长江口北支由于径流分流比很小，盐水入侵较强，特别是枯季大潮期盐水甚至倒灌进入南支，影响上海市和江苏省的水源地水质。为了进一步研究北支盐水入侵的规律及影响因素，2014年1月1-9日在北支进行了大小潮同步水文观测。本次观测到了北支异常强盐水入侵：小潮期发生强盐水入侵，且强度大于大潮期。小潮期强盐水入侵导致中下游河段被高浓度盐水控制，盐度从下游B01到中游B02几乎没有变化，且盐度的涨落潮变化几乎消失。分析认为，小潮观测期间长江入河口流量较小、河口潮差不是太小，加上强偏北风，三者的叠加是导致强盐水入侵的主要原因。%Due to the very small river discharge ratio, saltwater intrusion in the North Branch of the Yangtze Estuary is strong. Particularly during spring tide in the dry season, salt water even spills over into the South Branch, which affects water quality of the water intakes of Shanghai Municipality and Jiangsu Province. In order to further research the law and impact factors of saltwater intrusion in the North Branch, the synchronous hydrologic measurements were carried out during spring tide and neap tide on 1-9 January 2014. The abnormal strong saltwater intrusion was observed. During the neap tide, strong saltwater intrusion occurred, which was even stronger than spring tide. The strong saltwater intrusion during neap tide resulted in the high salinity in the middle and lower reach, almost without change from B01 in the lower reach to B02 in the middle reach. And the variations of salinity during flood and ebb disappeared. The analysis indicated that during neap tide, the river discharge into the estuary was small, the tidal range was not very small, and the wind was strong from the north, the combination of which was the main reason inducing the strong saltwater intrusion.
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