ABSTRACT: We have developed a computer model of soil loss on an upland watershed from the continuity considerations for sediment transport and from equations describing rill and interrill erosion. The model is based on dividing the upland area into a grid containing rill and interill zones, on the Universal Soil Loss Equation (USLE), and on equations describing detachment and transport capacity of rill flow. The USLE estimates the sediment load from the contributing areas. The location and amount of total erosion and deposition are determined by comparing the transport and detachment capacity of rill flow for specific storms. The model considers the mechanics of erosion process and can serve as basis for reservoir and channel design and land use planning.