DrainageStrategy

LandtotheRearof84WestonRoadAndChellastonLane

AstononTrent

SunriseHomes(Derbyshire)Ltd

ReportPreparedbyMJonesMRICS

Introduction:This report aims to identifypotential strategies fordealingwith the foul and surface

waterfromtheproposeddevelopmentonthesitetotherearof84WestonRoad.

Theareaconsideredinthisstrategyisedgedredandhatchedontheattachedplan.The

Areaedgedblueontheplanisdealtwithusingasoakawayschemeasdetailedinthe

releaseofconditionsforplanningapplication9/2015/0264.

FloodRisk:ThesiteliesinanareawhichhasbeendesignatedasaZone1floodriskfromriversand

thesea.Thismeansthatitisatverylowriskoffloodingandeachyearthisareahasa

chanceoffloodingoflessthan0.1%.

Fig1:FloodMap(EnvironmentAgency)

AccordingtotheEnvironmentagencytheareaisnotaffectedbysurfacewaterflooding.

Themappingfortheareaindicatesthatthereissomelocalizedsurfacewaterflooding

nearby,howeverthisismainlycontainedtothelargefieldadjacenttoWestonRoadand

Valerieroad.Analysisoftheflowdataanddirectionsindicatesthattheproposedsiteis

notthesourceofthesurfacewater.

Fig2:SurfacewaterfloodriskandFlow

Hydrogeology:With reference toEnvironmentAgencydata, the superficial hydrogeologyunderlying

the Site is classified as a Secondary (Undifferentiated) Aquifer (deposits with

variable/limited permeability) and the bedrock hydrogeology is classified as a

Secondary(B)Aquifer(formationswithlimitedpermeability).

The overlying soils are not given a separate soil vulnerability classification, however

theywouldgenerallyberegardedashavingalowpermeability.

According to information provided by the Environment Agency the Site does not lie

withinagroundwaterSourceProtectionZone(SPZ).Therearenoabstractionlicences

locatedwithin1000m.

Thenearestwaterfeature(afielddrain)islocated192msouth.

Nodesignatedeco-receptorswereidentifiedwithina1000mradiusoftheSite.

Surfacewaterrunoffcalculation:Withreference toHRWallingfordwebsiteanddatasuppliedbyFEHwebsite for the

sitealongsidesiteobservationswehavecompiledsurfacewaterrunoffcalculationsand

theyareattachedtothisdocument.

UsingMappingdatafromtheUKSUDSsitethe1:100yeargreenfieldrunoffis2.08l/sec.

WhenusingaHOSTmethodofcalculationwithrespecttothepredominantsoiltypeon

site this changes and the 1:100 figure to 0.61l/sec. Arguably both of these are low

values.

RainfallCalculation:ImpermeableRoofAreas 585m2

DesignStorm-10years:

SpecifiedReturnPeriod- 10Years

Duration Alldurations

M5–60Rainfall 20mm

RainfallRatio 0.40

M10-60=24.8mm

DesignStorm-30Years:

SpecifiedReturnPeriod 30Years

Duration AllMins

M5–60rainfall 20mm

RainfallRatio 0.4

M30–120Rainfall=30.9mm

DesignStorm–100YearsSpecifiedReturnPeriod 100years

SpecifiedDuration 360mins

M5–60Rainfall 20mm

RainfallRatio 0.4

M100-360Rainfall 51.9mm

BGSGeoreport:I have attached a copy of the BGS SUDS infiltration report for the plot. The report

detailsanyconstraintstogroundwaterinfiltration,whichcanbefoundonthesite.

The reportdoes identify constraints togroundwater infiltration,however it indicates

thatthesoiltypeintheareaispermeableenoughtopermitsomemoderateinfiltration

withaspatiallyvariableporosity.

The report does not indicate any ground stability issues in relation to infiltration on

site.

