Stormtools Design Elevation (SDE) Maps: Including Impact of Sea Level Rise

Abstract

Many coastal communities in the US use base flood elevation (BFE) maps for the 100-year return period, specified on Federal Emergency Management Agency (FEMA) Flood Insurance Rate Maps (FIRMs), to design structures and infrastructure. The FIRMs are increasingly known to have serious problems in accurately specifying the risk coastal communities face, as most recently evidenced during hurricanes Harvey and Irma in 2017 and Florence and Michael in 2018. The FIRM BFE maps also do not include the impact of sea level rise, which clearly needs to be considered in the design of coastal structures over the next several decades given recent National Oceanic and Atmospheric Administration (NOAA) sea level rise (SLR) projections. Here, we generate alternative BFE maps (STORMTOOLS Design Elevation (SDE) maps) for coastal waters of Rhode Island (RI) using surge predictions from tropical and extratropical storms of the coupled surge-wave models from the US Army Corp of Engineers, North Atlantic Comprehensive Coast Study (NACCS). Wave predictions are based on application of a steady state, spectral wave model (STWAVE), while impacts of coastal erosion/accretion and changes of geomorphology are modeled using XBeach. The high-resolution application of XBeach to the southern RI shoreline has dramatically increased the ability to represent the details of dune erosion and overtopping and the associated development of surge channels and over-wash fans and the resulting landward impact on inundation and waves. All methods used were consistent with FEMA guidelines for the study area and used FEMA-approved models. Maps were generated for 0, 2 ft (0.6 m), 5 ft (1.5 m), 7 ft (2.1 m), and 10 ft (3.1 m) of sea level rise, reflecting NOAA high estimates at various times for the study area through 2100. Results of the simulations are shown for both the southern RI shoreline (South Coast) and Narragansett Bay, to facilitate communication of projected BFEs to the general public. The maps are hosted on the STORMTOOLS ESRI Hub to facilitate access to the data. They are also now part of the RI Coastal Resources Management Council (CRMC) risk-based permitting system. The user interface allows access to all supporting data including grade elevation, inundation depth, and wave crest heights as well as corresponding FEMA FIRM BFEs and associated zones.

Flood risk in past and future: A case study for the Pawtuxet River's record‐breaking March 2010 flood event

“…To assess the maximum impact of SLR on flooding extent, the flooded area for a 100‐year event was plotted assuming the current mean sea level, and was compared with the flood area for an extreme scenario; based on NOAA's recent estimation in this region (Grilli, Spaulding, Oakley, & Damon, 2017; Spaulding et al, 2020) if sea level rises 3.5 m (Figure 18). In both scenarios, it was assumed that flood occurs during high tide.…”

STORMTOOLS, Coastal Environmental Risk Index (CERI) Risk and Damage Assessment App

“…All maps are available on the RI Shoreline Change Special Area Management Plan (Beach SAMP) web site (http://www.crmc.ri.gov/samp_beach.html, accessed on 20 December 2019). In addition, base flood elevation (BFE) maps including both surge and waves (called STORMTOOLS Design Elevation (SDE) maps) for various sea level rise (SLR) values (0 to 10 ft) have been developed to support the design of coastal structures [4] (http://www.beachsamp.org/stormtools-design-elevation-sde-maps/, accessed on 11 December 2019). In 2016, the RI Coastal Resources Management Council (CRMC) formally adopted STORMTOOLS as part of their coastal program and recommended the use of the tool to aid in designing coastal projects or assessing the vulnerability of existing public and private assets.…”

“…Senior students in the Ocean Engineering program at University of RI (URI) have applied CERI to Matunuck Beach, RI in 2015-2016 [14], to Misquamicut Beach, RI in 2016-2017 [15] to Providence and the Fox Point Hurricane barrier in 2017-2018 [16] and to the Narragansett Bay Commission (NBC) Wastewater Treatment Facility (WWTF), and adjacent above-ground storage tanks (AST) located on Fields Point in 2018-2019 [17]. The development of CERI and its application to coastal communities have been published in the peer-reviewed literature [4,5,8,9,11,18,19] and presented at a number of national conferences (e.g., ASCE Solutions to Coastal Disasters, Estuarine and Coastal Modeling, Coastal Geotools, Northeast Arc User Group Conference). One of the side benefits of CERI is that the data necessary to input to the method and generated as part of its application can be used to provide state-of-the-art flooding maps, equivalent to those developed by FEMA Flood Insurance Rate Maps (FIRMS), but explicitly including the effects of sea level rise (SLR).…”

“…Based on the success of STORMTOOLs and CERI, HUD CDGB funded an effort to generate STORMTOOLs Design Elevation (SDE) maps, including the effects of SLR for the entire state. This project generated BFE maps (including effects of SLR) for all coastal communities in RI and provides one of the fundamental building blocks for the application of CERI to the entire state [4]. The maps are available at http://www.beachsamp.org/stormtools-design-elevation-sde-maps/, accessed on December 11, 2019.…”

Application of STORMTOOLS Coastal Environmental Risk Index (CERI) to Inform State and Local Planning and Decision Making along the Southern RI Shoreline

“…Given the focus of the present study, Figure 3 shows the maps for the Southern RI shoreline for the cases of 0, 5, and 10 feet of SLR, reflecting the nominal values for today, 2070 and 2100, respectively. Details on the development of the SDE maps, including the modeling of the shoreline erosion for areas with significant wave heights is provided in Spaulding et al (2019) [14]. The GIS-based online maps allow the user to determine the inundation and the associated controlling wave height (average wave height of 1% of the highest waves, assuming that waves are Rayleigh distributed) that comprise of the BFE at the area of interest.…”