Abstract:

Soil erosion is one of the major environment problems in the Danjiangkou Reservoir Region (DRR) of China, the water source area of the SouthtoNorth Water Transfer Project (Middle Route). Soil erosion evaluation is urgently needed in this area, but it is difficult to assess because soil erosion patterns in watersheds are heterogeneous. The problem can be overcome by using soil erosion models. In this paper, soil erosion assessment was carried out in a typical watershed, the Wulongchi watershed in the DRR. The Universal Soil Loss Equation (USLE) was used to predict the spatial distribution of the average annual soil erosion modulus. There were five parameters in the USLE (i.e., R, K, LS, C, P), and the ArcGIS provided spatial input parameters using local data. The Yu Model and the daily rainfall data of the meteorological stations were used to derive the R parameter values. Through sampling in the field, analysis in the laboratory, model simulation and spatial interpolation, we got the K factor value needed in the USLE. The raster grid cumulation and maximum downhill slope methods were adopted to get the topographic (LS) factor values. The land use/land cover data derived from remote sensing images were used to get the C factor values. Combined with field survey and slope data, we determined the P factor value. Integrated with USLE and GIS, we simulated soil erosion modulus in the Wulongchi watershed. The modeling result was classified into five categories ranging from minimal risk to extreme erosion risk. The soil erosion map was linked to land use/land cover (LULC) and slope maps to display the relationship between soil erosion and environmental factors. The results showed that the mean R, K, LS, C, P values were 3 33785（MJ〖DK〗·mm）/（hm2〖DK〗·h〖DK〗·yr）, 0030 4（t〖DK〗·hm2〖DK〗·h）/（hm2〖DK〗·MJ〖DK〗·mm）, 1696, 0282 and 0675. Annual soil loss was 2414 t/（hm2〖DK〗·yr） in the study area, far above the soil loss tolerance 5 t/(hm2〖DK〗·yr). Most areas of the watershed (5527%) fell within the minimal erosion category (<5 t/（hm2〖DK〗·yr）). About 96% of the erosion area and nearly 95% of the total soil loss occurred in the zone with slope less than 25°. As far as LULC concerned, slope cultivated land was the main source of soil loss in this area. Field survey evidenced the effectiveness of this method. The results of the study provide useful information for the land managers in prioritizing the areas of erosion mitigation in the entire reservoir region.Study results also indicate that USLEGIS methodology is an efficient tool for assessing and mapping soil erosion risk at small watershed scale. The study also provides an idea on how to get the K factor value within the USLE when it has no soil map