ItIdentifiesanareaofminingtothenorthofthesite,whereinfiltrationcouldhavean

effect,thisishoweveratahigherlevelthanthesiteandassuchanyinfiltrationonsite

willhavenoeffectonthatground.

Runningsandisidentifiedasapossibility,siteinvestigationhasindicatedthatthereis

noevidenceofthisonsite.

The main constrain identified is a high and variable ground water table. Site

investigationoverthepast9monthshasindicatedthatthisisaround2.0-2.1macross

thesite.

Whilethisisahightable,itdoesnotprecludetheuseofspeciallydesignedsoakaways

wherethebottomofthesystemcanbemaintainedaminimumof1.0mabovethewater

table,asdetailedinthesectionsbelow.

MainsFoulDrainage:It is proposed that the foul drainage be piped by gravity and connected to themain

225mmfoulSewerinWestonRoad.ThisDrainhasaninvertofapproximately1.2mand

due to the slightly sloping nature of the site has sufficient depth to receive the flow

fromthesite.

Theareaedgedbluehasalreadyreceivedapproval fromSevernTrent foran indirect

connectiontoanexistingmanholeattheSouthEastentrancetothesite.Anadditional

connectionwillberequiredfortheproposeddevelopment.

It isproposedthatshouldplanningbegrantedanew150mmPVCufouldrainberun

fromthehatchedareatoanewmanholeatthesoutheastentrancetothesite.Thiswill

have sufficient capacity to serve both the existing granted development and the

proposednewdevelopment.

According toApproveddocumentH thiswouldequate toa total flowofbetween4.1

and4.6l/sfortheentiresite.Thiswouldalsoallowsurpluscapacitywithinthepipefor

potentialattenuatedsurfacewaterdischargeorfuturecapacityrequirement,ifneeded.

APlanoftheSevernTrentassetsintheareaisattached.

DrainageStrategiesforSurfacewater:Strategy1:SurfaceWaterDrainage:Ground investigations made during the course of the construction of the existing

permissionhaveindicatedthatthegroundwouldbesuitablefordisposalofthesurface

waterbyinfiltrationusingsoakawaycratesystems.

Thegroundconditionsareamixofastones,sand,withlightclayandsilt,andwhilenot

themosteffectiveintermsofpermeabilitytheabsenceofgroundwaterinthefirst2m

ofthetrialholesindicatethatinfiltrationdrainagemaybepossible.

WehaveattachedanemailfromJHallofSDDCLABCconfirmingthegroundconditions

observedonsite.

Wehavecarriedoutinfiltrationtestingonthesoilatseverallocationsonsiteandthe

infiltrationrateisoftheorderof4.4x10-6m/s

RoofAreas:

Attached isaplanof theproposeddrainagescheme.Wehave includeda largetrench

type soakawayunder the green areas andparking areaon thenorth sideof the site.

Thiswilldealwithpotentialrunofffromthefrontroofareas.Basedontheareatobe

drained a soakaway crate system such asWavinAquacellwouldbe suitable, stacked

crateswrappedingeotextilewouldprovideadequatedrainagetothefrontroofareas

and incorporating silt traps on inlet pipework would prevent future silting of the

soakawayvoids.Tomaintainaminimumof1mbetweenthebottomofthesystemand

thevisablewatertable,thebottomofthesoakawayshouldbeat1.0–1.1m,thiswould

give adequatedepth toprovide space for a single layerofAquacell Prime crates and

providesufficientcoveroverthesystemwhereitslocatedbeneathparkingareas.

Therearroofareaswillbedealtwithusingfurthercratesoakawaysystemsintherear

gardens of the properties. Paying attention to distances from boundaries and any

buildings.Eitheratrenchsoakawaydesignorindividualsoakawayswilldealwithrun

offfromtherearroofs,againviasilttraps.HoweverintheseareasAquacellEcocanbe

usedandcoveredwithaminimumof0.3m.Thiswouldenable2unitstobestackedand

stillmaintain1.0mtothewatertable,thissoakawaysystemcouldeithertaketheform

ofindividualunitsorabecombinedintoonesystem,theindicativedesignattachedis

foratrenchsystem.

