钱塘江河口段盐水入侵的时空变化及预测模型

Temporal-spatial variation of salt water intrusion in the estuarine reach of Qiantang River and its numerical simulation

杭州城市供水85%取自钱塘江河口段,取水水质在枯水大潮期都不同程度地受到盐水入侵的威胁,分析钱塘江河口盐水入侵时空变化及研制二维数值预测模型对保障城市供水安全十分必要。根据钱塘江河口段实测水文氯度资料,分析了强潮作用下盐水入侵的时空变化特征;据此构建考虑斜压作用的二维水流、盐度输移的耦合数学模型,计算格式采用守恒性较好的有限体积法;在模型验证的基础上,数值分析了径流和潮汐对钱塘江河口段盐水入侵的影响,结果表明河口段的盐水入侵明显地受径流和潮汐的影响,据此可通过增大上游新安江水库的下泄流量抑制盐水入侵上溯以减小取水口氯度及超标时间,确保用水安全。

The estuarine reach of Qiantang River provides 85% fresh water supply to Hangzhou city. However, the estuarine water quality is threatened by salt water intrusion during spring tides of dry seasons. It is thus important to analyze the temporal-spatial variation of salt water intrusion and to develop a two-dimensional （2D） numerical model for the estuarine reach of Qiantang River. In this study, the temporal-spatial variation of salt water intrusion is analyzed using observed chloride profiles collected during spring tides. A 2D numerical model for coupled fluid flow with salinity transport is developed accordingly. The governing equations of the model are solved by an explicit finite-vol- ume method with good conservation performance. The influence of river runoff and tidal current on salt water intrusion in the estuarine reach of Qiantang River is studied using the 2D numerical model. The result shows that both river run- off and tidal current have great influence on salt water intrusion in the estuarine reach. Countermeasures such as increasing discharge from the upstream Xin＇an reservoir can effectively restrain the salt water intrusion and thus to reducing the chloride concentration and the over-standard time in estuarine waters. As a result, good water quality at the intakes can be maintained at the level of safe water supply.