ESTIMATION OF UPLAND EROSION USING GIS

The Universal Soil-Loss Equation (USLE) is a widely used method for ca lculating annual soil erosion losses, based on rainfall, runoff, slope , runoff length, soil type, and landuse parameters. The equation was o riginally developed on small agricultural plots, but has since been ad opted for evaluating erosion from large watersheds under a wide range of landuses. This study was designed to compare USLE calculations in a GIS environment at grid sizes ranging from 30 x 30 m up to 6 x 6 km. The analysis of two watersheds in Mississippi shows that large grid si zes tend to underestimate soil losses. At grid sizes exceeding 100 x 1 00 m, a correction factor must be included in the calculations. With t he use of the correction factor, the USLE can be applied directly at m acroscales, providing an important tool for studies of basin-wide upla nd erosion rates. The proposed method is shown to be applicable for la rge watersheds under different climates. (C) 1998 Elsevier Science Ltd . All rights reserved.