Hydrodynamic Modeling of Tides and Hurricane Storm Surge for Pre- and Post-Dredging Conditions in the Lower St. Johns River, Florida

The United States Army Corps of Engineers (USACE), Jacksonville District, is conducting a study for improving navigation near Jacksonville Harbor in the lower St. Johns River (SJR), Florida. A two-dimensional hydrodynamic model (ADCIRC) of the SJR is employed to study the effects that deepening the channel may have on circulation within the river. Model results from an inlet-based modeling domain, forced with astronomic tides, show low sensitivity to mean low water (MLW) and mean high water (MHW) between pre- and post-dredging conditions. Results from a large-scale hydrodynamic model (ADCIRC+SWAN), forced by astronomic tides and winds from Hurricane Dora, show minimal difference in peak surge, timing of peak surge, and inundation area. The model is then used to determine possible impacts a 30 cm rise in sea level may have on flooding. Model results demonstrate that peak surge elevations do not increase by the rise in sea level, depicting the dynamic nature of the estuary.