Advancing Existing Assessment of Connecticut Marshes’ Response to SLR Final Report September, 2016 (corrected January 2019 to fix road-flooding-counting statistics) Prepared for: Northeast Regional Oceans Council Prepared by: Jonathan Clough President Amy Polaczyk Research Associate Marco Propato Research Associate NROC Report USF&W Grant Number F14AC01001 This project is supported in full by the U.S. Fish and Wildlife Service: Award # F14AC01001 Acknowledgements Warren Pinnacle would like to thank the following individuals for their support during this project: Sarah Hamm, Dewberry, LLC. David Kozak, CT DEEP Stephen Lloyd, The Nature Conservancy Kevin O’Brien, CT DEEP Nathan Vinhatiero, RPS Thanks to the Association of United States Delegates to the Gulf of Maine Council (USGOMA) for their assistance Table of Contents Table of Contents ............................................................................................................ iii Figure Listing ................................................................................................................. vi Table Listing ................................................................................................................. viii Acronyms and Abbreviations List ..................................................................................... x 1 Background ............................................................................................................ 11 1.1 Model Summary .............................................................................................................. 12 2 Methods.................................................................................................................. 13 2.1 Study Area ....................................................................................................................... 13 2.2 Spatial Data ..................................................................................................................... 13 2.2.1 Elevation Data ......................................................................................................... 14 2.2.2 Slope Layer ............................................................................................................. 15 2.2.3 Elevation transformation ........................................................................................... 15 2.2.4 Land coverage .......................................................................................................... 15 2.2.5 Dikes and Impoundments .......................................................................................... 16 2.2.6 Percent Impervious ................................................................................................... 16 2.3 Model Timesteps .............................................................................................................. 17 2.4 Sea Level Rise Scenarios .................................................................................................. 17 2.5 Tide Ranges .................................................................................................................... 18 2.5.1 Wetland Boundary Elevation ..................................................................................... 18 2.6 Inundation Heights ........................................................................................................... 19 2.6.1 30-day, 60-day, and 90-days inundation frequency ...................................................... 19 2.6.2 Storm Surge ............................................................................................................. 20 2.7 Accretion Rates .............................................................................................................. 21 2.8 Erosion Rates ................................................................................................................. 21 2.9 Marsh Collapse Data ........................................................................................................ 22 2.10 Infrastructure ................................................................................................................... 22 2.10.1 Roads and Railroads ................................................................................................. 23 2.10.1.1 Roads and railroads elevations ................................................................................ 24 2.10.2 Critical Infrastructure................................................................................................ 24 2.11 Model Calibration ............................................................................................................ 25 2.11.1 Hydrologic Enforcement ........................................................................................... 26 Advancing Existing Assessment of Connecticut Marshes’ Response to SLR iii 2.11.2 Muted-Tidal Areas ................................................................................................... 27 2.12 Model Setup .................................................................................................................... 28 2.12.1 Area 1 - Fairfield County .......................................................................................... 29 2.12.2 Area 2 - New Haven and Middlesex Counties ............................................................. 35 2.12.3 Area 3 - New London County .................................................................................... 41 2.13 Uncertainty Analysis Setup ............................................................................................... 48 2.13.1 SLR by 2100 ............................................................................................................ 49 2.13.2 Digital Elevation Map Uncertainty ............................................................................. 49 2.13.3 Vertical Datum Correction ........................................................................................ 50 2.13.4 Great Diurnal Tide Range ......................................................................................... 50 2.13.5 Wetland Boundary Elevation ..................................................................................... 50 2.13.6 Erosion .................................................................................................................... 50 2.13.7 Accretion ................................................................................................................. 50 2.13.8 Marsh Collapse ........................................................................................................ 50 3 Results and Discussion ............................................................................................ 51 3.1 Entire Study Area ............................................................................................................. 51 3.2 Road-Inundation Results ................................................................................................... 52 3.3 Infrastructure Results ........................................................................................................ 55 3.3.1 Schools.................................................................................................................... 57 3.3.2 Power Plants ............................................................................................................ 59 3.4 Effects of road elevation on marsh inundation ..................................................................... 60 3.5 Areas with muted tides ..................................................................................................... 61 3.6 Marsh migration ............................................................................................................... 63 3.7 Water connectivity ........................................................................................................... 65 3.8 Uncertainty results ........................................................................................................... 66 4 Conclusions (Lessons Learned) ................................................................................ 72 Literature Cited ............................................................................................................. 75 Appendix A: Previous SLAMM Application and GIS Methods ........................................ 77 Elevation transformation ............................................................................................................... 77 Wetland Layers and translation to SLAMM .................................................................................... 77 Dikes and Impoundments .............................................................................................................. 78 Historic sea level rise rates ............................................................................................................ 79 Tide Ranges ................................................................................................................................. 79 Elevations expressed in half tide units (HTU) ................................................................................. 80 Wetland Boundary Elevation ......................................................................................................... 81 Advancing Existing Assessment of Connecticut Marshes’ Response to SLR iv Accretion Rates ...........................................................................................................................