Research Of SWAT Model On Eroded Small Watershed In Yanghe Hilly Basin

The SWAT model is an important tool for studying soil erosion problem,and it was widely used in exploring the spatiotemporal distribution of soil erosion and runoff and sediment yield in watersheds of different scales.Aiming at the problem of soil erosion in the Yanghe hilly basin,this thesis constructed the SWAT models for the Taipingzhai Village's eroded small watershed and the Yanghe River basin,and obtained good simulation results of runoff and sediment output.The calibrated parameters of the SWAT model were analyzed on two scales.Moreover,Qingyangling small watershed was selected as a case to verify the applicability of the SWAT model parameters of the Yanghe River Basin to the eroded small watershed.The main research results of the thesis are as follows:(1)The hydrological data were obtained by setting up field automatic weather stations,flux stations,runoff plots and other methods in the small watershed of Taipingzhai Village.The obtain Digital Elevation Maps(DEM)were obtained by using drones scanning terrain.The soil physical and chemical properties data were determined through experiments.Based on the acquired data,the SWAT model was established and the parameters were calibrated.Through runoff and sediments simulations with the application of the SWAT model,it was found that the runoff simulation correlation reached 0.97,the efficiency coefficient reached 0.71,the sediments simulation correlation reached 0.90,and the efficiency coefficient reached 0.68,indicating that the simulation result of runoff and sediments is good.Through the study of the spatial distribution of soil erosion in the study area,it was found that the soil erosion in the small watershed of Taipingzhai Village is strong,that the soil erosion in the central channel of the small watershed has reached a severe degree,and that the erosion has a tendency to expand from the channel to the slope.(2)Due to the complex coverage of the small watershed in Taipingzhai Village,this thesis combined field sampling and simulation calculations to explore the influence of changes in leaf area index on the simulated soil erosion intensity.It was found that the maximum potential leaf area index(BLAI)has a negative correlation with the soil erosion degree of grassland and wasteland,a large impact on soil erosion degree of grassland,with a change of 54.89%,and a small impact on soil erosion degree of wasteland,with a change of only 0.064%.The optimal leaf area growth curve corresponds to the maximum leaf area index percentage at the first point(LAIMX1),and the maximum leaf area index percentage of the optimal leaf area growth curve corresponds to the second point(LAIMX2),have a greater impact on the soil erosion of grassland,respectively have first-order positive correlation and second-order negative correlation,but these two parameters have no effect on the erosion of wasteland.(3)Constructing the SWAT model of the Yanghe River Basin,calibrating the model parameters according to the hydrological observation data of Xiangshuibao Station and simulating the runoff lead to that the correlation coefficient of the runoff during the test period is 0.82 and that the efficiency coefficient is 0.62,indicating that the simulation results are relatively good.Comparing the main calibrated SWAT parameters of the watershed of Taipingzhai Village and the Yanghe River Basin,it was shown that the correlation between the calibrated parameters of the Yanghe River Basin and the watershed of Taipingzhai Village reached 0.90.Selecting the Qingyangling small watershed with a scale between the Yanghe River Basin and the watershed of Taipingzhai Village,and applying the calibrated SWAT parameters of the Yanghe River Basin.The simulation of soil erosion in different scales shows that the relative errors of the erosion modulus between Qingyangling small watershed and Taipingzhai village small watershed and Yanghe watershed are-6.07%and-22.42%,respectively.The relative error is small,indicating that the calibrated SWAT parameters and the simulation results of soil erosion have applicability in the Yanghe hilly basin.This result has important reference value for the construction of the SWAT model of the eroded small watershed in the Yanghe Hilly Basin.Based on the SWAT model,this thesis simulated the runoff and sediment output of the eroded small watershed of Taipingzhai Village and the Yanghe River Basin,studied the spatial distribution of soil erosion,and discussed the relevance of calibrated SWAT parameters and soil erosion simulation results among watersheds at different spatial scales.A set of applicable SWAT model parameters of the Yanghe River Basin were obtained,providing a reference for constructing the SWAT model for the eroded small watershed with the lacking of observation data in the Yanghe Hill Basin.