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

这项研究将集中于河口羽流的泥沙再悬浮和清除机制，该羽流具有强烈的淡水排放、层化引起的显著垂直切变和强烈的表面波条件。据推测，河流泥沙的扩散路径可能更多地受到泥沙捕捉区的再悬浮事件的控制，而不仅仅是河流流量的先验性质。此外，表面波被认为是底应力和泥沙在河口和沿海入海口再悬浮的整体物理机制的重要组成部分，从而大大增强了泥沙输送的潜力。为了解决这些假设，研究人员将进一步开发和利用一个非静力模型(NHWAVE)，该模型具有处理波浪分解和波浪平均形式的盐度分层和悬浮泥沙的能力，特别是使用NSF资助的正在进行的河流羽流动力学工作的结果。该模型将根据高分辨率的切变浮力羽流不稳定性数据集进行验证，以确定公式在高分辨率下的准确性，并将与来自哥伦比亚河入海口(MCR)的更大尺度的横断面数据进行验证，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和波浪的相互作用以及由此导致的落潮羽流升空附近沉积物的清除和再悬浮，并将进一步用于解释2013年6月由ONR赞助的RIVET-II实验的结果。河口和河口为河流向海岸供应沉积物以及向陆架和深海分配沉积物提供了途径。该项目将研究潮流、河流流量和面波对决定沿岸入海口泥沙运动状况的影响和耦合。第一项任务将是开发和测试灵活的、并行的非静力模式NHWAVE的波浪分辨和波浪平均版本，该模式最近已扩展到包括密度分层和悬浮泥沙负荷的存在，从而提供了高分辨率过程研究所需的基本工具。该模型的进一步发展具有重要意义，原因有几个。首先，与地面平流羽流中锋面的潮汐成因有关的强烈垂直运动分量，以及在羽流升空区域附近发生的强再悬浮事件，需要应用完全非静力模式。此外，现有的波浪解析模型或弱剪切环境中波浪平均流动的理论都不能很好地描述与地面平流羽流相关的强剪切流动中的波浪过程，因此需要改进模型公式。模型开发工作将通过结合波浪分辨能力，进一步推动在沿海海洋模型中使用非静力公式的最新趋势，从而能够在实际尺度上利用的共同计算框架中表示各种波浪、水流、层化、湍流和泥沙过程。所产生的模型将大大提高社区评估复杂、不规则的波浪过程对海底应力和泥沙再悬浮的影响的能力，从而更好地了解泥沙从河流到陆架的运动路径。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。PIS将继续努力，通过继续和扩大参与特拉华大学的项目，如海岸日、工程酷人夏令营和青年工程师夏令营，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.