Rhode Island Coastal Resources Management Council Shoreline Change SAMP Volume I CHAPTER 4 Rhode Island’s Exposure to Coastal Hazards Table of Contents List of Figures ........................................................................................................................... 3 List of Tables ............................................................................................................................ 5 4.1 Chapter Highlights ......................................................................................................... 7 4.2 Introduction ................................................................................................................ 11 4.3 Natural Environment ................................................................................................... 13 4.3.1 Beaches, Barriers and Headlands ................................................................................ 14 4.3.1.1 Overview ................................................................................................................. 14 4.3.1.2 Geologic Setting of the Rhode Island South Shore ................................................ 14 4.3.1.3 Geologic Setting of Narragansett Bay .................................................................... 16 4.3.1.4 Physical Processes .................................................................................................. 19 4.3.1.5 Shoreline Protection Structures ............................................................................. 30 4.3.2 Coastal Wetlands .......................................................................................................... 33 4.3.2.1 Overview ................................................................................................................. 33 4.3.2.2 The Effects of Sea Level Rise and Other Coastal Hazards on Coastal Wetlands .... 35 4.3.2.3 South County and Block Island ............................................................................... 39 4.3.2.4 Narragansett Bay .................................................................................................... 42 4.3.3 Other Coastal Habitats .................................................................................................. 45 4.4 Effects of Erosion on Rhode Island’s Coast .................................................................... 46 4.4.1 Historic Shoreline Change ............................................................................................. 46 4.4.2 Projected Shoreline Change .......................................................................................... 48 4.5 Built Environment ....................................................................................................... 49 4.5.1 CRMC Exposure Assessment ....................................................................................... 50 4.5.1.1 Exposed Residential Structures .............................................................................. 53 4.5.1.2 Exposed Commercial Structures ............................................................................ 57 4.5.1.3 Exposed Public Service Structures .......................................................................... 61 4.5.2 Other State Assessments .............................................................................................. 65 June 12, 2018 Page | 4‐1 Rhode Island Coastal Resources Management Council Shoreline Change SAMP Volume I 4.5.2.1 Demographics ......................................................................................................... 66 4.5.2.2 Critical Infrastructure .......................................................................................... 67 4.5.2.3 Wastewater Treatment Facilities ........................................................................ 68 4.5.2.4 Drinking Water Utilities ....................................................................................... 69 4.5.2.5 Transportation Infrastructure ............................................................................. 70 4.5.2.6 Public Access and Recreation Assets .................................................................. 72 4.5.2.7 Historic and Archaeological Assets ..................................................................... 74 4.6 Synthesis: Exposure of Rhode Island’s Coastal Region to Storm Surge, Coastal Erosion and Sea Level Rise .................................................................................................................. 75 4.6.1 At‐Risk Areas ............................................................................................................... 75 4.6.2 Storm surge, coastal erosion and sea level rise in RI .................................................. 75 4.6.2.1 Matunuck Headland ............................................................................................... 76 4.6.2.2 Misquamicut .......................................................................................................... 79 4.6.2.3 Barrington, Warren and Bristol ........................................................................... 81 4.7 Synergistic Effects of Storm Surge, Coastal Erosion and Sea Level Rise ........................ 82 4.8 Ongoing and Future Research and Analysis ................................................................. 85 4.8.1 Overview ..................................................................................................................... 85 4.8.2 Ongoing Research ....................................................................................................... 85 4.8.3 Future Research Needs ............................................................................................... 86 4.8.3.1 The Built Environment.............................................................................................. 86 4.8.3.2 The Natural Environment ........................................................................................ 88 4.9 References ................................................................................................................... 90 June 12, 2018 Page | 4‐2 Rhode Island Coastal Resources Management Council Shoreline Change SAMP Volume I List of Figures Figure 1. Shoreline type indicated as shoreline segments on the map as percentage (inset). Total shoreline change from 1939‐2014 (m) along the Rhode Island south shore on the graph plotted parallel to shore. In this figure and subsequent figures, red indicates erosion and green deposition (Hollis et al. in preparation; Oakley, Hollis and Boothroyd 2016). ............................. 15 Figure 2. Location map of Narragansett Bay ................................................................................. 17 Figure 3. In the Northern Hemisphere, the right front quadrant of a storm is the most destructive area of the storm, with the strongest winds, seas, and resultant storm surge. (Source: University of Rhode Island, “Hurricanes: Science and Society,” 2015; image adapted from the NOAA Atlantic Oceanographic & Meteorological Laboratory Hurricane Research Division.) .............................. 21 Figure 4. Wind, storm surge and wave height effects of westerly and easterly storm tracks (modified from Wright and Sullivan 1982) .................................................................................... 22 Figure 5. Map of historic hurricane tracks, Atlantic coast (Source: NOAA Digital Coast 2017, “Historical Hurricane Tracks,” https://coast.noaa.gov/digitalcoast/tools/hurricanes.html) ....... 23 Figure 6. Map of historic hurricane tracks, northeastern U.S. (Source: NOAA Digital Coast 2017, “Historical Hurricane Tracks,” https://coast.noaa.gov/digitalcoast/tools/hurricanes.html) ....... 23 Figure 7. Location of marsh units assessed for sea level rise vulnerability (based on data used by Cole Ekberg et al. 2017). ................................................................................................................ 37 Figure 8. Median marsh elevation above MHW as an indication of marsh vulnerability to SLR (Source: Cole Ekberg et al. 2017) .................................................................................................. 45 Figure 9. Barriers and headlands of the Rhode Island South Shore with headlands labeled in bold font. Modified from Boothroyd et al. 1998. .................................................................................. 47 Figure 10. Long‐range Planning Scenario (7‐foot SLR + 100‐year storm surge, representing projected conditions in 2100). This figure shows the density of inundated structures based on the number of structures by square mile, with red indicating the highest density of inundated structures and grey indicating the lowest.. ................................................................................... 53 Figure 11. Portion of the Matunuck Headland Shoreline Change Map (Boothroyd et al. 2016). 76 Figure 12. Projected shoreline position, controlling coastal feature, residential and commercial setbacks of Matunuck headland for the year 2100, where historical shoreline change between 1939 and 2014 was exponentially accelerated to the year 2100 (Source: Hollis, Oakley, Rasmussen, Boothroyd, Freedman and Fugate 2016). ................................................................. 78 June 12, 2018 Page | 4‐3 Rhode Island Coastal Resources Management Council Shoreline Change SAMP Volume I Figure 13. Five‐foot SLR plus a 100‐year storm surge affecting