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一项关于河口锋生和高度分层河口沉积物捕获的实地和建模研究。河口锋生是影响河口水动力和泥沙运移的一个基本机制，但目前对其了解甚少。河口锋面是在任何海洋环境中观测到的最强锋面之一，产生强烈的局部密度梯度、分层突变、底部应力和湍流、强烈的垂直速度和强烈的沉积物捕获。导致沉积物捕获的过程依赖于相同的物理变量，并且与产生河口锋的过程在相同的尺度上发生，这为河口锋动力学和相关沉积物捕获的跨学科研究提供了强大的动力。康涅狄格河河口是一个充满活力的地区，具有强烈的和高度依赖时间的锋面和短暂的细颗粒沉积物捕获。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，以及使用固定和船上安装的仪器进行密集的高分辨率测量，以获得前所未有的物理状态的空间和时间分辨率。同时，悬浮沉积物的浓度和性质将通过光学和声学方法进行量化，并进行广泛的实验室和现场校准工作。水柱观测将与床沙特征相结合，以解决泥沙通量收敛、短暂沉积以及可再生沉积物的空间和时间变化之间的相互作用。观测测量将与水动力学和沉积物输运的高分辨率数值模型相结合，以帮助解释观测结果，并研究导致锋生和相关沉积物捕获的主要物理过程的细节。该研究将对河口锋生进行全面的研究，将目前对准稳定水力学的理论认识与部分混合河口的动力学联系起来，以理解、量化和参数化锋生及其对整个河口制度的影响。通过高分辨率测量和建模的结合，研究小组将对沉积物捕获机制进行严格的检查，特别是在河口锋面和相关的细颗粒沉积物的短暂沉积所产生的强烈但高度依赖时间的收敛的背景下。这项研究将根据观测到的强迫变化和模式敏感性研究，探讨这些水动力和沉积物输运过程对河口强迫条件变化的敏感性。模式敏感性研究也将用于确定锋面辐合过程是否可以解释河口形态的长期演变，以及强迫变量变化对整个河口状况的潜在影响。更广泛的影响：本研究将有助于理解和改进对河口锋面形成的预测，以及锋面对细沉积物和相关污染物的命运和运移的影响。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组成部分：为来自国际河口研究界的研究生提供高级实地方法的短期课程，以及将与研究生水平实地课程相结合的本科实地研究课程。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.