Nantucket Insights by Brent

Reading Nantucket's Coastal Erosion and Flood Maps

Written in 2021, so the tool and its data may have been updated since. Adapted from my original piece, The New FEMA Maps, October 2021.

On an island, the shoreline is part of the property conversation. FEMA's long-standing flood maps date back to the 1960s and rely on historical data. A newer online coastal erosion and sea level rise map adds a forward-looking layer, and it is worth knowing how to use it.

What to understand first

• It is a planning tool. FEMA describes these maps as non-regulatory products meant to identify coastal erosion hazard areas and support mitigation planning.
• It looks ahead. The tool models sea level rise scenarios through 2100, with target years of 2030, 2050 and 2100. The local rate cited at the time was about 3.57 millimeters per year.
• It combines two forces. Erosion and rising water together paint a fuller picture than either one alone. Chuck Larson, the Town's Manager of Strategic Projects, presented how the tool estimates that combined effect.

How to use it

• Enter the property address.
• Turn on one scenario at a time so the view stays readable.
• Use the print and measuring options to document what you see.
• Compare it with the traditional flood map from FEMA's Flood Map Service Center.

These maps are a starting point, not a verdict. Flood zones affect insurance and lending, and erosion risk varies a great deal along the island's shoreline, from 'Sconset bluff to Madaket.

This is educational information. Please talk with your insurance agent and lender about how a specific property is treated.

Keep reading: Buying on Nantucket and Special permits and zoning. Weighing a waterfront or near-water home? Let's walk through it together.

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