Research On Optimal Allocation Of Non-point Source Pollution And Management Measures In River Basins

BeiZhai small watershed located in Beijing Water Source Protection Area, This water resources have been fundamental for the development of the manufacturing, recreation, construction, and agriculture sectors. Among this watershed is the HuaiJiuhe River. With the development of economy and society, soil erosion and point&non-point source pollution is a growing problem, and it has been a major reason for deterioration of water quality. Control the non-point source pollution from the upstream of HuaiRou Reservoir, and provide a scientific basis for watershed protection of water resources has become an urgent problem.In this study, Improved Export Coefficient Model (IECM) is introduced for NPS pollution loads estimation in BeiZhai small watershed by analyzing social economy data, land use, soil, soil conservation, and farmland management. At the GIS platform, the critical source area was identified according to the pollution loads.10structural practices was selected based on the implementation of the existing water and soil conservation practices. Then an assessment system was established with criteria selected for BMPs site suitability, performance evaluation, and cost&maintenance to serve as a first screen and selection reference for the BMP planning. At the last step of this study, three different scale watershed was extracted from the BeiZhai small watershed, and used a nondominated sorting GA(NSGA-?) to evaluate the optimal fitness of each BMP combination, and according to the local control target, the planning scenario was optimized to find the most cost-effective scheme for this three subwatershed.The main conclusions are as following:(1) The pollution estimation result indicated that the highest NPS loads is from livestock.The other pollution source with their pollution load in a descending order are rural life pollution and land use pollution. Big livestock is the major contributor for the livestock pollution load, and the contribution rate of TN?TP loads from big livestock are99%and98%, respectively. In terms of different land use type, the main pollution sources were corn land, Chinese chestnut forest and bushes with the contribution rate of91%and90%, respectively.(2) The result of the critical source areas identified indicated that the high-risk areas are mainly concentrated in the residential areas and livestock farm where it located in eastern of the BeiZhai village, and the most of the CSAs were locates beside the stream, throughout the watershed, where most high or relatively high population density or livestock&poultry excretion.(3) Normalization calculation method is introduced for estimation the comprehensive index values of10structural BMPs. The result deemed that the comprehensive index values in a descending order are constructed wetlands, infiltration basin, green roof, wet detention pond, porous pavement. The various measures listed above can be used as the mainly practices for the BMP planning.(4) Watershed scale study area, community scale study area and farmer scale study area were selected based on the different spatial scales, and according to the control target of the pollution loads, the planning scenario was optimized to find the most cost-effective scheme for the watershed NPS management BMP planning. The optimized result indicated that the TN and TP loads were reduced by45%while the total cost(TC) is574,560yuan for watershed, the TN and TP loads were reduced by46%while the TC reach to374,660yuan for the community scale, the TN and TP loads were reduced by65%while the TC reach to1518yuan for the farmer scale. At the same time, the cost of the individual practice is given, respectively. So as to provide the decision-making support for the watershed non-point source pollution management.