基于GIS和USLE的小流域土壤侵蚀定量评价

通过气象数据分析、实地调查、野外采样及室内分析、DEM计算、遥感解译等，建立了南水北调中线水源地丹江口水库区典型小流域地理数据库，确定了计算USLE因子指标的方法。在ArcGIS支持下，模拟了小流域土壤侵蚀强度的空间分布。将模拟结果分为微度、低度、中度、强度、剧烈侵蚀5级，建立土壤侵蚀与土地利用/土地覆盖类型及坡度之间的关系。结果表明：研究区年均土壤侵蚀量2414 t/hm2，远超该地区容许土壤流失量5 t/（hm2·a）。96%的侵蚀区及95%的土壤侵蚀总量位于<25°区域。就土地利用/土地覆盖类型而言，陡坡耕作区是主要的土壤流失区。研究结果为水源区的土壤侵蚀治理提供参考意见，同时为USLE在无土壤类型图地区的应用提供一种方法借鉴

ASSESSMENT OF SOIL EROSION BASED ON GIS AND USLE IN A SMALL AGRICULTURAL WATERSHED,CHINA

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