A large, low pressure Nor’easter storm and Hurricane Joaquin contributed to multiple weeks of sustained, elevated wave and water level conditions along the southeastern Atlantic coast of the United States in Fall 2015. Sea level anomalies in excess of 1 m and offshore wave heights of up to 4 m were recorded during these storms, as observed at the U.S. Army Corps of Engineers’ Field Research Facility in Duck, NC, USA. In response to these energetic oceanographic conditions, there were highly variable morphologic changes to the dune over short spatial scales (<km) which included a range of responses from vertical dune scarping to no measureable response. The portion of the study area with the largest dune erosion occurred at a location fronted by an abnormally deep nearshore bathymetric feature, which altered surf-zone waves and hydrodynamics. The pre-storm beach and dune topography also varied throughout the study area, additionally influencing the frequency of dune collision and contributing to the spatially variable erosion patterns. This work uses field datasets and numerical modeling tools to investigate the causation of hotspot dune erosion at the Field Research Facility. Three different numerical models were tested against the available data in order to assess model skill at resolving complex spatial dune erosion patterns. The three models successfully reproduce the general spatial trends in alongshore variable responses, although not necessarily the details of profile response or net erosion magnitude. Analysis of the model outputs, in conjunction with the available field data, suggests that the observed hotspot dune erosion is related to a complex combination of both topographic and bathymetric controls on the processes driving dune erosion. Therefore, the most simplistic model tested, which only accounts for alongshore variations in topographic profile details, can only predict hotspot dune erosion in locations where steep beach and/or dune topography is the primary control on collisional dune impacts. The higher fidelity models, which account for feedback effects from subaqueous morphology, are similarly able to predict the locations of maximum hotspot erosion, but are sensitive to beach over-steepening and/or errors in wave runup calculations that can lead to over-prediction of simulated dune erosion. This work highlights that numerous existing tools are capable of identifying the foredune regions at most risk from hotspot erosion, as well as the need for continued research to improve representation of all relevant intra-storm morphodynamic processes.

2015 年秋季，一场大型低压 Nor'easter 风暴和飓风华金导致美国东南大西洋沿岸持续数周的海浪和水位升高。海平面异常超过 1 m，离岸海浪高度正如在美国北卡罗来纳州达克市的美国陆军工程兵团实地研究设施所观察到的那样，在这些风暴期间记录了高达 4 m 的风暴。为了应对这些充满活力的海洋条件，沙丘在短空间尺度 (<km) 内发生了高度可变的形态变化，其中包括从垂直沙丘陡坡到无法测量的响应的一系列响应。研究区中沙丘侵蚀最大的部分发生在一个异常深的近岸测深特征前面的位置，这改变了冲浪带波浪和流体动力学。风暴前的海滩和沙丘地形在整个研究区域也各不相同，另外影响沙丘碰撞的频率并导致空间变化的侵蚀模式。这项工作使用现场数据集和数值建模工具来调查现场研究设施中热点沙丘侵蚀的原因。针对可用数据测试了三种不同的数值模型，以评估模型在解决复杂空间沙丘侵蚀模式方面的技能。这三个模型成功地再现了沿岸变量响应的一般空间趋势，尽管不一定是剖面响应或净侵蚀幅度的细节。结合可用的现场数据分析模型输出，表明观察到的热点沙丘侵蚀与对驱动沙丘侵蚀过程的地形和测深控制的复杂组合有关。因此，所测试的最简单的模型只考虑了地形剖面细节的沿岸变化，只能预测陡峭海滩和/或沙丘地形是碰撞沙丘影响的主要控制点的热点沙丘侵蚀。考虑水下形态反馈效应的较高保真度模型同样能够预测最大热点侵蚀的位置，但对海滩过度陡峭和/或波浪爬高计算中的错误敏感，这可能导致过度预测模拟沙丘侵蚀。