Study On Topographical Factors Of Soil Erosion In Karst Area Based On Multi-Scale DEM

Soil erosion research is one of the important contents of soil and water conservation research.Guizhou karst area is one of the areas with the most severe soil erosion in China.It is of great significance to study the soil erosion in Guizhou karst area for the prevention and control of soil erosion in the karst region.The occurrence of soil erosion is affected by many factors such as soil,vegetation,topography,rainfall,etc.The terrain conditions determine the formation and redistribution of ground matter and energy,which is one of the important factors affecting soil erosion.For small-scale studies on slopes,small watersheds,etc.,the terrain factors required for soil erosion studies usually use slopes and slope lengths;for large-scale studies such as regional studies,topographic factors required for soil erosion studies usually use topographic relief and surface conditions.Roughness,depth of surface cut,and height coefficient of variation.Such factors as soil erosion topography evaluation indicators.GIS technology can achieve rapid extraction of terrain factors,but different scales of DEM will affect the accuracy of terrain factor extraction results.For the study of soil erosion in karst areas,this paper selects terrain factors such as slope,slope length,terrain relief,surface roughness,surface cutting depth and elevation coefficient of variation,applies GIS theory and technology,combines geomorphology,soil and water conservation Basic theory and methods,the scale effect of topographic factors such as slope,slope length,topography relief,surface roughness,surface cutting depth and elevation coefficient of variation was analyzed,and elevation coefficient of variation,and have determined the area of study 1 based on information content analysis.Using the idea of information content analysis to determine the optimal resolution of 1:10000 and 1:50000 scale DEM in the study area,the paper finally uses the principle of histogram matching to establish a scale conversion model of slope,slope length and other factors.The research results of the thesis improve the theory and methods of terrain information acquisition for soil erosion studies in the karst area,and provide important guidance for the study of soil erosion in the karst region.The main research contents and research conclusions of the paper are summarized as follows:(1)The paper analyzes,summarizes,and selects topographic factors needed for soil erosion studies at different scales.For small scales on slopes and small watersheds,slope and slope length are selected as topographic factors for soil erosion studies;for large-scale areas,topographic relief,ground roughness,surface cutting depth,and elevation coefficient of variation are selected as topographic factors for soil erosion studies.The topographic factor studied.The scale effect of the variation of DEM resolution with the local factors required for soil erosion research was studied.The best resolution of DEM in the study area was determined,and a scale conversion model for slope and slope length was established.(2)Using the DEM data of the study area,the scale effect produced by the variation of the local shape factor with DEM resolution was discussed.The results show that the slope decreases with the decrease of the resolution,the average value,the maximum value,the standard deviation decrease,the minimum value increases,the proportion of gentle slopes increases,and the range of gradient values decreases.The slope length varies with the resolution.The average value,maximum value,and standard deviation are reduced,the minimum value is not changed,the proportion of long slopes is increasing,and the range of slope length changes more and more.The lower resolution will lead to distortion of the slope length.Inconsistent with the actual ground conditions;the terrain relief decreases as the average resolution,minimum value,maximum value,and standard deviation decrease,but it can still express surface undulations,and the proportion of lower terrain undulations slightly increases.The range of topographic relief values is getting smaller and smaller;the surface roughness decreases with decreasing resolution and the average value decreases with decreasing DEM resolution.Even the study area is modeled as an approximately flat terrain,leading to distortion of the true representation of the surface morphology.The surface roughness ratio accounts for more and more of the surface roughness,and the range of the surface roughness value changes more and more.The surface cutting depth decreases with the resolution and its average value,minimum value,and maximum value.The standard deviation has decreased,and the proportion of small values of surface cutting depth has slightly increased,and the larger value has slightly decreased.The statistical values and frequency curves of the elevation coefficient of variation basically do not change with the change of DEM and are distinguished from DEM.The rate is less dependent.(3)The variation of shape factor with DEM resolution is compared.It can be concluded that the order of influence of DEM resolution on topographic factors is: slope length > surface roughness > slope > surface cutting depth > terrain fluctuation > elevation coefficient of variation.(4)The top resolution of the DEM was comprehensively analyzed by selecting three topographic factors such as the slope of the study area,topographic relief and surface roughness,and the DEM and the scale of 1:50 000 scale DEM in the study area were determined.The optimum resolution of DEM in the study area 1:10000 scale is 5 meters,and the optimal resolution of DEM in the study area 1:50 000 scale is 20 meters.(5)The slope and slope length scale conversion models were constructed using a DEM with a resolution of 5m in the study area of 1:10000 scale and DEM with a scale of 1:50000 and a resolution of 20 m.The results of slope and slope conversion model constructed show that the slope and slope length extracted by DEM based on 20 m resolution are more similar to the statistical data of DEM with 5m resolution after the scale conversion,and the surface morphology can be expressed more realistically.The slope and frequency curves of the converted slope are similar to those of the 5m resolution DEM slope and slope frequency curves.The converted slope and slope length cumulative curves basically coincide with the 5m resolution slope cumulative curves,and the conversion effect is good.The slope and slope length values extracted by DEM at 20 m resolution were corrected,and the slope attenuation and slope length expansion were corrected to some extent.