Improvements To Sand Production Modules Of SWAT Models And Simulation Of Runoff And Sand Production In Typical Basins Of The Loess Plateau

Yanhe River Basin is located in the middle reaches of the Yellow River Basin.It is a serious area of soil and water loss in the Yellow River Basin.It is also a representative basin.It is of great significance to study the characteristics of water and sediment changes in the basin for soil and water loss control,scientific management and planning of land use in the Yellow River Basin.Based on the measured data of runoff and sediment in Yanhe River Basin in recent 50years,this paper analyzes the variation trend of runoff and sediment in Yanhe River Basin,and then establishes SWAT model by using Arc GIS,and simulates the runoff and sediment transport of Yanhe River Basin from 1979 to 1990,and analyzes the adaptability of SWAT model in runoff and sediment transport simulation of Yanhe River Basin,On this basis,the sediment yield module of the model was improved and the sediment yield simulation was conducted again.The changes of sediment yield simulation effect before and after the improvement of the model were compared.Finally,the SWAT model was used to simulate different land use scenarios to study the response of runoff sediment transport to land use change.The main conclusions are as follows:(1)The results of Pettitt and m-k trend test show that the year of abrupt change of runoff and sediment transport in Yanhe River Basin from 1960 to 2009 is 1996,and the runoff and sediment transport can be divided into four stages:1960-1969 is the rising period of runoff and sediment transport;1960-1969 is the rising period of runoff and sediment transport;From1980 to 1989,runoff and sediment transport fluctuated;From 1980 to 1996,runoff and sediment transport increased;From 1996 to 2009,the runoff and sediment transport decreased.The main reason for the different change stages of runoff and sediment transport is the implementation of soil and water conservation project,which leads to the change of underlying surface.(2)SWAT model is used to simulate the monthly runoff and sediment transport of Ganguyi hydrological station in Yanhe River Basin from 1979 to 1990.The R~2 of monthly runoff simulation rate is 0.76 and 0.73 respectively,and the NS coefficient is 0.53 and 0.72respectively.The R~2 of monthly sediment transport simulation is 0.5 and 0.63,and the NS coefficient is 0.47 and 0.55 respectively.The results show that SWAT model is applicable to the simulation of monthly runoff in Yanhe River Basin,but it needs to be improved in the simulation of monthly sediment transport.(3)The simulation rate and validation period R~2 of the improved model are 0.53 and 0.71respectively,which are 6%and 8.5%higher than those before improvement,and NS coefficients are 0.51 and 0.58 respectively,which are 12%,7%and 5.5%higher than those before improvement.(4)The increase of cultivated land area will lead to the increase of runoff and sediment discharge,while the increase of woodland and grassland area can reduce runoff and sediment discharge.The results showed that the runoff decreased by 12.6%and 10.7%,and the sediment transport decreased by 57%and 53%respectively under the scenarios of farmland conversion to woodland and farmland conversion to grassland.The runoff increased by 19%and the sediment transport increased by 83%under the scenarios of woodland conversion to grassland.For watershed 25°The runoff of the watershed was reduced by 2.5%and 2%respectively,and the sediment transport was reduced by 14.3%and 11%respectively.The runoff of the watershed decreased by 6.12%and 4.8%respectively,and the sediment discharge decreased by 31%and 23%respectively.