Overwash threshold for gravel barriers
Overwash threshold for gravel barriers
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DOI：
10.1016/j.coastaleng.2011.12.006
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发表时间：
2012-05
影响因子：
4.4
通讯作者：
A. Matias;J. Williams;G. Masselink;Ó. Ferreira
中科院分区：
文献类型：
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作者：
A. Matias;J. Williams;G. Masselink;Ó. Ferreira
本文使用的大规模BARDEX实验在三角洲水槽中进行的形态反应的原型砾石屏障的波浪和潮汐强迫过冲条件下进行调查的结果。砾石屏障的性能取决于许多因素，如沉积物特性（孔隙度、渗透性、粒度）、地质环境和波浪气候。由于已知过洗过程控制短期砾石屏障动态和长期屏障迁移，因此开发一种可靠的定量方法来定义导致砾石屏障过洗的临界条件对于科学和实际管理目的都很重要。众所周知，当波浪爬高超过堰顶高程时，可能会出现三种结果：1）当波浪爬高刚好超过堰顶且流速非常弱时，形态变化不明显; 2）漫顶，导致堰顶区域堆积和堰稳定; 3）过冲，导致侵蚀、堰顶区域降低，最终导致堰淹没。这项研究提供了一个洞察的关键条件，区分这两种可能的结果和不同的机制，提供所需的积极和消极的反馈沉积动力学。为了定义过洗阈值条件，并预测特定过洗事件的形态结果，此处使用过洗势（OP），其定义为波浪爬高和屏障波峰高程之间的差值。为了有效地利用OP，有必要确定可靠的助跑预测器。在使用12个助跑方程的测试之后，Stockdon等人[Stockdon，H.F.，Holman，R. A.，Howd，P.A.，Sallenger，A.H.，2006.设置、斜流和起动的经验参数化。海岸工程师：53，573-588]方法已被确定为产生OP正值所需的爬高条件的最佳预测器，预计分别在平均OP值为0.2m和0.5m时发生越顶和过洗。OP值的使用提供了一种实用的方法，通过这种方法可以识别与砾石屏障过洗过程相关的潜在沿海危害，并被认为具有一系列实际的沿海管理应用。
This paper uses results obtained from the large-scale BARDEX experiments undertaken in the Delta flume to investigate the morphological response of a prototype gravel barrier to wave and tidal forcing during overwash conditions. Gravel barrier behaviour depends upon a number of factors such as sediment properties (porosity, permeability, grainsize), geological setting and wave climate. Since overwash processes are known to control short-term gravel barrier dynamics and long-term barrier migration, the development of a robust quantitative method to define the critical conditions leading to gravel barrier overwashing is important both for scientific and practical management purposes. It is known that when wave runup exceeds the barrier crest elevation, three outcomes are possible: 1) insignificant morphological change, when wave runup just overtops the barrier crest and flow velocities are very weak; 2) overtopping, resulting in accretion on the barrier crest region and barrier stabilisation; and 3) overwashing, resulting in erosion, lowering of the crest region and ultimately to barrier inundation. This study provides an insight into the critical conditions that distinguish these two possible outcomes and to the different mechanisms that provide the required positive and negative feedbacks to the sediment dynamics. In order to define the overwash threshold condition, and to predict the morphological outcome of particular overwash events, use is made here of the Overwash Potential (OP), defined as the difference between the wave runup and the barrier crest elevation. To make effective use of OP it is necessary to identify a reliable runup predictor. Following tests using 12 runup equations the Stockdon et al. [Stockdon, H.F., Holman, R.A., Howd, P.A., Sallenger, A.H., 2006. Empirical parameterization of setup, swash, and runup. Coast. Eng., 53, 573–588] approach has been identified as the best predictor of runup conditions necessary to generate positive values of OP, with overtopping and overwashing predicted to occur for average OP values of 0.2m and 0.5m, respectively. The use of OP values provides a practical means by which to identify potential coastal hazards associated with gravel barrier overwash processes and is considered to have a range of practical coastal management applications.