Storm overwash of a gravel barrier: Field measurements and XBeach-G modelling
Storm overwash of a gravel barrier: Field measurements and XBeach-G modelling
复制标题
DOI：
10.1016/j.coastaleng.2016.11.009
复制
发表时间：
2017-02-01
影响因子：
4.4
通讯作者：
Russell, Paul
中科院分区：
文献类型：
--
作者：
Almeida, Luis Pedro;Masselink, Gerd;Russell, Paul
砾石屏障为英国和世界各地的许多地点提供了自然形式的海岸保护和防洪。预测它们对导致漫溢和过度冲刷的不同风暴影响状况的脆弱性至关重要，因为这些过程可能导致危险后果，例如屏障背面被淹没或决口。本文首次对砾石海滩（英格兰康沃尔郡 Loe Bar）的风暴泛滥事件进行了现场测量。使用二维激光扫描仪进行高频现场观测（2 Hz），可以完整表征溢流（速度和深度）以及沿屏障横岸部分的形态响应。这些新颖的测量结果用于验证数值模型 XBeach-G，以预测溢流流量。使用 XBeach-G 进行了多次模拟，以研究在给定各种水位和波浪高度的情况下不同风暴影响状况的阈值。发现波周期和波谱形状显着影响这些阈值。虽然短周期波在到达斜流区之前通过破裂而消耗了大部分能量并产生短的助跑偏移，但长周期波由于其低陡度而未破裂地到达斜流区，并且高度增加（由于浅滩），从而促进了大的助跑偏移。当近海波浪谱具有双峰形状时，浅水中的波浪变换导致长周期峰值主导斜盘，从而产生大的上升偏移。长周期波或强双峰波会导致增强的上升，从而降低屏障越顶或过度冲刷的阈值。
Gravel barriers provide a natural form of coastal protection and flood defence for many sites around the UK and worldwide. Predicting their vulnerability to different storm impact regimes that cause overtopping and overwash is crucial as these processes can lead to hazardous consequences such as inundation of the back of the barrier or breaching. This paper presents the first field measurements of storm overwash events on a gravel beach (Loe Bar, Cornwall, England). High frequency in-situ observations (2 Hz) were performed using a 2D laser-scanner and allowed a complete characterization of the overwash flows (velocity and depth) and morphological response along a cross-shore section of the barrier. These novel measurements are used to validate the numerical model XBeach-G, to forecast overwash discharge. Several simulations were performed with XBeach-G to investigate the thresholds for the different storm impact regimes, given a variety of water levels and wave heights. Wave period and wave spectral shape are found to significantly affect these thresholds. While short period waves dissipate most of their energy by breaking before reaching the swash zone and produce short runup excursions, long period waves due to their low steepness arrive at the swash zone unbroken with enhanced heights (due to shoaling) thus promoting large runup excursions. When the offshore wave spectrum has a bimodal shape, wave transformation in shallow water causes the long period peak to dominate the swash giving large runup excursions. Long period waves or strongly bimodal waves result in enhanced runup thereby reducing the thresholds for barrier overtopping or overwashing.