Theindicatedareasontheplanare2mwidesohavedoublethewidthrequiredinthe

calculationsbelow,indicatingthatmorethansufficientcapacityisavailable.

The volumes required will be confirmed with LABC prior to installation. However

initialcalculationsusingtheHRWallingfordsoakawayvolumespreadsheetsandusing

guidance on recommended return periods fromCIRIA 156 of 10 years, indicates the

following:

FrontRoofAreas:Inputdata:

Roofareatotalapprox 300m2

Infiltrationrate 0.0000044

Width 1.0m

Length 32m

VoidRatio 0.95

ReturnPeriod 10Years

SafetyFactor 1.5

Intensityfactorforclimatechange 1.2(20%)

Designsoakawayheight–0.37m(<1cratedepth@0.40m)

RearRoofAreas:Inputdata:

Roofareatotalapprox 300m2

Infiltrationrate 0.0000044

Width 1.0m

Length 17m

VoidRatio 0.95

ReturnPeriod 10Years

SafetyFactor 1.5

Intensityfactorforclimatechange 1.2(20%)

Designsoakawayheight–0.75.m(<0.8mofferedby2cratesstacked)

Thesedesignsfallwellwithinthesiteconstraintswehaveidentifiedintermsofspace

andpermeability, there is scope forextendingboth frontandrearsoakawaysystems

furthershouldadditionalvolumebeshowntoberequired.Weranthesimulationsfora

50 year return period. This increase the required length of the soakaways to be

increased to 45m and 22.5m for front and rear areas respectively, again achievable

withintheconstraintsofthesite.

Driveways:We propose that the individual driveways and parking areas be dealt with using a

permeablepaving laidoverabase courseofpermeable type3 roadstone (MOT).For

exampleBrettAquafloworBradstoneIn-filta.

Anyadditionalrunoffwillbedrainedintoadjacentgrassedareas.

Anapproximatecalculationperparkingbay:5.0mx2.4m=12.5m2

Basedona30yearrainfallacapacityof0.38m3(0.0304m3perm2ofdriveway)per

parkingbaywouldbe sufficient,Thiswould easilybe accommodatedby theuseof a

250mmtype3subbasetoeachbay,whichwouldprovide0.9m3ofuseableinfiltration

voidperparkingbay.Intheoryprovidingenoughvoidfor100year(+20%forclimate

change)eventalso.

Gardenareasandgreenspaces:

Garden areas and green spaces will be grassed and will have similar drainage

characteristicstotheexistingfield.Thesewillbeallowedtodrainnaturally,noexcess

runoffisanticipated.Pavedpatioareaswilldraintotheadjacentlawnedareas,again

noextradrainagewillberequired.

SharedDrivewaySpace:

The shared driveways will be paved in a permeable asphalt such as Aggregate

Industries“drainasphalt”.Thiswillbelaidovera250mmpermeablesubbaseoftype3

roadstone(MOT).Effectivelyprovidingalargeselfdrainingarea,removingtheneedfor

additionalinfiltrationcapacity.

AswiththeDrivewaysthecapacityprovidedbyusingafreedrainingmaterialasasub

basewillbeadequatefora30and100yearrainfallevent

Any occasional additional surface runoff will be dealt with by draining to adjacent

grassedareas.

Summary:Site investigations and research have indicated that infiltration should be possible,

space constraints and volume requirements indicate that soakaway systems should

adequatelydraintherainfallfromroofareaswithintheconfinesofthesitearea.

Ifintheunlikelyeventthatsignificantdifferencesingroundconditionsarefound,itis

proposedthatanalternativesolutionbeimplemented.

Strategy2:

SurfaceWaterDrainageAttenuation:Should space constraints, high ground water levels or inadequate percolation data

indicate that infiltration is not an option then a different solution will be required.

UsingtheSUDSHierarchythenextoptiontoexplorewouldbetheuseofAttenuation.

