CAPE ELIZABETH — A coastal geologist on Oct. 29 will discuss the potential impact of sea level rise and storm surge, as the town’s Planning Board determines how to revise its shoreland zoning ordinance.

Peter Slovinsky, an expert in beach erosion and shoreline change mapping with the state’s Bureau of Geology, Natural Areas, and Coastal Resources, will analyze data on sea level change over the past 100 years, and simulate scenarios for possible sea level change in Cape Elizabeth using geographic information systems.

The town asked Slovinsky to present at workshop after realizing its shoreland zoning ordinance was vague and open to interpretation, and failed to account for sea level rise.

“What they have in the books is kind of a gray area,” Slovinsky said. “It’s a very loosey-goosey written definition in terms of how it can be interpreted.”

That has led to litigation between landowners and the town, said Code Enforcement Officer Ben McDougal, who recently brought the issue to the Town Council.

The shoreland zoning ordinance governs residential development within 250 feet of the ocean shoreline. It takes into account both environmental and aesthetic factors. Houses must be 75 feet from the water. So-called impervious surfaces – driveways, decks, the footprint of a house – may cover no more than 20 percent of a given lot. Vegetation removal is also regulated.

The challenge is determining where exactly to mark the shoreline, given that it’s moving inland, slowly but surely, over time as the sea level rises.

“You go landward of this 250-foot zone and you have a lot more latitude,” McDougal said. “If you want to do a big paved basketball court, you can do that. If you want to cut down every tree on your lot, you can do that. In the shoreland zone, you can’t do that stuff.

“A lot of modest houses on the ocean are selling, and the people who buy them want to expand them significantly,” he said. “So where that 75-foot line comes through the property is crucial.”

The Planning Board is looking at revising its ordinance to take into account not the highest annual tide, but the the highest astronomical tide – the highest tide over a nearly 20-year cycle.

“You’re latching on to a number that’s slightly higher, but it provides more stability because it’s not changing year by year,” Slovinsky said.

On top of that, the committee will consider adding an additional foot or two to account for future sea level rise.

“So say the astronomical tide in that area is usually right around 11.7 or 11.8 feet,” Slovinsky said. “Plus one or two feet of sea level rise. From that line, you do your 250-foot setback, and that would establish the shoreland zone.”

Cape Elizabeth is one of many communities in southern Maine reviewing its shoreland ordinances, Slovinsky said.

Old Orchard Beach and Saco, for instance, are especially susceptible to sea level rise because they have sandy beach systems with extensive barrier marshes.

Much of Cape Elizabeth, on the other hand, is naturally protected by a steep, rocky coastline. Some areas, including the area along Portland Harbor, have an almost vertical face where sea level rise has little impact.

But there are pockets of vulnerability.

“Where you see significant impacts are those lower-lying areas along Crescent Beach State Park, along the Spurwink River as it divides Cape Elizabeth and Scarborough,” Slovinsky said. “Those areas are currently prone to flooding from coastal storms, so I think it does make sense to potentially be a little more restrictive, or at least look at the vulnerabilities in those areas a little bit more.”

Tuesday’s Planning Board special workshop will be held at 7 p.m. at Town Hall.

Brendan Twist can be reached at 781-3661 ext. 123 or btwist@theforecaster.net. Follow him on Twitter: @brendantwist.

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