Simulation Of Non-Point Source Pollution In The Drinking Water Basin Of Tie Shan Reservoir

The Reservoir of TieShan,a large reservoir in the upper reaches of the new Wall River of the East Dongting Lake,is an important drinking water source in Hunan province,and it is necessary to analyze the characteristics of Non-point source pollution in the watershed of the water source.This study collected three periods of TM remote sensing images in the drinking water source area of Reservoir of TieShan,obtained three time land use data by ENVI Software Supervision Classification tool,calculated the land use type situation in different period,analyzed the land use change tendency and the transfer situation.By collecting soil data,meteorological data and hydrological data,this paper establishes a distributed hydrological model SWAT model for the drinking water source area of Tie Shan Reservoir,simulates runoff and non-point source pollution in the watershed,obtains good results,analyses the non-point source pollution load and spatial distribution of the watershed,and finally sets four kinds of land use scenarios,The variation of Non-point source pollution under different land use scenarios was simulated.The main conclusions obtained are as follows:(1)The Land use types in the water source area of Tie Shan reservoir are mainly woodland,followed by water and grassland,the increasing trend of woodland in the basin is obvious,the decreasing trend of construction land and arable land is obvious,which has a great relationship with the implementation of "returning farmland to forest";The main change trend of the watershed is the increase of woodland area,the decrease of arable land and building land,and the conversion of farmland,building and grassland to woodland.(2)The runoff simulation rate of SWAT model is R2=0.91,EnS=0.95,and the simulated value is in good agreement with the measured value,the rate parameter is reliable,the effect of the verification period is less than the rate and the simulation result is R2=0.88,Ens=0.89.The Nash efficiency coefficient of total nitrogen in 6 Ene is greater than 0.7,has reached the requirement,but the simulation results of each watershed are smaller than the measured values,while the simulation effect of total phosphorus is not good,but the Nash efficiency coefficient of 3 is greater than 0.69,and the accuracy of the simulation is also reached.(3)The largest proportion of TN pollution contribution rate in the drinking water source area of Tie Shan Reservoir is the Sub basin controlled by the TieShan Dam site,the second is the ShaGang River basin,and the proportion of the pollution contribution rate of TP in the watershed is the sub basin controlled by the TieShan Dam,followed by the JiangJiaWan River basin.In the pollution load of tn in the water source area of Tie Shan Reservoir,the largest load is the ZhuGang River basin,followed by the MaoTian River basin and the JiangJiaWan River basin,and the largest proportion of the pollution load of TP in the watershed is the ZhuGang River basin,followed by the JiangJiaWan River basin.Overall,the pollution load in the ZhuGang River basin and the JiangJiaWan River basin is relatively high.(4)By analyzing the results of non-point source pollution in 4 different scenarios,from 1995 to 2015,the storage quantity of Non-point source pollution in the drinking water source area of Tie Shan reservoir is decreasing gradually,and the decrease ratio of TN to 49.26%,TP is 86.66%.The least amount of non-point source pollution is the L4 scenario,that is,all the land and farmland in the basin are transformed into woodland,which indicates that the reduction of farmland and building land is advantageous to the Non-point source pollution control of the watershed.