8. Soil Erosion on Upland Areas by Rainfall and Overland Flow

Soil erosion in agricultural watersheds is a systemic problem that has plagued mankind ever since the practice of agriculture began some 9000 years ago. It is a worldwide problem, the severity of which varies from location to location depending on weather, soil type, topography, cropping practices, and control methods. Research to address and predict soil loss from agricultural land and in watersheds began in earnest in the 1930s following the events of the Dust Bowl. Early research primarily consisted of monitoring of soil loss from natural runoff plots and small watersheds. Gradually and over time, the focus shifted toward the development of prediction equations based on the acquired soil loss database. With computer technology, modeling watershed erosion and sedimentation processes became routine. Also, fundamental research was conducted to acquire a better understanding of the complex aspects of soil erosion and sediment transport processes and to fill in knowledge gaps in cases where data were not readily available. In recent years, most soil loss from upland areas occurs as gully erosion. This chapter presents a background of the knowledge that was systematically acquired in predicting soil erosion from upland areas and the technology that was developed and is used today. This chapter does not address all the aspects of upland soil erosion, but focuses primarily on the erodibility (K-factor) and hydrological aspects (R-factor) of the most widely used erosion prediction equations: the revised universal soil loss equation, version 2 (RUSLE2) and water erosion prediction project model (WEPP) models-based formulae. This chapter also includes a presentation of the Chinese approach of adapting gully erosion predictions according to the universal soil loss equation (USLE) format. Finally, ongoing research and technology development using light detection and ranging (LiDAR) and photogrammetry in gully erosion predictions is discussed.