Rip Currents: Coupling and Feedback between Waves, Flows, and Morphology

离岸流：波、流和形态之间的耦合和反馈

• 批准号: 1536365
• 负责人: Steve Elgar
• 金额: $ 54.24万
• 依托单位: Woods Hole Oceanographic Institution
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2015
• 资助国家: 美国
• 起止时间: 2015-09-01 至 2018-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1536365&HistoricalAwards=false
• 关键词: Rip; Currents; Coupling; Feedback; between

Rip currents transport biota, pollutants, and sediment from the shoreline to the continental shelf, and are a hazard to swimmers with over 100 fatalities per year. These narrow, transient, offshore-directed jets are difficult to observe, and thus there are few field tests of hypotheses for their generation, evolution, three-dimensional structure, and feedback with evolving seafloor morphology. Rip currents can be driven by alongshore variations in wave breaking, often associated with gaps in sandbars or depressions in the surf zone seafloor. Existing field observations near channels dredged across the surf zone and a numerical model tested with the field observations will be used to investigate the coupling and feedback between waves, currents, and morphology in and near rip channels. Although the main focus of the project is on the fundamental physics of hydrodynamics and morphodynamics near large perturbations to the surfzone seafloor, the project investigators will be collaborating with colleagues from federal agencies with more applied interests in nearshore processes. In particular, the post-doctoral fellow will work closely with the USGS colleagues who developed the model and other federal agency scientists to perform model simulations designed to provide results in line with their missions. The model will be a useful tool for these agencies to predict waves, flows, and beach changes, including responses to storms and engineering projects. In addition, the project investigators will collaborate with National Weather Service and National Ocean Service scientists to improve forecasts and warnings of rip currents and other hazardous beach conditions.In 2012 large shore-perpendicular channels were dredged in the surf zone with the underlying hypothesis that alongshore changes in wave breaking over the channels would drive strong rip current circulation cells (shore-parallel feeder currents converging and turning seaward at an offshore-directed rip jet). The three-dimensional circulation and evolving morphology was measured for a range of wave conditions and channel sizes, and included transitions from rip currents flowing offshore through the channels to alongshore currents flowing across the channels, and channels that migrated and filled. The field observations of waves, currents, and bathymetry in the presence of dredged shore-perpendicular channels will be used to ground truth and calibrate the numerical model. The numerical model will be used to investigate the hydrodynamic and morphologic response for a range of wave forcing and bathymetric perturbations. Although this study will focus on the rip channels we excavated, the results will be applicable to a wide range of nearshore systems, with or without complex bathymetric features. Specifically, the following questions will be addressed: (i) How does the three-dimensional nearshore circulation respond to different wave conditions and bathymetries, and what forces control transitions between alongshore flows and rip currents? (ii) What are the couplings and feedbacks between waves, currents, sediment transport, and morphological evolution that lead to channel migration, growth, or decay?

裂流将生物群、污染物和沉积物从海岸线运送到大陆架，每年有100多人死亡，对游泳者构成威胁。这些狭窄的，短暂的，离岸指向的射流是难以观察的，因此，有几个现场测试的假设，其生成，演变，三维结构，并与不断变化的海底形态的反馈。离岸流可以由波浪破碎的沿岸变化驱动，通常与碎波带海底的沙洲或凹陷中的间隙有关。现有的现场观测附近的渠道疏浚冲浪区和数值模型测试的现场观测将被用来调查波，电流和形态之间的耦合和反馈和附近的RIP通道。虽然该项目的主要重点是在冲浪带海底大扰动附近的流体动力学和形态动力学的基础物理学，但项目调查人员将与联邦机构的同事合作，对近岸过程有更多的应用兴趣。特别是，博士后研究员将与开发模型的USGS同事和其他联邦机构科学家密切合作，进行模型模拟，旨在提供符合其任务的结果。该模型将成为这些机构预测波浪、水流和海滩变化的有用工具，包括对风暴和工程项目的反应。此外，本发明还提供了一种方法，该项目的研究人员将与国家气象局和国家海洋局的科学家合作，以改善对离岸流和其他危险海滩条件的预报和预警。2012年，在碎波带中疏浚了大型垂直于海岸的通道，其基本假设是，波浪在通道上破碎的沿岸变化将驱动强大的离岸流循环单元（平行于海岸的馈线电流在离岸方向的撕裂射流处会聚并转向大海）。三维环流和不断变化的形态进行了测量的范围内的波浪条件和通道的大小，并包括从离岸流通过渠道沿岸流流经渠道，迁移和填充的渠道。在疏浚的海岸垂直通道存在的情况下，波浪、海流和水深测量的现场观测将用于地面实况和校准数值模型。数值模型将用于研究一系列波浪强迫和水深扰动的水动力和形态反应。虽然这项研究将集中在我们挖掘的撕裂渠道，结果将适用于广泛的近岸系统，或没有复杂的测深功能。 具体而言，将解决以下问题：（一）三维近岸环流如何响应不同的波浪条件和水深，以及什么力量控制沿岸流和离岸流之间的转换？(ii)波浪、水流、沉积物输运和形态演变之间的耦合和反馈是什么，导致了河道的迁移、生长或衰退？