However looking at the site area is likely that itwill beplausible to use someof the

methods described above for large areas of the site, such as driveways, patio areas

shareddriveways andgarden space, and itwill just be the volumesproducedby the

roofareaswhichwillneedtobedealtwith.

Lookingatthe layoutplanthereareareaswhichcouldbeusedforasmallamountof

surface attenuation, however constraints on required roadway space would make

undergroundattenuationamoreviablealternative.

Wehavereviewedatthetoolsforestimatingthevolumeofstoragerequired,however

these are designed for larger scale developments and results can be skewed, and

indicatealargeramountthanisnecessary,fortheareastobedrainedinrelationtoour

site.

Lookingat theRunoff rates for theareaof landweare considering, evenusingmap

values,thegreenfieldrunoffratesforthatplotoflandareoftheorderof0.6-2.08l/s.

Therunofffromimpermeableareaswillbehigherproportionallyasthereisnoability

tosoakthewater.

Impermeableareasontheplanareintheorderof585m2.

DesignStorm-10years:

SpecifiedReturnPeriod- 10Years

Duration Alldurations

M5–60Rainfall 20mm

RainfallRatio 0.40

M10-60=24.8mm

StormDuration 60mins

Volume 14.5m3(14,500L)

Flowratel/sec 4.03l/s

DesignStorm-30Years:

SpecifiedReturnPeriod 30Years

Duration AllMins

M5–60rainfall 20mm

RainfallRatio 0.4

M30–120Rainfall=30.9mm

CriticalstormDuration 120mins

Volume 18.1m3(18,100L)+20%forclimatechange

21.7m3

Flowrate 3.01l/sec

DesignStorm–100YearsSpecifiedReturnPeriod 100years

SpecifiedDuration 360mins

M5–60Rainfall 20mm

RainfallRatio 0.4

M100-360Rainfall 51.9mm

CriticalstormDuration 360mins

Volume 30.36m3(30,360L)+20%forclimatechange

36.43m3

FlowRate 1.67l/sec

TheMaximumflowrateofthedesignstormsis4.03l/sec.

Guidanceindicatesthattherunofffromthesiteshouldnotexceedthegreenfieldrunoff

rates,howeverthisismoreapplicabletolargerdevelopmentswhererunoffvaluescan

bemuchgreater.Allresearchdoneindicatesthattheminimumlevelofattenuatedflow

when discharged to drains of any type should be of the order of 5 l/s to prevent

blockageoftheattenuationsystems.

With this inmind theneed to attenuate the surfacewater run off from the site is in

question.Iftheattenuatedminimumflowlevelis5l/sandtheanticipatedrunofffrom

theroofsisonly4.03l/secthenattenuationshouldnotberequired.

Dischargepoint:

Wehavecarriedoutawalkoverofthesiteandtherearenonotablewatercourseson

site,thereisadrainageditchinanadjacentgarden,whichentersaculvertandheadsin

thedirectionofWestonRoadItispossiblethatthisenterstheSurfacewaterdrainage

systematthefrontof98WestonRoadhoweverthisculvertdoesnotappearonSevern

Trent mapping and the out flow of this culvert is unknown. In addition to this

permissiontocrossthe3rdpartylandisunlikelytobegiven.Assuch,althoughitseems

idealthisculvert isunlikelytorepresentauseabledischargepoint. Investigationsare

ongoing,asitmaybethecasethatriparianrightsexistovertheditchandculvert.

Using the STW mapping the nearest indicated surface water drains are in Ellison

Avenue and Bell Avenue. Accessing these drains directly would again require the

pipework to cross 3rd party land. This and local topographymeans that these drains

wouldbebothtoohightoaccessandsubjecttoransomdemandsforcrossing3rdparty

land.

