Application Of SCS Model To Simulate Runoff In Tumen Xigou Watershed

As one of the most important water resources in Beijing, Miyun reservoir is facing more and more severe environment problems. On one hand, due to the variation of climate and the reduction of the rainfall around this area, the runoff yield and the runoff which is able to enter the Miyun reservoir becomes relatively low and the quantity of the reservoir is decreasing. On the other hand, along with the increasing of the pollution load into this area and the decreasing of the self cleaning capacity, the water pollution is aggravated. Based on these two reasons, in order to save the water crisis in Beijing, it is of great significance to improve the water quantity and quality in Miyun reservoir. The latest researches have shown that the rainfall and runoff have great influence on river flow. Therefore, studies on the relationship between Miyun reservoir water storage and those two factors are of great importance on improving the water quantity and quality in Miyun reservoir. Experience-frequency curve was used in the simulation of rainfall to analysis the rainfall characteristic of this area; runoff was simulated by association of GIS and SCS technology, to study the pathway identity.Experience-frequency curve was used in the simulations of annual rainfall at different probabilities and according to the linear dependence relation between rain capacity and raining days. The simulation result shows that the rain capacity is 595.83 mm when P is 50%. Based on the liner relationship between rainfall and raining days, the same simulation method was used to simulate the number of monthly rainfall, then raining days. When P equals to 0.01%, the simulated number of raining days in July was 26.By analyzing the geographic information, the outcome of CN was calculated; therefore, the application of model SCS in Miyun reservoir was completed. Comparison between the simulated and the actual runoff data,35.9% of the simulation results was within allowable range. The lack of accuracy in the simulation probably resulted from the loss of documents, the misreport of data and the lack of consideration on the gradient in this area.