Calculation Of Slope Length And Slope Gradient Factors Based On GIS In The Small Watershed

Gradient slope and slope length factor (LS Factor) is a mainly topographical factor which influences soil erosion. In empirical Soil erosion models, LS factor can characterize the impact that terrain influences the soil erosion. Extraction algorithm of slope has already been very mature while there are many problems in extraction of slope length. As a result, this research mainly analyses and concludes the definition framework of slope length by predecessor, construct the theory system of slope length, analyze the advantages and disadvantages of different slope length extraction methods, build slope length extraction model and method of small watershed and analyze the space differentiation rules of slope length in small watershed and the relations between slope length and other terrain factors. At last, this essay uses the modified slope length algorithm and the slope extracted from ARCGIS to get the values of slope factor and slope length factor of small watershed. The main research results are as follows:(1) Slope length method based runoff accumulation can calculate slope length quickly. By improving the flow algorithm; we can get more realistic slope length. And the slope length has a good relationship with terrain features. Total flow catchment area of the unit slope length method, is influenced by the slope length factor index m, the choice of multiple flow direction algorithm, coefficient contour length of the impact and constraints, so the error is larger.(2) Different runoff algorithms can get the significantly different slope length. In order to get more real geological simulation results, the LS factor calculation process must fully consider the characteristics of runoff algorithm. Single flow algorithm water flow single the steepest only, can't really reflect downhill direction terrain. The results of different algorithms on extracting slope length have great difference. Multiple flow direction algorithms are more suitable than the single flow direction algorithms for simulating overland flow. The surfaces of multiple flow direction algorithms on extracting slope length are continuous and smooth. The spatial pattern of multiple flow direction algorithms is better than single flow direction algorithms.(3) There are many differences in the two algorithms. When the slope is more gentle, slope length is lager. Especially in 0-3 degrees, slope lengths are very large. When slope is steep, slope length is less. The maximum and minimum values of slope length in different aspect are similar, but the mean value and standard deviation of slope length in southern slope and northern slope are the largest. The mean value of slope length in concave slope is the largest, but in convex slope is the smallest. The mean value of plan areas is between concave slope and convex slope.(4)Through single flow and multiple flow LS frequency and spatial pattern analysis,there are many differences between LS factor of two different algorithms. LS factor was significantly more than the flow of a single flow of LS factor. Overall, the multiple flow LS factor was relatively good.