Inthepavementtothefrontofoursitethereisa450mmVCsurfacewaterdrain.Thisis

not marked on STW plans however was uncovered during the installation of the

services for the approved development. Further investigation is required, however

there is no othermapped surfacewater drainage in this location and it is generally

acceptedthatsomeofthewaterfromtheexistinghousesinthispartofthevillagedoes

outflowintothedrainagesystem.Asthemainsewerisindicatedasafoulonlysewerit

islikelythatthereisasurfacewaterdraininthepavementorroadnearbyanditisnot

yetincludedinthemapping,itispossiblethatthe450mmpipeworklocatedisaviable

dischargepoint,investigationsareongoing.

Mapping indicates the presence of Surfacewater drainage at the front of 98Weston

Road. Though this is some distance from the site it could be used. There is an

adequatelydeep invert level to laypipe to thissurfacesewer.Althoughtheremaybe

significantcostimplications,itcouldbeused.

Conclusion:

Weproposethatweimplementastrategybasedalongthefollowingprinciples:

Groundconditionsandspaceconsiderationsindicatethatroofwatercanbedrainedto

Soakaway crate systems along the lines of those indicated above. The relatively high

watertableindicatedbytheBGSreportisnotsufficientlyhighastoprecludetheuseof

soakawaysystems,solongasaminimumof1mismaintainedbetweenthebottomof

thesystemandthewatertable.Theavailablespaceonsitewouldallowforadequate

volumestobeaccommodatedwithinthesiteboundary.

TrenchSystemsindicatedontheattachedplanwouldbeimplemented,withadditional

drainageareasavailable toaccommodateany further increase incapacitywhichmay

beencountered.

Hardstandingareaswillbelaidinpermeablematerialswithapermeablesubbase,to

minimizerunoffandprovideanadequatelevelof infiltrationdrainagetotheground.

The level of the water table should not compromise this approach, and the level of

interceptionstoragewouldbesufficientinafairlyshallowlayerofpermeablesubbase

toprovideforsignificantrainfallevents.

FoulWaterwillbedisposedofviaanewinterceptmanholeand150mmPVCu drain

connectingtotheexisting225mmSevernTrentSewer.

Shouldwatertablelevelsorspaceconstraintsdictatethatsoakawaysystemscannotbe

used for thedisposalof the roofwater, then, as the flowrate from the roofdrainage

should be acceptably low then this will be discharged into the closest available and

acceptabledrain/sewer,thisistheleastpreferredmethod.

EmailFromJohnHall

STWGISMapping

Abandoned Gravity Sewer

Private Combined Gravity Sewer

Private Foul Gravity Sewer

Private Surface Water Gravity Sewer

Public Combined Gravity Sewer

Public Foul Gravity Sewer

Public Surface Water Gravity Sewer

Trunk Combined Gravity Sewer

Trunk Foul Use Gravity Sewer

Trunk Surface Water Gravity Sewer

Combined Use Pressurised Sewer

Foul Use Pressurised Sewer

Surface Water Pressurised Sewer

Highway Drain

Combined Lateral Drain (SS)

Foul Lateral Drain (SS)

Surface Water Lateral Drain (SS)

All Private Sewers are shown in magenta All section 104 sewers are shown in green All Sewers that have been transferred to Severn Trent Water after the 1st October 2011, but have not been surveyed and confirmed by Severn Trent Water are shown in orange

Culverted Watercourse

Cable, Earthing

Cable Junction

Cable, Optical Fibre/Instrumentation

Cable, Low Voltage

Cable, High Voltage

Cable, Other

Housing, Building

Housing, Kiosk

Disposal Site

Sewage Treatment Works

Housing, Other

Pipe Support Structure

Sewage Pumping Facility

Sewer Facility Connection Inlet / Outlet

Blind Shaft

Combined Use Manhole

Flushing Chamber

Foul Use Manhole

Grease Trap

Head Node

Hydrobrake

Lamphole

Outfall

Overflow

Penstock

Petrol Interceptor

Sewer Chemical Injection Point

Sewer Junction

Sewerage Air Valve

Sewerage Hatch Box Point

Sewerage Isolation Valve

Soakaway

Surface Water Manhole

Vent Column

Waste Water Storage

Pre-1937 Properties

TABULAR KEY

A.Sewer pipe data refers to downstream

sewer pipe.

