Nested Hydrodynamic Modeling of a Coastal River Applying Dynamic-Coupling

Abstract

This paper presents a nested hydrodynamic model of the Fish River, a tributary of the sub-estuary Weeks Bay located in Mobile Bay, Alabama. The Environmental Fluid Dynamics Code (EFDC) and a novel dynamic-coupling tool were used to link three EFDC hydrodynamic models corresponding to Mobile Bay, Weeks Bay, and the Fish River. The dynamically-coupled models were used to simulate inundation scenarios for combinations of 2-, 7.5-, 10-, 25-, and 100-year floods, and the hurricane surge that occurred during hurricane Katrina. The nested and dynamically-coupled model was developed using available public-access bathymetry and topography databases (National Elevation Dataset, and NOAA bathymetry), and run without recurring to calibration techniques. The simulation of combined scenarios showed that inundated areas increase from 0.07 % up to 189 % with respect to the actual flood that took place during the Katrina event (Katrina + 1-year flood). The results suggest that increases in inundated area are relatively much higher from a 1-year flood to a 7.5 year-flood (128 % flooded area increase) than for higher return periods. For the 25-year and the 100-year floods, inundated areas almost triple from the area corresponding to the base-case (Katrina event), with percent increases of 182 % and 189 % respectively.