Simulation Of Runoff And Sediment Yield In Zhuxi Watershed Based On SWAT Model

Southern red soil erosion area is one of the most densely populated areas in China.For one thing,the region whose range is big,soil layers are thin and erosion resistance is poor belongs to the humid subtropical monsoon climate,so it has rich heat,as well as much and concentrated rainfall.For another,human beings,irrational use caused serious loss of its soil and water.Therefore,the region's ecosystem is extremely unstable and fragile.Zhuxi is one of the representative watersheds of granite red soil erosion areas in southern China,and the study on its runoff and sediment yield will be of great theoretical significance and practical value.In this paper,the hydrological model of small watershed is mainly constructed by using SWAT distributed hydrological model.Through simulating the region's different weather conditions and different land use/cover scenarios,we can research the corresponding hydrological responses.The results can mainly be divided into three aspects:(1)Construct Zhuxi watershed's SWAT model database.We analyze the sensitivity of the model's parameters,and then use the runoff and sediment data of Youwuzhen's sub basin in east Hetian hydrological station for the model's calibrations and correction.The simulation results show that:for the monthly runoff in calibration period and validation period,the Re were respectively 9.5 and 20.6,R2 were respectively 0.91 and 0.86,and ENS were respectively 0.88 and 0.47.At the same time,for the daily sediment concentration on the period of calibration and validation,Re were respectively 19.25 and 7.43,R2 were respectively 0.85 and 0.78,and ENS were respectively 0.79 and 0.70.The experimental results show that,the runoff and sediment's simulation results by the SWAT model after correcting the parameters can be more objective to reflect the actual situation of the study area.Therefore,the SWAT model constructed in this paper has a good applicability.Meanwhile,the estimation result of Zhuxi watershed's soil erosion modulus and researching the sediment situation under different land use modes.The results show that the soil erosion of this region is mainly light,and the middle or high soil erosion is mainly distributed in the region's central part;of all kinds of land use modes,the soil erosion modulus of bare land is maximal,and the absolute value of sediment yield in forest land is largest as well..(2)The hydrological responses under the different weather conditions in Zhuxi watershed.By using the assumed climate scenario method,15 different climate scenarios were simulated to study the hydrological response under the different weather conditions in Zhuxi watershed.The results show that it had a positive relationship between the runoff and rainfall in the watershed,and a negative relationship between the runoff and the temperature.Moreover,compared with the temperature,the impact of the rainfall on the research area's runoff will be greater,and thus the rainfall is the more main influence factor.(3)The hydrological responses under different land use/cover modes.We construct four different land use/cover scenarios and discuss the corresponding hydrological responses.The results show that:The impact of land use change on the runoff of different scenarios is:land cover scene>garden cover scene>retuming farmland to forest scene>forest land cover scene.By comparing the average monthly runoff with the actual measured values,it can be found that the runoff decreased by 14%under the scenario of forest land cover,the runoff increased by 15%under the scene of the cultivated land cover,the runoff in the garden was reduced by 5%,and the runoff from farmland to forest was reduced by 6%.Therefore,the results show that the large increase in the area of cultivated land can cause the increase of runoff,and woodland and garden can greatly reduce runoff,in which the effect of forest land is more obvious.