Influence of tidal motion on discharge distribution in Yangtze Estuary
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摘要: 汊口分流是河流动力学中一个经典的科学问题，感潮河段内的汊口由于受到潮波运动的影响，会产生明显的剩余环流，使其分流过程与非感潮河段汊口存在明显不同。为揭示潮波运动对汊口分流的影响，引入分流不均匀系数概念，以长江口为研究对象，依据2002年地形建立平面二维数学模型。分别开展"无径"、"无潮"和"径潮"3种情况模拟，定量地分解出径流、潮流和径潮相互作用对分流的影响程度，并探讨深水航道整治工程对分流过程的影响。结果表明：潮波运动在枯季和洪季分别以32.95% 和35.71%的程度对南北港分流不均匀系数产生抑制作用，使分流趋于均匀。深水航道整治工程使得南港的径潮相互作用增强，潮平均水位壅高，减弱了径流向南港分配增加的趋势。Abstract: Flow division is a classic issue encountered in river dynamics. Bifurcations in subtidal estuarine environments are influenced by river discharge as well as tidal motion. Residual circulation usually occurs in estuaries owing to the effect of tidal dynamics. Flow divisions that occur at bifurcations are generally more complicated compared to those occurring in regions without tides. This study aims at quantifying tidal influence on subtidal discharge distribution in the Yangtze Estuary through application of the discharge asymmetry index. A 2-D numerical model was developed based on the bathymetry of the estuary, as measured in 2002. To decompose the effect of tidal motion, river discharge, and river-tide interactions, the model was subjected to three independent operating conditions-river discharge and tides, river discharge only, and tides only. In addition, the effect of Deepwater Navigation Channels on flow division has been qualitatively explained. Through use of the proposed model, the discharge asymmetry index at the South and North Channel bifurcations was reduced by 32.95% and 35.71%, respectively, during the dry and wet seasons. As observed, the general effect of tides is to make flow divisions more even. In the South Channel, river-tide interactions were strengthened by construction of the Deepwater Navigation Channel. Consequently, the subtidal water level was enhanced, and the dominant trend of flow allocation to the South channel was weakened.
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