Morphological Evolution of an Energetic Tidal Channel: Quantifying Frictional Feedbacks Across Multiple Scales Using High Resolution Observations and Modeling

该项目将把先进的观测技术与高分辨率的水动力学模型结合起来，以量化潮汐水道中河床形态的演变及其与水动力粗糙度的反馈。在复杂的沿海环境中，我们理解多个尺度上的相互作用的能力往往受到观测数据或建模框架中的差距的限制。这项研究将跨越这些差距，以解决关于形态演变和摩擦效应的基本问题。地貌动力学模型在模拟几个世纪到几千年的盆地尺度演化方面取得了很大进展，但基于定量技术和过程的评估仍然受到观测的限制。同样，水动力模型包含了各种过程，这些过程可能会导致有效粗糙度并改变预测的速度和床面应力，但在模型参数化级对摩擦力的定量评估使包含复杂粗糙度公式的优点变得模糊。这项研究将直接解决这些在空间和时间分辨率方面的限制，结果将更广泛地适用于更大规模和更缓慢演变的沿海环境。这将大大提高我们描述和管理广泛的沿海进程的能力。洪水泛滥、富营养化、有害的藻类水华，以及屏障后和浅水河口环境中对海平面上升的长期形态响应，都依赖于这里研究的小尺度水动力和床面耦合。该项目将支持研究生和博士后的培训。这一多学科的主题和一种结合了先进的观测和建模工具的研究方法将使它们做好准备，以便在基础研究或沿海系统的工程和管理方面做出贡献。在近岸海洋中，床形在空间和时间尺度上相互作用。涟漪响应潮汐速度，而涟漪迁移中的汇聚和发散导致巨型涟漪的生长和运动。类似地，春潮到事件时间尺度的巨型波纹演化有助于沙丘和更大尺度特征的形成。使用自主水面和空中飞行器，该团队将绘制出在这一强迫条件范围内动态潮汐通道的演变，明确地解析从10s厘米到100s m波长的光谱演变。船上和系泊观测还将测量床面对多个尺度上覆流动的摩擦效应，提供局部湍流应力和正压压力梯度之间的直接比较。空间有限和动态演变的区域允许对系统中的水动力学和沉积物传输进行高分辨率建模，包括对形态响应进行前所未有的定量评估。小尺度、基于过程的建模将与大尺度的地貌动力学模拟相结合，以将床型尺度上的水动力特征与对有效粗糙度的综合影响联系起来。次网格尺度粗糙度的参数化将与观测值进行比较，以评估不同尺度的河床如何随着潮汐强迫的变化而影响摩擦响应。

This project will combine advanced observational techniques with high resolution hydrodynamic modeling to quantify the morphological evolution of bedforms in a tidal channel and their feedbacks with hydrodynamic roughness. In complex coastal environments, our ability to understand interactions across multiple scales is often limited by gaps in the observational data or modeling framework. This study will span those gaps in order to address fundamental questions on morphological evolution and frictional effects. Morphodynamic modeling has made great progress at simulating basin-scale evolution over centuries to millennia, and yet quantitative skill and process-based assessments remain limited by observations. Similarly, hydrodynamic models have incorporated various processes that can contribute to effective roughness and alter predicted velocities and bed stress, and yet quantitative assessment of friction at the scale of the model parametrizations makes the merits of the inclusion of complex roughness formulations ambiguous. This research will directly address these limitations in spatial and temporal resolution, and the results will be applicable more broadly to larger scale and more slowly evolving coastal settings. This would significantly improve our abilities to characterize and manage a wide range of coastal processes. Inundation, eutrophication, harmful algal blooms, and long-term morphological response to sea level rise in back-barrier and shallow estuarine environments all depend on the small-scale hydrodynamic and bedform coupling studied here. This project will support the training of both a graduate student and postdoc. The multidisciplinary topic and a research approach that integrates advanced observational and modeling tools will prepare them to make contributions either in basic research or engineering and management of coastal systems.In the nearshore ocean, bedforms interact across a cascade of spatial and temporal scales. Ripples respond to tidal velocities, and convergences and divergences in ripple migration lead to the growth and movement of mega-ripples. Similarly, mega-ripple evolution at spring-neap to event time scales contributes to the formation of dunes and larger scale features. Using autonomous surface and aerial vehicles the team will map out the evolution of a dynamic tidal channel across this range of forcing conditions, explicitly resolving the spectral evolution from wavelengths of 10s of cm to 100s of m. Shipboard and moored observations will also measure the frictional effects of the bedforms on the overlying flow across multiple scales, providing a direct comparison between local turbulent stresses and the barotropic pressure gradient. A spatially limited and dynamically evolving domain permits high resolution modeling of the hydrodynamics and sediment transport in the system, including unprecedented quantitative evaluation of the morphological response. Small scale, process-based modeling will be paired with larger scale morphodynamic simulations to link hydrodynamic features at the bedform scale with the integrated effect on effective roughness. Parameterization of subgrid-scale roughness will be compared with observations to assess how multiple scales of bedforms affect the frictional response with changing tidal forcing.