Research On Analysis Units Of Slope Length Extraction

Slope gradient and length (LS) are two important indexes in topographical factors, andthe calculation of LS factor at the watershed scale is one of the subjects in regional soilerosion assessing and mapping. The algorithm of extracting slope gradient has beenwell-developed, whereas there still have many problems about slope length extraction. Theextraction of slope length was performed with watersheds as units, but there were lack ofstudies on how to determine the data unit of extracted slope length with regard to a large area.Therefore, focusing on analyzing and summarizing the defined framework about slope lengthpresented by previous works, this study established the theoretical system about slope length.Based on Hc-DEM with fine relationship between hydrology and topography, this paperanalyzed the relationship between the slope length of the watershed and the boundary of thewatershed by calculating the slope length of single and multiple flows on the unit of themiddle watershed with LS_Tool software. Our work finally concluded that the data boundarydoesn't need to be the watershed boundary at the same level, and it was fine to be thewatershed boundary. The main results and conclusions were as follows:(2) Based on the Hc-DEM with a resolution of10m and according to the relationshipamong threshold of catchments area, total lengths of river network and river density, the mostreasonable threshold of the catchment area in the hilly region of the Loess Plateau and theNortheast Hilly are concluded as0.5km2and1km2respectively.(3) Based on the maximum diameter of the watershed, the linear density of the flow, themean slope length, the maximum slope length and incomplete watershed belt, the uncertainwatershed belt on the rectangular map sheet was determined: the hilly region of the LoessPlateau is3km, and the hilly region of Northeast Hilly is5km. The method process and resultsof extracting slope length by taking the sheet boundary as the data boundary were obtained bytaking this factor as the buffer distance of the sheet boundary.(4) Comparisons between the results of slope length extraction at the watershed level andthe results of slope length extraction by taking the sheet boundary as the watershed boundaryindicate that results of slope length calculation using above-mentioned methods are same inthe same region. However, for a large area, the extraction of slope length by taking the databoundary as data units can reduce data uncertainties.