An average high tide combined with strong winds from a winter storm led to flooding that topped tide barriers and left Portland waterfront condos and piers inaccessible on Jan. 17.
Troy Moon, the city’s sustainability director, said the high point of 12.6 feet wasn’t even as bad as it could have been.
“We dodged a bullet,” Moon said. “It could’ve been a lot worse.”
The approximately 3-foot surge was one of the top 20 highest storm surges ever in Maine, according to data from the Gulf of Maine Research Institute. Even though predicted tides were average – between 9 and 10 feet – the weather created the potential for extreme flooding that could be an indicator of what typical flooding could look like in the future.
At its highest point, last week’s tide created flooding in coastal areas around the Portland Pier and Willard Beach in South Portland. While this is considered nuisance flooding today, Moon said Portland is seeing weather events like these more often, and events like this one should be expected at increasing frequencies.
Additionally, the high tide remained much longer than it should have. Rather than cresting and going back out to sea, it lasted for up to 90 minutes, according to Gayle Bowness, a sea-level-rise expert at GMRI.
Bowness said Portland has seen the sea level rise about half a foot since 1950, but it could double by 2030 and reach 1.5 feet by 2050. When that time arrives, the natural high tides and storm surges could be identical to the flooding experienced on Jan. 17.
That would also mean the rate of flooding events could increase tenfold as soon as 2030, from as few as 10 times a year now to as many as 100 times a year, Bowness said.
Flooding typically occurs in Portland when tides reach 11.5 feet, and surges as high as 3 feet or more on top of that could create serious problems for Portland’s vulnerable areas.
“The timing for a perfect storm is lined up. It just hasn’t happened yet, but it could,” Bowness said. If the record surge on Jan. 17 had occurred with an 11.5-foot high tide, flooding would have been even worse.
Moon said a team in the city’s sustainability office is working to adjust to these impending changes.
A new hydrodynamic model of flooding is in the works that uses the topography of coastal areas, he said. It will be a more detailed, useful method of anticipating flooding, and should be available in the coming months.
How flooding will be addressed in Portland in the future will have to include updating code and observing the most and least vulnerable areas to flooding in the city to protect people and property from the danger of future storms, Moon said.
He said he expects to have policy discussions with the Planning Board and City Council in the next year about sea level rise, storm surge, and flooding.
“It is happening,” Moon said. “It’s happening sooner than people thought.”
Bowness suggested that adapting to tidal changes and flooding will eventually become an everyday process for many people, like it is now for those who work on the waterfront.
“Those of us who are more land-based, who are just existing, working, playing, living in these coastal communities, we’re going to have to check the tides as we plan how we get from A to B, or which areas of our town are accessible or not,” she said.