SedimentTransportbyWater-Aworldtop100University输沙的水世界100强大学

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

2、sportsedimentTypesofflowinopenchannelsLaminarFlowEachfluidelementmovesalongaspecificpathwithnosignificantmixingbetweenlayersBoundarylayerincontactwiththebedhasnoforwardvelocityEachlayercanslippasteachotherTurbulentflowAtacriticalvelocityordepthlaminarflowbecomesunstableandtheparallelstreamlinesar

3、edestroyedAdjacentlayersmix,transferringmomentumbylargescaleeddiesVelocitymoreevenlydistributedwithdepthSteepernearbedvelocitygradientReynoldsNumber(Re)Re=hu/where=fluiddensityh=flowdepthu=fluidviscosity=viscositylargervalues,largerturbulenceEntrainmentMovementofmaterialdependsonitsphysicalpr

4、operties;grainsizeshapedensitystructualarrangementBasicdistinction;cohesive(silt-claysize)non-cohesiveShearstressCausesinitialmovementShearstress=estimateofforceexertedonthebedbythefluidcrDbutdoesn’tincludeliftforcesLiftdueto:eddiesdifferenceinvelocityattopandbottomofgrainCriticalshearstressShi

5、elds(1936)DimensionlesscriticalshearstressPlotagainstparticleReynoldsno.(ratioofgrainsizetothicknessoflaminarsublayer)FactorsproducingscatteruseofaverageorspatialvariabilityoverbedchannelsizeirregularityofeddiesdegreeofexposurepivotanglesimbricationdegreeofpackinggrainshapemicrotopographyErosio

6、nEntrainment/detatchmentTransportDetatchmentvsTransportRainsplashWeatheringTillageTramplingRunoffRainsplashOverlandflowRillflowGullyflowRainsplashvarieswithrainfallintensityvarieswithlandcovervarieswithslopevarieswith%ofareawhichisrilledvarieswithlithologycrusting?SurfaceWashparticlesdetatchedand

7、transportedbysurfaceflowingwaterforce=velocityxmass(i.e.Q)controlsrelatetocharacterofmaterials,especiallyabilitytoproducerainfallexcessResistancetodetatchmentnon-uniformvarieswithparticlesizecyclicvariationwithseasonsa