΣ Outflow(l/s)

MaxVolume(m³)

Status





120 min Winter 1.047 1.047 12.4 5.0 17.4 1749.9 O K

StormEvent

Rain(mm/hr)

OverflowVolume(m³)

Time-Peak(mins)





120 min Winter 28.397 96.0 134






StormEvent

MaxLevel(m)

MaxDepth(m)

MaxControl(l/s)

MaxOverflow(l/s)

MaxΣ Outflow(l/s)

MaxVolume(m³)

Status



10080 min Winter 0.786 0.786 10.7 0.4 11.1 1249.5 O K

StormEvent

Rain(mm/hr)

OverflowVolume(m³)

Time-Peak(mins)



10080 min Winter 0.776 21.7 6264




Rainfall Details





Time / Area Diagram


Time(mins)

Area(ha)

Time(mins)

Area(ha)

Time(mins)

Area(ha)

Time(mins)

Area(ha)

Time(mins)

Area(ha)

0-4 0.764 4-8 0.764 8-12 0.763 12-16 0.764 16-20 0.764




Model Details






0.000 1345.0 1.900 2528.0










StormEvent

MaxLevel(m)

MaxDepth(m)

MaxControl(l/s)

MaxOverflow(l/s)

MaxΣ Outflow(l/s)

MaxVolume(m³)

Status





120 min Winter 1.400 1.400 14.4 15.1 29.6 2494.3 O K

StormEvent

Rain(mm/hr)

OverflowVolume(m³)

Time-Peak(mins)





120 min Winter 40.647 433.6 132






StormEvent

MaxLevel(m)

MaxDepth(m)

MaxControl(l/s)

MaxOverflow(l/s)

MaxΣ Outflow(l/s)

MaxVolume(m³)

Status



10080 min Winter 0.961 0.961 11.9 3.1 15.0 1579.6 O K

StormEvent

Rain(mm/hr)

OverflowVolume(m³)

Time-Peak(mins)



10080 min Winter 0.965 309.4 6152




Rainfall Details





Time / Area Diagram


Time(mins)

Area(ha)

Time(mins)

Area(ha)

Time(mins)

Area(ha)

Time(mins)

Area(ha)

Time(mins)

Area(ha)

0-4 0.764 4-8 0.764 8-12 0.763 12-16 0.764 16-20 0.764




Model Details






0.000 1345.0 1.900 2528.0





addendum to flood risk assessment november 2017 land … · 1.5.1 the surface water storage...

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