Scale Effect Of DEM Data In Watershed Hydrological Analysis And Simulation

DEM data is the basis of watershed hydrological analysis and simulation.The DEM data of different sources have different accuracy and resolution,which have a profound impact on the results of hydrological analysis and hydrological simulation.In the paper,the Tang River upstream basin of Hebi city is taken as the study area,SRTM DEM and ASTER GDEM is contrasted based on DEM data acquired by airborne LiDAR,and the differences and reasons of different resolution and DEM of different sources in terrain expression factor extraction,hydrological index analysis and watershed feature parameter extraction is analyzed.Based on the SWAT distributed hydrological model,the hydrological effects of DEM data with different resolutions and different sources are simulated and studied.The main research contents are divided into five parts.(1)DEM data preprocessing.The technical flow of airborne LiDAR data processing is studied in the paper.Gross error removal,filtering and interpolation processing method of point cloud data is selected for the study area,and LiDAR data processing and DEM construction of 170km~2 study area is completed,100 kinds of different resolution DEM range from 1m to 100m is generated based on resampling method.The SRTM DEM and ASTER GDEM data of the study area are collected,which provide the basic data for the follow-up study.(2)Analysis of terrain expression factor.According to the DEM data of different scales and different sources,the terrain factors such as slope,aspect and elevation are extracted,and the variation characteristics are counted.The results show that,with the decrease of the resolution of LiDAR DEM,the slope mean value,the maximum value and the standard deviation of the study area are reduced.When the DEM resolution is reduced from 1m to 100m,the average value is changed from 9.47°to 4.51°,and the change rate of the average value is 52.37%,which indicates that the detail information of the terrain is lost with the decrease of the resolution,and it leads to the decrease of the slope statistics.While the change of resolution has little effect on the expression of elevation and aspect.The statistics of different sources of DEM data indicate that compared with the LiDAR DEM data,the elevation extracted from the same resolution SRTM DEM data is larger,while the slope value is small,which indicate that the data precision is high,but the expression of terrain details is vague,and the elevation value extracted from ASTER GDEM data is lower,pseudo terrain noise is serious,which leads to the slope extraction is not accurate enough,and it is higher overall.The different data sources have little influence on the slope extraction and the difference of the mean value is less than 0.15.(3)Topographic hydrological index analysis.The extraction method of topographic and hydrological indices such as TWI,SPI,LSF,etc.is studied in the paper,and the extraction results of multi-scale DEM data are analyzed and compared.The results show that,when the resolution of DEM is higher,the average value of TWI is larger,the average value of SPI is smaller,and the expression of topographic details and the ability of runoff sediment transport is better,but the LSF value is maximum at10m resolution,and the potential value of soil erosion is also the largest.Extraction results of different sources of DEM show that:the LSF value and SPI value extracted from ASTER GDEM and SRTM DEM are small than the value that extracted from LiDAR DEM,while the value of TWI is opposite and extracted TWI value of ASTER GDEM and LiDAR DEM is close.(4)Extraction and analysis of watershed characteristic parameters.The extraction of river network is studied,and the extracted characteristic parameters are compared and analyzed.The results show that the spatial resolution of DEM has little effect on the watershed area,while the river length and the density of river network decrease with the decrease of resolution.For different sources of DEM data,compared with the basin area extracted from the same resolution LiDAR DEM,the value extracted from ASTER GDEM is the smallest,while the SRTM DEM the largest,and the difference is3.92km~2 and 0.11km~2 respectively,which is related to the lower accuracy of ASTER GDEM data and the overall higher accuracy of SRTM DEM data.The length and density of river networks extracted from ASTER GDEM and SRTM DEM is small than the value extracted from LiDAR DEM.(5)Simulation and analysis of SWAT model.In the paper,the SWAT hydrological model is established based on DEM of different resolution and different data sources and the evapotranspiration,soil leakage,underground runoff and surface runoff are extracted analyzed.The results indicate that with the lower resolution and the smaller value of the slope,Topographic Wetness Index becomes larger,evapotranspiration increases,surface runoff depth reduces while the amount of soil leakage and underground runoff is first decrease and then increase and 10m is the turning point.The results of different data sources DEM show that,compared with the same resolution Li DAR DEM,the evapotranspiration extracted from ASTER GDEM and SRTM DEM is larger,the surface runoff depth,soil leakage and underground runoff are small.On the whole,different resolution and different data sources will affect the SWAT model simulation.