Study On The Impact Factors Of Basin Erosion And Sediment Yield Based On SWAT Model

Soil erosion can result in land degradation and sediment deposition of a river. Study of the relationships between the changes of basin soil erosion and the impact factors such as rainfall, soil, land use and landform systematically, obtaining the regularity of runoff and sediment yield under different influence factors, not only can strengthen the pertinence of soil and water conservation measures in the different regions of the world, but also can deepen the understanding of physical process of the earth and improve the level of the theory of land use change science research.Liusha basin is a typical fragile area of ecological environment at Southwest Sichuan province. Severe soil erosion, drought, floods, landslides, debris flow and other mountain disasters occur frequently. The broken ecological environment has become the main limiting factor for the regional economic and social development.In this paper, the Liusha basin was selected as the study area, built the distributed model SWAT based on ArcGIS to study the relationship between sediment yield and the influence factors by simulating different land use scenarios of different rainfall intensity, different soil types, calculating the index for different landscape patterns in the river basin as well. The main research contents and conclusions are as follows:(1)Established the Liusha basin distributed hydrological model, the model was validated and calibrated by using 1980-2006 year’s observational runoff and sediment data. The results (monthly runoff Ens>0.71, R2>0.95, monthly sediment Ens>0.75, R2>0.87) show that the model has good accuracy, can be used to explore the characteristics of water and sediment transport under the influence of many factors. Returning the grain plots to forestry and grass to farmland were two kind of land use change as input to the model, obtained the simulation result of sediment yield. The results showed sensitivity of sediment yield to rainfall intensity in two land use changes, returning grass to farmland was far greater than returning grain plots to forestry. For different soil types, loess will produce a greater amount of erosion under same land use change than black soil、red loam、purple soil; Their sensitivity to rainfall intensity is the opposite.(2)Take sub basin as sample, using the Fragstats software to calculate the landscape index of the sub basin in 1986,1995,2000, and established the corresponding relationship between the variation of the landscape pattern and the variation of the sediment yield in the sub watershed. Through the SPSS analysis software, the method of multiple linear regression based on the least square method was analyzed, selected 4 typical landscape pattern indexes that affect the change of the basin erosion and got the multiple regression equation for the change of soil erosion modulus and the change of typical landscape pattern index. According to the actual physical meaning of the variables in the regression equation and the meaning of the corresponding landscape index, analyzed the correlation between the sediment yield and some landscape indices in the basin erosion to provide a theoretical reference for the water and soil conservation, land use landscape optimization management and other work.