A Numerical Investigation of Flood and Sediment Dynamics over the Coastal Watersheds During Hurricane Events

Landfalling tropical cyclones can cause catastrophic floods and sediment disturbance over the coastal watersheds. This study aims to unravel the contribution of different processes to hurricane-induced flooding, to assess the uncertainties in flood modelling and forecasting, and to advance the techniques in sediment simulation over coastal watersheds during hurricanes. First, I examined the hydrometeorology and hydrology of Hurricane Florence (2018) induced inland flooding. My results suggest that the slow motion in combination with the “L-shaped” path was the most distinctive feature of the hurricane that incurred catastrophic and widespread rainfall and flooding over the Cape Fear River Basin (CFRB). Second, I adapted the WRF-Hydro modeling system to Hurricane Florence (2018) to assess the influence of initial soil moisture and precipitation magnitude on flood simulation over the CFRB. Model results suggest that initial soil moisture modulates the flood peak in a non-linear way with a threshold value. In flooding modeling with a hydrometeorological modeling chain, modeling uncertainty is dominated by the precipitation forecast. Spin-up induced uncertainty can be minimized once the model reaches the “practical” equilibrium. Third, I investigated the relative contributions of different physical components to extreme water level over Delaware Estuary during Hurricane Isabel (2003). Model results suggest that storm surge is the dominant component of extreme water level and is seconded by the astronomical tide. The contribution of river discharge is mainly restricted to the upper part of the estuary while the local wind-induced water level is more pronounced over most of the estuary. Fourth, I developed a soil erosion and sediment transport model (WRF-Hydro-Sed) by adapting the sediment code in CASC2D-Sed into WRF-Hydro. The model can reliably reproduce the annual and event-based sediment yield at the watershed scale. Last, I coupled WRF-Hydro-Sed with the Regional Ocean Modelling System (ROMS) using the Model Coupling Toolkit (MCT) on the platform of the Coupled Ocean-Atmosphere-Wave-Sediment Transport Modeling System (COAWST). Preliminary model results demonstrate the new model’s potential in simulating soil erosion, sediment transport, and deposition over the land-to-ocean system. Further efforts such as including bedload transport are needed to reproduce the sedimentary processes more realistically