Collaborative Research: Frontogenesis and Fine-Sediment Trapping in a Highly Stratified Estuary

智力优势：将在康涅狄格河河口进行河口锋生和高度分层河口泥沙捕获的现场和模拟研究。河口的锋生作用知之甚少，但它是影响河口水动力和泥沙运动许多方面的基本机制。河口的锋面是所有海洋环境中观察到的最强的锋面之一，产生强烈的局部密度梯度，层化、海底应力和湍流的突然转变，强烈的垂直速度和强烈的沉积物捕获。导致泥沙捕获的过程取决于与产生河口锋面的过程相同的物理变量，并且发生在相同的尺度上，这为对河口锋面及其相关泥沙捕获的动力学进行跨学科研究提供了强大的动力。康涅狄格河河口是现场--一个具有强烈且高度依赖时间的锋面和细粒沉积物的短暂圈闭的能量状况。观测计划将包括测量锋面结构在潮汐和季节时间尺度上的变化，以及使用固定和船载仪器进行密集的高分辨率测量，以获得前所未有的物理状况的空间和时间分辨率。同时，将用光学和声学方法量化悬浮泥沙的浓度和性质，并进行广泛的实验室和现场校准工作。水柱观测将与河床-沉积物特征相结合，以解决沉积物通量汇聚、短暂沉积和可再悬浮沉积物的时空变化有效性之间的相互作用。观测数据将与高分辨率的水动力学和泥沙输运数值模式相结合，以帮助解释观测结果，并调查导致锋生和相关泥沙滞留的主要物理过程的细节。研究将全面检查河口锋生，将目前对准稳定水力学的理论理解与部分混合河口的动力学联系起来，以了解、量化和参数化锋生及其对整个河口局势的影响。通过结合高分辨率测量和建模，研究小组将对沉积物捕获机制进行严格检查，特别是在河口锋面和相关的细粒沉积物短暂沉积产生的强烈但高度依赖时间的会聚的背景下。这项研究将根据观测到的强迫变化和模型敏感性研究，讨论这些水动力和泥沙输送过程对河口强迫条件变化的敏感性。模式敏感性研究也将被用来确定锋面辐合过程是否可以解释河口形态的长期演变以及强迫变量的变化对整个河口水系的潜在影响。更广泛的影响：这项研究将有助于理解和改进对河口锋面的产生和锋面对细微沉积物和相关污染物的去向和输送的影响的预测。这些发现将应用于世界各地人口稠密、工业化和其他受人类影响的河口的建模和管理。该项目包括实施新的教育内容：为来自国际河口研究界的研究生开设高级实地研究方法短期课程，以及将与研究生水平的实地课程相结合的本科生实地研究课程。该项目还将支持两名研究生的论文工作。

Intellectual merit: A field and modeling study of estuarine frontogenesis and sediment trapping in a highly-stratified estuary will be conducted in the Connecticut River estuary. Frontogenesis in estuaries is poorly understood, yet it is a fundamental mechanism influencing many aspects of estuarine hydrodynamics and sediment transport. The fronts in estuaries are among the strongest observed in any marine environment, producing intense, localized density gradients, abrupt transitions in stratification, bottom stress, and turbulence, strong vertical velocities and intense sediment trapping. The processes that lead to sediment trapping depend on the same physical variables and occur at the same scales as those producing estuarine fronts, providing a strong motivation for an interdisciplinary study of the dynamics of estuarine fronts and associated sediment trapping. The Connecticut River estuary is the field site - an energetic regime with intense and highly time-dependent fronts and ephemeral trapping of fine-grained sediment.The observational program will include measurements of the frontal structure as it varies at tidal and seasonal timescales, as well as intensive, high-resolution measurements with fixed and ship-mounted instruments to obtain unprecedented spatial and temporal resolution of the physical regime. Simultaneously, suspended-sediment concentrations and properties with optical and acoustic methods will be quantified and subjected to an extensive laboratory and field calibration effort. The water-column observations will be coupled with bed-sediment characterization to address interactions among sediment flux convergence, ephemeral deposition, and spatially and temporally varying availability of resuspendable sediment. Observational measurements will be paired with a high-resolution numerical model of the hydrodynamics and sediment transport to help interpret the observations and to investigate the details of the dominant physical processes leading to frontogenesis and associated sediment trapping.The study will provide a comprehensive examination of estuarine frontogenesis, linking current theoretical understanding of quasi-steady hydraulics with the dynamics of partially-mixed estuaries in order to understand, quantify and parameterize frontogenesis and its influence on the overall estuarine regime. Through the combination of high-resolution measurements and modeling, the research team will perform a rigorous examination of the mechanisms of sediment trapping, particularly in context with the strong but highly time-dependent convergence resulting from estuarine fronts and the associated, ephemeral deposits of fine-grained sediment. The study will address the sensitivity of these hydrodynamic and sediment-transport processes to variations in estuarine forcing conditions, based both on the observed variation of forcing and model sensitivity studies. Model sensitivity studies will also be used to determine whether frontal convergence processes may explain the long-term evolution of estuarine morphology and the potential implications of shifts in forcing variables on the overall estuarine regime.Broader impacts: This study will lead to the understanding and improved prediction of the generation of fronts in estuaries and the influence of fronts on the fate and transport of fine sediment and associated contaminants. These findings will have application to the modeling and management of the heavily populated, industrialized and otherwise human-impacted estuaries around the world. This project includes implementation of new educational components: a short-course in advanced field methods for graduate students from across the international estuarine research community, and an undergraduate field research class that will be coupled to the graduate-level field class. The project will also support the thesis work of two graduate students.