Shoal margin collapses of several million cubic meters have occurred in the Western Scheldt estuary, the Netherlands, on average five times a year over the last decades. While these collapses involve significant volumes of material, their effect on the channel‐shoal morphology is unknown. We hypothesize that collapses dynamicize the channel‐shoal interactions, which could impact the ecological functioning, flood safety, and navigation in the estuary. The objective is to investigate how locations, probability, type, and volume of shoal margin collapse affect the channel‐shoal dynamics. We implemented an empirically validated parameterization for shoal margin collapses and tested its effect on simulated estuary morphological development in a Delft3D schematization of the Western Scheldt. Three sets of scenarios were analyzed for near‐field and far‐field effects on flow pattern and channel‐shoal morphology: (1) an observed shoal margin collapse of 2014, (2) initial large collapses on 10 locations, and (3) continuous collapses predicted by our novel probabilistic model over a time span of decades. Results show that a single shoal margin collapse only affects the local dynamics in the longitudinal flow direction and dampen out within a year for typical volumes, whereas larger disturbances that reach the seaward or landward sill at tidal channel junctions grow. The direction of the strongest tidally averaged flow determined the redistribution of the collapsed sediment. We conclude that adding the process of shoal margin collapses increases the channel‐shoal interactions and that in intensively dredged estuaries shoal margins oversteepen, amplifying the number of collapses, but because of dredging the natural morphological response is interrupted.

中文翻译：

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滩缘塌陷对沙质河口形态动力学的影响

过去几十年来，荷兰西斯海尔德河口平均每年发生五次浅滩边缘塌陷，损失达数百万立方米。虽然这些塌陷涉及大量物质，但它们对河道浅滩形态的影响尚不清楚。我们假设崩塌使河道-浅滩相互作用变得动态化，这可能会影响河口的生态功能、洪水安全和航行。目的是研究浅滩边缘塌陷的位置、概率、类型和体积如何影响河道-浅滩动力学。我们对浅滩边缘塌陷实施了经过经验验证的参数化，并在西斯海尔德河的 Delft3D 模式化中测试了其对模拟河口形态发育的影响。分析了三组情景对流型和河道浅滩形态的近场和远场影响：(1) 2014 年观察到的浅滩边缘塌陷，(2) 10 个地点的初始大塌陷，(3) 连续的塌陷我们的新颖概率模型预测了几十年时间跨度的崩溃。结果表明，单个浅滩边缘塌陷仅影响纵向流动方向的局部动态，并在一年内减弱典型体积，而到达潮汐通道交汇处的向海或向陆基台的较大扰动会增加。最强潮汐平均流的方向决定了塌陷沉积物的重新分布。我们的结论是，增加浅滩边缘塌陷的过程会增加河道与浅滩的相互作用，并且在集中疏浚的河口，浅滩边缘过度陡峭，增加了塌陷的数量，但由于疏浚，自然形态响应被打断。