Water Environment Simulation And Ecological Environment Assessment Of The Coastal Zone In Bohai New Area

Coastal zone is defined as the junction region with significant land-ocean interactions.Its sustainable development is very important.With the development of social economy,the environmental pollution in the coastal zone of Bohai New Area has become more serious.Therefore,it is of great practical significance to study the water environment simulation and ecological environment assessment of the coastal zone of Bohai New Area for pollution control,planning and construction,and sustainable economic development.Moreover,from the perspective of model construction methods,it has general applicability to the simulation calculation of rainfall runoff and pollutant migration and diffusion in river network in plain area.In this paper,the water environment simulation and ecological environment assessment of the coastal zone of Bohai new area are carried out under the current and planned situation..Water environment simulation is mainly realized by estimating pollution load,simulating rainfall runoff and simulating pollutant migration and diffusion.Ecological environment assessment mainly includes surface water environmental assessment and comprehensive assessment of ecological environment.In this paper,the research area is first meshed to generate unstructured hybrid meshes.Considering the topographic condition and the distance between the mesh center and the river course,the meshes which merge into the same river course are merged to form a sub-region corresponding to the river course one by one.The river course is classified and sequenced to determine the confluence relationship between rivers and sub-regions.Industrial pollution,residential life,livestock and poultry breeding,agricultural fertilizer and aquaculture are the sources of pollution in the estimation of pollution load.The output coefficient method was used to calculate the total nitrogen(TN),total phosphorus(TP),chemical oxygen demand(COD)and ammonia nitrogen(NH3-N)of villages.And then the calculation results of the pollutant emissions of each cell mesh and each sub-region are obtained through the Tyson polygon.The rainfall runoff model is established by coupling the hydrodynamic model of plain river network with the river's Quasi-sequential confluence model.Within each sub-region,the two-dimensional unsteady shallow water motion equation is taken as the governing equation.The finite volume method is used to solve the discrete problem,then the water level,flow velocity of each cell mech and runoff yield amount of each sub-region are obtained.Between different sub-regions,according to the principle of water balance and the confluence relationship between rivers,the amount of inflow,outflow and pondage of each sub-region are calculated.Finally,the amount of water entering into the Bohai Sea of the main rivers are obtained.It is verified by the measured rainfall data that the model is reliable.Pollutants are driven by water and migrate with the confluence of rainfall runoff.Following the principle of balance of pollutant quantity,the temporal and spatial distribution of pollutant concentration,and the amount of po llutant inflow,outflow and residue in each sub-region were calculated.Finally,the pollutant quantity and concentration in the main estuaries were obtained.It is verified by the measured pollutant concentration data that the model is reliable.According to the calculation results,the ecological environment evaluation is carried out in this paper:surface water environmental assessment is based on the calculated residual pollutant concentration,which is compared with the limit concentration of Class III water quality standard of surface water environmental quality,to evaluate whether the sub-region meets the standard;the comprehensive assessment of ecological environment adopts PSR model to establish evaluation index system,the weight of each index are determined by analytic hierarchy process,and then the comprehensive evaluation index of sub-regions is calculated to evaluate the ecological environment status of the study area.