Abstract Tidal sand ridges are large-scale bottom features that occur on continental shelves with strong tidal currents and abundance of sand. These ridges have longshore spacings of several kilometres, heights of tens of metres, they evolve on centennial time scales and their crests are cyclonically rotated with respect to the direction of the dominant tidal currents. The coupled Delft3D-SWAN numerical model is used to study the natural morphodynamic evolution of tidal sand ridges and their response to interventions (sand extraction and construction of islands) in a setting that resembles the Belgian shelf. New aspects in this study are that a sophisticated wave model (SWAN), a shelf with a sloping bottom and state-of-the-art formulations for sediment transport (including suspended load) are considered. Starting from an initially flat bed, model results show that sand ridges develop on the shelf that have similar characteristics as those of observed tidal sand ridges. Results further show that ridges recover after sand extraction, i.e., the original sand volume of the ridge crests is recovered on decadal time scales. Deepening of the troughs provides sand for this recovery. The recovery of the ridges is weaker when pits are located further offshore and/or are deeper. Ridges recover faster when waves are included. If a sand pit is too deep ( > 4 m), the ridge loses sand in the first tens of years prior to its recovery on longer time scales. This initial sand loss seems to agree with the observed loss of sand volume from a tidal sand ridge on the Belgium shelf (Kwinte Bank), which has been subject to intense extractions. Model results further show that islands lose sand on decadal time scales until they eventually disappear. This sand loss is deposited on the crests and in the troughs. The presence of islands causes the surrounding ridges to break into smaller ridges that have smaller orientation angles than those of the natural case. Using different island configurations (location, geometry and number of islands, longshore distance between islands) does not lead to qualitative changes of the model results.

中文翻译：

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陆架上的潮汐沙脊：自然形态动力学演化和​​干预响应的数值研究

摘要 潮汐沙脊是发生在潮汐流强、沙质丰富的大陆架上的大尺度海底特征。这些海脊的海岸间距为数公里，高度为数十米，以百年时间尺度演变，其波峰相对于主导潮汐流的方向呈气旋性旋转。耦合的 Delft3D-SWAN 数值模型用于研究潮汐沙脊的自然形态动力学演变及其对类似比利时大陆架环境中的干预（沙子提取和岛屿建造）的响应。本研究的新方面是考虑了复杂的波浪模型 (SWAN)、底部倾斜的架子和最先进的沉积物运输公式（包括悬浮载荷）。从最初的平床开始，模型结果表明，陆架上发育的沙脊与观测到的潮汐沙脊具有相似的特征。结果进一步表明，抽砂后山脊恢复，即在十年时间尺度上恢复了山脊顶部的原始砂量。槽的加深为这种恢复提供了沙子。当矿坑位于离岸更远和/或更深时，山脊的恢复较弱。当包含波浪时，山脊恢复得更快。如果沙坑太深（> 4 m），山脊会在更长的时间尺度上恢复之前的前几十年失去沙子。这种最初的沙子流失似乎与观察到的比利时大陆架（Kwinte Bank）潮汐沙脊的沙子体积流失一致，该沙脊受到了强烈的开采。模型结果进一步表明，岛屿在十年时间尺度上会失去沙子，直到它们最终消失。这种砂损失沉积在波峰和波谷中。岛屿的存在导致周围的山脊分裂成更小的山脊，这些山脊的方向角比自然情况下的更小。使用不同的岛屿配置（位置、几何形状和岛屿数量、岛屿之间的长岸距离）不会导致模型结果发生质的变化。