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| Hydraulic geometry of branching channels in Yangtze estuary |
| SUN Zhi-lin, YANG Zhong-tao, GAO Yun, XU Dan, HU Shi-xiang |
| Institute of Port, Coastal and Offshore Engineering, Zhejiang University, Hangzhou 310058, China |
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Abstract For the purpose of revealing the mechanism of morphological evolution in the branching estuary which is a prominent type of tidal estuaries and reducing siltation in the Yangtze Estuary deepwater channel, a new relation for the hydraulic geometry of branching estuary was developed by solving the 2D continuity equation in integral form, 2D resistance equation, dimensionless width-depth ratio relation and time-dependent sediment transport capacity formula. The ratio of mean depths of a distributary channel and the main stream is a power function of its bifurcation ratio with an exponent of 2/7. The maximum equilibrium depth at the top of mouth bar in the Yangtze Estuary was calculated as 6.91 m by the proposed hydraulic geometry relation. The result agrees well with the depth acquired from long-term measurement data, which proves the reasonability of the new relation. Furthermore, the hydraulic geometry relation was modified to consider the effect of the groins built in the North Passage by introducing the concept of main channel discharge proportion. The maximum equilibrium depth of the North Passage after the three stages of deepwater channel regulation project was hereby calculated as 8.40, 8.91 and 9.92 m. This lays a theoretical foundation for developing strategies to regulate the Yangtze estuary.
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Published: 01 December 2014
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长江分汊河口水力几何形态
为了揭示潮汐河口中居显著地位分汊河口的演变机理,减轻长江口深水航道淤积.基于积分形式二维连续方程、二维阻力公式、无因次宽深比关系与时变水流挟沙能力公式,建立分汊河口水力几何形态理论关系,且表明汊道与单一河道平均水深之比为分流比的2/7次方.据此计算获得了长江口拦门沙顶部最大平衡水深为6.91 m,与长期实测的自然水深相一致,显示了水力几何形态关系的合理性.引入主槽流量比例概念,进一步修正水力几何形态关系,使之适合于丁坝作用河段.据此计算得到在一、二和三期治理工程后北槽的最大平衡水深分别为8.40、8.91和9.92 m,为制定长江口治理方略提供了理论依据.
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