Knowledge of exchange flow and its variations is important, because it determines the distribution of salt, nutrient, pollutant, and suspended sediment in estuaries. Although exchange flow has been studied extensively, their variations over the spring–neap tidal cycle remain unclear. Many studies have indicated that the exchange flow is weaker during spring tides than neap tides, but others have reported that it might be stronger during spring tides. Therefore, we investigated the spring–neap variation of an exchange flow and its cause based on intensive observational data and an analytical model applied to the Sumjin River estuary (SRE), Korea. The observations revealed that exchange flow increased during the spring tide but decreased during the neap tide. The horizontal salinity gradient increased about seven times more during spring tide than during neap tide in the middle of the estuary. The analytical model implied that the exchange flow in the SRE is mainly driven by the horizontal salinity gradient. The large horizontal salinity gradient and tidal current amplitude ratio in the SRE between the spring and neap tides suggests that the horizontal pressure gradient driven by the salinity gradient overwhelms vertical mixing in driving exchange flow in the SRE.

中文翻译：

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韩国Sumjin河口春季潮气交换流量增加及其原因

交换流量及其变化的知识很重要，因为它决定了盐，养分，污染物和河口悬浮沉积物的分布。尽管已经对交换流量进行了广泛的研究，但它们在春季-春季潮汐周期中的变化仍不清楚。许多研究表明，春季潮汐的交换流量比潮汐潮弱，但其他研究则报告说，春季潮汐的交换流量可能更强。因此，我们基于大量的观测资料和应用于韩国Sumjin河口（SRE）的分析模型，研究了交换流的春季-春季变化及其成因。观测结果表明，交换流量在春季潮汐期间增加，而在净潮期则减少。河口中部的盐度水平上升比潮汐中的盐度上升高出七倍。分析模型表明，SRE中的交换流量主要由水平盐度梯度驱动。春季和潮汐之间SRE中较大的水平盐度梯度和潮汐电流振幅比表明，盐度梯度驱动的水平压力梯度压倒了SRE中驱动交换流的垂直混合。