HCPC conducted a flood vulnerability assessment for the Town of Frenchboro as a part of their Coastal Communities Grant in 2025. As an island community with critical waterfront and nearshore infrastructure, the Town of Frenchboro is especially vulnerable to hazards including sea level rise, storm surge, and coastal erosion. These hazards put critical infrastructure, private property, and natural resources at risk of incurring damage and ultimately loss of use or access.
This vulnerability assessment focuses on the impacts of flooding, sea level rise, and storm surge. While this assessment provides an analysis of the aforementioned hazards, it is not a comprehensive overview of all the vulnerabilities and hazards faced by the Town of Frenchboro. The Maine Climate Council’s Scientific and Technical Subcommittee’s 2024 report recommends communities “commit to manage” 1.5 feet of sea level rise by 2050 and 3.9 feet of sea level rise by 2100 relative to the 2000 mean sea level. The Subcommittee also recommends communities “prepare to manage” for 8.8 feet of sea level rise by 2120. For the scenario of the highest astronomical tide plus 1.5 feet of sea level rise, the closest available inundation scenario data (highest astronomical tide plus 1.6 feet of sea level rise) was used.
The culmination of this vulnerability assessment is the Flood Vulnerability Map Viewer below. Flood scenarios included in the analysis are the 100-year (base) flood, 1.6, 3.9, and 8.8 feet of sea level rise, and hurricanes (categories 1-4). Road segments at risk of inundation under several flooding scenarios are highlighted.
Click here to view the map in full screen.
In the map viewer you can turn on or off different flooding scenarios by checking and unchecking the boxes on the right side. You may need to open the map in full screen to view all features and for best functionality.
Data sources for the map include Beginning with Habitat, FEMA, Maine Coast Heritage Trust, Maine GeoLibrary, Maine Geological Survey, MEGIS, Town of Frenchboro, USGS, and Western Mountain Mapping.
The data depicted in the map is derived from a variety of sources, with different approaches to flood modeling.
The Highest Astronomical Tide (HAT) represents the elevation of the highest predicted astronomical tide expected to occur over the National Tidal Datum Epoch. In other words, this is the highest water level recorded for a given area. This water level is greater than Mean High Water, the average of all high water heights observed over the National Tidal Datum Epoch. For more information see resources from the Maine Geological Survey and the National Oceanic and Atmospheric Association.
The Maine Geological Survey’s Sea Level Rise/Storm Surge data approximates the potential inland extent of inundation from several scenarios of sea level rise or storm surge on top of the highest astronomical tide. The data were developed with a static (“bathtub”) inundation model that uses LiDAR topographic data as a base digital elevation model, and first adjusts highest astronomical tide tidal predictions to take into account variability in elevation datums along the Maine coastline, and then adds the storm surge/sea level rise scenarios to that initial starting elevation. This modeling method may not take individual landscape features (such as marshes) into account.
The Maine Geological Survey Sea, Lake, and Overland Surges from Hurricanes (SLOSH) maps were created to show potential hurricane inundation areas at mean high tide. This model uses topographic data and the National Hurricane Center’s SLOSH model showing potential storm tide water elevations. These data are appropriate for general planning and emergency preparedness.
FEMA uses a more dynamic approach for flood hazard analysis to create flood maps. The coastal flood hazard analysis and mapping process generally includes evaluating topographical (land surface) data, water levels and storm surge, natural and man-made features along the shore, and wave hazard modeling. The 100-year flooding event used for these analyses includes FEMA Zones A, AE, and VE.
Using ArcGIS, land inundation from flooding scenarios was calculated based on projections using the best available science and data. They should be viewed as approximations that can help identify and plan strategies and actions to increase resilience.
| Flood Scenario | Acres of Land Inundated | Percent of Total Land Area |
|---|---|---|
| 100-Year Flood | 377 acres | 12% |
| 1.6 Feet of Sea Level Rise | 114 acres | 4% |
| 3.9 Feet of Sea Level Rise | 167 acres | 5% |
| 8.8 Feet of Sea Level Rise | 299 acres | 10% |
| Category 1 Hurricane | 99 acres | 3% |
| Category 2 Hurricane | 170 acres | 6% |
| Category 3 Hurricane | 248 acres | 8% |
| Category 4 Hurricane | 327 acres | 11% |
Roads are the major infrastructure at risk from flooding, particularly around the harbor. There is a risk that the Western and Eastern parts of Long Island will be cut off from each other at the head of the harbor. Incorporating these projections into infrastructure, community, and emergency management planning will be critical for the Town. The projected feet of road inundated below are derived from flood scenarios using different modeling methods, so may not be directly comparable.
| Flood Scenario | Feet of Road Inundated |
|---|---|
| 100-Year Flood | 3,813 feet |
| 1.6 Feet of Sea Level Rise | 827 feet |
| 3.9 Feet of Sea Level Rise | 1,590 feet |
| 8.8 Feet of Sea Level Rise | 3,515 feet |
| Category 1 Hurricane | 673 feet |
| Category 2 Hurricane | 1,803 feet |
| Category 3 Hurricane | 2,808 feet |
| Category 4 Hurricane | 3,576 feet |
This project was funded under award CZM NA24NOSX419C0024 to the Maine Coastal Program from the National Oceanic and Atmospheric Administration, U.S. Department of Commerce. The statements, findings, conclusions, and recommendations are those of the author(s) and do not necessarily reflect the views of the National Oceanic and Atmospheric Administration or the Department of Commerce.
