Bore collapse and wave run-up on a sandy beach
Bore collapse and wave run-up on a sandy beach
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DOI：
10.1016/j.csr.2019.01.009
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发表时间：
2019-02-15
影响因子：
2.3
通讯作者：
Melo de Almeida, Luis P.
中科院分区：
文献类型：
--
作者：
Bergsma, Erwin W. J.;Blenkinsopp, Chris E.;Melo de Almeida, Luis P.
在海滩和海岸结构上的波浪上升是由坍塌的事故钻孔引发和驱动的，这一过程通常被认为是确定冲刷带向海的界限。因此，它是近岸波浪过程的一个关键特征，因为在风暴条件下，极端的上升可能导致结构溢出和海岸淹没。此外，入射钻孔的湍流性质及其崩塌使沉积物悬浮平流，从而形成一个高度形态动态的冲积带。跨岸钻孔崩塌的位置随波浪的变化而变化，其过程在空间和时间上都是非常有限的，给直接测量带来了困难。本文介绍了高时空分辨率的激光雷达在海浪和冲浪区自由面演变的现场测量，使166波的钻孔塌陷检测成为可能。这些测量结果用于研究钻孔崩塌时破碎波特性与波浪上升之间的联系。在LiDAR剖面的向海边界处识别入射钻孔，并通过内部冲浪和冲刷区跟踪到上升极限。研究发现，在所测的井眼中，有24%的井眼的垂直上升高度超过了在井眼坍塌过程中将势能完美转化为动能的预期高度。通过回归到现有的弹道型模型来描述单个波浪的上升，我们表明波浪的上升可以分为三个部分：孔崩塌，末孔速度和它们的非线性相互作用。对于目前的数据集，井眼崩塌和末端井眼速度的贡献分别为26%和27%，而两者之间的非线性相互作用占主导地位，占测量上升的47%。加入末孔速度后，预测俯仰的能力提高了30%，决定系数r由0.573提高到0.785。同样，波浪上升的rms误差从0.325米减少到0.295米，减小了约10%。
Wave run-up on beaches and coastal structures is initiated and driven by collapsing incident bores, this process is often considered to define the seaward limit of the swash zone. It is hence a key feature in nearshore wave processes as extreme run-up can lead to structure overtopping and coastal inundation during storm conditions. In addition, the turbulent nature of incident bores and their collapse suspends and advects sediment, resulting in a highly morphologically dynamic swash zone. The cross shore bore collapse location varies from wave to wave and the process is very limited in both spatial and temporal extent, making direct measurement problematic. This paper presents high spatial-temporal resolution LiDAR field measurements of the evolving free-surface in the surf and swash zone which enable the bore collapse detection for 166 waves. These measurements are used to investigate the link between broken wave properties at bore collapse and wave run-up. Incident bores are identified at the seaward boundary of the LiDAR profiles and tracked through the inner surf and swash zones to the run-up limit. It is found that the vertical run-up height exceeds that which would be expected for a perfect conversion of potential to kinetic energy during bore collapse for 24% of the bores measured. By returning to an existing ballistic-type model to describe the run-up of individual waves, we show that wave run-up can be divided into three components: the bore collapse, terminal bore celerity and their non-linear interaction. For the present dataset, the contribution of the bore collapse and terminal bore celerity is 26% and 27% respectively, while non-linear interactions between the two dominates and account for 47% of the measured run-up. By including the terminal bore celerity, the ability to predict run-up is increased by 30% with the determination coefficient r increasing from 0.573 to 0.785. Likewise, the RMS-error for the wave run-up shows an approximately 10% reduction from 0.325 to 0.295 m.