简介：Bridgepressureflowscouratclearwaterthresholdconditionisstudiedtheoreticallyandexperimentally.Theflumeexperimentsrevealthatthemeasuredscourprofilesunderabridgearemoreorless2-dimensional;allthemeasuredscourprofilescanbedescribedbytwosimilarityequations,wherethehorizontaldistanceisscaledbythedeckwidthwhilethelocalscourbythemaximumscourdepth;themaximumscourpositionislocatedjustunderthebridgeabout15%deckwidthfromthedownstreamdeckedge;thescourbeginsataboutonedeckwidthupstreamthebridgewhilethedepositionoccursatabout2.5deckwidthsdownstreamthebridge;andthemaximumscourdepthdecreaseswithincreas-ingsedimentsize,butincreaseswithdeckinundation.Thetheoreticalanalysisshowsthat:bridgescourcanbedividedintothreecases,i.e.downstreamunsubmerged,partiallysubmerged,andtotallysubmerged.Fordownstreamunsubmergedflows,themaximumbridgescourdepthisanopen-channelproblemwheretheconventionalmethodsintermsofcriticalvelocityorbedshearstresscanbeapplied;forpartiallyandtotallysubmergedflows,theequilibriummaximumscourdepthcanbedescribedbyascourandaninundationsimilaritynumber,whichhasbeenconfirmedbyexperimentswithtwodecksandtwosedimentsizes.Forapplication,adesignandfieldevaluationprocedurewithexamplesispresented,includingthemaximumscourdepthandscourprofile.