The race to rebuild living shorelines

Along the New England coast, recreated ‘nature-based systems’ such as salt marshes will boost resilience to the rising sea—when we figure out how to build them at scale.

The idea behind “living shorelines” engineering is straightforward: Natural defenses such as salt marshes and oyster reefs often can guard vulnerable stretches of coastline better than seawalls and other forms of gray infrastructure, and help to restore endangered coastal ecosystems at the same time.

Case in point: An eroding sandy bluff above Narragansett Bay in East Providence’s Rosa Larisa Park. Concrete walls weren’t stopping the bluff’s erosion, said Leah Feldman of the Rhode Island Coastal Resources Management Council at a December 9 meeting on nature-based adaptation in Boston. In contrast, two living shoreline measures, a salt marsh planted with Spartina cordgrass (above) and a bank stabilized with coir logs and beach grass, are performing well.

However, despite a sprinkling of early success stories like this one, “there’s hardly any practice of living shorelines in New England,” said Alison Bowden of the Nature Conservancy at the meeting, which was sponsored by the Environmental Business Council of New England and the Sustainable Solutions Lab at UMass Boston. “So why is that and what are we going to do about it?”

She pointed to two holdups specific to New England plus two barriers on the federal level.

One nagging problem is the common doubt that nature-based approaches can deal effectively with the rigors of our coastal environment—the short growing system, ice and high tide range. But believing that a salt marsh that has withstood every storm for thousands of years is less resilient than a wall “is kind of nuts,” Bowden remarked. “Does anybody think a seawall will have a 6,000-year design life?”

Another big hurdle is that each New England state ignores the national wetlands permitting process and sets its own rules. The resulting lack of design standards endlessly complicates regulatory reviews. (Bowden and many allies took on this challenge in a regional analysis that drew lessons from 15 projects.)

At the federal level, the Clean Water Act was written in the 1970s primarily to keep developers from fouling up bodies of water. That goal made a great deal of sense at the time, but the lawmakers didn’t imagine today’s needs to restore badly damaged ecosystems and to protect against the ever-more-obvious effects of climate change. “I’ve spent a good part of my 21 years at the Nature Conservancy working on figuring out how to get the regulatory environment to let us do things like dam removal and salt marsh restoration,” said Bowden.

Moreover, federal regulatory reviews focus on protecting what is there today rather than what may be there in a few decades. “We can’t really keep what we have over time,” Bowden emphasized. Instead, we need to think carefully about tradeoffs—like, when does it make sense to work toward an ecosystem that’s healthy but not the original ecosystem?

This question already looms for Belle Isle Marsh, Boston’s last salt marsh (above), which doesn’t have much room at all to migrate inland to accommodate rising sea levels.

Better planning for such environmental puzzles needs better data. And while coastal engineers can tap into many decades of information about seawalls and other gray infrastructure, relatively little is known about the performance over time of living shoreline engineering with our region’s salt marshes, oyster reefs, dunes, beaches or seagrass meadows.

Small pilot projects such as Rosa Larisa Park are starting to fill in the gaps, but truly scaling up will demand information we just don’t have. Gathering that knowledge is the mission of Boston’s Stone Living Lab, now conducting a wide range of experiments with various partners. Perhaps SLL’s most intriguing project is to try defending the eastern shore of Rainsford Island (above) with a combination of rocky reef and cobble berm.

The most spectacular living shorelines initiative on the U.S. Atlantic coast, New York’s $107 million Living Breakwaters project (below), also is producing a flood of data.

Scheduled to wrap up construction by 2024, this project on Staten Island, which was the epicenter of drownings in Superstorm Sandy, is designed not to keep the ocean entirely out but to reduce storm risk, enhance ecosystems and foster social resilience along the coast. The centerpiece is a half mile of near-shore breakwaters that not only will bring down storm waves but capture sediment and build the shoreline back, said Pippa Brashear of SCAPE, the lead designers.

The breakwaters aren’t oyster reefs but are carefully crafted to be similarly hospitable to marine life. “Like any good designer, you ask, What does my client need?” Brashear said. “In this case, we were asking how fish, crabs, lobsters and benthic invertebrates will use this.”

Across the country in San Francisco Bay, the Oro Loma Living Laboratory presents another innovative take on living shoreline studies. Built in 2018, this research platform examines “horizontal levees” that install a broad wedge of wetland between a levee and the bay (below, left to right).

“The idea behind the horizontal levee is that you can provide flood protection through a natural system, while also treating wastewater within that system,” said Heidi Nutters of the San Francisco Estuary Partnership. “The freshwater input can also increase the plant growth and improve success of restoration just by having water at the site. And the brackish marshes can build organic soils and help keep pace with sea level rise.”

The Oro Loma lab has demonstrated that microbial processes at work below ground in the wetland wedge can remove contaminants such as nitrogen from treated wastewater. Investigators now are testing the levee on highly saline water trucked in from a desalination plant.

Down on the Gulf Coast, Bowden and colleagues analyzed Google Earth images to make a striking finding about Hurricane Michael, which hit the Florida panhandle in 2018 as the first category 5 hurricane to make landfall in the U.S. in almost 30 years. “Pretty much no gray infrastructure survived,” she said, but only 2% of the salt marshes in the study area were damaged.

“That’s a pretty impressive performance on the part of nature,” Bowden remarked. “Natural processes know how to stand up to nature, and we need to learn from them… to help us as the climate changes.”

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