Application Of WEPP Model To Soil Erosion And Sediment Yield Simulation In Guizhou Mountainous Area

The various topographic types,abundant rainfall and the contradiction between human and land in Guizhou Karst area,leading to serious soil erosion.Rocky desertification phenomenon even appeared in part of the area,soil erosion control and erosion prediction should be carried out urgently.As a new soil erosion prediction model,WEPP model has been widely used around the world.WEPP was introduced into China in 1990s.Many researches on soil erosion using WEPP model have been carried out in the black soil region of northeast China and the hill-gully region of the Loess Plateau,however,the application of the WEPP model for studying soil erosion in the southwest Karst area is still less.Based on the rainfall and sediment data obtained from the field runoff plots in Bijie Shiqiao and Zunyi Huyangshui small watershed,soil data and the daily meteorological data of the study area in the past 60 years,WEPP model database was established.The applicability of WEPP model in soil erosion prediction in small watersheds in mountainous area of Guizhou and the effects of rainfall factors and topographic factors on USLE model were analyzed.The WEPP model and USLE model were used to simulate sediment yield and the simulated results are compared.The main conclusions are as follows:(1)Sensitivity analysis of soil parameters and rainfall factors of WEPP model was carried out,relevant results show that soil albedo and soil erodibility of rill area have no effect on sediment yield simulation;the simulated value of sediment yield increases with the increase of soil erodibility of inter-rill area and initial saturation;the simulated value of sediment yield decreases with the increase of critical shear power and effective hydraulic conductivity;sediment yield are positively related to the peak occurrence,rainfall and maximum rainfall intensity,sediment yield is negatively related to the duration of rainfall events.(2)The model efficiency were 0.136,0.139,0.148,0.606 and 0.445 when using WEPP model to simulate sediment yield of rainfall events under different slope gradient(5°,10°,15°,20°and 25°),the simulation results are better under steep slopes.The model efficiency were 0.188,0.293,0.327,0.298 and 0.337 when using WEPP model to simulate sediment yield of rainfall events under different slope length(5m,10m,15m,20m and 25m),the simulated results under different slope length are the same.(3)Both maximum rainfall intensity and rainfall amount have huge impacts on the simulate sediment yield of WEPP model.Under different slope gradient conditions,WEPP model has good simulation effect under conditions of moderate rainfall and low rainfall intensity;under different slope length conditions,WEPP model has good simulation effect under conditions of heavy rain and high rainfall intensity.(4)The model efficiency were 0.72,-0.39,0.05,0.42,0.47 and 0.46 when using WEPP model to simulate sediment yield of rainfall events under different water conservation measures(corn,evergreen,osmanthus,camphor,cypress and Janan Fatsia),indicating good effects on corn plot,ordinary effects in camphor,cypress and Janan Fatsia plots,bad effects in evergreen and osmanthus plots.The specific parameters of initial condition in project management files of the WEPP model have great influence on the simulation results,the reason is the management files cannot describe different water conservation measures accurately,only a few parameters can describe a general picture of the field situation,which lead to big simulation errors.(5)The model efficiency coefficients were 0.407 and 0.510 when using WEPP model to simulate annual sediment yield on slope plot and length plot,indicating ordinary effects for slope plot and good effects for length plot.The model efficiency coefficients were 0.022 and 0.789 when using WEPP model to simulate average annual sediment yield for slope plot and length plot,indicating bad effects for slope plot and good effects for length plot.The annual rainfall erosivity∑EI30 has a great influence on the simulated sediment yield by the WEPP model.Whether applied in the slope plot or the length plot,when the rainfall erosivity is heavy,the WEPP model has a better simulation effect on sediment yield.(6)In the standard runoff plot,the model efficiency were 0.440 and 0.337 when using WEPP model and USLE model to simulate sediment yield of the 31 rainfall events,the simulation results of the WEPP model is slightly better than that simulated by the USLE model;However,under conditions of high rainfall intensity and large rainfall amount,the simulated results by USLE model is better than that by the WEPP model.(7)When using USLE model to simulate sediment yield of rainfall events,the simulated results under gentle slopes are better than that of steep slopes.The simulated results under long slope length were slightly better than that under short slope lengths.Under gentle slopes condition,USLE model is better than WEPP model when simulating sediment yield of rainfall events;under steep slopes condition,WEPP model is better than USLE model when simulating sediment yield of rainfall events.Under all slope length condition,WEPP model is better than USLE model when simulating sediment yield of rainfall events.