Elise Leduc

Elise Leduc, a coastal scientist for the Woods Hole Group, presented the results of a study on how climate change will affect flooding in Falmouth.

Building earthen berms in certain areas of Falmouth to protect vulnerable town infrastructure from flooding—and also creating a new harbor in Woods Hole—were among the ideas a Woods Hole Group scientist raised at a public presentation at the Falmouth Public Library Tuesday, October 29.

The Falmouth-based environmental consulting organization has worked with a town steering committee for the past year on a climate change vulnerability assessment and an adaptation planning project.

These two projects focus solely on town-owned assets, and the group will soon present a report to the board of selectmen, Charles T. McCaffrey, chairman of the Falmouth Coastal Resiliency Action Committee, said to the audience of nearly 50 people.

Also in attendance were Town Manager Julian M. Suso, selectman Douglas C. Brown and members of the water quality management and coastal resiliency action committees.

The main speaker, Elise Leduc, a coastal scientist for Woods Hole Group, said carbon dioxide-fueled climate change is warming not only the air, but Earth’s surface and ocean waters, as well.

“Sea-level rise is the fastest it’s been in more than 2,000 years, so warming seas, rising seas, are going to result in more frequent flooding on the coastline,” she said.

The current state projections show a 10-foot rise in sea levels by 2100. The sea level in Woods Hole has risen about a foot in the past century, Ms. Leduc said.

“If it were to continue at that same rate, you’d expect another foot in the next 100 years, except it doesn’t seem to be doing that. It’s accelerating as it’s rising,” she said.

The data used for the vulnerability assessment is from a Massachusetts Department of Transportation-funded project.

“The DOT is taking a slightly conservative approach and wanted to go with a high sea-level rise scenario for planning—something that we are 99.9 percent unlikely to exceed based on the current modeling,” Ms. Leduc said.

The state projects 1.1 feet of sea-level rise on Cape Cod by 2030, 2.4 feet by 2050, 4.2 feet by 2070 and 7.7 feet by 2100.

Falmouth Town Hall is among the important town assets at risk of flooding due to storms and tides, Ms. Leduc said. These assets include town-owned buildings, above-ground utilities, sewer mains and lift stations, roads, bridges, parking lots, recreational facilities, bike paths, storage sheds, docks, boat ramps and piers.

Town Hall has a critical elevation of 6.7 feet that the town must keep water from exceeding to prevent flood damage, Ms. Leduc said.

“There is a 5 percent chance even today that town hall would flood in a big storm. When you move to 2030, you have a 20 percent chance in any given year [of town hall flooding]. And by the time you get to 2070, it’s a 100 percent chance,” she said. “Town hall is vulnerable today, and it’s going to be increasingly vulnerable in the future.”

Woods Hole Group now has data of this type for every town-owned asset and can compare the composite risk of flooding for each of those assets, based on the asset’s type, location, importance to the town and critical elevation for flooding.

Marine assets that are right on the water tend to be highest on the at-risk list, but many other assets are also high on the list. These include the Ellen T. Mitchell Bathhouse at Surf Drive Beach, Water Street in Woods Hole, the Woods Hole drawbridge hut, Green Pond Bridge in East Falmouth and portions of Chapoquoit Road in West Falmouth.

Road infrastructure tends to be at higher risk than are buildings in flood situations, especially in a 100-year storm, which has a 1 percent risk of happening in a given year, Ms. Leduc said.

Natural resources such as wetlands are also crucial assets to the town, and the Woods Hole Group study seeks to identify the risk to those wetlands and where they can persist in the future.

“Salt marshes like to be in a particular range in the tide; freshwater wetlands don’t want to be tidal, so as the water comes up, things will convert, things will change,” Ms. Leduc said. “By 2070, a lot of the salt marshes will disappear from drowning [due to increased tidal inundation daily]. The amount of wetland in town is going to go down, and the amount of open water is going to go up.”

For example, the Great Sippewissett Marsh is expected to become a mudflat by 2050 and a pond by 2070.

“This is a problem that all of the Massachusetts coastline is going to have as salt marshes struggle to keep up with sea-level rise,” Ms. Leduc said.

For its proposed adaptive management strategies, Woods Hole Group looked at three different categories: site-specific asset-based, regional and natural resource.

In the regional category, Ms. Leduc gave the example of building earthen berms that could take the form of small grassy parks in specific places to protect town infrastructure from flooding.

The Cape Cod Commission is working with the Town of Falmouth on long-term proposals for creating salt marshes and green space in areas of town such as the Falmouth Harbor area and on Davis Straits in the Little Pond area, in the current Walmart parking lot.

“There would have to be tons of real estate transactions for something like this to happen, but it’s good to dream big and think of positive changes for the town,” Ms. Leduc said.

In planning for Woods Hole, where large storms and high tides are a significant risk, Ms. Leduc said her colleague, senior coastal engineer Kirk F. Bosma, described the philosophy needed to ensure the village’s future as “living with water.”

“We have to re-envision Woods Hole and work with and around the water that’s going to be there,” she said, noting the particular risk to roads and to the access for Penzance Point.

Woods Hole Group has envisioned removing the drawbridge hut, building a new bridge with better tide controls and routing the roads in and out of Woods Hole from another direction. This includes creating “living-with-water zones” that are a combination of living space, green space and salt marshes enclosed by earthen berms.

The proposal also involves creating a new inlet for a new harbor, and sediment dredged up could be used to raise the roads, making them more flood-proof, Ms. Leduc said.

She acknowledged that these might sound like “crazy ideas” politically and economically.

“This is a huge step, maybe even impermissible in today’s political climate, but that doesn’t mean that it shouldn’t be envisioned or considered. The world is going to change in really big ways, and I think we have to be innovative about how we can make some good things come out of the scary stuff that’s going to happen,” she said.

Woods Hole Group will make the data available to Falmouth residents on the town’s website, Ms. Leduc said.

Early next month the coastal resiliency action committee will host a public information forum on Woods Hole Group’s Surf Drive Vulnerability Assessment. The date and location have not been determined.

(1) comment

Gadfly

It seems to me that one of the most vulnerable areas that can affect most people living in Falmouth is Menahaunt Road between Bristol Beach and the Great Pond Bridge. That road diverts a large amount of traffic off of Route 28 from East Falmouth to Falmouth, both in summer and winter. After a hurricane with southeast winds, the road would likely be torn up and possibly difficult to rebuild given current environmental restrictions. It's also one of best ocean-view roads. It's an asset we need to protect.

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