董家口尾水排海环境影响数值预测及排放口比选研究

Study on predicting environmental impact of marine sewage discharge project and selecting the effluent discharge points in Dongjiakou

采用二维平面潮流数值模拟的方法对董家口港区尾水排放口位置进行比选研究,预测4个拟选排污口分别在尾水正常排放和事故排放两种工况下各水质污染因子的环境影响范围,并结合水深、动力条件等因素最终选定最优排污口.结果表明:研究海区海流以潮流为主,潮流性质为半日潮流,潮流运动形式以往复流为主,旋转为辅,海域涨落急流向为SW—NE向,整体上西防波堤—LNG码头连线南侧海域的水动力条件较好.经数值模拟预测研究,位于西防波堤南侧的P4排污口所在海域水动力条件活跃,水深条件适宜,有利于物质扩散,且事故条件下对日照海域和日照西施舌种质资源保护区影响小,为较优尾水排放点.同时P4排污口所在海域执行三类水质标准,污水数值模拟结果显示该排污口各污染因子超三类水质标准的面积均小于0.742 km2,NS向扩散距离均小于0.34km,扩散趋势与潮流方向一致,有利于其污染物稀释扩散.本次模拟预测客观地反映了污染物排海后的浓度变化和运动规律,为尾水排海污染物进行总量控制及海洋环境开发管理规划提供了科学依据和技术保障.

The two-dimensional tidal current numerical model was used to predict the environmental impact of 4 drains and simulated under the condition of normal discharging and accident discharge. Combined the impacts with factors of water depth, dynamic conditions and others the optimal effluent discharge points for the marine sewage discharge were selected in Dongjiakou port. The results show that current in the area studied is mainly of semi- diurnal and the movement type places alternating current first, rotational flow the second and the maximum velocity of fluctuation directs to SW-NE. Generally, sea area in the south of connection between western bulwark and LNG wharf has a better hydraulic condition. As result, the outlet P4 is optimal due to active hydrodynamic condition with suitable water depth and advantages of pollutant dilution and diffusion. Besides, it impacts little on Rizhao seawater and the Rizhao Coelenterate antiquate Germplasm Reserve in case of accident discharge. At the same time, considered that the seawater around P4 follows the Grade Ⅲ of Water Quality Standards, the areas around the outlet with water quality not better than Grade Ⅲ would be smaller than 0. 742 km^2 and the length of North-Southward diffusion would be less than 0. 34km by the simulation. As the diffusion direction is consistent with the current, the condition is favor for pollutant dilutions and dispersions. The numerical simulation reflects objectively the concentration changes and pollutant movements and it is a fundamental support for the marine environmental management planning and total amount control of effluent discharge.