Application Of SWAT Model To Non-point Source Pollution In Westlake Basin

As the only Lake Cultural Heritage in China,West Lake is faced with water environmental problems characterized by eutrophication and ecological degradation.Non point source pollution has become one of the main obstacles affecting the fundamental improvement of water quality in the lake area.In this paper,based on the collection and processing of basic data,the basic database of non point source pollution in West Lake basin was set up,and the SWAT model was thereby used to simulate the non point source pollution in the basin.SWAT-CUP was additionally adopted to calibrate and validate the runoff,TN and TP simulation results,and the precision requirements for the model application was thus guaranteed.Based on statistical analysis of simulation results,it was found that the annual nutrient load of the Jin Sha Jian watershed was the largest,in terms of 8.254t/a of TN and 1.269t/a of TP.While as to the pollution load per unit aerea,Chang Qiao Xi watershed presented the higherst values with 17.134kg TN/hm~2and 3.61kg TP/hm~2.Acooring to the spatial distribution of pollution load in the sub-basin,it was determined that the key source areas of the non-point source pollution load in the West Lake basin were the Chang Qiao Xi watershed,the middle and upper reaches of the Long Hong Jian watershed,and the upper reaches of the Jin Sha Jian watershed.Three scenarios were simulated in the Chang Qiao Xi watershed,and the TN and TP load decreased by(1)857.48kg/a,121.47kg/a,(2)346.91kg/a,50.27kg/a,and(3)567.11kg/a,136.35kg/a.Finally,several control measures of non-point source pollution were put forward in consideration of the actual situation.By analyzing the effects of different DEM resolutions on the simulation of non-point source pollution in the West Lake basin,it was concluded that the DEM resolution of 5-100m has no obvious effect on the runoff simulation,whereas the reduction of DEM resolution had a significant effect on TN and TP simulations.When the DEM resolution is lower than 60m,the nutrients simulation by the SWAT model cannot meet the accuracy requirements.It is therefore determined that 5~30m is the best DEM resolution range for non-point source pollution load simulation in the West Lake basin.