natural flood management: current status and needs for the future · 2019. 7. 3. · natural flood...
TRANSCRIPT
NaturalFloodManagement:CurrentStatusandNeedsfortheFuture
DrIanPattison
(FromAugust2019)
SchoolofEnergy,Geoscience,InfrastructureandSociety,HeriotWattUniversity,Edinburgh
[email protected]@GoWithTheF1ow
Currently
Outline
• WhatisNFM?
• ProblemofUpscaling
• Designing/TargetingNFMatcatchmentscale
• FallaciesaboutNFM
• Conclusions
- Arable - Ploughing - Pasture – Stock density - compaction (overgraze/compact)
- Winter crops - Land Drainage (bare ground) - Urbanisation - Intensification
InfiltrationCapacity
AntecedentConditions
CatchmentCharacteristicse.g.TopographyGeologySoilType/Structure
Interception/Stemflow
Partitioningbetweenoverlandandsubsurfaceflows
Partitioning Rainfall into Runoff
Runoff
Rateofdeliveryofoverlandflow
HydrologicalConnectivityHillslope
Connectivity
BaseflowRelativeTiming/
Sequence/Volumeoftributaryinputs
Conveyance/DegreeofAttenuation
ChannelCharacteristics/Change
Channel Conveyance
o Wetlandso Abstraction
SurfaceStorage
Storage
SubsurfaceStorage
o Forestry o Agriculture
RainfallCharacteristics
ClimateEvapotranspiration
WeatherSystem
EffectivePrecipitation
o ChannelModification
o Buffer Zones o Gripping/Ploughing o Urbanisation
LowFlowsFloods
Process Based Understanding of Effect of NFM on Floods
What is NFM ?
Measures that help to protect, restore and emulate the natural functions of catchments, floodplains, and rivers
ProblemofUpscalingSimpleextrapolationfromtheplotscaletothecatchmentscaleisnotpossible- Individualinterventionimpactreduces(attenuates)- InterventionsareDiffuse,andweneedtounderstandcombinedimpact- Differentpractices(amplify/balanceout)
Result=Non-Linearrelationshipe.g.volumeofstorage≠peakreduction
PattisonI,LaneSN.(2012).Thelinkbetweenlandusemanagementandfloodrisk:achaoticconception?,ProgressinPhysicalGeography.
WhereyoudoNFMeffectstheresult• DriversoffloodingvaryoverSpaceandTime
• Therefore,thisheterogeneitywithincatchmentsneedstobeaccountedfor,whendesigningNFMschemes.
PattisonI,LaneSN.(2012).Thelinkbetweenlandusemanagementandfloodrisk:achaoticconception?,ProgressinPhysicalGeography.
Slowingtheflow
LinkingUpstreamtoDownstream
WhatdrivesfloodinginCarlisle?- Convolutionoftributaryhydrographs
SensitivityoffloodingtotributaryhydrographsintermsofmagnitudeandrelativetimingTestedusingaHydraulicmodelofJanuary2005Carlisleflood
TargetingSub-Catchments
• Delayingupstreamtributarieshasbeneficialimpact(U.Eden=0.32m)• Speedinguplowlandtributariesreducesdownstreampeak(Caldew=0.33m)
• Reducingtributaryflowshasdifferingimpactsdownstream• UpperEden(0.33m),Petteril(noimpact)
Magnitude
EarlierDelayed
PattisonI,LaneSN,HardyRJ,ReaneySM,(2014),Theroleoftributaryrelativetimingandsequencingincontrollinglargefloods,WaterResourcesResearch,50,5444-5458.
Timing
EffectivenessdependsonLocation
<6mm
-7cm
15min
55min
1.5km
1.6km
BamptontoGreenCrook
WhaleBecktoCrookwathBridgeMagnitude (Stage) Timing (Hours)
1st Flood 2nd Flood 1st Flood 2nd Flood Bampton-Green Crook 0.002
(0.002%) -0.037
(-0.03%) 15 155
Whale Beck - Crookwath Bridge -0.072 m (-0.06%)
-0.059 m (-0.05%)
55 170
AndEvent
FallaciesaboutNFM• “Onlyworksinsmallcatchments”• “Onlyworksforlowreturnperiodfloodevents”
“LargeamountsofuncertaintyassociatedwithNFMespeciallyforlargecatchmentsandmajorfloods”BUTnostrongevidenceeitherway.
• “NFMisalwaysbeneficial(whereveritis)”
“Inappropriatelylocatedinterventionsmayworsenfloodingduetosynchronisationofpeaks”(Dadsonetal2017)
• “AnyonecandoNFM”“Localinitiativesneitherplannedorevaluatedatlargerspatialscales”
• “NFMprovideslotsofMultipleBenefits”Yes,butagainthetypesandlocationsarehighlyuncertain,andtheprimaryfocusofNFMshouldbefloodprevention.Othertermsshouldbeused“CatchmentBased
Approach”“NatureBasedSolutions”
BeingStrategicaboutNFMWhereyoudothingsmatters!
CurrentlyNFMisfartoopportunistic,itneedsdesigned(likeanyotherfloodmanagementscheme)atacatchmentscale.
OtherwiseNFMmay,atbest,failtoachievetheoptimumfloodreductionbenefitdownstream,or,atworst,actuallymakefloodingmoresevere
WeruntheriskthatNFMisnoteffectivesimplybecauseithasnotbeenappliedin;(a)themosteffectivemeasuresforthespecificcatchmentcharacteristics;(b)enoughlocations(scale);and(c)theoptimumsetoflocations.(magnitude,stormtrack,antecedentconditions,locations)
Apositiveimpactondownstreamfloodingcannotbeguaranteedforallpossibleeventsinalllocations.=NFMOptimisation
