Sediment Transport by Water A world top 100 University 输沙的水世界100强大学ppt课件.ppt

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1、SedimentTransportbyWaterTheoryProcessesRainsplashoverlandflowtransportRillingandgullyingMassmovementsWeatheringlimitedversussupplylimitedTheextremeeventTheoryMechanicsofflowStreamenergyEntrainmentMechanicsofflowWaterissubjecttotwoforces:gravity(Wa=gsin)frictionDefinesabil

2、ityofwatertoerodeandtransportsedimentTypesofflowinopenchannelsLaminarFlowEachfluidelementmovesalongaspecificpathwithnosignificantmixingbetweenlayersBoundarylayerincontactwiththebedhasnoforwardvelocityEachlayercanslippasteachotherTurbulentflowAtacriticalvelocityordepthlamin

3、arflowbecomesunstableandtheparallelstreamlinesaredestroyedAdjacentlayersmix,transferringmomentumbylargescaleeddiesVelocitymoreevenlydistributedwithdepthSteepernearbedvelocitygradientReynoldsNumber(Re)Re=hu/where=fluiddensityh=flowdepthu=fluidviscosity=viscositylargerva

4、lues,largerturbulenceEntrainmentMovementofmaterialdependsonitsphysicalproperties;grainsizeshapedensitystructualarrangementBasicdistinction;cohesive(silt-claysize)non-cohesiveShearstressCausesinitialmovementShearstress=estimateofforceexertedonthebedbythefluidcrDbutdoesn’t

5、includeliftforcesLiftdueto:eddiesdifferenceinvelocityattopandbottomofgrainCriticalshearstressShields(1936)DimensionlesscriticalshearstressPlotagainstparticleReynoldsno.(ratioofgrainsizetothicknessoflaminarsublayer)Factorsproducingscatteruseofaverageorspatialvariabilityov

6、erbedchannelsizeirregularityofeddiesdegreeofexposurepivotanglesimbricationdegreeofpackinggrainshapemicrotopographyErosionEntrainment/detatchmentTransportDetatchmentvsTransportRainsplashWeatheringTillageTramplingRunoffRainsplashOverlandflowRillflowGullyflowRainsplashvariesw

7、ithrainfallintensityvarieswithlandcovervarieswithslopevarieswith%ofareawhichisrilledvarieswithlithologycrusting?SurfaceWashparticlesdetatchedandtransportedbysurfaceflowingwaterforce=velocityxmass(i.e.Q)controlsrelatetocharacterofmaterials,especiallyabilitytoproducerainfall

8、excessResistancetodetatchmentnon-uniformvarieswithparticlesizecyclicvariationwithseasonsa