RAPID - Plume Dynamics under Increased Sediment Discharge following Floods

2015年10月2日至4日，南卡罗来纳州遭受了创纪录的暴雨，导致大规模的侵蚀和洪水，大坝决堤，湖泊和池塘漫顶。洪水像漂浮的烟柱一样在沿海扩散。这项快速研究的目的是检查在沉积物排放增加但在其他方面接近大陆架正常海洋条件的情况下的羽流动态。将在南卡罗来纳州温雅湾的淡水羽流内进行反复的船上盐度、温度、沉积物浓度和流速调查，那里是皮迪河和瓦卡莫河的排放地。随着沉积物排放量的减少，将在几周内重复进行调查。这些洪水将影响沿海沉积物收支、海滩和内大陆架形态，沿海开发商、管理人员和其他利益攸关方应考虑到这一点。观察到的洪水非常“浮华”，由于污水处理厂多次故障和其他泄漏，由此产生的淡水脉冲携带了浓度增加的污染物。更好地了解淡水排放在沿海海洋中的扩散和混合将有助于减轻未来类似事件的影响，并最终更好地保护脆弱的沿海生态系统。该项目将为南加州大学海洋科学项目的几名本科生提供所需的实地研究经验。该活动是一个机会，以调查淡水排放驱动的沿海浮力羽流动力学的一个新元素：与低盐水分散和混合之前的重沉积物负荷沉积相关的密度变化。这些密度的变化可能会产生重要的后果，羽流动力学：增强电流进一步离岸，形成二次隆起和涡流驱动的离岸质量和示踪剂通量。10月初，SC的破纪录的闪光灯与海岸上的轻至中等风力强迫条件相结合，使研究能够捕获两种含泥沙排放调整制度：（i）由于最初缺乏浮力，排放迅速混合，以及（ii）一旦沉积物沉积和排放恢复浮力，羽流“重新充满活力”。

South Carolina suffered from record rainfalls on 2-4 October 2015 resulting in massive erosion and flooding, dam breaching and overtopping of lakes and ponds. The floodwaters spread in the coastal ocean as a buoyant plume. The objective of this RAPID study is to examine the plume dynamics under increased sediment discharge but otherwise close to normal oceanic conditions on the shelf. Repeated shipboard surveys of salinity, temperature, sediment concentration and flow velocity will be conducted within the freshwater plume originating from Winyah Bay, SC, where the Pee Dee River and the Waccamaw River discharge. The surveys will be repeated over the course of a few weeks as the sediment discharge subsides. These floods will affect coastal sediment budget, beach and inner shelf morphology, and should be accounted for by coastal developers, managers and other stakeholders. The observed flood was extremely "flashy" and the resulting freshwater pulse carried an increased concentration of pollutants due to multiple failures of sewage treatment plants and other leaks. Better understanding of the freshwater discharge dispersal and mixing in the coastal ocean will help to mitigate similar events in the future and ultimately to better protect a fragile coastal ecosystem. This project will provide the required field research experience for several undergraduate students from the USC Marine Science Program.This event is an opportunity to investigate a new element to the dynamics of freshwater discharge-driven coastal buoyant plumes: density variations associated with deposition of heavy sediment load prior to the dispersal and mixing of the low saline water. These density variations might have important consequences for the plume dynamics: enhancement of currents further offshore, formation of secondary bulges and the eddy-driven offshore mass and tracer fluxes. Record-breaking flashy rainfalls in SC in early October in combination with light to moderate wind forcing conditions on the coast allow the study to capture two regimes of the sediment-laden discharge adjustment: (i) rapid mixing of the discharge due to its initial lack of buoyancy, and (ii) "re-energizing" of the plume once sediments are deposited and the discharge regains its buoyancy.