Analysis Of Sediment Reduction After Soil And Water Conservation In Yanhe Watershed And Its Effect On Reservoir Design

The development of economy and society has been severely restricted by soil and water loss on Loess Plateau in north Shaanxi province. A series of practices of soil and water conservation have been carried out in Yanhe watershed in recent decades as well as the massive construction of returning the sloping farmland to forest and grass lands in recent years, and the obvious effects are obtained. However, the existing research on the quantitative evaluation on the effect of water and soil conservation, especially on the quantitative calculation of sediment reduction in large watersheds and its effect on the reservoir design can not meet the needs of practices. So, based on the measured data, the change of runoff-sediment and the benefits of sediment reduction after control and ecological construction in Yanhe watershed are analyzed, and the reasonable determination of sediment quantity in reservoir design with practical examples are discussed. The main contents and results of this paper are as follows: 1. The impacts of soil and water conservation on the change of runoff-sediment in Yanhe watershed are analyzed with quantitative and qualitative, as well as forecast and measuring methods, according to longseries of data of Yan'an, Ansai, Xinghe and Zaoyuan hydrological stations in Yanhe watershed. The results showed that the sediment yield of watershed reduced obviously after implementation of soil and water conservation practices. The average reduction in sediment yield reached 25.47% and 21.85% for two stages for Yan'an station, and 11.82%, 30.42% and 67.86%, for Ansai, Xinghe and Zaoyuan respectively.2. The quantitative relationships between the reduction benefits of water and sediment yield and vegetation coverage are established on the basis of the rainfall-runoff and rainfall-sediment yield data monitored in flood season.3. Taking adjacent built reservoirs as a reference, the sediment quantities of Yuetungou, Anshenggou and Hongzhuang reservoirs are determined considering the vegetation conditions in their watersheds. The results indicate that the reduction of sediment yield due to water and soil conservation should be considered in engineering design, and then the construction scale and investment can be rationally determined.