Topographic factor of water erosion – analysis of watershed morphometry and RUSLE LS factor in GIS environment

Soil erosion is the most serious soil degradation factor on the territory of Bulgaria. Nearly 66 % of its area have slopes in a range greater than 3°. The predominant hilly-mountainous relief and high slope degrees are prerequisites for development of water erosion. The properties of the topographic surface as a conditioning factor of erosion processes are evaluated in the current study on the example of the Dzhebelska River watershed (Southern Bulgaria). The following morphometric parameters are considered: basin relief, Melton index, slope and stream power index (SPI). Slope length and steepness factor (LS factor) is calculated using the slope degree and specific contributing area. The values vary between 0 and 43.36. The results of the analysis of the morphometric parameters indicate high erosion susceptibility in the upper and the middle part of the watershed but active erosion can be observed too in the low part of the watershed, where first order streams (Strahler’s method) flows directly to the river of fifth order. The current study is done in GIS environment on the base of 12 m digital elevation model.