Coastal Storm Surge Analysis: Modeling System Validation. Report 4: Intermediate Submission No. 2.0

The Federal Emergency Management Agency, Region III office, has initiated a study to update the coastal storm surge elevations within the states of Virginia, Maryland, and Delaware, and the District of Columbia including the Atlantic Ocean, Chesapeake Bay including its tributaries, and the Delaware Bay. This effort is one of the most extensive coastal storm surge analyses to date, encompassing coastal floodplains in three states and including the largest estuary in the world. The study will replace outdated coastal storm surge stillwater elevations for all Flood Insurance Studies in the study area, and serve as the basis for new coastal hazard analysis and ultimately updated Flood Insurance Rate Maps (FIRMs). The end-to-end storm surge modeling system includes the Advanced Circulation Model for Oceanic, Coastal and Estuarine Waters (ADCIRC) for simulation of two-dimensional hydrodynamics. ADCIRC was dynamically coupled to the unstructured numerical wave model Simulating WAves Nearshore (unSWAN) to calculate the contribution of waves to total storm surge. The modeling system validation included a comprehensive tidal calibration followed by an assessment using carefully reconstructed wind and pressure fields from three major flood events for the Region III domain: Hurricane Isabel, Hurricane Ernesto, and Extratropical Storm Ida. Model skill was accessed by quantitative comparison of model output to wind, wave, water level, and high water mark observations. Prior reports covered Submittal 1 requirements by providing details on the bathymetric/topographic digital environmental model (Report 1.1), description of the computational system (Report 1.2), and documenting the selection process for storms used in the study (Report 1.3). This report (2.0) completes the required Submittal 2 documentation by providing details of the modeling system calibration and performance. Sponsored in part by USACE. Prepared in cooperation with Renaissance Computing Institute, Chapel Hill, NC and ARCADIS, Boulder, CO.