长江口盐水入侵特征及规律

在分析长江口2002年3月枯季全潮水文测验资料的基础上,建立了“长江口—杭州湾—舟山群岛”海域大范围二维水流盐度数学模型,对长江口盐水入侵的特征及规律进行了研究。结果表明:受北支盐水倒灌影响,时间上南支某些水域不同于一般的涨(落)憩时盐度达到峰(谷)值,而是涨憩时盐度达到谷值,落憩时盐度达到峰值;空间上南支盐度分布在大潮期间呈现出“高—低—高”的格局,口门处的盐度在涨憩时明显大于落憩时,数值模型计算结果与实测数据分析相一致。同时,通过对北支潮径动力分析可发现,外海潮差越大,上游径流量越小,北支盐水倒灌南支的可能性越大,即北支口分流比随上游径流量呈指数增长,而与外海潮差成反比。研究成果可供研究长江口盐水入侵科技人员参考。

Characteristic and Law of Saltwater Intrusion in Yangtze River Estuary

To investigate the characteristics and laws of saltwater intrusion in the Yangtze River estuary, a 2D mathematical model of flow salinity in a wide scope covering Yangtze River estuary, Hangzhou Bay, and Zhoushan islands is established according to tidal hydrological data of the Yangtze River Estuary in March 2002 during dry season. Results suggest that in temporal scale, the salinity in some water areas of the south branch reduces to valley at spring tide while reaches peak at ebb opposite to general regularity due to the saltwater flowing backward from the north branch; in spatial scale, the distribution of salinity in the south branch displays a pattern of “high-low-high” during spring tide, and the salinity in the entrance at tide is significantly higher than that at ebb. Numerical analysis results are consistent with model test data. Moreover, tidal diameter dynamic analysis for the north branch reveals that a bigger tidal range in open sea leads to smaller upstream runoff and larger possibility of saltwater intrusion into the south branch from the north branch, which indicates that the diversion ratio at north branch increases exponentially with runoff in the upper reach, but is inversely proportional to tidal range.