Collaborative Research: Physics of Dune Erosion during Extreme Wave and Storm-Surge Events

沙丘通常是沿海基础设施的主要，有时是唯一的“防线”，并且越来越多地建造和积极管理以防止极端事件。海岸管理人员需要了解沙丘在这些事件下的反应，以便预先定位资产。天然沙丘和人工沙丘都通过改变破碎的海浪和坡面来消耗能量，从而限制过度冲刷，从而在极端海浪和风暴潮事件期间最大限度地减少沿海洪水。然而，由于极端物理力与沙丘的相互作用时间相对较短，但在水位上升的关键时间内，人们对沙丘沉积物和植被如何改变水动力和改变海滩-沙丘剖面演变的理解有限。这项研究的重点是沙丘对一系列水位和强迫条件的反应，模拟极端风暴事件的通过。一个接近原型规模的实验室实验将在俄勒冈州立大学的大波浪水槽的移动床上进行。物理模型研究将在光秃秃的沙丘上进行，在波浪侵蚀下快速建造（松散压实）的沙丘，以及有活植被的沙丘。将收集和分析与从短期（湍流）到较长时间尺度（个别事件）的过程有关的数据，以便对影响沙丘稳定性的流体-沉积物-植被动态以及对极端事件的损害减轻战略有基本的了解。收集的数据将用于验证数值模型。多相流模型sedwaveFoam（在开源的OpenFOAM框架中创建）能够模拟真实波浪下沉积物运输的完整剖面，将扩展到有或没有植被的沙丘侵蚀。详细的模拟将进一步为在事件尺度形态动力学模型XBeach中创建改进的湍流和波浪尺度过程参数化提供信息。将建立一个与基于风险的决策支持工具相一致的脆弱性框架，以预测在给定的水动力强迫水平和持续时间内发生破坏状态（例如沙丘体积损失）的可能性。收集的数据和广泛的XBeach模拟将为脆弱性分析提供所需的输入参数。不同沙丘原型的数据和建模将用于：(i)确定在极端事件期间驱动沙丘演变的基本过程（包括波浪、湍流和沉积物运输）；（ii）界定沙丘易受侵蚀程度随堤岸侵蚀而增加的条件；（iii）研究不同过程之间的相互作用，确定植被不再增强沙丘恢复力的阈值强迫条件和时间尺度；（iv）检验脆弱性建模框架在极端风暴潮和波浪事件中改善沙丘侵蚀风险决策的程度。来自联邦和州（特拉华州，德克萨斯州）的自然资源经理和具有实地经验的实践工程师将通过计划于第三年举行的利益相关者研讨会为该项目做出贡献。脆弱性框架将与来自特拉华州和德克萨斯州的管理人员合作开发，允许根据常用的风暴强度测量来预测沙丘损害。该项目将支持博士和本科生。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。

Sand dunes are often the primary and sometimes only 'line of defense' for coastal infrastructure, and are increasingly constructed and actively managed to protect against extreme events. Coastal managers require knowledge of how dunes will respond under these events so assets can be pre-positioned. Both natural and constructed dunes dissipate energy by modifying breaking waves and runup to limit overwash, thereby minimizing coastal flooding during extreme waves and storm-surge events. However, because extreme physical forces only interact with the dune for a relatively short, yet critical time when the water level rises, there is limited understanding on how dune sediments and vegetation can modify hydrodynamic forces and alter beach-dune profile evolution. This research focuses on dune response to a range of water level and forcing conditions that mimic the passage of an extreme storm event. A near prototype-scale laboratory experiment will be conducted over a mobile bed in the large wave flume at Oregon State University. Physical model studies will occur over a bare dune, a rapidly constructed (loosely compacted) dune following wave-induced erosion, and a dune with live vegetation. Data related to processes ranging from short-term (turbulence) to longer time scales (individual events) will be collected and analyzed to develop a fundamental understanding of the fluid-sediment-vegetation dynamics affecting dune stability, as well as damage mitigation strategies for extreme events. The collected data will be used to validate numerical models. A multiphase flow model sedwaveFoam (created in the open-source OpenFOAM framework), capable of simulating the full profiles of sediment transport under realistic waves, will be extended for dune erosion with or without vegetation. Detailed simulations will further inform the creation of improved parameterizations of turbulence- and wave-scale processes in the event-scale morphodynamic model XBeach. A fragility framework, consistent with risk-based decision support tools, will be created to predict the probability of damage states (e.g., dune volume loss) for a given level and duration of hydrodynamic forcing. The collected data and extensive XBeach simulations will provide required input parameters for the fragility analysis. The data and modeling for different dune archetypes will be used to: (i) identify the fundamental processes (including waves, turbulence, and sediment transport) that drive dune evolution during extreme events; (ii) define the conditions by which dune vulnerability increases as function of berm erosion; (iii) investigate the interaction between the different processes and identify the threshold forcing conditions and time scales beyond which vegetation no longer enhances dune resilience; and (iv) examine the extent a fragility modeling framework can be used to improve risk-based decision for dune erosion during extreme surge and wave events. Natural resource managers and practicing engineers with on-the-ground experience, from Federal and State (Delaware, Texas) levels will contribute to this project through a stakeholder workshop planned for year 3. The fragility framework will be developed in collaboration with managers from Delaware and Texas, allowing prediction of dune damage based on commonly used measures of storm intensity. The project will support PhD and undergraduate students.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.