Horizontal shear flows and lateral mixing in estuaries and the coastal ocean: Sediment transport in the shoal-channel estuary

智力优势：这是一个观测研究，以解决两个基本问题，在河口和沿海海洋流动和运输的分析。第一个地址的机制，负责横向混合的水平剪切的存在。在许多河口和海岸流中，横向输运被认为是由横向环流与垂直混合相互作用所主导的。据推测，横向剪切不稳定性可以发挥重要作用，在建立跨水平剪切层的交换。虽然是间歇性的，但这些不稳定性会产生相干的横向涡流，产生广泛的横向交换，特别是当它们沿沿着垂直分层的通道形成时。第二个重点领域集中在潮汐和风引起的变化，在浅滩河道河口的沉积物动力学。检查这些过程的方法依赖于基于现场的流体动力学和悬浮沉积物动力学的观察，以及结合床样分析和床的声学成像。该战略是采用两个不同但互补的仪器阵列：一个将横向横跨海峡和浅滩，另一个将纵向沿着浅滩-海峡界面。对这些观测结果的分析将利用纵向动量、盐度和悬浮沉积物的局部和体积综合预算，以确定造成横向交换以及交换和再悬浮的相关可变性的机制。这两个基本过程的检查将被带到一起的背景下，在一个浅滩-河道河口的泥沙输运。更广泛的影响：拟议的工作将在科学界和旧金山弗朗西斯科河口的管理方面产生广泛的影响。首先，横向混合的检查，特别是横向剪切不稳定性的作用，将有重要的影响河口和海岸流的建模。在粗分辨率模式中，必须指定水平扩散系数。随时间变化的扩散系数几乎从来没有选择用于此目的，但随时间变化的扩散系数对大尺度传输的影响将是深远的。随着计算能力的提高，包括大涡模拟（LES）在内的更高分辨率的模式变得越来越容易实现。在这些情况下，次网格尺度参数化成为建立未解决的过程交换和混合的关键组成部分。如果横向剪切不稳定性，事实上，横向混合的一个重要组成部分，LES的方法将可能能够解决它们，但现场规模的数据集，以建立分层潮流中的横向剪切不稳定性的性质是不可用的。这项工作对旧金山弗朗西斯科湾河口管理的潜在影响与科学影响一样重要，如果不是更重要的话。在南旧金山弗朗西斯科湾周边的潮汐沼泽恢复中，沉积物再分布的动态是高度不确定的，但也是恢复成功的关键。由于要恢复的土地的沉降，大量的沉积物必须积累，使这些地区的沼泽平原海拔，这将显着改变整个河口的沉积物动力学，这里提出的工作的结果将直接通知模型开发工作和管理决策的恢复活动。

Intellectual Merit: This is an observational study to address two fundamental issues in the analysis of estuarine and the coastal ocean flows and transport. The first addresses the mechanisms responsible for lateral mixing in the presence of horizontal shears. In many estuarine and coastal flows, lateral transport is assumed to be dominated by transverse circulation interacting with vertical mixing. It is hypothesize that lateral shear instabilities could play a major role in establishing exchange across horizontal shear layers. Although intermittent, these instabilities create coherent lateral eddies that produce extensive lateral exchange, particularly when they are formed along a vertically stratified channel. The second area of emphasis focuses on the tidal- and wind-induced variability of sediment dynamics in a shoal-channel estuary. The approach to examining these processes relies on field-based observations of the hydrodynamics and suspended sediment dynamics, as well as a combination of bed sample analysis and acoustic imaging of the bed. The strategy is to pursue two distinct, but complementary, instrument arrays: one will be oriented laterally across the channel and shoals, the other will be oriented longitudinally along the shoal-channel interface. Analysis of these observations will utilize budgets, both local and volume integrated, for longitudinal momentum, salinity and suspended sediment in order to establish the mechanisms responsible for lateral exchange and the associated variability of exchange and re-suspension. The examination of these two fundamental processes will be brought together in the context of sediment transport in a shoal-channel estuary. Broader Impacts: The proposed work will have broad impacts both in the scientific community and in the management of the San Francisco Estuary. First, the examination of lateral mixing, particularly the role of lateral shear instabilities, will have important implications for the modeling of estuarine and coastal flows. In coarse resolution models, horizontal diffusion coefficients must be specified. Time varying diffusion coefficients are almost never chosen for this purpose, but the implications of a temporally varying diffusion coefficient on larger-scale transport would be profound. As computational capability increases, higher resolution models, including large-eddy simulation (LES), are becoming more realizable. In these cases, the subgrid- scale parameterization becomes the critical component in establishing exchange and mixing by unresolved processes. If lateral shear instabilities are, in fact, an important component of lateral mixing, LES approaches would likely be able to resolve them, but field-scale data sets to establish the nature of lateral shear instabilities in stratified tidal flows are not available. Just as significant as the scientific impacts, if not more so, are the potential impacts of this work on the management of the San Francisco Bay Estuary. In the restoration of tidal marshes around the perimeter of South San Francisco Bay, the dynamics of sediment redistribution are highly uncertain, but also critical to the success of the restoration. Due to the subsidence of the lands to be restored, a large quantity of sediment must accumulate to bring these areas to marsh plain elevation, which will significantly alter the sediment dynamics throughout the estuary.The results of the work proposed here will directly inform that model development effort and management decision-making regarding restoration activities.