Potential Tidal Marsh Migration Map

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Data Description and Usage

These eight datasets identify current tidal marshes and non-tidal lands within existing tidal estuaries that could be inundated and facilitate the development of new areas of tidal marsh if sea level rises by 0, 1.2, 1.6, 3.9, 6.1, 8.8, or 10.9 feet above current highest astronomical tide (HAT). The data were developed using a static ("bathtub") inundation model that uses LiDAR topographic data as a base digital elevation model, and then 1) adjusts HAT tidal predictions to take into account variability in the water surface elevations along the Maine coastline, and 2) adds scenarios of 0, 1.2, 1.6, 3.9, 6.1, 8.8, or 10.9 feet of sea level rise to that initial starting elevation. The primary purpose of these data is to enable appropriate land use planning for lands that may become future tidal marshes, and to inform other investigations as to the impacts of and strategic conservation, restoration, and management planning for predicted sea level rise on critical coastal habitats.

Data Disclaimer

Users assume responsibility in determining the usability of this data for their purposes. Metadata is included for all of the downloadable layers and should be reviewed for more specifics on how these data were created. Neither the Maine Natural Areas Program nor the Department of Agriculture, Conservation and Forestry, nor its employees or agents: (1) make any warranty, either expressed or implied for merchantability or fitness for a particular purpose, as to the accuracy or reliability of the information shown on the map; nor are they (2) liable for any damages, including consequential damages, from using the map or the inability to use the map.

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Frequently Asked Questions

Do marsh migration areas take into consideration culverts or other road crossings of tidal streams?

No. The tidal marsh migration scenario is not hydrodynamic; in other words it is "blind" to structures that may currently be barriers to tidal flow or marsh movement. This can be useful to identify built areas or infrastructure that may be inundated or compromised under various sea level rise scenarios, and inform restoration or planning related to infrastructure.

How does this dataset differ from the Sea Level Rise/Storm Surge layer?

The potential marsh migration dataset was developed using the sea level rise scenarios created by the Maine Geological Survey and displayed at http://www.maine.gov/dacf/mgs/hazards/slr_ss/index.shtml. This potential marsh migration dataset uses the highest annual tide (HAT) as a proxy for the upper boundary of the existing tidal marsh. In many locations, this differs from the actual boundaries of the existing tidal marsh, as mapped in the field by the Maine Natural Areas Program and shown on the viewer as Current Tidal Marshes. Thus, the boundary for existing mapped wetlands may differ from the upper boundary of the highest astronomical tide and the starting point for mapping of future tidal marsh conditions. Also, potential marsh migration areas were only mapped in areas where tidal marsh currently exists, or within estuarine settings that could support marsh migration. As such, small, fringing marsh areas (below 2.5 acres) or stretches of open coastlines – where conditions would likely not support marsh migration - have been removed. The Sea Level Rise/Storm Surge dataset is different from the potential marsh migration dataset in that the former depicts sea level rise coastwide, regardless of marsh size, existing development footprints, or association with estuary.

Why does it look there is a gap in some places between the edge of Current Tidal Marsh and drawing of potential marsh migration under 1 foot of sea level rise?

Current tidal marsh was drawn based on aerial photography and field observations. In most cases this margin aligns very closely with the current Highest Astronomical Tide (HAT0) line. However in some places these two data sets do not perfectly line up due to differences in mapping precision and methodology. As a result there may appear to be a gap between the upper edge of current tidal marsh and the start of projected 1.2 foot sea level rise (which is based on the HAT0 line).

More Help

Contact the Maine Natural Areas Program at maine.nap@maine.gov.

A good reference is Marshes on the Move, published by The Nature Conservancy and the National Oceanic and Atmospheric Administration.

Updated: 4/16/2024