The Effect Of Land Use Change On Water And Soil Loss In Typical Small Watershed Of Loess Hilly-gully Region

This paper took Luoyugou watershed as study area, which is a small watershed in the third subplot of Loess Plateau Hilly and Gully Region, SWAT model and WetSpa Extension model were used to simulate hydrology and sediment process of Luoyugou watershed, compared and analyzed the applicability of the two models. Combined of spatial distribution of rainfall erosivity, soil erosion intensity and the slope of all land use types, the study adjusted the land use pattern in order to obtain better water and sediment response. Through the analysis, conclusions are following:(1) This paper compared the SWAT and WetSpa Extension from the aspects of input data, model parameters and model simulation results. These two models both have a good applicability in the Louyugou watershed, Nash-Suttcliffe coefficient Ens, relative error Re and related coefficient R2all meet the minimum requirement, but we need to do large numbers of tests to get the local soil, land use and meteorological attribute database. Both of the two models have speciality in the application process, the former is appropriate to simulate the hydrology, soil erosion, nutrients migration transport and non-point source pollution in long period,while the later is suitable for short time step flood process simulation.(2) In recent years, soil erosion of Louyugou watershed has been eased with the increasing regulation efforts, but the land use pattern still has some unreasonable places. After the analysis of the basin’s actual situation, the study adjusted the land use pattern based on the GIS platform, combined with the basin rainfall erosivity spatial distribution, soil erosion intensity and the slope of each land use type distribution. The specific contents are as follows:insure the quantity of terraces preferentially, adjust sloping farmland and terraces with slope greater than25°to woodland, adjust sloping farmland with slope greater than8°to terraces, adjust orchard with slope greater than25°to woodland, adjust serious soil erosion areas with slope greater than8°to woodland and less than8°to terraces.(3) Adjusted and optimized the land use types based on2001, and use that as the SWAT model land use input data to simulate the scene, simulated the condition of runoff and sediment in valley export observatory station, the study compared and analyzed the difference between existing land use pattern and that after adjusting and optimizing. After adjusting and optimizing, the land use pattern reduced water and soil loss effectively, the runoff reduced by17.6%and the sediment reduced by17.7%.