‘Living Shoreline’ Projects Protect Vulnerable Coast
June 21, 2020
EAST PROVIDENCE, R.I. — There is no foolproof approach to stopping coastal erosion, but an experimental “living shoreline” is being tested at a local beach in an attempt to lessen the destructive effects of the climate crisis.
Current waterfront defenses such as stone barriers, known as riprap, and cement seawalls protect what’s behind them but they decimate beaches and natural buffers like salt marsh and seagrass beds. These human-made barricades accelerate the degradation of nearby natural habitat by deflecting wave energy. Thirty percent of Narragansett Bay’s waterfront is already “hardened” by development. But even with a Rhode Island prohibition on new coastal stone and cement barriers the damage is worsening.
“As sea levels rise, the intertidal habitat and limited lateral shoreline access will disappear altogether,” said Janet Freedman, coastal geologist with the Coastal Resources Management Council (CRMC).
Existing natural habitat like salt marsh is the ideal defense, but the Ocean State’s shoreline is losing its protective vegetation to higher tides, intensifying storms, and wave action from boat wakes.
Using a combination of stone, biodegradable materials, and native plants to absorb wave energy, related projects at Rose Larisa Memorial Park seek a hybrid approach to preserving the recreation area and its natural features.
“One of the goals of this project is to find an effective, convenient erosion-control method that does not worsen erosion in adjacent areas, and also provides habitat benefits,” Freedman said.
The unassuming public beach and park has been a retreat for generations. Worn wooden posts and concrete rubble from failed walls are reminders that the beach was developed extensively. A boardwalk, bathhouse, and 400-foot steamship pier were part of the former Crescent Park amusement center. A massive shore dinner hall sat atop the bluff overlooking Narragansett Bay. The park’s remnants show nature’s capacity to reshape and reclaim places — a force that is accelerating with the climate crisis.
Higher seasonal tides are scraping the base of the buff, exposing tree roots. While increased precipitation — another effect of global warming — is causing trees to fall as rain washes away soil through stormwater and groundwater runoff.
“There is a long history of fighting the tide here,” said Grover Fugate, former director of CRMC, one of the organizations collaborating on the project.
To protect the 20- to 30-foot-high bluff behind the beach, two systems of stone and beach grasses were installed in April and May. A beach-level project includes the planting of 2,000 grass plugs with hopes of establishing a salt marsh. Low-lying stone walls, called sills, were installed at the edge of the water. Gaps between the sills allow water, sediment, and sea life to pass through, while waves lose strength as they wash over the aquatic speed bumps and reach the base of the bluff.
A few hundred feet down the beach, a second project consists of dual installations embedded in the slope of the bluff: a stone wall at the base and beach grass plantings above it. This “stone toe” prevents the bluff’s sandy soil from washing away while impeding beach movement from regular tides and low-level storms.
Coconut-fiber logs were installed above the 100-foot-long stone toe, then covered in natural-fiber mats. The vegetation at both sites is blanketed with the mats to reduce erosion from runoff and deter geese from eating the roots of the new plantings.
A third control area consists of beach grass plantings sewed directly into the beach with no protective fiber mat or stone wall.
“This is a great laboratory to look at,” said Tim Mooney, communications manager for The Nature Conservancy, one of the project’s partner organizations.
Wooden posts at each site provide camera mountings for monitoring changes in the beach systems. Stephen Licht, associate professor in the University of Rhode Island’s ocean engineering program, conducted pre- and post-construction beach profiles using drones to monitor changes from above. The aerial surveys will be taken regularly and after storms to see if the installations move horizontally, vertically, or remain in place. Using “structure from motion technology,” this monitoring collects elevation data within 2.5 centimeters to create 3-D images of the sites.
The experiments are a compromise between nature and hard materials that, if successful, may protect smaller beaches and structures such as waterfront homes. The installations likely won’t prevent damage from storm surge and other impacts from a hurricane or tropical storm, but instead they will slow perpetual erosion.
Biodegradable core logs, marsh-grass plantings, and stone breakwaters are helping protect and rebuild dunes and marshes elsewhere in the United States, but only a few of these projects have been permitted, built, and evaluated in New England. So far, core logs and bags filled with oyster shells have shown mixed results protecting eroding marshes along the Narrow River in Narragansett. Other projects using only natural-fiber material have failed to withstand the forces of erosion.
The Nature Conservancy worked with the city of East Providence and CRMC on this project. The environmental group partnered with coastal zone management programs like CRMC and local organizations to monitor 15 demonstration projects in Connecticut, Massachusetts, New Hampshire, and Maine.
Findings from these projects will be compiled into a regional database that will be shared with coastal engineers and permitting agencies. The results are expected to provide new concepts for developers and engineers looking to protect shorelines with sustainable methods.
“This compliments what we’re looking to do with CRMC policy, to encourage these nature-based strategies, and we hope to show that they’re just as viable as other structures,” said Caitlin Chaffee, CRMC’s coastal policy analyst.
Total cost for the various installations is $232,000. The stone sills and salt marsh were funded with $142,000 from a Coastal Resilience Fund grant from the National Oceanic and Atmospheric Administration (NOAA). The NOAA funds were part of a $1 million grant awarded to study living shoreline projects in New England. The Nature Conservancy raised $50,000 from the 11th Hour Racing foundation in Newport. The Rhode Island Coastal and Estuarine Habitat Restoration Trust Fund paid $40,000 for the coconut-fiber logs and stone toe.