Abstract Foreshores consisting of both bare tidal flats and vegetated salt marshes are found worldwide and they are well studied for their wave attenuating capacity. However, most studies only focus on the small scale: just some isolated locations in space and only up to several years in time. In order to stimulate the implementation of foreshores serving as reliable coastal defense on a large scale, we need to quantify the decadal wave attenuating capacity of the foreshore on the scale of an estuary. To study this, a unique bathymetrical dataset is analyzed, covering the geometry of the Westerschelde estuary (The Netherlands) over a time-span of 65 years. From this dataset, six study sites were extracted (both sheltered sites and exposed sites to the prevailing wind direction) and divided into transects. This resulted in 36 transects covering the entire foreshore (composed of the bare tidal flat and the vegetated salt marsh). The wave attenuation of all transects under daily conditions (with and without vegetation) and design conditions (i.e. events statistically occurring once every 10,000 years) was modelled. Overall, the spatial variability of the geometry of a single foreshore was observed to be much larger than the temporal variability. Temporal changes in salt marsh width did not follow the variability of the entire foreshore. Both under daily and design conditions, vegetation contributes to decreasing wave energy and decreases the variability of incoming wave energy, thereby decreasing the wave load on the dike. The southern foreshores, sheltered from the prevailing wind direction, were more efficient in wave attenuation than the exposed northern foreshores. A linear relation between marsh width and wave attenuation over a period of 65 years was observed at all marshes. The present study provides insights needed to calculate the length of a salt marsh to obtain a desired minimum wave attenuating capacity.

中文翻译：

---

滩涂盐沼地基十年波衰减能力

摘要 由裸滩涂和植被盐沼组成的前滨在世界范围内都有发现，它们的波浪衰减能力得到了很好的研究。然而，大多数研究只关注小规模：只是空间中的一些孤立位置，时间最长可达几年。为了促进前滩作为可靠海防的大规模实施，我们需要在河口尺度上量化前滩的年代际波浪衰减能力。为了研究这一点，我们分析了一个独特的测深数据集，涵盖了 65 年时间跨度内 Westerschelde 河口（荷兰）的几何形状。从这个数据集中，提取了六个研究地点（包括遮蔽地点和暴露于盛行风向的地点）并划分为横断面。这导致 36 条横断面覆盖了整个前滨（由裸露的潮滩和植被茂盛的盐沼组成）。模拟了在日常条件（有和没有植被）和设计条件（即统计上每 10,000 年发生一次的事件）下所有断面的波浪衰减。总体而言，观察到单个前滨几何形状的空间变异性远大于时间变异性。盐沼宽度的时间变化并没有随着整个前滨的变化而变化。在日常和设计条件下，植被有助于降低波浪能并降低传入波浪能的可变性，从而降低堤坝上的波浪载荷。南部的前滩，不受盛行风向的影响，在波浪衰减方面比暴露的北部前滩更有效。在 65 年的时间里，所有沼泽都观察到沼泽宽度和波浪衰减之间的线性关系。本研究提供了计算盐沼长度以获得所需的最小波浪衰减能力所需的见解。