Nantucket committee advances planning for downtown neighborhood flood barrier as homeowners raise groundwater and cost concerns

Leah Hill, the Town of Nantucket coastal resilience coordinator, outlined a proposed downtown neighborhood flood barrier on Jan. 28, saying the concept responds to updated NOAA projections and the Massachusetts Coastal Flood Risk Model and would be implemented in phases over 10 to 15 years.

Hill told the Coastal Resilience Advisory Committee that the barrier concept, drawn from recommendations 2-2 and 2-6 in the town's Coastal Resilience Plan, would combine raised roadways, raised wharves, berms, reinforced dunes and selected deployable gates while preserving access to key facilities such as Steamboat Wharf, Straight Wharf and the Town Pier. “We’re planning for the worst and hoping for the best,” she said, describing the town’s recommendation that departments and consultants use the NOAA high sea-level-rise scenario for planning.

The recommendation responds to local flood projections that show daily high-tide flooding increasing in the downtown core: Hill noted NOAA gauge data and explained why the town is using the Massachusetts Coastal Flood Risk Model (MCFRM) — which incorporates tides, storm surge, wave run-up and future storm probabilities — as the town’s “best available” flood mapping. She said a simple linear calculation using NOAA’s 4.01 millimeters-per-year figure…