January 30, 2017 06:08AM
By Catherine Hewitt
Sun staff writer
CHARLESTOWN — The dredging portion of a project to restore salt marsh habitat and ease navigation along the Charlestown Breachway is wrapping up.
The project was designed to use sediment removed from the breachway as material to increase the elevation of Ninigret Marsh. The project was funded as part of a $3.25 million grant from the U.S. Department of Interior that was awarded after Superstorm Sandy in 2012.
The undertaking was a collaboration among the town, the Salt Ponds Coalition, the Coastal Resources Management Council and the state Department of Environmental Management.
J.F. Brennan Company, Inc., an environmental services and marine construction firm that specializes in waterway remediation, has been working on two dredges 24 hours a day, six days a week, since the end of November. The company was on target to finish ahead of schedule, said Caitlin Chaffee, coastal policy analyst at the Coastal Resources Management Council, who was on-site at the breachway Tuesday.
The dredges removed about four feet of material on average from two basins in the channel, which had become as shallow as two feet in some areas. Some material was piped east of the channel to an intertidal area along Charlestown Beach, but most of it was discharged to the marsh west of the breachway to raise the area’s elevation.
“We’re seeing the marshes subsiding and getting more and more inundated — they’re losing elevation and vegetation and the idea is to use this material as a resource to help the marsh keep up with sea level rise,” Chaffee said.
Salt marshes are important because they act as a natural buffer to coastal storms and serve as an ecosystem for fish and birds. Marshes have natural processes that adapt to sea level rise, but over the last 30 years the rate of sea level rise has increased and marshes have begun to “drown in place.”
With the goal of meeting a target elevation, the dredged material was spread over the marsh in varying thicknesses from a few inches to more than a foot.
“If you go into a marsh and take a sediment core you can actually see where there’s organic material and then sand on top of it and then organic material, so this is kind of a continuous process of how these marshes develop,” Chaffee said. “In a way we like to think we’re kind of mimicking the process by helping it along by putting material on the marsh.”
The next step will be to encourage the creation of salt marsh habitat through growth of vegetation, which will be jumpstarted by planting native plants.
“We’re working with Save the Bay, they’re doing the planting plan for us and they’ll be looking for volunteers in March,” Chaffee said. “We actually worked with the New England Wildflower Society to collect local seed from this area and that seed has been grown in a nursery in New Jersey, so the seedlings that we’ll get from that nursery will actually be a local genotype.”
Chaffee said her team would also monitor drainage on the marsh to make sure the area is not inundated for extended periods, which would kill the vegetation.
“If we get those high marsh grasses back… we know the marsh has more elevation capital against sea level rise,” she said.
The project has been a positive example of a multi-level partnership, Chaffee said.
“What I hope is that when it’s done that we’ll see benefits for everyone: the species on the marsh, the community, if we can improve resilience of the marsh as a protection from storms the town will see easier navigation and better access to the pond, which will improve the recreational use of the pond,” she said. “We try to design these things so everyone’s got a stake and everyone benefits.”