Numerical Simulation Of Flow And Pollutant Distribution In West Lake In Response To Abstraction Works

West lake, a famous tourist spot, has very important touring value and environmental significance. However, due to the influences of human activities, unreasonable exploiture and the release of nitrogen and phosphorus which have accumulated in the bottom mud for a long time, the West Lake's eutrophication increased severely, which affected its visual value seriously and restricted the local social and economic development.The West Lake's water quality and space-time character have been analyzed by using the measured data from 2002 to 2006. Meanwhile, based on the international well-known software-Delft 3D, the West Lake's hydrodynamic mathematical model was constructed to simulate the flow field and pollutant distribution field before or after abstraction works. The calculations were well tallied with the measured data, which proved the model was true and credible. Furthermore, the structure of field and the distribution rule of pollutant under different abstraction programs have been studied emphatically and applied to the optimization of abstraction program.The analysis of water quality's measured data reveals that the West Lake's eutrophication is controlled by phosphorus, and the water quality has reached the second class of surface water's environmental quality criterion after the abstraction works;and the water quality presents obvious seasonal variety and distribution otherness in different lake areas.The results of numerical simulation shows that without considering the influences of wind field, the influx and the positions of infalls and outfalls decide the West Lake's field structure which would further decide the rule of water's process and distribution. As a whole, the water's process and distribution effect in Nan Lake is the best, followed by Xili Lake, Wai Lake and Yue Lake and finally the Beili which basically can't be replaced under any of the programs. Under the small influx program at least two months are required in order to replace the water in West lake completely whereas under the large influx program one month is enough.The effect of replacing the water in West lake is mostly rested on the area which can be replaced and the influx, whenas the size of the area is mostly related with field structure. Consequently, the fundamental approach to optimize the replacement effect is to adjust the positions of infalls and outfalls and influx, which changes the field structure finally.