Rhode Island - Major Event Modelled Hurricane Inundation 100 year return period - RIGIS

The North Atlantic Comprehensive Study (NACCS) performed simulations of 1050 synthetic tropical storms using a fully coupled ADCIRC/WAM/STWAVE with a very high resolution grid primarily covering the Mid Atlantic study area (Cialone, 2015). Simulations were performed for surge only and surge plus tidal cases, with predictions being saved at 18,000 grid locations; 1000 in RI. Return period analyses were performed by USACE for each save point and the predicted water level values at the mean, upper and lower 95% confidence intervals were provided. In the present effort, data from the NACCS RI save points were analyzed and spatially scaled to develop a series of projected flood inundation surfaces to visualize multiple storm return periods and sea level rise scenarios. Mean projections were used for events with a return period of 10 years or less, while the upper 95% confidence interval (CI) values were applied to events with return periods 25 years and greater to provide an extra measure of protection. These NACCS-derived flood surfaces show projected water levels that include both storm surge and tidal effects and correct major deficiencies with the widely used bath tub models.
Impacts of recent coastal storms such as Superstorm Sandy (October 2012) reveal the need to address the vulnerability of populations, infrastructure, and resources at risk from storm surge throughout Rhode Island. The U.S. Army Corps of Engineers (USACE) completed the North Atlantic Comprehensive Study (NACCS) in 2015, which provides new tools and information to assess coastal storm and flood risks. Information from the NACCS was integrated into STORMTOOLS. These coastal inundation modeling results can be used by state government and local communities to identify storm surge flooding risks and develop adaptation strategies to reduce those risks now and into the future.

The vision for STORMTOOLS is to provide access to a suite of high-resolution coastal planning tools (numerical models, etc.) that can be used to develop adaptation policies and actions to reduce storm surge vulnerability. The STORMTOOLS inundation mapping effort represents the first step in the development of an integrated toolset that includes the development of simplified flood maps for varying storm return periods and sea level rise scenarios, incorporating the effects of both storm surge and tide as derived from the NACCS. These NACCS-derived flood surfaces correct major deficiencies with the widely used bath tub models by taking in to account the shape/orientation of the Narragansett Bay basin and the resulting funneling effects on water levels during storm events (Spaulding, 2014).