Assessing Soil Erosion And Sedimentation Using Nuclear Tracing Technique And The WEPP Model

The Sichuan Hilly Basin is one of the most densely populated agricultural regions in China and the area represents one of the most severely eroded regions in the Upper Yangtze River basin because the purple soils, which are fertile soils in the Sichuan Hilly Basin, are highly susceptible to erosion. Also, it is very difficult to assess the soil and water conservation benefits of different management methods since the"Changzhi Project"and"harness of small catchment"were hold on 1998 due to lacking effective soil erosion data. And so reliable data for soil erosion rates of sloping field, sediment delivery ratio of small catchment are very important to assess the soil and water conservation benefits and establish sound policies about land use.Shangqiao Gully, a small catchment near the Shangqiao Village, was selected as the focus of the investigation. The effect of water erosion, tillage erosion and traditional soil and water conservation method to the soil redistribution in the sloping field were analyzed.In the same time, the sediment budget of the small catchment was investigated clearly and the sediment delivery ratio was estimated. Some conclusions are shown as below.1) The soil redistribution rates for the sloping field was 3100.84 t·km^-2·a^-1 and present similar trend along the slope. This further confirmed the potential for ²¹⁰Pb_ex measurement to estimate soil redistribution rates.2) Traditional soil and water conservation methods such as"Tiaoshamiantu"and hoe tillage resulted in the difference of spatial pattern of soil redistribution rates by the radionuclide tracing methods and the WEPP model.3) The catchment sediment output is estimated, and the sediment budget of the catchment is completed clearly through the investigation of soil erosion, deposition and land use change after 1963. In the 41 years after 1963, the sum and annual of erosion quantity of the Shangqiao Gully are 17594.56 t and 429.14 t·yr^-1, respectively, the 62 % sediment came from the cultivated slopes and the 38 % came from the grass-wood slopes. The sum and annual of deposition quantity of the Shangqiao Gully are 14495.27 t and 353.54 t·yr^-1, respectively. So the sediment delivery ratio for Shangqiao Gully is 0.18 regarding the outlet of pond as the outlet of the small catchment and is 0.38 regarding the inlet of the pond as the outlet of the small catchment.