nofmodelscaleandsurfaceroughnesseffectsareinvestigatedindetailbyusingthecommercialCFDmodel,FLOW-D,whichiswidelyverifiedandusedinthefieldofspillwayflowanalysis.Numericalerrorsinthedischargeflowrate,watersurfaces,andcrestpressuresduetothesurfaceroughnessareinsignificantifwejustuseageneralroughnessheightofconstructionmaterials,andthescaleeffectsofthemodelareinanacceptableerrorrangeifthelengthscaleratioislessthanor.Theroughnessandscaleeffectsaremoreseverebelowhm,wherethemaximumvelocityoccursinperpendicularcoordinatetotheweircrest.Thevelocityoftheprototypeislargerthanthatofthescaledmodelbelowbutthephenomenaarecontraryabovehm.Maximumvelocityatanysectionslightlydecreasesasthesurfaceroughnessandthelengthscaleratioincrease.Theverticallocationwheremaximumvelocityoccursislocatedonalowerpositionastheupstreamwaterheadincreasesandthelocationalmostlinearlyincreaseswiththedistancefromthefrontofthespillway.Keywords:FLOW-D,ogee-spillway,roughnes