NUMERICAL SIMULATION STUDY ON ENVIRONMENTAL IMPACT OF SEWAGE DISCHARGE ON ESTUARY WATER FUNCTIONAL AREA

The two-dimensional hydrodynamic water environment numerical simulation method was used to study the influence of sewage discharge from Yuyao sewage plant on water environment, when multiple water functional zones coexisted in Hangzhou bay estuary. And the influence of envelope range, plane distribution characteristics of COD_Mn, NH₃-N and TP on each water functional zone were analyzed. The results showed that when the single increment of pollutants was discharged normally, the pollution zone formed a thin and long pattern along the direction of water flow. The enveloping area of the pollution zone with equal concentration was larger than neap tide, the maximum value was significantly larger than the average value, and the pollution area in the accident condition was larger than that in the normal condition. Combining the discharged from the other pollution sources and environmental background, the mixing area of the discharge outlet was 0.20 km², which met the coresponding requirements. According to the environmental impact assessment method of multi-functional areas, the most stringent water quality management objectives were met, and the marine function zoning and water quality classification management objective of a seawater function zoning was not affected. This research case was typical in practical engineering application. The results could provide reference for similar projects such as the demonstration of sewage outlet site selection in tidal estuary and simulation of water environment impact.