Aspects of Coupled Hydrologic-Hydrodynamic Modeling for Coastal Flood Inundation

The hydrodynamic model ADCIRC has been used extensively to model hurricane storm surge inundation. ADCIRC utilizes an unstructured triangular mesh that allows sufficient resolution of important features and has been coupled to STWAVE or SWAN to account for wind waves. However, river inflows applied to ADCIRC are usually constant values representative of flow rates during landfall. This may be adequate for systems producing flooding dominated by storm surge, but some systems cause significant precipitation-induced flooding as well as surge, e.g. Hurricane Floyd produced only 3 meters of storm surge, but precipitation resulted in over 500-year flood levels on the lower Tar River. Current NOAA and DBS projects seek to produce holistic coastal flood inundation modeling by coupling hydrologic models, HL-RDHM and Vflo, to ADCIRC. Results from an idealized study show routing using a dynamic wave approximation for the momentum equation is necessary to accurately handle backwater effects; kinematic wave approximation routing should only be used upstream of backwater effects. The initial target area is the Tar and Neuse River region of coastal North Carolina. Preliminary application of ADCIRC, to a domain that includes major rivers in this area subject to backwater effects, forced with a discharge hydrograph at the upstream boundary produces promising results.