Soil conservation planning at the small watershed level using RUSLE with GIS: a case study in the Three Gorge Area of China

The Three Gorge Project (TGP) of China necessitates the resettlement of over 1 million population (mostly farmers) to more rugged and isolated areas than their original settlements. Soil erosion is a serious environmental and production problem in this area. To decrease the risk on environmental impacts, there is an increasing demand for sound, and readily applicable techniques for soil conservation planning in the Three Gorge Areas (TGA). The objectives of the study were to develop and validate a soil erosion-predicting model based on the revised Universal Soil Loss Equation (RUSLE) in a geographic information systems (GIS) environment. The use of GIS to develop conservation-oriented watershed management strategies in the Wangjiaqiao watershed is presented. Data used for the RUSLE were either determined or taken from published literature pertaining to the Wangjiaqiao watershed. In combination with IDRISI, GIS software (Eastman, R.J., 1997. IDRISI for Windows: User's guide (Version 2.0). Clark University, Graduate School of Geography, Worcester, MA, Chapters 4-17) was used to evaluate different agricultural management strategies in terms of predicted soil loss in the watershed. This model allowed for easy assessment of soil erosion hazards under different crop and land management options over the entire watershed. The study revealed that the annual average soil loss rate from relatively flat agricultural land was approximately 26 t/ha, whereas 52 t/ha was found on the cultivated sloping lands, which constitutes a large proportion of soil loss in the watershed. In the watershed, approximately 38 ha of agricultural land had slopes >47% (25degrees) and should be reforested or returned to pasture. Contour tillage (CT) and contour farming with a seasonal no-till ridge (CTN) were most effective in reducing soil loss rates. If CT and CTN were implemented, approximately 31% and 70%, respectively, of the areas with soil loss >T-EP would be reduced to <T-EP. T-EP is soil loss tolerance for economic planning and was set at less than or equal to 10 t/ha year. In addition to soil loss reduction, the CTN has the potential to increase crop yield. Soil erosion hazards may be alleviated in over 91% of the agricultural lands if combined conservation measures including terraces, CTN, CT, and crop rotations were implemented in the watershed. The results of the study indicate that the RUSLE-GIS model is a useful tool for resource management and soil conservation planning. This technology is readily transferable and accessible to other land managers and agronomists in the TGA. (C) 2003 Elsevier B.V. All rights reserved.