Mattapoisett Neck residents are eventually going to have to move up, so they don’t have to move out.
Flooding, not only from coastal storms of historic magnitude but a science-based projection of rising tides under sunny skies, threatens access to the approximately 250 residents of the neck at increasing levels in this century, according to a study presented on March 24.
Mean Higher High Water (MHHW), otherwise known as sunny-day flooding, will by 2030 bring the expectation of 3.4 feet. This is not the result of a coastal storm. By 2050, 4.7 feet will be expected at high tide and, by 2070, 6.5 feet.
“By 2070, it might not be feasible to plan your way out of harm’s way,” said Woods Hole Group Inc. coastal scientist Adam Finkle, estimating up to 20 feet of depth of water in low-lying areas. While Mattapoisett Neck Road, he said, remains relatively resilient to sunny-day, sea-level rise past the year 2050, the road could see up to 3 feet of water during storm in the year 2070.
“What our data told us is that it’s going to be really hard to plan in this location for the big one,” said Finkle. “It’s going to be really hard to have a dry road during a storm event.”
In the second of three stakeholder meetings via Zoom, Fuss & O’Neill project manager Eileen Gunn led participants through a program involving presenters Dean Audet on water resiliency, and geo-scientists Finkle, Andrea Judge, and Joe Famely.
Made possible by a $74,981 reimbursable grant awarded last fall by Coastal Zone Management for the purpose of formulating a long-term answer to the flood risk along Mattapoisett Neck Road’s north and south causeways and the land in between, the Mattapoisett Neck Road Flood Resilience Project will, with a 25-percent financing match from the town, arrive at a final design by June 30.
The Town of Marion is similarly addressing future flood concerns with a proposal to reinvent its Creek Road pumping station. Marion’s plan would submerse a specially-designed pump to operate underwater, while a new control room would be constructed at an elevation that cannot be threatened.
Mattapoisett Neck Road is the only access to and from the peninsula for residents, and according to the study, the tipping point for catastrophic flooding there is projected sometime between 2050 and 2070.
A vulnerability assessment discussed the role of the culvert – there are two at the north end of the Mattapoisett Neck Road causeway and one at the southern end of the causeway at Molly’s Cove – and shared conceptual designs asking for feedback while anticipating a public meeting on Tuesday, April 13. The timeline extends to a final stakeholders meeting in May, followed by public meetings.
Soon-to-retire Highway Surveyor Barry Denham pointed to the Molly’s Cove culvert, saying it is filled with numerous sinkholes and expressed concern that saltmarsh-area water trying to get back to the ocean might accelerate the culvert’s deterioration.
Addressing the culverts in the area, Audet said the ponding water stressing out the marsh vegetation is not due to the culverts. “The water atop that surface can’t get out to the culverts,” he said, explaining that larger culverts would not help with high tide and might compound the stress eroding the creeks and exacerbate the ponding problem.
Mattapoisett resident Mike Huguenin, who is involved in the saltmarsh program with the Buzzards Bay Coalition and the Buzzards Bay National Estuary Program run by the Massachusetts Department of Environmental Protection, cited three rain events between December 7 and January 10, asking if the current situation is indicative of average tide.
“We watch the water velocity on these culverts, moving really fast and see scouring,” said Huguenin, wondering if larger culverts that should reduce water velocity would add benefit.
Audet said that, when water levels in the Brandt Cove get above 2 or 3 feet, they will flood the marsh, regardless of the size of the culvert, and then drain out to Brandt Cove, as well as out of the culvert.
The statewide expansion on the Boston Harbor Flood Risk Model is based on the governor’s executive order (No. 569) integrating climate change to assessments on flood risk. The state Department of Transportation uses the Massachusetts Coast Flood Risk Model as its standard for assessing coastal assets.
The model was presented with three sets of figures, one addressing sea-level rise (high tide levels over course of time), a second addressing coastal flood exceedance probability and its impact based on 6 inches of water disabling public vehicles and 18 inches disabling emergency vehicles, and the third looking at the probability of inundation and the point of elevation where water would reach.
Huguenin asked about “joint probabilities,” identifying sea-level rise as well as storm conditions as climate change progresses and how the levels step up in time as a result. He was told that present surface elevations for a 100-year storm would be 10.7 feet of water.
Road-raising alternatives were discussed with four options, settling on a plan that will allow continued use of Mattapoisett Neck Road by vehicles.
“We can’t fill in a wetland, so we’re limited in how high we can raise the road,” said Judge, adding that the Woods Hole Group is involved in nature-based solutions to provide a transition and embankment.
Resident David Behenna suggested measuring the traffic counts in both winter and summer months at a point south of Town Landing and before the northern-most culvert. He also asked if it would be possible to utilize the Old Mattapoisett Road right-of-way while the culvert is under construction.
Audet said that with precast sections, “This is a pretty quick installation,” estimating a week for work on one side of Mattapoisett Neck Road, then a switch to the other side of the road. “You wouldn’t want to have people walking through there. There might be a couple of weeks where you can’t walk or ride your bike through there.”
The third of three public access stakeholders’ meetings will be held on May 19 at 6:00 pm.
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