Assessment of soil erosion and sediment delivery ratio using remote sensing and GIS: a case study of upstream Chaobaihe River catchment, north China

Soil erosion in catchment areas reduces soil productivity and causes a loss of reservoir capacity. Several parametric models have been developed to predict soil erosion at drainage basins, hill slopes and field levels. The well-known Universal Soil Loss Equation (USLE) represents a standardized approach. Miyun reservoir, which sits on Chaobaihe River, is the main surface source of drinking water for Beijing, the capital of China. Water and soil loss are the main reasons for sediment to enter a reservoir. Sediment yield is assessed using a version of the universal soil loss equation modified by Chinese researchers. All year 2001 and 2002 data for factors in the equation are obtained from remote sensing or collected to form an analysis database. These factors are computed and mapped using Geographic Information System tools. Based on the complex database, the modified model is developed. Through pixel-based computing the sediment yield per hydrological unit is calculated. The model does not consider sediment deposition occurring on hillslopes. Gross soil loss is often higher than the sum of those measured at catchment outlets. The sediment delivery ratio (SDR) per hydrological unit is also computed. This study analyzes the main contributions of sediment yields on sub-basins of the Chaobaihe River to the Miyun Reservoir, and discusses the possible reasons for the difference between SDRs in 2001 and 2002 at different outlets. The result shows that in the upper basin of the Miyun Reservoir, in 2001 the area of erosion that could be neglected was 8,202.76 km(2), the area of low erosion 3,269.59 km(2), the area of moderate erosion 3,400.97 km(2), the area of high erosion 436.89 km(2), the area of strong erosion 52.19 km(2) and the area of severe erosion 3.13 km(2). The highest soil loss was 70,353 t/km(2). yr in Fengning County in 2001, followed by 64,418 t/km(2). yr by Chicheng County in 2001. The SDR in 2002 was lower than that in 2001, The main reasons are the decreasing rainfall erosivity and total runoff.