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”，越来越多的建设和积极管理，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波和爬高来限制过度冲刷，从而最大限度地减少极端波浪和风暴潮事件期间的沿海洪水。然而，由于极端的物理力量只与沙丘的相互作用相对较短，但关键的时间，当水位上升，有有限的了解如何沙丘沉积物和植被可以修改水动力和改变海滩沙丘剖面演变。这项研究的重点是沙丘响应的范围内的水位和强迫条件，模拟极端风暴事件的通道。将在俄勒冈州州立大学的大型波浪水槽中的一个移动的床上进行一个接近原型规模的实验室实验。物理模型研究将在裸露沙丘、波浪侵蚀后迅速形成的（松散压实的）沙丘和有活植被的沙丘上进行。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，以便从根本上了解影响沙丘稳定性的流体-沉积物-植被动态，以及极端事件的减轻损害战略。收集的数据将用于验证数值模型。一个多相流模型sedwaveFoam（在开放源代码OpenFOAM框架中创建），能够模拟真实波浪下的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通知创建改进的参数化的湍流和波浪尺度的过程中的事件尺度的形态动力学模型XBeach。将创建与基于风险的决策支持工具一致的脆弱性框架，以预测损坏状态的概率（例如，沙丘体积损失）。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模型将用于：（i）识别基本过程（包括波浪、湍流和沉积物搬运）在极端事件期间驱动沙丘演变;（二）确定沙丘脆弱性随着护堤侵蚀而增加的条件;（三）调查不同过程之间的相互作用，并确定阈值强迫条件和时间尺度，超过这些条件，植被不再增强沙丘的韧性;和（iv）检查脆弱性建模框架可用于改善极端浪涌和波浪事件期间沙丘侵蚀的风险决策的程度。来自联邦和州（得克萨斯州特拉华州）的具有实地经验的自然资源管理人员和执业工程师将通过计划在第3年举办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得克萨斯州的管理人员合作开发，允许根据常用的风暴强度措施预测沙丘破坏。这个奖项反映了NSF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.