Towards a Comprehensive Understanding of Ocean and Riverine Hydrodynamics and Their Interaction in the Intercoastal Zone

Coastal regions are home to roughly 40 percent of the global population. These regions are vulnerable to flooding from both inland rivers and tidal/ocean processes, with climate change expected to contribute to increased coastal flood risk. Accurate coastal hydrodynamic models are needed to anticipate and mitigate coastal flooding risks. Traditionally, hydrologic (river) and ocean models have been treated independently, resulting in ocean models that oversimplify or ignore the inland river network and hydrologic routing models that stop the rivers at their outlet. This research seeks to meaningfully couple ocean hydrodynamics to inland hydrologic processes by expanding the range of scales and processes that can be simultaneously solved in numerical models. I propose to address this problem in three steps: 1) design and implement basin-to-channel scale ADCIRC-based ocean models, 2) couple the hydrologic inland processes (rainfall-runoff) into the model's physics, and 3) use the model to explore ocean-river interactions under variable weather conditions. I will focus on the US's East and Gulf of Mexico Coasts, considering the high complexity and variability of its coast and the high frequency of storms that affects this region.

In this research, I demonstrate the capability to develop computationally-efficient models that maintain high levels of accuracy in deep ocean and inland complex channel systems. I designed meshes for ocean hydrodynamic models separating the waterside from the floodplain, which was crucial to correctly incorporating the complex inland riverine network's representation. The mesh design was also crucial in my methodology to couple a traditional ADCIRC-based ocean model with inland hydrology. I utilized the National Water Model v2.1 inputs to couple river flow and precipitation. I validated the methodology, simulating tides, and eight historical storms. During tides, I found minimal effect on the river flow, except for the Hudson River, whose hydrodynamics highly depends on the water level adjustments after incorporating river discharge. During historical storms, incorporating hydrology improved the error statistics for most of the storms when comparing the results with observations. However, I identified a couple of problems that revealed the need for incorporating smaller-scale channels in future generations of the grid. Thus, future research should focus on incorporating small-scale channels across the floodplain, utilizing subgrid methods. They will help to improve drainage of flooding, especially those highly induced by rain and to avoid the missing interaction of the one-way coupling between hydrology and ocean/atmospheric forces.