污水排放对河口水功能区环境影响的数值模拟

通过二维水动力水环境数值模拟方法，研究了杭州湾河口地区多种水功能区并存情况下余姚污水厂污水排放对水环境的影响，分析了COD_Mn、NH₃-N、TP的包络范围、平面分布特征和对各水功能区的影响。研究表明:污染物单增量正常排放时，污染带形态沿水流方向呈瘦长型；等浓度污染带包络面积大潮大于小潮，最大值显著大于平均值，事故工况污染面积大于正常工况；叠加其他污染源和环境本底正常排放时，排放口混合区面积为0.20 km2，满足要求；根据多功能区环境影响评价方法，满足最严格的水质管理目标，对海洋功能区划、一类海水功能区划水质类别管理目标未产生影响。研究在工程实际应用中具有典型性，研究成果可以为潮汐河口的排污口选址论证，水环境影响模拟等相似工程提供参考。

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.