Critical Area Identification of Potential Soil Loss in a Typical Watershed of the Three Gorges Reservoir Region

Identifying critical soil loss-prone areas is necessary to better control soil loss in the Xiangxi watershed, the river basin nearest the Three Gorges Dam. A crucial element of this scheme is the development of a risk assessment model that can identify critical potential soil loss areas for land use prioritization and soil conservation. An assessment model for the risk of potential soil loss based on the revised universal soil loss equation and sediment delivery ratio was developed in this work. The proposed model consists of five multiplied factors: the rain and runoff erosivity, soil erodibility, slope steepness and length, vegetation cover, and sediment delivery. The risk of potential soil loss in the Xiangxi watershed was assessed using the developed model integrated with the ArcGIS platform along with precipitation data, soil data, DEM, and MODIS NDVI images. The risk values ranged from 0 to 478.18, and were categorized into four classes. The classification showed that critical and sub-critical areas accounted for 4.48% and 6.05% respectively, of the entire Xiangxi watershed area. The results of the identification of critical and sub-critical areas were verified by analyzing the relationship between the variations of the agricultural land area and those of sediment discharge. Statistical relationship analysis between the distribution of critical/sub-critical areas and two parameters (the cell distance to the nearest river channel and the slope) showed that the critical and sub-critical areas for potential soil loss in the Xiangxi watershed assemble in the zone with a cell distance below 2,000 m, or in the zone with slopes above 25°.