PETER SLOVINSKY, left, a marine geologist with Maine Geological Survey, leads a discussion Tuesday night in Harpswell.
Causeways endangered by sudden storm surges and the effects of gradual sea level rise were key topics at a workshop attended by 50 Harpswell residents at the Town Office on Tuesday night.
Harpswell Town Planner Carol Eyerman and the Harpswell Conservation Commission worked with representatives of the Midcoast Council of Governments and Maine Geological Survey to compile data on sea level rise pertinent to Harpswell.
Situated mostly on granite with tall bluffs along the shore, Harpswell is geologically well positioned to limit the effects of sea level rise to the immediate coastal area, according to Peter Slovinsky, a marine geologist with Maine Geological Survey, part of the Maine Department of Agriculture, Conservation and Forestry.
Several roads, however, and causeways connecting the islands that make up Harpswell are at risk in storm events, said Slovinsky, particularly if the sea level rises one foot — as it is predicted to by 2050.
Current configurations of coastal landforms, such as wetlands and sand beaches, were set down over a period of 5,000 years, said Slovinsky, when sea level changes occurred at 1 millimeter per year, or less.
Sea levels recorded at the Portland tidal station between 1912 and 2014 indicate an average sea level rise of 1.9 millimeters per year, said Slovinsky, doubling the typical rate of the previous 5,000 years.
“Over the last 21 years … we’re looking at sea level changes of about 3.2 millimeters per year on a global scale,” said Slovinsky. “Not quite a doubling, but there is an increase in the rate of sea level rise in the global oceans.
“Going back to the Portland tidal station … if we look at just that data, we’re up to about 4.2 millimeters per year,” added Slovinsky, noting an increase to 6.7 millimeters per year in the past 10 years.
Factoring in other elements of climate change, “if we take those and extrapolate those out,” said Slovinsky, “we should expect about one foot of sea level rise by 2050.”
Extrapolating further out, said Slovinsky, different studies present scenarios for sea level rise over the course of 100 years that range from a low of 1.6 feet to a high of 6.6 feet.
Storm tide and storm surge were also discussed, both as separate phenomena and in concert with longterm trends in sea level rise.
Storm tide is the observed sea water level during a storm, while storm surge is an abnormal water level caused by a storm that is over and above a predicted tide.
A higher surge that occurs at a higher tide poses the greatest likelihood of flooding, said Slovinsky, however, a higher sea level could also increase the frequency of flooding events owing to storm surges.
Using Light Detection and Ranging, or LIDAR, technology, a digital elevation model was generated, which was used by Audra Caler-Bell and Scott Hastings of the nonprofit Midcoast Council of Governments to illustrate how areas of Harpswell may be affected by sea level rise and storm surge.
Of the roughly 153 miles of roads in Harpswell, 4.5 miles are at risk of flooding, and these at-risk roads are primarily causeways connecting the islands.
According to the mapping data, a category 1 storm — a hurricane that has sustained winds of 74 to 95 miles per hour — could cause flooding on Route 123, also called Harpswell Neck Road.
A category 1 storm could slightly affect areas of Route 24, also called Harpswell Islands Road. A category 2 storm, with winds of 96 to 110 mph, could endanger certain bridges along that road, including the approaches to the Cribstone Bridge, and could flood nearby properties.
Areas of Mountain Road, High Head Road, Bethel Point Road, Long Point Road, Gun Point Road and Johnson Point Road are also at risk.
“The big thing in my mind is the impact to your causeways,” said Slovinsky. “You probably know that already, this is just confirming that.”
The data gathered is a planning tool for municipalities to look at their critical infrastructure and use for emergency management planning, said Slovinsky, and can easily be incorporated into existing planning documents, such as the town’s comprehensive plan.
“Use a scenario-based approach — look at the range of different potential scenarios and look at the impacts in your community,” when planning for sea level rise, said Slovinsky. “Tie these to potential planning horizons.”
Participants were given surveys to indicate how residents would like the sea level rise study to be used in town planning.
For more information, visit the town website at www.harpswell.maine.gov. To view the mapping data for Harpswell, visit the Midcoast Council of Governments website at www.midcoastcog.org/projects/coastal -hazard-resiliency-sea-levelrise.
Elevation model
USING LIGHT DETECTION and Ranging, or LIDAR, technology, a digital elevation model was generated, which was used by Audra Caler-Bell and Scott Hastings of the nonprofit Midcoast Council of Governments to illustrate how areas of Harpswell may be affected by sea level rise and storm surge.
OF THE ROUGHLY 153 miles of roads in Harpswell, 4.5 miles are at risk of flooding, and these at-risk roads are primarily causeways connecting the islands.
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