RAPID: Lidar and Sonar Surveys of a Dune Reinforced with Geotextile Sand Containers Impacted by Tropical Storm Hermine

2012年飓风桑迪对美国东北部造成的破坏性影响凸显了提高沿海社区迅速应对自然灾害并从灾害中恢复的能力的必要性。采用“软”工程解决方案是一种趋势，例如用土工织物砂容器（GSC）加固沙丘，以提高弹性，而不是像石头护岸这样的传统硬化结构。这些有可能保护社区免受较小风暴事件（例如25年一次的风暴）的影响，同时考虑到海平面上升速度和风暴频率的不确定性，在设计上提供灵活性。“软”工程解决方案也可能比硬化结构对屏障海滩系统的自然形态破坏更小。然而，波浪作用下影响加固沙丘稳定性的机理仍存在相当大的不确定性。该快速响应研究（Rapid）项目的目标是收集易变质的数据，以评估2016年9月受到热带风暴Hermine影响的纽约蒙托克1000米长的GSCs加固沙丘的稳定性和性能。加固沙丘于2016年3月建成，热带风暴Hermine导致防护护堤完全被侵蚀，GSC核心暴露，GSC下层移动。将建立侵蚀海滩（地形）和近岸水深的详细三维数字高程模型。这将通过两项调查来完成：一项是使用无人机系统（UAS）的空中激光雷达调查，另一项是联合舰载激光雷达和干涉声纳系统。这些数据将为波浪作用对有GSCs加固的沙丘的影响提供详细的案例研究。这将允许将数值和波浪水槽研究的结果应用于实验室无法复制的实际现场案例。通过缩小尺寸试验，假设现有的土工布容器稳定性方程存在不保守性，低估了土工布容器的水力稳定性。对这一案例研究的分析也将提高我们对加固沙丘是否表现为“软”海岸结构的理解，并且不会显著改变海岸线的自然形态。

The devastating effects of Hurricane Sandy in 2012 on the northeast United States highlighted the need to improve the ability of coastal communities to quickly respond and rebound from natural hazards. There is a trend towards implementing "soft" engineering solutions such as dunes reinforced with Geotextile Sand Containers (GSC) to improve resiliency rather than traditional hardened structures like stone revetments. These have the potential to protect communities from smaller storm events (e.g. 25-year storms) while at the same time providing flexibility in design considering the uncertainty regarding rates of sea level rise and storm frequency. "Soft" engineering solutions may also be less disruptive to the natural morphology of barrier beach systems than hardened structures. However, there is still considerable uncertainty regarding the mechanisms that affect the stability of reinforced dunes under wave attack. The objective of this Rapid Response Research (RAPID) project is to collect perishable data to assess the stability and performance of a 1000 m section of a dune reinforced with GSCs in Montauk, NY that was impacted by Tropical Storm Hermine in September 2016. The reinforced dune was constructed in March 2016, and Tropical Storm Hermine resulted in complete erosion of the protective berm, exposure of the GSC core, and movement of the lower level of GSCs. A detailed 3-D digital elevation model of both the eroded beach (topography) as well as the near-shore bathymetry will be constructed. This will be accomplished through two surveys: an aerial LIDAR survey using an Unmanned Aerial System (UAS) and a combined ship-mounted LIDAR and interferometric sonar system. These data will provide a detailed case study of the effects of wave action on a dune reinforced with GSCs. This will allow for the application of findings from numerical and wave flume studies to an actual field case at a scale not reproducible in the laboratory. It is hypothesized that current stability equations are unconservative in that they underpredict the hydraulic stability of geotextile containers associated with reduced scale experiments. Analysis of this case study will also improve our understanding of whether reinforced dunes perform as "soft" coastal structures and do not significantly modify the natural morphology of the shoreline.