Post-hurricane field survey in the wake of hurricane Irma on the British Virgin Islands - documentation and analyses of inundation parameters and hurricane sediments

严重的风暴事件和相关的风暴潮是对沿海社区和生态系统的主要威胁。目前的风暴季节有大量破坏性风暴，如飓风哈维，伊尔玛和玛丽亚，再次引起人们对这一风险的关注。事件后的实地调查使研究人员有机会直接评估事件对生态系统，景观和沿海基础设施的影响。在英属维尔京群岛的伊尔玛之后进行的飓风后调查将提供研究5级飓风影响的独特机会。地势低洼的阿巴达岛是一个非常适合的实地考察地点，因为它可以直接比较飓风的影响及其在各种环境中的相关沉积和侵蚀证据，如珊瑚礁、泻湖、桑迪海岸、海滩山脊平原、盐池和沿海石灰岩平台。证据可能包括海滩上和盐池中的桑迪冲刷扇、泻湖附近的珊瑚碎石堆积和粗碎屑脊、盐池中的泥团、沿海平台上的单一碎屑搬运（珊瑚或石灰石巨石）、沙丘的破坏和海岸侵蚀（例如，陡崖、海岸线后退）。将测量岸上淹没参数（水流深度、淹没距离），采访目击者，并记录任何类型的侵蚀或沉积证据。2017年9月拍摄的航拍照片显示，南部海岸内陆约300米处出现了严重的海岸侵蚀和过度冲刷，北岸沿着海拔至少2-3米。该项目将利用早些年在阿瓦杰拉达收集的事件前现场数据，对伊尔玛事件前后的数据进行详细比较。2013年2月至2017年3月监测了一个与海岸平行的珊瑚碎石脊。在这段时间内，热带风暴仅对洋脊朝海的下部产生了轻微影响。因此，有人提出，该脊可能意味着该岛易受风暴潮的影响，其影响比最近的任何风暴都大。飓风后的调查旨在记录Irma是否形成了新的山脊，或者先前存在的山脊是否发生了重大变化或改造。此外，这项研究将提供新的见解，有助于1）更好地确定热带环境中风暴沉积的特征; 2）确定沉积记录中的风暴单元，以建立复发间隔; 3）了解碎石山脊动力学; 4）了解风暴的起源。4）量化飓风对珊瑚礁造成的破坏; 5）了解风暴潮和海浪的相互作用，成千上万的海浪淹没海岸线几个小时。该项目与气候变化有着重要的相关性，其中大部分与海面温度上升，海平面上升和珊瑚礁的消亡有关，因为这些过程将大大增加热带风暴的频率和强度。

Severe storm events and related storm surges are a major threat to coastal communities and ecosystems. The current storm season with a large number of devastating storms, such as hurricanes Harvey, Irma and Maria drew renewed attention to this risk. Post-event field surveys give researchers the opportunity to directly evaluate an event’s impact on ecosystems, landscapes, and coastal infrastructures. A post-hurricane survey in the wake of Irma on the British Virgin Islands will offer the unique opportunity to study the effects of a category 5 hurricane. The low-lying island of Anegada is a highly eligible field site because it allows for a direct comparison of the effects of the hurricane and its related depositional and erosional evidence in various settings, such as reef, lagoon, sandy coast, beach ridge plain, salt pond and coastal limestone platform. Evidence could include sandy washover fans on beaches and into the salt ponds, coral rubble accumulations and coarse-clast ridges close to the lagoon, mud units in salt ponds, single clast transport on coastal platforms (coral or limestone boulders), breaching of dunes, and coastal erosion (e.g., scarps, shoreline retreat). Onshore inundation parameters (flow depth, inundation distance) will be measured, eyewitnesses will be interviewed, and any kind of erosional or depositional evidence will be documented. Aerial photos taken in September 2017 show significant coastal erosion and overwash that reached ~300 m inland on the southern shore and at least 2-3 m above sea level along the north shore.This project will take advantage of pre-event field data collected on Anegada in earlier years that allows for a detailed comparison of pre- and post-Irma data. A coast-parallel coral rubble ridge was monitored from February 2013 to March 2017. During this time span tropical storms only slightly modified the lower seaward part of the ridge. Consequently, it was proposed that the ridge may imply that the island is vulnerable to storm surges of greater impact compared to any of the recent storms. The post-hurricane survey aims to document if Irma emplaced a new ridge or if the pre-existing ridge was significantly modified or reworked.Furthermore, this study will provide new insights that can help to 1) better define characteristics of storm deposits in tropical environments; 2) identify storm units in the sedimentary record in order to set up recurrence intervals; 3) understand rubble ridge dynamics; 4) quantify the destruction of a coral reef caused by a hurricane; 5) learn about the interplay of storm surge and wave action of thousands of waves that inundate a shoreline for several hours.The project has a significant relevance in the light to climate change, most of all related to the increase in sea surface temperatures, sea level rise and the demise of coral reefs, as these processes will dramatically raise the frequency and intensity of tropical storms.