Capacity Calculation And Loads Allocation In Plain Bays: Case Study In Zhushan Bay

With the increasing of water pollution, the limitations of total amountcontrol, which is China’s traditional main technology of water environmentalmanagement, has become increasingly evident. It is necessary to establish acapacity-based water quality objective management technology system inorder to improve that system of plain bays. This thesis, based on hydrologyand water quality characteristics, studied the technologies of capacitycalculation and pollutant load allocation.Dynamic algorithm of pollutant capacity of plain bays was based onmulti-dimensional dynamic water quality model, which had been establishedin this thesis. Taking the spatial and temporal differences of hydrology andwater quality in plain bays into account, as well as a variety of factors andtheir interactions, the pollutant capacity calculated by the dynamic algorithmwill be more accurate, more targeted and more practical.Plain bays always have many pollution sources. Many kinds and a largenumber of pollutants, after a complex migration and transformation process,converge to plain bays. From this point of view, hierarchy allocation, whichwas based on the relationship between sources and sinks, taking the efficiencyand fairness into account, was proposed to allocate allowed pollution load ofplain bays.Zhushan Bay of Taihu Lake was taken as empirical districts. Waterenvironmental quality assessment showed that the water quality of ZhushanBay is poor, and the major pollutants are TN, TP, NH₄-N and COD_Mn.Accordingly, the water quality control objectives were determined as follows:for TN, TP and COD_Mn, no cumulation in a year, and the percent of areaexceed acceptable levels should be less than10%; for NH₄-N, the percent ofarea exceeded acceptable level should be less than10%, and accordingly setthe season average concentration limits.Based on EFDC and WASP, a three-dimensional dynamic water qualitymodel was developed for Zhushan Bay. Then, according to the correspondingrelationship of pollutant load and water quality, Zhushan Bay’s allowedpollution load was calculated: TN2058.5t·a^-1; TP92.1t·a^-1; NH₄-N, based on the current emissions process,1193.5t·a^-1, and the average concentrationlimits for four seasons are respectively0.90mg·L^-1,0.94mg·L^-1,0.87mg·L^-1,0.85mg·L^-1; COD_Mn5102.2t·a^-1.Pollutants got into plain bays in such four ways: atmospheric deposition,endogenesis release, source at shore and river input. For Zhushan Bay, riverinput is the major source, and also the most controllable one. Based on thespecies composition, spatial distribution, and migration path of pollutionsources, a hierarchy allocation system was established. With a Retained amargin of safety, allowed pollutant load was allocated to pollution sources ofall hierarchies. The result of model simulation shows that the load allocationscheme made Zhushan Bay’s water quality reach the preset target.