Impacts of Sea-Level Rise on Morphodynamics and Flooding in an Idealized Estuary

Abstract:

Estuaries are susceptible to compound flooding resulting from both coastal and fluvial processes. Quantifying changes in flood risk due to a changing climate can be difficult in estuaries because of the combined effects of various factors like precipitation, sea level, and sediment transport processes. Nonetheless, coastal flood risk in general is expected to increase with a warming climate. Sea-level rise (SLR), for example, is expected to increase estuarine flood risk due to landward inundation, increased wave energy, and higher tailwater elevation. The altered hydrodynamics associated with SLR can also feed back into channel morphology in ways that affect channel carrying capacity and flood risk. To date, few studies have investigated the impacts of SLR on channel morphology and the effect on flood behavior. This study focuses on sediment transport patterns, channel morphology and flood behavior in a tide-dominated, idealized estuary using a three-dimensional physics-based numerical model (Delft3D). Initial bathymetry is obtained from a 1000-year morphodynamic model under equilibrium conditions in a 30 km-long funnel-shaped estuary with a maximum width of 3 km at the mouth. Test simulations represent a period of 100 years with SLR derived from four different greenhouse gas scenarios. The resultant morphologies are then subjected to a flood test with a simplified flood hydrograph to evaluate the sensitivity of flooding and sediment budget to different SLR scenarios. Findings from this study can aid in better understanding the morphological and hydrodynamic response and associated flood dynamics in an estuary to SLR.