Application Of Integrated Design Flood Hydrograph Method In The Loess Hill And Gully Area Of Northern Shan Xi

There are three elements of design flood,flood peak,flood volume and flood hydrograph.In the traditional design flood calculation,often ignore the shape of the design flood hydrograph information,just select a typical flood hydrograph for amplification.Due to the intluence of-human activity,the underlying surface conditions changed.The result is that the shape of flood hydrograph changes.The shape of the typical flood hydrograph in the past.,will not be able to represent the current underlying surface conditions may be the shape of the flood hydrograph.In recent years,some foreign hydrologists have made use of the similarity between the normalized flood hydrograph and the probability density of Beta,a comprehensive design flood process line model is proposed..This paper applied the model to our country northern Shaanxi loess hilly-gully region.Combined with the characteristics of the flood hydrograph in this area,and improvement this application.Typical linear watershed by two parameters of the Beta distribution Pprobability density function to the three parameters instead of the Gamma function.The main tingings o.f the study are:(1)Analyzed the flood hydrograph of Qingyangcha、Mahuyu and Heimutouchuan river basin from a rmacroscopic perspective.Rratio of rising flow and recession flow rates all changed,Rratio of rising flow changed significantly.Analyzed the shape parameters of flood hydrograph,with mathematical statistics method.Shape parameters have trend with time,Qingyangcha、Mahuyu river basin’s trend were significant.HeimLutouchuan river basin’s trend was no significant.(2)River basin’s represent line is beta probability density function,simulation design flood hydrograph was close to normal line,and the design flood hydrograph were short-and-fat-type.There is great difference in diversity in beat lines and practical flood hydrograph.(3)Combined with the characteristics of study river basin,choose the three parameters’gamma probability density function as represent line.and the design flood hydrograph’s characteristics accord with study river basin’s characters.The flood peak present time close to the typical flood.Recession flow rates less then typical flood.(4)Using the Beta function model,the flood volume of the design flood is slightly larger than that of the frequency analysis method.But the flood peak is smaller than the design value.The flood peak and volume calculated by the Gamma function model are slightly larger than those calculated by the univariate frequency analysis method.The difference range of flood peak is 20%and the difference of flood volume is less than 30%.The flood peak by the same multiple method can reach the design value,because of choosing different typical flood hydrograph,the design flood volme not unique,and there are great difference with design value.