Global warming seen as Scarborough flood risk - KeepMEcurrent.com

Posted: Wednesday, July 4, 2012 3:00 am | Updated: 12:46 pm, Tue Jul 3, 2012.

SCARBOROUGH â€" Officials in Scarborough are raising the roof over global warming â€" literally.

At the June 26 ordinance committee meeting, Peter Slovinsky of the Maine Geological Survey asked the town to amend its floodplain ordinance to increase “freeboard” â€" the distance between the floorboards of a home and the high-water mark of a 100-year flood â€" from 1 foot to 3 feet.

A “100-year flood” has a 1 percent chance of happening in any given year. The last such storm occurred in 1978 when a 3.5-foot storm surge coincided with an astronomical high tide.

The problem, said Slovinsky, is that a 2010 study prepared by the Saco Bay Sea Level Adaptation Working Group, a joint effort of Scarborough, Biddeford, Old Orchard Beach and Saco, predicts local sea levels will rise 2 feet over the next 100 years. That would make water levels seen in the 2007 Patriots Day storm the norm. Meanwhile, adding 2 feet to the 1978 storm would put approximately 95 Higgins Beach homes under water.

Under the proposal, which the ordinance committee will take up at its July 31 meeting, new homes built in the floodplain would have to meet the 3-foot freeboard. Also, any “substantial renovation” â€" defined as new construction worth at least half of the existing home’s value â€" would trigger the need to raise the entire structure 2 feet.

Between 1912 and 2011, the Portland tide gauge showed a sea level rise of 7.5 inches, the fastest increase at any time in the past 3,000 years. According to the Potsdam Institute for Climate Impact Research, that rate is tracking more recently, using 1993-2011 data, to an equivalent of 16 inches per century.  

That data, based on satellite altimetry, does not account for melting of the Greenland ice sheets, said Slovinsky. When that impact is factored in, local mean sea levels are expected to rise 13 inches by 2050 and “a minimum” of 2 feet by 2100.

“We can expect a storm surge to hit at high tide about once every seven years,” said Slovinsky. “We need to plan for tomorrow’s storms today even if sea levels don’t rise as much as we think they might.”

According to Slovinsky, a 2-foot rise in mean sea level means storm surges that now reach flood stage 11 times per year in the Saco Bay area would do so 281 times per year, inundating beachfront homes in roughly 40 percent of all high tides.

“That’s a significant thing when you’re planning for the future,” said Slovinsky. “Essentially, think of the storm surges of today as the normal sea levels of tomorrow.”

While about 95 Higgins Beach homes would end up under water in flooding similar to the 1978 storm plus 2 feet, J.T. Lockman, of the Southern Maine Regional Planning Commission, says adding 2 feet to the normal high tide would still inundate 20 homes in the historic beachfront neighborhood.

“Increasing the freeboard is a cost-effective means to protect buildings that will only impact structures that need to meet the minimum freeboard anyway, because of new construction or substantial renovations,” said Lockman. “The cost difference between raising a home the 1 foot it might need to go up anyway, and 3 feet, is really quite minimal.”

In fact, said Lockman, the 60 percent savings on flood insurance premiums â€" up to $3,400 per year, depending on zone and premium variables â€" should more than recoup any added construction costs.

According to Slovinsky, Scarborough has the most buildings in the tidal flood plain of any Saco Bay community. About 1,000 buildings are at risk in town, he said.

Under questioning from Councilor James Benedict, Slovinsky said the proposed amendments to the town’s floodplain management ordinance would not impact septic system requirements.  However, he appeared to catch some change proponents unaware when asking what happens if a mandated height increase smacks against Scarborough’s ceiling on building heights.

“We can take a look at drafting language to provide for an exemption, if you will, if adding the 3-foot freeboard requires a homeowner to break the existing 35-foot height limit,” said Assistant Town Planner Jay Chace.