Study On The DEM Date Preprocessing Method And Rainfall Runoff Simulation

The numerical simulation of rainfall runoff is an important technique for the urban waterlogging prediction,risk assessment,storm sewer system optimization,and low impact development facilities layout,etc.The accuracy of simulation results has important influence on the research and decision-making of urban waterlogging control and low impact development facilities.In view of the shortcomings of the current mainstream surface rainfall runoff simulation software in sub-catchment area and people overlook a spurious depressions in the DEM that cause simulated water circulation and the uncertainty of flow direction,which lead to the simulation results have larger error problem,the paper puts forward a method of correcting the sub-catchment area divided automatically by the simulated software for surface rainfall runoff simulation on the basis of pretreatment and slope direction analysis on DEM spurious depression data through integrating RS and GIS technology.This method improved the simulation accuracy of surface rainfall runoff model,and the simulation results before and after correction are compared and verified by the measured data of the Rongqiao district D of 2nd period,Nan'an district,Chongqing.The main research contents and results are as follows:(1)This paper studied the methods of J&D algorithm,M&V algorithm and three-direction search method to deal with DEM spurious depression data,and analyzed the characteristics,shortcomings and application scope of the three algorithms.An modified M&V algorithm is proposed to improve the computational efficiency.Results show that J&D algorithm principle is simple and easy to operate,but has a problem of low processing efficiency,the ground slope after processing unclear,and think all default spurious depressions be concave pseudo-depressions.The J&D algorithm is applicable to DEM that with small area and all spurious depressions to be concave spurious depressions.M&V algorithm and modified M&V algorithm have a high efficiency of processing.The ground slope after processing by M&V algorithm and modified M&V algorithm is clear.They are suitable for processing all kinds of size of DEM.But there is also a problem of thinking all spurious depressions be concave spurious depressions.The three-direction search method can not only deal with the obstructive spurious depression,but also the concave spurious depressions.However,the processing efficiency of three-direction search method is the lowest.It is applicable to the DEM of various types of depressions.(2)The preprocessing program of the modified M&V algorithm and the three-direction search method to deal with DEM spurious depression data were developed based on the MATLAB software platform.Rongqiao district D of 2nd period is the study area.Using J&D algorithm carried by ArcGIS,M&V algorithm,modified M& V algorithm and three-direction search method carried by programming to preprocessing the DEM with spurious depressions.Respectively by comparing the untreated and treated with three kinds of algorithms of the DEM elevation data,analysis of slope aspect and processing time of three algorithms,determines the optimal data preprocessing method of spurious depressions.Results show that after processed by the J&D algorithm,modified M&V algorithm and three direction search method,the elevation value of the spurious depression was increased by 0.8053 m,0.8183 m and 0.8483 m respectively,DEM elevation data was increased by 115.766 m,118.357 m and 99.458 m respectively,among which the data of the three-direction search method was closest to the original DEM data;There are flats after processing of J&D algorithm,which lead to the ground slope aspect unknown.There is no flat after processing of modified M&V algorithm and three direction search method,which makes the ground slope aspect clear.However,due to the large number of searching paths in the three-direction search method,the slope aspect is chaotic.The processing time of J&D algorithm,modified M&V algorithm and the three-direction search method were 20s69,3s10 and 3min21s33.In considering of the factors such as the elevation increment of the depression,the analysis result of slope aspect and the processing time,the modified M&V algorithm is better.(3)Clarified the principle of correction of sub-catchment area;Import the slope aspect analysis chart of the pre-processed DEM into the Digital Water,and corrected the sub-catchment area of study area.The rainfall sequence was simulated from 17:00 to 21:00 on May 30,2017,and the results of rainfall runoff simulation before and after the correction of sub-catchment area were compared.Results show that before the correction of sub-catchment area,the maximum error of the monitoring point flow appeared at 17:15,the maximum runoff error was 11.52%,the peak time of runoff was 19:30,and the peak flow error was 8.09%.After the correction of sub-catchment area,the maximum error of the monitoring point flow appeared at 17:15,the maximum runoff error was 6.81%,the peak time of runoff was 19:30,and the peak flow error was 4.34%.Compared with the simulation results before the correction of the sub-catchment area,the maximum error of the monitoring point flow was reduced by 4.71%,the flow peak time was unchanged,and the flow peak flow error decreased by 3.75%.