Modeling the formation of a sand bar within a large funnel-shaped, tide-dominated estuary: Qiantangjiang Estuary, China
Modeling the formation of a sand bar within a large funnel-shaped, tide-dominated estuary: Qiantangjiang Estuary, China
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DOI：
10.1016/j.margeo.2011.12.008
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发表时间：
2012-03
期刊：
影响因子：
2.9
通讯作者：
Qian Yu;Yunwei Wang;Shu Gao;B. Flemming
中科院分区：
文献类型：
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作者：
Qian Yu;Yunwei Wang;Shu Gao;B. Flemming
位于中国东岸的羌塘江河口(外称杭州湾)是一个大型漏斗状、潮汐控制、混合良好的河口。河口地貌已达到平衡，其特征是总长125公里的大沙洲，海拔高于平均相邻海床10米。为了研究这种形态特征形成的物理过程，以羌塘江河口为例，对宽度呈指数递减的漏斗状区域进行了基于深度平均过程的二维地形动力学模拟(Delft3D)。该模型模拟了一个6000年的周期，输出显示了沙洲在大约3000年内达到平衡的发展过程。模拟沙洲的总体形状、大小和位置与观测结果一致。初期水动力和泥沙输移过程的短期模拟表明，受漏斗形状影响较大的河流流量和潮流的相互作用，沙洲发育在以河流为主的上游河口和以洪水为主的下游河口之间的过渡带，泥沙输送路径在此汇聚。一系列敏感性分析表明，河口汇流速度、泥沙粒度和河道流量是沙坝形成的主要控制因素。与世界上其他大型漏斗状、潮汐控制的河口相似，充足的细小无粘性泥沙(来自邻近的长江口)、大的河流流量和强大的岸线收敛速度形成了羌塘江河口的大型沙洲。
The Qiangtangjiang Estuary (the outer part being known as Hangzhou Bay) located on the east coast of China is a large funnel-shaped, tide-dominated and well-mixed estuary. The equilibrium estuarine morphology has been attained and characterized by a large sand bar having a total length of 125km and an elevation of 10m above the average adjacent seabed. In order to investigate the physical processes governing the formation of this morphological feature, two-dimensional depth-averaged process-based morphodynamic modeling (Delft3D) was carried out on a schematized funnel-shaped domain with exponentially decreasing widths based on the dimensions of the Qiangtangjiang Estuary. The model simulated a 6000-year period, the output showing the development of a sand bar that reached equilibrium within about 3000years. The general shape, size and position of the modeled sand bar are consistent with the observations. Short-term simulations of hydrodynamic and sediment transport processes at the initial stage indicate that, in response to the interactions between river discharge and tidal currents, which are strongly influenced by the funnel-shape, the sand bar developed in the transition zone between the river-dominated upper estuary and the flood-dominated lower estuary where sediment transport pathways converge. A series of sensitivity analyses suggest that the estuarine convergence rate, sediment grain size, and river discharge are the main controlling factors of sand bar formation. Similar to other large funnel-shaped, tide-dominated estuaries of the world, a sufficient supply of fine cohesionless sediment (derived from the adjacent Changjiang Estuary), a large river discharge, and a strong shoreline convergence rate have shaped the large sand bar in the Qiangtangjiang Estuary.