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

该项目将先进的观测技术与高分辨率的水动力模拟相结合，量化潮汐通道中河床的形态演变及其与水动力粗糙度的反馈。在复杂的沿海环境中，我们理解跨多个尺度相互作用的能力往往受到观测数据或建模框架空白的限制。本研究将跨越这些空白，以解决形态学进化和摩擦效应的基本问题。形态动力学建模在模拟盆地尺度上数百年至数千年的演化方面取得了很大进展，但定量技能和基于过程的评估仍然受到观测的限制。同样，流体动力学模型也包含了各种过程，这些过程可以影响有效粗糙度并改变预测的速度和床层应力，然而，在模型参数化的尺度上对摩擦进行定量评估，使得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空间和时间分辨率的限制，其结果将更广泛地适用于更大尺度和更缓慢演变的沿海环境。这将大大提高我们描述和管理各种海岸过程的能力。在后屏障和浅水河口环境中，淹没、富营养化、有害藻华以及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河床耦合。该项目将支持培养一名研究生和一名博士后。多学科课题和综合先进观测和建模工具的研究方法将使他们准备在基础研究或沿海系统的工程和管理方面作出贡献。在近岸海洋中，河床在一系列空间和时间尺度上相互作用。波纹对潮汐速度有响应，波纹迁移过程中的收敛和发散导致了巨型波纹的生长和运动。同样，从春季小潮到事件时间尺度的大波纹演化有助于沙丘的形成和更大尺度的特征。利用自主的水面和空中交通工具，研究小组将绘制出动态潮汐通道在这一强迫条件范围内的演变，明确地解决从波长10厘米到100米的光谱演变。船上和系泊的观测也将测量河床在多个尺度上对上覆水流的摩擦影响，提供局部湍流应力和正压梯度之间的直接比较。空间有限和动态发展的区域允许对系统中的水动力学和沉积物输运进行高分辨率建模，包括对形态响应的前所未有的定量评估。基于过程的小规模建模将与更大规模的形态动力学模拟相结合，将河床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。亚栅格尺度粗糙度的参数化将与观测结果进行比较，以评估多尺度的地形如何影响潮汐强迫变化下的摩擦响应。

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.