Watershed Water Environment System Modeling And Its Application

Currently, the overall situation of water environment in China has already entered to the new stage with serious ecological degradation and complex environmental pollution. China is confronting certain water environmental problems simultaneously, from which the developed countries had suffered gradually during the whole industrialization, such as increasing pollution load, difficult pollution control progress, aggravated water pollution, and serious surface water pollution. However, we are lack of systematic, collaborative and innovative scientific research on the basin water pollution problems for a long time, the technical support for water pollution control is relatively weak. The worsening trend of the basin water pollution has not been fundamentally reversed, the potential danger that water environment situation decreases and even mutates with the rapid development of the socio-economic still exists. With the rapid development of our country, the bottleneck restriction and stress effect of resources and environment will become increasingly severe.The research results on the river basins water pollution processes is an important basis for making water environmental protection measures. Water pollution of river basins is a combined result of many factors such as socio-economic development, pollution emissions, climate and water circulation system changes, wherefore the evolution mechanism is extremely complex. This paper analysis pollutants migarition and transformation mechanism in the different regions of river basins, develop the integrated model covering society-economic-hydrology-water environment-water ecology, simulate the process of water cycle, socio-economic development and water quality changes, analyze the quantitative coupled response relationship between socio-economic, the process of urbanization, water resource utilization, pollutant discharge and water environmental quality, reveal the formation mechanism of basin water pollution and the discipline of water environment evolution. The main contents of this paper are as follows:(1) Based on the demand of water quality target management of basin ecological function regionalization, establish the multi-factors coupling theoretical framework of basin water environment system covering the major system characterization indicators such as society, economic and environment.(2) Considering the water environment process of human activities such as industrial and municipal water taken, wastewater discharge, agricultural irrigation water taken, food delivery of fishery breeding and shipping, establish the socio-economic model to predict the water demand, drainage water volume and pollution load of industrial and domestic, to forecast water demand and drainage water volume of agricultural irrigation, to predict the pollution load of aquaculture and shipping traffic.(3) Considering the spatial differentiation of underlying surface condition, simulate the hydrological process of canopy interception, evapotranspiration, soil water movement, surface runoff, and based on analysis the mechanism of the combination of plant growth model and the nutrient migration-transformation dynamic model, a coupled plant-growth and nutrients circulation model is developed which considering the water and nutrients circulation in water-soil system. Then, considering the impact of soil temperature changes on the migration transformation process of water and pollutants, establish a distributed tank model to realize simulating the process of water cycle, pollutants migration transformation and energy cycle in areas outside of rivers.(4) Establish a coupled lD river networks water quality model and2D lake water quality model to realize the dynamic simulation of the water environment process, considering the influence of gate station control, ship disturbance on water flow regime and internal release, and the exchange of water quantity, water quality and energy caused by the process of abstraction and return waters and later soil water exchange in areas outside of the river. Finite volume method is used to solve the governing equations of the model system. The developed model can be a effective tool for the water dynamic and water quality simulation of complex river network and lake-land regions.(5) Coupling the socio-economic model, the tank model of areas outside of the river and the water quality and quantity model of river channel itself, establish the integrated model covering multi-factors such as socio-economic, hydrology and water environment.(6) By using the basin water environmental system model coupled multi-factors, simulate the process of water cycle, socio-economic development and water quality changes in Gehu Basin, analyze the quantitative coupled response relationship between socio-economic, water resource utilization, pollutant discharge and water environmental quality, reveal the formation mechanism of Gehu basin water pollution and the evolution trend of water environment system.