Establishment And Extraction Of Topographic Parameters System For Watershed Soil Erosion Assessmentabstract

Terrain is an important feature of surface which affect soil erosion various aspect. topo-graphic parameters impacted importantly on the results analysis of soil erosion assessment and measures setting of soil and water conservation.This paper selects a mesoscale watershed as a study asample of Yan River Basin.its area approximately2000Km2.based on high-resolution hydrologically correct DEM (Hc-DEM), were extracted from discrete terrain feature (vector) and continuous topographic parameters (grid) for soil erosion evaluation on the micro scale and macro scale. constructed a topo-graphic parameters system for medium-scale basin soil erosion evaluation. Eventually come to the following conclusions:(1) In terms of form, topographic parameters for watershed soil erosion assessment were divide local and non-local parameters, the former including the top of the hill, saddle points, valleys nodes, valleys source point, ridge line, assembly line, basin, slope, aspect, local curvature, etc.they extraction by Adjacent regions operation.the latter including slope length, LS factor, wetness index, regional curvature, etc. From the data format, including continuous parameters and discrete object. the former including the top of the hill, saddle points, valleys nodes, valleys source point, ridge line, assembly line, basin, the latter including slope length, LS factor, wetness index, regional curvature, etc. All basic indicators can be extracted in the general GIS software, but need special into individual indicator, such as erosion slope length.(2) Continuous topography paramters show that slope is first derivative of altitude on the horizontal direction.profile curvature is the first derivative of slope and is the second derivativeof altitude on the horizontal direction. the higher derivative tends to describe more local rough surface. The relationship between the moment of variables show that standard deviation of altitude is a measure of vertical dimition (relief),and skewness of altitude is an inverse measure of regional convexity (dissection, aeration). standard deviation of altitude is a measure of relief.standard deviation of slope is another expression of degree of local curvature,but does not distinguish convexity from concavity. Statistical relationship between topography paramters show that slope and slopelength were higher positive correlation with LS factors. specific catchment area was positive correlation with topographic wetness index and single flow slope length. Slope is negatively related to the topographic wetness index.(3) Continuous topography paramters show, the macro distribution of slope length and specific catchment area are similar. larger values are in the larger channel.but slope to0value impact slopelength lager than specific catchment area.their Frequency curve were positively skewed distribution.the distribution of topographic wetness index is opposite to LS factor.regional curvature indicates that the dissection and aeration of the study area were in the prime of life.the mean value of LS factor in north aspect was greater than the average of the south ascpect. LS factor in Half cloudy slope were lager than half sunny slope.the distribution of the LS factor as a whole and the slope is relatively similar, smaller in the river and and larger in the hilly; profile curvature shows that the value of LS factors on the concave were greater than on the convex. the broken microstructure show that the plan curvature Reflects the convergent and the divergent.(4) Discrete object show, the mean value of LS factor on valleys node were less than Valleys source point.all the value of LS factor on river is lesser.but the LS factor on different levels rivers is different. the mean value of LS factors on convergent line is lager than rivers.