Collaborative Research: Rip Current Dynamics in a Complex Beach Environment

在过去的三十年里，野外实验主要在平面形状相对简单(直线和平行等高线)的海滩上进行。这些观测被用来验证深度平均的波浪驱动流模型。在很大程度上，近岸流和底层流中的局部垂向流结构是在缺乏近岸变异性的海滩上理解的。然而，笔直和平行的海底等高线或简单的海滩平面并不是稳定的地形动力海滩状态，复杂的地形是常态。这促使人们在复杂的海滩上进行实验。激流、瞬变激流和海浪带涡流与重力波(入射海浪和亚重力)在海浪带共存，但由于缺乏对复杂地形海滩系统的全面现场测量和数值模型验证，它们的重要性和动力耦合尚未得到认识。在这个项目中，我们将参加一项旨在了解与急流形态相关的近岸环流的欧洲野外实验。计划于2008年春季在法国Truc Vert海滩进行一次多机构和国际实地试验。这个海滩的特点是充满活力的波浪气候，强烈的潮汐调制，以及典型的复杂的海滩平面形态，由新月形沙洲、裂口水道和带有海脊和沟渠系统的潮间带组成。科学目标是通过观测和先进的数值模拟来研究低频撕裂流脉动的近岸混合、平均流型、沉积物输送和水深耦合。嵌入在跨岸和近岸固定仪器阵列中的新拉格朗日观测，使用一支廉价的冲浪带漂移器舰队，将提供重要的环流模式空间地图。密集的欧拉和拉格朗日观测以及数值模拟工作将被用来评估近岸动量和能量的跨岸和近岸分布，对沉积模式和输送的影响，以及这一海洋频繁利用区段的水团混合。研究的更广泛影响包括预测为游泳人员安全的激流的位置、持续性和强度，了解近岸混合，模拟污染物的扩散，以及预测海岸线和沙丘侵蚀。这种类型的海滩平面比以前以综合方式进行的任何研究都要复杂，因此，拟议的数据在世界任何地方获得的现有数据集中都是独一无二的。在更广泛的传授中，这一努力将为多达6名研究生提供实践研究和论文机会。

Over the past three decades, field experiments have been performed primarily on beaches with relatively simple planforms (straight and parallel contours). These observations were used to verify depth-averaged wave-driven flow models. To a large extent, the local vertical flow structure in alongshore currents and undertow is understood on beaches lacking alongshore variability. However, straight and parallel bottom contours, or simple beach planforms are not a stable morphodynamic beach state, with complex morphology being the norm. This has motivated experiments on complex beaches. Rip currents, transient rip currents, and surf zone eddies co-exist with gravity waves (incident sea-swell and infragravity) in the surf zone, yet their importance and dynamic coupling have gone unrecognized owing to a lack of comprehensive field measurements and numerical model verification on complex morphologic beach systems. For this project, we will participate in a European field experiment aimed at understanding nearshore circulation associated with rip current morphology. A multi-institutional and international field experiment is planned for the spring of 2008 at Truc Vert Beach, France. This beach features an energetic wave climate, strong tidal modulation, and a typically complex beach planform composed of crescentic bars, rip channels, and an inter-tidal zone with ridge and runnel systems. The scientific objectives are to examine the nearshore mixing, mean flow patterns, sediment transport, and bathymetric coupling of low frequency rip current pulsations through observations and advance numerical modeling. Imbedded in cross- and alongshore fixed instrument arrays, new Lagrangian observations using a fleet of inexpensive surf zone drifters will provide vital spatial maps of circulation patterns. The dense Eulerian and Lagrangian observations along with the numerical modeling efforts will be used to evaluate the cross- and alongshore distribution of momentum and energy in the nearshore, the influence sedimentation patterns and transport, and the mixing of water masses in this heavily utilized segment of the ocean.The broader impacts of the research include predicting location, persistence, and strength of rip currents for swimmer safety, understanding nearshore mixing, modeling dispersion of pollutants, and anticipating shoreline and dune erosion. This type of beach planform is more complex than any that has been previously studied in a comprehensive fashion, and thus the proposed data will be unique among available data sets obtained anywhere in the world. Among the broader imparts, this effort will provide hands-on research and thesis opportunities for up to six graduate students.