Alongshore Variable Dune Erosion During Extreme Storms

尽管沙丘很重要，但在极端风暴期间，很少有同时进行的冲浪和冲刷带波浪和流以及海滩和沙丘形态的野外观测。因此，模式模拟通常通过与观测到的风暴前后地形变化进行比较来校准和评估。驱动这些地形变化的波浪和洋流过程，以及极端风暴活动期间变化的时间和空间尺度，目前还没有得到很好的理解。该项目研究了极端风暴期间的水动力过程，这些风暴由于波浪碰撞导致100米尺度的沿岸可变沙丘侵蚀。该项目的成果将改善沿海管理，帮助保护沿海社区，并维持沿海资源。该项目将为本科生、应届毕业生和从事沿海工作的年轻专业人士提供为期2至3周的实地实习，为他们提供实地培训。这个实习项目将为参与者提供重要的经验，提高他们在海岸工程领域的潜在就业机会。此外，研究生将接受使用数值模型模拟近岸过程的训练。通过对3次大风暴之前、期间和之后的独特海浪和冲刷带波浪以及海浪、海滩和沙丘形态的观测，结合数值模式模拟，确定了100米尺度上沙丘侵蚀沿岸变化的原因。研究的假设是：(1)海岸带变化的沙丘侵蚀和退缩率取决于初始冲浪带的水深和相关的流体动力学；(2)在风暴期间，沙丘脚尖的波浪上升、反射和离岸运输之间的正反馈导致了侵蚀热点。探讨了风暴期间冲浪带测深和水动力对沙丘演化的重要性，以及冲浪带和冲荡带过程与侵蚀热点之间的反馈关系。pi将研究在极端风暴期间波浪如何在冲浪区和海滩上传播，以及在更温和的条件下，数值模型中使用的波浪过程参数化如何可能不同。沙丘演变的数值模拟对用户选择的参数以及近海和冲浪区的水深测量很敏感，而这些通常不为人所知。实验室观测表明，给定最佳拟合的泥沙输运系数，模式可以相当好地模拟沙丘变化，尽管高估了水位而低估了上升波动。作为该项目的一部分进行的研究将确定模拟的流体动力学在极端风暴中是否准确，以及模拟的沙层变化的时间历史是否正确。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Despite the importance of dunes, there are few concurrent field observations of surf and swash zone waves and currents, and beach and dune morphology during extreme storms. Thus, model simulations usually are calibrated and evaluated by comparison with observed pre- to post-storm changes in topography. The wave and current processes that drive these topographic changes, and the time and space scales of changes during periods of extreme storm activities, are not well understood. The project examines hydrodynamic processes during extreme storms that result in alongshore variable dune erosion over 100-m scales owing to wave collision. The outcomes of the project will improve coastal management, help protect coastal communities, and sustain coastal resources. The project will provide field training to undergraduates, recent graduates, and young professionals embarking on coastal careers by offering 2- to 3-week-long fieldwork-focused internships. This internship program will provide critical experience to participants enhancing the potential job placement in the field of coastal engineering. In addition, a graduate research student will be trained in the use of numerical models for the simulation of nearshore processes. Unique observations of surf and swash zone waves, and surf, beach, and dune morphology before, during, and after 3 large storms, combined with numerical model simulations, are used to determine the causes of alongshore variability of dune erosion, over 100-m scales. The hypotheses examined are: (i) alongshore variable dune erosion and recession rates depend on the initial surf zone bathymetry and associated hydrodynamics, and (2) positive feedbacks between wave runup, reflection, and offshore transport at the dune toe lead to erosional hotspots during storms. The importance during storms of surf-zone bathymetry and hydrodynamics to dune evolution, and the feedbacks between surf- and swash-zone processes and erosional hotspots are examined. The PIs will investigate how waves propagate across the surf zone and beach during extreme storms, and how parameterizations of wave processes used in numerical models may be different during more moderate conditions. Numerical simulations of dune evolution are sensitive to user-selected parameters, as well as to the offshore and surf-zone bathymetry, which often are not well known. Laboratory observations indicate that given best-fit sediment transport coefficients, models may simulate dune changes reasonably well, despite overestimating water levels and underestimating runup fluctuations. The research undertaken as part of this project will determine if the simulated hydrodynamics are accurate throughout extreme storms, and if the time history of simulated sand-level change is correct.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.