RAPID: Examining Seafloor Dynamics offshore Bogue Banks, North Carolina, Related to Hurricane Florence

美国东海岸和墨西哥湾沿岸的许多社区正在经历中度到严重的侵蚀。北卡罗莱纳州海岸管理部门确定的十年海岸线侵蚀率表明，北卡罗莱纳州海岸线的侵蚀率不到65%。长期的侵蚀和风暴的间歇性影响促使该州的大多数沿海社区利用当地的离岸沙源进行海滩营养。一个关切是，目前关于近海沙滩（补充海岸沙丘和海滩的潜在借用区）如何因应风暴条件和疏浚活动而演变的知识有限。2018年9月，飓风“佛罗伦萨”严重影响北卡罗来纳州南部和南卡罗来纳州北部，造成海岸侵蚀和洪水。因此，由于这些影响，预计将作出重大的减缓侵蚀努力。该项目将收集近海沙滩的海底测量数据，这些数据可用于评估飓风驱动的变化。这项工作的更广泛影响包括学生培训和沿海土地管理者和决策者可以使用的信息。2018年9月14日上午，飓风佛罗伦萨在北卡罗来纳州威尔明顿附近登陆，成为1级风暴，但就在登陆之前，风暴是一场强大的2级飓风，低于几天前的4级飓风。大片地区经历了飓风强度的大风，这些大风在东海岸中部地区产生了明显的风暴潮和强大的海浪。陆上和水下地貌的变化可能是由于强大的波浪和潮汐活动引起的沉积物运动造成的。这项研究是收集海底测绘数据（即多波束测深）的快速反应，覆盖了北卡罗来纳州威尔明顿附近的一部分先前调查过的区域，即莫尔黑德市海洋疏浚材料处理场。工作将包括收集和解释海底（CHIRP地震）剖面，还将收集和分析地表沉积物样品的粒度，以确定碎屑大小和砂输运参数。这些数据将告知与佛罗伦萨飓风有关的陆架沉积物运输的性质，并为解释强风暴事件期间的沉积物运输和再分配提供必要的地面真相。调查和取样将沿着内大陆架进行，在距离北卡罗莱纳州海岸16公里范围内，水深一般小于20米。这是一个经常被用作海滩营养的近海借沙地点所在的地区。它也是一个沿海地区，由于其浅而充满活力的性质，研究相对不足。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。

Many communities along the East and Gulf Coasts of the United States are experiencing moderate to severe erosion. Decadal shoreline erosion rates determined by the North Carolina Division of Coastal Management indicate that less than 65 percent of the North Carolina shoreline is eroding. Chronic long-term erosion and episodic impacts from storms have encouraged most coastal communities in this state to conduct beach nourishments using local off shore sand sources. One concern is present limited knowledge of how offshore sand shoals (potential borrow areas for replenishment of coastal dunes and beaches) are evolving in response to storm conditions and dredging activity. In September, 2018, Hurricane Florence severely impacted southern North Carolina and northern South Carolina, causing coastal erosion and flooding. As a result, significant erosion mitigation efforts are anticipated due to these impacts. This project will collect seafloor measurements from an offshore sand shoal which can be used to evaluate hurricane-driven changes. Broader impacts of the work include student training and information that can be used by coastal land managers and policy makers.Hurricane Florence made landfall as a Category 1 storm near Wilmington, North Carolina on the morning of September 14, 2018 but, just prior to making landfall, the storm was a powerful Category 2 hurricane, down from Category 4 status days prior. Hurricane-force winds were experienced over a large region, and these yielded significant storm surges as well as powerful waves along the central East Coast. Subaerial and subaqueous geomorphic changes likely resulted due to sediment movement resulting from forceful wave and tidal activity. This research is a rapid response to collect seafloor mapping data (i.e., multibeam bathymetry) over a portion of a previously surveyed area near Wilmington, North Carolina, known as the Morehead City Ocean Dredged Material Disposal Site. Work will involve the collection and interpretation of sub-bottom (CHIRP seismic) profiles, Samples of surface sediments will also be collected and analyzed for grain-size to determine clast size and sand transport parameters. These data will inform the nature of shelf sediment transport associated with Hurricane Florence and provide essential ground-truthing for interpretations of sediment transport and redistribution during a strong storm event. Surveys and sampling will take place along the inner continental shelf, within 16 kilometers of the North Carolina shore and water depths generally less than 20 meters. This is the region where offshore sand borrow sites used for beach nourishment are often located. It is also a coastal area that has been relatively understudied due to its shallow and energetic nature.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.