Collaborative Research: The interaction of waves, tidal currents and river outflows and their effects on the delivery and resuspension of sediments in the near field

本研究将重点研究河口羽流的近场沉积物再悬浮和去除机制，该羽流具有强淡水排放、分层引起的显著垂直剪切和强表面波条件的组合特征。据推测，河流沉积物的扩散路径可能更多地受沉积物捕获区域的再悬浮事件的支配，而不仅仅是河流排放的先验性质。此外，表面波被假设为河口和海岸入口底部应力和沉积物再悬浮的整体物理机制的重要组成部分，从而大大增强了沉积物的输运潜力。为了解决这些假设，研究人员将进一步开发和利用非流体静力模型（NHWAVE），该模型具有处理盐度分层和悬浮沉积物的能力，包括波浪解析和波浪平均形式，特别是使用正在进行的美国国家科学基金会资助的河流羽流动力学研究的结果。该模型将针对剪切浮力羽流不稳定性的高分辨率数据集进行验证，以确定该公式在高分辨率下的准确性，并针对来自哥伦比亚河口（MCR）的更大规模样带数据进行验证，以验证模型中的基本波浪和环流过程。该模型将应用于MCR，以研究潮汐脉冲河流羽流与波浪的相互作用，以及由此产生的潮汐羽流上升附近沉积物的去除和再悬浮，并将进一步用于解释2013年6月进行的onr赞助的RIVET-II实验的结果。河口和河口为沉积物向海岸的河流供应和沉积物向陆架和深海的分布提供了通道。本项目将研究潮流、河流流量和表面波对确定沿海入海口泥沙输运机制的影响和耦合。第一项任务将是开发和测试一个灵活的、并行的非流体静力模型NHWAVE的波浪解析和波浪平均版本，该模型最近被扩展到包含密度分层和悬浮泥沙负荷的存在，从而为高分辨率过程研究提供所需的基本工具。由于几个原因，该模型的进一步发展很重要。首先，与表面平流羽流锋面潮汐成因相关的强垂直运动分量，以及羽流上升区域附近强再悬浮事件的发生，需要应用完全非流体静力模型。此外，与表面平流羽流相关的强剪切流中的波浪过程，无论是现有的波浪解析模型，还是目前在标准沿海海洋模型中使用的弱剪切环境中波浪平均流的理论，都不能充分描述，因此需要改进模型公式。这项研究将促进对河流和海岸环境交汇处沉积过程的认识。模型开发工作将进一步推动最近在沿海海洋模型中使用非流体静力公式的趋势，纳入波浪解析能力，从而能够在现实尺度上使用的共同计算框架中表示波浪、洋流、分层、湍流和沉积过程的全部范围。由此产生的模型将大大提高群落评估复杂、不规则波浪过程对底部应力和沉积物再悬浮的影响的能力，从而更好地理解沉积物从河流到大陆架的运动路径。这笔资金将通过现有的REU项目部分支持三名博士研究生研究人员和本科生暑期研究员。pi将继续努力，通过持续和扩大参与特拉华大学的项目，如海岸日、工程酷东西营地和青年工程师营地，向K-12人口推广科学和研究。

This study will focus on the mechanisms for sediment resuspension and removal in the near field of a river mouth plume characterized by a combination of strong freshwater discharge, significant vertical shear resulting from stratification, and strong surface wave conditions. It is hypothesized that the dispersal pathway of river-borne sediment is possibly more often governed by resuspension events in the region of sediment trapping, as opposed to only being an a priori property of the riverine discharge. Further, surface waves are hypothesized to be an important component of the overall physical mechanism of bottom stress and sediment resuspension in river mouths and coastal inlets, leading to greatly enhanced potential for sediment transport. In order to address these hypotheses, the researchers will further develop and utilize a nonhydrostatic model (NHWAVE) with capabilities to handle salinity stratification and suspended sediment in both wave-resolving and wave-averaged forms, using, in particular, results from ongoing NSF-funded work on river plume dynamics. The model will be validated against a high-resolution data set for instabilities in sheared buoyant plume flow in order to establish the accuracy of the formulation at high resolution, and against a larger scale transect of data from the Mouth of the Columbia River (MCR) to verify basic wave and circulation processes in the model. The model will be applied to the MCR in order to study the interplay of tidally pulsed river plume and waves and the resulting removal and resuspension of sediments in the vicinity of ebb-tidal plume liftoff, and will be further used in interpreting results from the ONR-sponsored RIVET-II experiment, conducted in June 2013.Estuaries and river mouths provide the pathway for riverine supply of sediments to the coast and the distribution of sediments to the shelf and deep ocean. This project will study the influence and coupling of tidal currents, river discharges and surface waves in determining the sediment transport regime in coastal inlets. The first task will be to develop and test both wave-resolving and wave averaged versions of a flexible, parallelized nonhydrostatic model NHWAVE, which has recently been extended to incorporate density stratification and the presence of a suspended sediment load, thus providing the basic tools needed for high resolution process studies. The further development of the model is important for several reasons. First, the strong vertical components of motion associated with the tidal genesis of fronts in surface advected plumes, and the occurrence of strong resuspension events near regions of plume liftoff, require the application of fully nonhydrostatic models. In addition, wave processes in strongly sheared flows associated with surface-advected plumes are not adequately described by either existing wave resolving models or by theory for wave-averaged flows in weakly sheared environments as presently used in standard coastal ocean models, thus requiring improved model formulations.This research will advance the understanding of sedimentation processes at the intersection of river and coastal environments. The model development effort will further the recent trend towards use of nonhydrostatic formulations in coastal ocean models by incorporating wave-resolving capabilities, leading to the ability to represent a full range of wave, current, stratification, turbulence and sediment processes in a common computational framework utilized at realistic scales. The resulting model will greatly enhance the community's ability to assess the effect of complex, irregular wave processes on bottom stress and sediment resuspension, leading to a better understanding of the pathways for sediment motion from river to shelf. The resources from the grant will partially support three doctoral graduate researchers, and undergraduate summer fellows through an existing REU program. The PIs will continue their efforts to promote science and research to a K-12 population through continued and expanded participation in University of Delaware programs such as Coast Day, Engineering Cool Stuff Camp and Young Engineers Camp.