CHATHAM — If you’re wondering about the validity of sea level rise, visit Jackknife Harbor Beach. An unofficial sign erected there warns visitors that the sandy parking area floods at extreme tides, but somebody has scratched off the “extreme” and written “every.”
With erosion threatening the beach’s access road, the Pleasant Bay Alliance and the town are working on solutions that preserve public access while protecting the environment.
The Alliance is completing work under the first round of a state Coastal Resilience Grant issued by the Massachusetts Office of Coastal Zone Management, which is using the funds to increase understanding of climate impacts and to identify and plan for coastal vulnerabilities. Speaking to the Chatham Parks and Recreation last week, Alliance Coordinator Carole Ridley said the grant aims to find places on the Pleasant Bay shoreline where officials can try out “some innovative strategies for shoreline protection.”
The traditional approach to fighting erosion involves hard structures like rock revetments, groins and seawalls, but those tactics often do more harm than good, or merely move the erosion to a new location. Though sometimes less effective in the short term, soft solutions like fiber rolls and beach grass plantings are favored under state conservation rules. At Muddy Creek and another test site in South Orleans, the goal is to use natural features, grasses and shells “to try to mimic the natural functioning of coastal processes to protect the shoreline from sea level rise, storm surge” and other threats, she said.
“There are a number of different challenges at the site,” Chatham Coastal Resources Director Ted Keon said. The entry road is at a low elevation, there is erosion from the tidal flow in and out of Muddy Creek, cars are parked all over, and dinghies and kayaks are stored on the shoreline. But a key issue, he said, is the “deterioration of the marsh system, in many ways, from the human interaction.” In addition to the cars, people have made paths through the marsh to access the beach.
Consultant Seth Wilkinson of Wilkinson Ecological Design showed the parks and recreation commission various options that could be used at Jackknife Harbor, and said the best approach is probably a combination of several technologies to create a “living shoreline” that resists erosion. Closest to the water, he recommended the use of biodegradable shell bags, a plant-based plastic bag filled with oyster or mussel shells which can be packed under parts of the marsh bank that have been undercut by erosion.
“Pleasant Bay is looking at some pretty considerable sea level rise projections,” and has already experienced the effects, Wilkinson noted.
Above the shell bags would be a single roll of coconut fiber husk, anchored in place, with “cobble-reinforced salt marsh” landward of that. That consists of a mixture of about half cobblestones and half organic growing media, assembled in a kind of biodegradable blanket. The blanket remains intact long enough for plants to take root, mimicking the effects of natural peat beds. Those three layers would be expected to help preserve the vehicle entryway, even raising its elevation somewhat, Wilkinson said.
Parks and Rec Commissioner Ira Seldin asked whether it’s really necessary for anything to be installed at Jackknife Harbor.
“What would happen if nothing’s done?” he asked.
Wilkinson said that even if foot traffic through the marsh is stopped and vehicles are controlled, “a lot of the damage has already been done. And with sea level rise, these areas don’t usually heal themselves.” Erosion could be expected to continue.
Seldin also asked who would pay for the remediation, should it be approved.
The grant which is now coming to a close involved the investigation of a variety of strategies, Ridley said, and the Alliance has applied for a second grant to further study a specific design and begin permitting. There is no commitment to build any of the remediation at this point, she said.
While the work so far has been done by the Alliance, the town of Chatham has a planning effort underway that sought to identify ways to control erosion at the beach. Had the work not been funded by the CZM grant obtained by the Alliance, “that would’ve all been done presumably through town funds, or at least [Community Preservation Act] funds as appropriate,” Keon said.
Jackknife Harbor Beach is directly exposed to winds and wave action during nor’easters in the fall and winter. Parks and Rec Commissioner David Eldredge asked how well the “living shoreline” would fare during severe weather.
There’s always the risk of a winter like the one in 2018, which brought multiple coastal storms to the area, Wilkinson acknowledged. “We had miles of living shoreline that did well,” he said. Some repairs might be needed after storms, “but it’s rare that there is a total loss,” he said.
Commission Chairman Meredith Fry said she supports the living shoreline concept, and other commissioners unanimously agreed. Protecting Jackknife Harbor isn’t just about the environment, she noted.
“It’s thoroughly enjoyed by so many people,” Fry said.