Study On Calculation Method Of Distributed Unit Hydrograph

With the intensification of human activities on the environment,disasters happened more frequently,especially floods,which are still the main natural disasters in face of mankind.The frequently occurring of floods not only damage people's life and property tremendously,but also set higher requirements for flood disaster forecasting work.With the development of RS technology,GIS technology and computer science,the distributed unit hydrograph,reflecting the physical process of the convergence,has become the main convergence calculation method for the flood forecasting of ungauged watersheds.By focusing on the time-variant distributed unit hydrograph based on the fluid state method,the paper propose a flow state determination method based on the area threshold and theoretical derivation of time-variant parameters.Furthermore,setting the Peihe,Tanjiahe and Lixin Watershed as research watersheds,the Three Water Sources Xin'anjiang Model are applied to respectively discuss the simulation accuracy of time-variant and time-invariant unit hydrographs and the applicable conditions of distributed unit hydrograph.The main research contents and results are as follows:(1)The overland flood computation method based on the flow type.Utilizing the ArcHydro Tools in ArcGIS,the paper puts forward a method for determining the flow type based on the drainage area.With Peihe Watershed as research watershed,the paper apply the method to the calculation of the distributed unit hydrograph based on the flow type,based on which the Xin'anjiang Model is conbined for floods simulation,and the simulation results turn out to be satisfactory.(2)The time-variant distributed unit hydrograph computation method.The paper verifies an velocity calculation equation by the theoretical derivation,which considers the rain intensity.Then taking the Peihe watershed as the research watershed,the paper performs a flood simulation using the time-variant unit hydrograph.And the results of the time-variant distributed unit hydrograph could have higher simulation accuracy,compared with the results of the time-invariant unit hydrograph.(3)The applicable conditions of distributed unit hydrograph.The Xin'anjiang Model is applied to the Tanjiahe Watershed,and it is found that the distributed unit hydrograph is not suitable for area with too large watershed.Therefore,large watershed should be partitioned into small sub-watershed in order to achieve the ideal simulation accuracy.(4)The treatment of small slope grids in the watershed.An empirical equation is proposed to deal with small slope grids in the watershed.Based on the distributed unit hydrograph before and after the slope processing,the Xin'anjiang Model is applied to flood simulation in the Lixin Watershed.The results show that the distributed unit hydrograph does not apply to the watershed with small slope of the watershed,and the simulation accuracy is improved after the processing of the watershed slope.With solid physical foundation,the time-variant distributed unit hydrograph provides a reliable and effective solution for flood forecasting in ungauged watershed and areas under the great influences of human activities.