B.Where the node bifurcates (splits) X and Y

indicates downstream sewer pipe.

C. Gradient is stated a 1 in...

MATERIALS

- - NONEAC - ASBESTOS CEMENTBR - BRICKCC - CONCRETE BOX CULVERTCI - CAST IRONCO - CONCRETECSB - CONCRETE SEGMENTS (BOLTED)CSU - CONCRETE SEGMENTS (UNBOLTED)DI - DUCTILE IRONGRC - GLASS REINFORCED CONCRETEGRP - GLASS REINFORCED PLASTICMAC - MASONRY IN REGULAR COURSESMAR - MASONRY RANDOMLY COURSEDPE - POLYETHLENEPF - PITCHPP - POLYPROPYLENEPSC - PLASTIC STEEL COMPOSITEPVC - POLYVINYL CHLORIDERPM - REINFORCED PLASTIC MATRIXSI - SPUN (GREY) IRONST - STEELU - UNKNOWNVC - VITRIFIED CLAYXXX - OTHER

SHAPE PURPOSEC - CIRCULAR C - COMBINEDE - EGG SHAPED E - FINAL EFFLUENTO - OTHER F - FOULR - RECTANGLE L - SLUDGES - SQUARE S - SURFACE WATERT - TRAPEZOIDALU - UNKNOWN

CATEGORIES

W - WEIRC - CASCADEDB - DAMBOARDSE - SIDE ENTRYFV - FLAP VALVEBD - BACK DROPS - SIPHONHD - HIGHWAY DRAINS104 - SECTION 104

Severn Trent Water Limited

Asset Data Management

PO Box 5344

Coventry

CV3 9FT

Telephone: 0845 601 6616

SEWER RECORD (Tabular)

O/S Map scale:

Date of issue:

Sheet No.

This map is centred upon:

O / S Grid reference:

x :

y :

Disclaimer Statement:

1. Do not scale off this Map.

2. This map and any information supplied with it is furnished as a general guide, is only valid at the date of issue and no warranty as to its correctness is given or implied. In particular this Map and any information shown on it must not be relied upon in the event of any development or works (including but not limited to excavations) in the vicinity of Severn Trent Water’s assets or for

the purposes of determining the suitability of a point of connection to the sewerage or distribution systems.

3. On 1 October 2011 most private sewers and private lateral drains in Severn Trent Water's sewerage area, which were connected to a public sewer as at 1 July 2011, transferred to the

ownership of Severn Trent Water and became public sewers and public lateral drains. A further transfer takes place on 1 October 2012 (date to be confirmed).Private pumping stations, which form part of these sewers or lateral drains, will transfer to the ownership of Severn Trent Water on or before 1 October 2016.

Severn Trent Water does not possess complete records of these assets.These assets may not be displayed on this Map.

4. Reproduction by permission of Ordnance Survey on behalf of HMSO. © Crown Copyright and database right 2004. All rights reserved. Ordnance Survey licence number 100018202.

Document users other than Severn Trent Water business users are advised that this document is provided for reference purpose only and is subject to copyright, therefore, no further copies

should be made from it.

