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

沙丘往往是沿海基础设施的主要防线，有时也是唯一的防线，越来越多的人建造沙丘，并积极管理，以防范极端事件。沿海管理人员需要了解沙丘在这些情况下会如何反应，这样才能预先部署资产。天然沙丘和人工沙丘都通过修改破碎的波浪和爬升来限制溢流，从而在极端海浪和风暴潮期间将沿海洪水降至最低，从而消散能量。然而，由于极端物理作用力只在水位上升时与沙丘相互作用的时间相对较短，但却是关键的一段时间，人们对沙丘沉积物和植被如何改变水动力和改变海滩-沙丘剖面演变的了解有限。这项研究的重点是沙丘对一系列水位和强迫条件的响应，这些条件模拟了极端风暴事件的经过。俄勒冈州立大学将在大型波浪水槽中的移动床上进行接近原型规模的实验室实验。物理模型研究将在裸露的沙丘、波浪引起的侵蚀后快速建造的(松散的)沙丘和有活植物的沙丘上进行。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，以加深对影响沙丘稳定性的流体-沉积物-植被动力学的基本了解，以及极端事件的损害缓解策略。收集到的数据将用于验证数值模型。在开源的OpenFOAM框架中创建的多相流模型sedwave Foam，能够模拟真实波浪下泥沙运动的全剖面，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地形动力学模型X海滩中创建改进的湍流和波浪尺度过程的参数化提供信息。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，以预测给定水平和持续时间的水动力强迫的损害状态(例如沙丘体积损失)的概率。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拟将用于：(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、湍流和泥沙输送)；(Ii)确定沙丘脆弱性作为护堤侵蚀的函数而增加的条件；(Iii)调查不同过程之间的相互作用，并确定植被不再增强沙丘弹性的阈值强迫条件和时间尺度；以及(Iv)研究脆弱性模拟框架可在多大程度上用于改进极端潮汐和波浪事件期间沙丘侵蚀的基于风险的决策。来自联邦和州(得克萨斯州特拉华州)的自然资源经理和具有实地经验的执业工程师将通过计划在第三年举行的利益相关者研讨会为该项目做出贡献。脆弱性框架将与特拉华州和德克萨斯州的经理合作开发，允许根据常用的风暴强度测量来预测沙丘损害。该项目将支持博士生和本科生。这一奖项反映了NSF的法定使命，并通过使用基金会的智力优势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.