Study On Best Management Practices Of Soil And Water Loss In The Yixun River Basin Based On SWAT Model

The Yixun river basin is the largest tributary in the upper reaches of Panjiakou reservoir of Luanhe river,and it is an important part of Beijing-Tianjin-Hebei water conservation functional area..Panjiakou reservoir is the main water source of the water supply system in the middle and lower reaches of Luanhe river.The basin is located in the plateau and middle-low mountain areas,with high mountains and steep slopes,thin soil layer,frequent extreme weather such as torrential rain and long-term drought,which can easily lead to natural disasters such as floods,landslides and debris flows,and the intensity of soil erosion is high.Excessive reclamation in the basin leads to the dispersion of sloping land,and sloping land is the main source of soil and water loss in the basin.Serious soil erosion leads to the weakening of soil fertility,the decline of land productivity,the erosion of cultivated land,the weakening of the functions of regional soil and water conservation,water conservation and ecological maintenance,which seriously affects the agricultural production and ecological environment of the basin.Due to unreasonable land reclamation and over-exploitation of human beings,the Yixun river has become the largest tributary of sediment transport in the upper reaches of Panjiakou reservoir.A large amount of sediment discharge in the basin caused serious sediment deposition in Panjiakou reservoir in the lower reaches,which seriously affected the regulation function of the reservoir and the development and utilization of water resources.Therefore,in order to enhance the function of water conservation in the basin,improve the production capacity of agriculture and forestry,reduce the sediment deposition in the lower reaches,and effectively avoid the harm caused by soil and water loss,it is an urgent problem to explore scientific and effective prevention and control measures of soil and water loss.The best management practies（BMPs）are a kind of measures that can control and reduce soil and water loss and nutrient loss.The assessment of BMPs has important guiding significance for the prevention and control of regional water environment,and has been widely used in the control of soil erosion and non-point source pollution.In this paper,taking the Yixun river basin as an example,SWAT model is constructed to simulate the runoff and sediment in the study area,and the simulation results are used to analyze the temporal and spatial distribution characteristics of water and sediment in the basin.A variety of BMPs scenarios are set in the model,scenarios are evaluated by SWAT model,and the soil erosion control measures suitable for the watershed are discussed.The main conclusions are as follows:1.The input database of SWAT model is established through the basic data of the study area,including digital elevation model（DEM）,land use database,soil type database,meteorological database and hydrological database.Based on the DEM map,the Yixun river basin is divided into32 subbasins,and then further divided into 764 hydrological response units by using land use,soil and slope data.The sensitive parameters of Hanjiaying and Xiahenan hydrological stations are calibrated and verified by using the runoff and sediment data from 2009 to 2014.The evaluation indexes R~2 and NSE of runoff and sediment simulation are both greater than 0.5 and PBIAS are all less than±25%.The SWAT model has strong applicability in the basin..2.Based on the established water and sediment model,the temporal and spatial distribution characteristics of runoff and sediment in the study area are analyzed.The results show that the change trend of runoff and sediment in the basin is consistent with that of rainfall,and there is a strong linear correlation.Through the analysis,rainfall is the main driving factor of runoff and sediment yield in the study area.The spatial distribution of water yield and sediment yield is not obvious,but in the sub-basin with more water and sediment yield,the area of cultivated land and bare land is relatively high,indicating that cultivated land and bare land are the main sources of water and sediment in the study area.3.Using the validated SWAT model,combined with the actual ecological environment of the Yixun river basin,a total of 8 scenario measures of 4 BMPs are set up on the watershed scale,and evaluate the effect of each scenario on runoff and sediment reduction.Through comparison,it is found that the sediment control effect of engineering measures is better than that of non engineering measures.The reduction rate of runoff in different scenarios is 0.83%-12.57%,of which the reduction rate of stubble mulch tillage is the largest,and that of other scenarios is no more than 5%.the sediment reduction effects of different scenarios are quite different,in general,the sediment can be reduced by 14.42%-56.12%,of which the reduction effect of vegetation filter belt with 5m bandwidth is the best.