Study On The Characteristics And Control Of Non-point Source Pollution In The Hanjiang River Basin

Non-point source pollution is one of the important factors affecting the water environment and water ecological security of the river basin.The Han River is an important water source area for the South-to-North Water Diversion Project in my country.The quality of the water source area in the Han River Basin is directly related to the success or failure of the National South-to-North Water Diversion Project,In view of this,this study analyzes the characteristics of non-point source pollution in runoff communities,typical small watersheds,and river basins above Yangxian section of the Hanjiang River.The four state-controlled sections of the main stream in the study area are used as control sections to calculate the main stream of the river above Yangxian section of the Hanjiang River.Water environment capacity,analyze the current water quality of the section and determine the water quality target,propose a non-point source pollution control plan,use the Load Calculator and MIKE 11 model to simulate the water quality plan,and evaluate the effect of the control plan.The main research conclusions are as follows:(1)Use Load Calculator to establish a non-point source pollution load assessment model for the Yangxian and above section of the Hanjiang River Basin,and use MIKE 11 to establish a hydrodynamic and water quality model for the river above the Yangxian section of the Hanjiang River.The annual water quality and quantity data are used to calibrate and verify the MIKE 11 model.The R2 of the calibration and verification results are all greater than 0.72,surface runoff.Among the five runoff plots under different vegetation types,peanuts have the largest pollution output.In the non-point source pollution control plan,it can be considered to increase the utilization rate of chemical fertilizers and pesticides to reduce the agricultural pollution load.(3)The average concentration method is used to calculate the non-point source pollution load of different hydrological years in Zhangjiagou small watershed,and the pollutant load of different hydrological years is quite different.In general,the pollution load of the river basin is wet year>normal water year>dry year.The load per unit area of ammonia nitrogen in Zhangjiagou small watershed is 50.07 kg/hm2/a,and the load per unit area of COD is 745.05 kg/hm2/a.According to the Load Calculator model,the non-point source pollution load in the basin above the Yangxian section of the Hanjiang River is calculated.The simulation results show that the unit area load rate of ammonia nitrogen in the basin above the Yangxian section section is 23.64 kg/hm2/a,and the unit area load rate of COD is 495.52 kg/hm2/a.The area load rate of non-point source pollution in the Zhangjiagou small watershed is greater than that of the watershed above the Yangxian section.(4)The model method is used to calculate the water environment capacity of the river channel above the Yangxian section.The calculation results show that the water environment capacity of the river channel during the flood season(May to October)and the non-flood season are very different.The water environment capacity of ammonia nitrogen and COD in the flood season are 26.42 t/d respectively,363.13 t/d,and the water environmental capacity of ammonia nitrogen and COD in non-flood season are 6.46 t/d and 170.28 t/d,respectively.With the development of the acceleration of urbanization,the basin is still facing the pressure of receiving pollution and increasing capacity.(5)According to the analysis results of non-point source pollution load and the actual situation,it is proposed that agricultural non-point source cultivating ground source pollution will be reduced by 30%(option 1),livestock and poultry breeding pollution will be reduced by 50%(option 2),and surface runoff pollution will be reduced by 30%(option 3),agricultural non-point source pollution is reduced by 30%and livestock and poultry breeding pollution is reduced by 50%(option 4)Four schemes,the four schemes are simulated in Load Calculator,and the simulation results are added to the MIKE 11 model as boundary conditions.Simulate and calculate the reduction of pollutant concentration in the river channel by the four schemes.From the simulation results,it can be obtained that the four options have played a certain role in optimizing the water quality of the section.Among the individual measures,the second option has the best effect on reducing the concentration of pollutants,and the combined measures have better control effects on non-point source pollution than single measures.The four programs have different effects on the reduction of pollutant concentration in each section.The overall reduction effect is Liangxidu>Nanliudu>Huangjinxia>Liejinba.