Sensitivity of an ADCIRC Tide and Storm Surge Model to Manning's n

In this study, the sensitivity of the ADCIRC hydrodynamic model to Manning's n is explored. Using methods presented in hydraulic literature, low, average, and high values of Manning's n are assigned to the overland and channel regions in the study domain of Florida's Big Bend Region. To determine sensitivity and astronomic tides, a hindcast of Hurricane Dennis' storm surge and synthetic hurricane storm surge are simulated through the use of bottom friction formulated as a function of Manning's n. A simulation with a constant quadratic bottom friction formulation is also conducted for comparison. Results show that the ADCIRC model is sensitive to Manning's n in this study region. Rivers showed more sensitivity to tidal effects than marshes, where tidal influences are not as strong. Inland areas, areas in close proximity to rivers, and areas around the maximum envelope of water show the most sensitivity, with variations in the peak water levels produced by the storm surge simulations as large as 1.92 m. Constant quadratic bottom friction produces tidal signals very close to those produced by using the low Manning's n value, but overpredicts water levels in the overland areas for surge simulations as a result of a small bottom friction term. The results of this research show the importance in developing a method to accurately describe bottom friction in a given study domain.