Coupling Hydrologic and Surge Processes to Examine Two Distinct Flood Transition Zones in Coastal Louisiana

Abstract:

Traditional coastal flood hazard studies do not typically account for rainfall runoff processes in the quantification of flood hazard and related cascading risks. This study addresses the potential impacts of antecedent rainfall runoff, tropical cyclone-driven rainfall, and tropical cyclone-driven surge on total water levels and its influence in delineating a coastal flood transition zone. First, we developed and applied a new rain-on-mesh module to route spatially and temporally variable rainfall across the coastal region within the ADCIRC model framework. Second, we developed a set of plausible realizations of pre-tropical cyclone antecedent rainfall scenarios and synthetic tropical cyclones with associated rainfall to force the hydrodynamic model. Our modeling methods are applied for two distinct coastal basins in southeastern Louisiana that are heavily impacted by inland and coastal flooding events – Lake Maurepas and Barataria watersheds. We demonstrate how the inclusion of antecedent conditions alters the flood hazard, especially within the low-lying Barataria watershed. We also examine how the inclusion of tropical cyclone-driven rainfall amplifies coastal flooding and widens the coastal flood transition zone. Our results emphasize the need and begin to define how to further develop and refine coastal flood models to include both coastal shallow water flow and hydrologic processes in a tightly-coupled framework. Such improvements in our ability to understand and model compound flooding can enhance our preparedness and resilience strategies across low-lying coastal landscapes.