Collaborative Research: Rip Current Dynamics in a Complex Beach Environment

在过去的三十年中，实地实验主要是在具有相对简单的平台（直线和平行等高线）的海滩上进行的。这些观测结果用于验证深度平均波浪驱动流模型。在很大程度上，在缺乏沿岸变异性的海滩上，可以理解沿岸流和暗流的局部垂直流动结构。然而，直、平行的底轮廓或简单的海滩平台并不是稳定的形态动力学海滩状态，复杂的形态是常态。这激发了对复杂海滩的实验。激流、瞬态激流和激波区涡旋与激波区重力波（入射海浪和次重力）共存，但由于缺乏对复杂形态滩系的综合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，我们将参加一个欧洲的实地实验，旨在了解与离岸流形态相关的近岸环流。计划于2008年春季在法国的Truc Vert Beach进行多机构和国际实地试验。这个海滩的特点是一个充满活力的波浪气候，强烈的潮汐调制，一个典型的复杂的海滩平台，由新月形的沙洲、裂口通道和带山脊和流道系统的潮间带组成。科学目标是通过观测和先进的数值模拟来研究近岸混合、平均流型、沉积物输运和低频离岸流脉动的水深耦合。新的拉格朗日观测，嵌入在跨岸和沿岸的固定仪器阵列中，使用一组廉价的冲浪区漂浮器，将提供环流模式的重要空间地图。密集的欧拉和拉格朗日观测以及数值模拟工作将用于评估近岸动量和能量的跨岸和沿岸分布，影响沉积模式和运输，以及这一海洋大量利用部分的水团混合。研究的更广泛影响包括预测离岸流的位置、持续时间和强度，以确保游泳者的安全，了解近岸混合，模拟污染物的分散，以及预测海岸线和沙丘的侵蚀。这种类型的海滩平台比以前以综合方式研究过的任何海滩平台都要复杂，因此所提出的数据在世界上任何地方获得的可用数据集中都是独一无二的。在更广泛的传授中，这项努力将为多达六名研究生提供实践研究和论文的机会。

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.