Sewer Node Sewer Pipe DataREFERENCE COVER LEVEL

INV LEVELUPSTR

INV LEVELDOWNSTR PURP MATL SHAPE

MAXSIZE

MINSIZE GRADIENT

YEARLAID

SK41290303 41.23 39.60 39.51 F VC C 150 nil 226.67 nill

SK41290304 41.12 40.02 39.60 F VC C 150 nil 108.60 nill

SK41290305 41.10 39.51 39.14 F VC C 150 nil 168.05 nill

SK41290308 41.07 39.77 39.66 S CO C 300 nil 439.36 nill

SK41290309 41.46 40.20 39.77 S CO C 300 nil 67.12 nill

SK41290310 41.01 40.24 40.20 S VC C 225 nil 608.75 nill

SK41291302 40.67 38.79 38.44 F VC C 225 nil 253.26 nill

SK41291303 40.70 39.18 38.70 S CO C 750 nil 25.35 nill

SK41291305 40.81 39.29 39.18 S CO C 450 nil 49.00 nill

SK41291306 40.79 39.39 39.32 S CO C 450 nil 172.57 nill

SK41291307 nil nil 39.39 S nil nil nil nil 0.00 nill

SK41291401 40.75 38.44 38.22 F VC C 225 nil 270.05 nill

SK41291501 43.40 41.05 39.34 F VC C 225 nil 52.85 nill

SK41292301 38.92 36.89 37.31 F CO C 300 nil 0.00 nill

SK41292401 40.63 38.08 37.68 F VC C 300 nil 132.88 nill

SK41292402 40.62 38.21 38.12 F VC C 225 nil 388.78 nill

SK41292502 41.57 39.29 38.13 F VC C 225 nil 53.82 nill

nil nil nil nil F VC nil nil nil 0.00 nill

1:1250

19.01.1719.01.17

329454

4411731 of 1

HRWallingfordGreenfieldRunoffRate

This report was produced using the greenfield runoff tool developed by HR Wallingford and available at www.uksuds.com. The use of this tool is subject to the UK SuDS terms and conditions and licence agreement, which can both be found at http://uksuds.com/terms-and-conditions.htm. The outputs from this tool have been used to estimate storage volume requirements. The use of these results is the responsibility of the users of this tool. No liability will be accepted by HR Wallingford, the Environment Agency, CEH, Hydrosolutions or any other organisation for use of this data in the design or operational characteristics of any drainage scheme.

Greenfield runoff estimation for sites

www.u suds.com Greenfield runoff tool

This is an estimation of the greenfield runoff rate limits that are needed to meet normal best practice criteria in line with Environment Agency guidance Preliminary rainfall runoff management for developments , W5 0 4/A/TR1/1 rev. E (2012) and the SuDS Manual, C 53 (Ciria, 2015). This information on greenfield runoff rates may be the basis for setting consents for the drainage of surface water runoff from sites.

Site name:

Calculated by:

Latitude:

Longitude:

Reference:

Date:

Site coordinates

Site location:

Site characteristicsTotal site area (ha)

MethodologyQbar estimation methodSPR estimation method

Default Edited

SOIL typeHOST classSPR/SPRHOST

Hydrological characteristics Default Edited

SAAR (mm)Hydrological region Growth curve factor: 1 year Growth curve factor: 30 year Growth curve factor: 100 year

Notes:(1) Is QBAR < 2.0 l/s/ha?

(2) Are flow rates < 5.0 l/s?

(3) Is SPR/SPRHOST ≤ 0.3?

Greenfield runoff rates Default Edited

Qbar (l/s)1 in 1 year (l/s)1 in 30 years (l/s)1 in 100 years (l/s)

Methodology IH124

0.21

0.67

2 for disposal of surface water runoff.

0.61

0.83 0.83

Lower consent flow rates may be set in which case blockage

4

0.3158

2017-04-23T12:27:21

Aston on Trent

7 5.0l/s if blockage from vegetation and other materials is possible.

1.39108° W

0.2

Whitelands Close

0.24

Mark Jones

2.57

0.81

Calculate from dominant HOST

52.86131° N

636635Where groundwater levels are low enough the use of

33

2.08

2.57

Calculate from SPR and SAAR

4

7

1.62 0.47

soakaways to avoid discharge offsite may be a requirement

are set at 2.0 l/s/ha.

Normally limiting discharge rates which are less than 2.0 l/s/ha

2

5929672

work must be addressed by using appropriate drainage elements.

0.37

Where flow rates are less than 5.0 l/s consents are usually set at

IndicativeDrainageLayout