Integrated Hydrologic-Hydrodynamic Modeling of Estuarine-Riverine Flooding: 2008 Tropical Storm Fay

Soil and water assessment tool (SWAT) and advanced circulation (ADCIRC) models were integrated to generate a hydrologic (SWAT)-hydrodynamic (ADCIRC) model applicable for flood prediction in coastal areas. The model is applied to the lower St. Johns River Basin for a holistic postevent analysis of Tropical Storm Fay (2008). Validation of the model is presented, followed by physical-forcing and temporal assessments of inundation within the river-adjacent watershed basins. The model validation and inundation assessment demonstrates the need to apply watershed runoff as an additional boundary condition in order to more fully capture the peak surge and recession, which added similar to 0.5 m to storm tide elevation in the lower St. Johns River, extended the surge recession by nearly 5 days, and increased the inundated watershed area by almost 50%. Watershed inundation ranges between similar to 33 km(2) for normal tide conditions and similar to 150 km(2) for an approximate 1-in-100-year event (Tropical Storm Fay). Implementation of the approach requires careful definition of the SWAT-ADCIRC interfaces at tributaries and river offshoots, which for the case of the lower St. Johns River Basin was accomplished with 8 inflow boundary condition locations. Other details of the approach are discussed, and general guidance for application to other estuaries is provided. (C) 2017 American Society of Civil Engineers.