Runoff Response To Land Use Change In The Yan River Using SWAT Model

This paper selects the typical watershed in loess plateau – Yan river watershed as the study area.The basic database and parameter system of SWAT model are constructed to simulate and validate the monthly runoff in the Yan river watershed. Then we studied the runoff response to land use change in the watershed. The main conclusions of the study are as follows:1) The basic database of SWAT model is constructed. The basic data of the Yan river watershed are collected and processed, including DEM data, the land use data, soil data,meteorological data and the other data SWAT model needed.2)The SWAT model’s input parameters and its applicable value were determined.Digital filtering method is used to calculate the base flow index, then the SWAT-CUP is selected to calibrate and validate the input parameters, the values of 14 sensitive parameters are determined. The five parameters which have great influence on the runoff simulation results are: CN2(Runoff curve number), SOL_BD(Moist bulk density),SOL_K(Saturated hydraulic conductivity), ALPHA_BNK(Base flow alpha factor for bank storage), GWQMN(Threshold depth of water in the shallow aquifer required for return flow to occur).3) To evaluate the applicability of the SWAT model in Yan river watershed. The monthly runoff data of the Ganguyi hydrological station from 1982 to 1988 are used for model calibration. In the calibration period, R2=0.74 and NS=0.69. The monthly data from1991 to 1996 are used for model validation. In the validation period, R2=0.79 and NS=0.72.The results can meet the evaluation criteria, but in the validation period simulation values are lower than the measured values in the month with larger runoff.4) Analysis of hydrological response to land use change show that vegetation restoration has greate influence on stream flow, which reduces the runoff. The annualsurface runoff is 30.26 mm, the annual base flow is 14.60 mm and the base flow index is0.48 under the land use situation in 1985; The annual surface runoff is 24.03 mm, the annual base flow is 12.87 mm and the base flow index is 0.53 under the land use situation in 2010. The annual simulation value of stream flow is 5.21 m3 / s at the Ganguyi hydrological station under the land use situation in 1985. The annual simulation value of stream flow is 4.47 m3/ s at the Ganguyi hydrological station under the land use situation in 2010, which decreased by 0.74 m3 / s, the rate of change is-14.2%.