As rising seas raise more urgent questions about how to defend Delaware’s low-lying shore, environmentalists and state authorities are renewing their advocacy for “living shorelines” as a way of cushioning the impact of higher waters on coastal property and the natural environment.
The technique uses barriers made of natural materials like coconut logs and oyster shells to reduce the impact of waves on coastal marshes, helping them to build up and defend upland areas from encroaching seas.
Responding to the growing threat from higher ocean levels and the bigger storms that are forecast to come with climate change, state officials are offering landowners a new tool describing how living shorelines work, how they can be adapted to specific locations, and how they can be a better solution than so-called hard defenses like bulkheads.
Called the Living Shoreline Monitoring Framework, the program identifies whether existing living shorelines are achieving goals such as shoreline stabilization, improved water quality and habitat creation, and recommends ways of managing a site better if those goals are not being met.
The framework, offered by the Department of Natural Resources and Environmental Control, and several state and federal partners, allows for different levels of technology, expertise and financial resources for existing living shorelines, and encourages the creation of new installations.
“Whether you are putting in a living shoreline for water quality or habitat components or restoration for oysters, how do you track whether it has done what you wanted it to do?, said Alison Rogerson, an environmental scientist at DNREC’s Division of Watershed Stewardship. “Maybe you got funding to improve water quality, and the funders say: ‘prove it to me.’
“The monitoring framework helps you build a plan and monitor for things so that you can figure out whether you have met specific goals,” she said.
DNREC and its partners base their expertise on a number of living shoreline projects that have been in operation for several years, and show that the technique has helped wetlands to rebuild naturally and protect the coast, albeit temporarily, from rising waters.
At Indian River Marina in Rehoboth Beach, a five-year-old living shoreline program in an area of low tidal energy has created 64 square meters of marsh with just 48 linear feet of shoreline, while an adjoining “control” area where no shoreline was installed has lost 10 square meters of marsh to inundation by sea water.
During a recent visit to the Indian River site, a line of wooden posts was partially submerged about 20 yards from the control area of the shore at low tide. The posts marked the edge of the marsh at the start of the DNREC project in 2014, and showed that the rest of the marsh would have been inundated if it hadn’t been protected by the living shoreline during that time.
By contrast, the section of marsh where the living shoreline was installed has thrived and is now colonized with dense clumps of the marsh grass spartina alterniflora, thanks to the sediment that has been trapped there by the living shoreline.
The technique is based on the accumulation of sediment that gets deposited in the wetlands by incoming tides, allowing the intertidal areas to gradually build up and resume their traditional role as a buffer between land and sea.
“Every time this murky water comes up at high tide, the sediments that are in the water column fall out and stay there,” Rogerson said, while standing in the water dressed in waders. “Over time that builds up. They are feeding themselves but if they are not getting enough, they can’t keep up with the rate of sea level rise.
Although some of the material such as shredded coconut husk in the living shoreline breaks down over time, the bags of oyster shells continue to act as a brake on wave action, as well as providing habitat for aquatic organisms long after other elements have disappeared. At the Indian River site, the oyster shells could be seen just below the water, marking the line where the living shoreline was built in 2014.
By creating the conditions for the marsh to survive, installation of a living shoreline will also allow different species of animals, birds and plants to inhabit the area, boosting biodiversity.
The benefits can also be seen at Lewes, where a companion project has added 82 square meters of wetland while an adjacent control site has lost 22 square meters, Rogerson said.
In addition to trapping sediment, a living shoreline built on the edge of a marsh will absorb some of the wave energy that would otherwise directly impact the edge of the upland. According to federal government scientists, 15 feet of marsh can absorb 50 percent of incoming wave energy.
The technique won’t hold back the inexorable rise of global sea levels, but it will help marshes move steadily inland and maintain their traditional role as coastal buffers, even as seas steadily cover coastal areas. DNREC has forecast a meter or more of sea-level rise, inundating 8-11 percent of Delaware’s land area, by the end of century.
Hardened shorelines such as bulkheads, riprap or seawalls eliminate the intertidal area and contribute to the erosion of nearby shoreline that has not been reinforced, scientists say. The hardened defenses simply deflect incoming tides and storms rather than absorbing them, and so may only be suitable for sites with high levels of wave energy.
But even if hardened infrastructure has already been installed, living shorelines can be built in front of them, as at the Indian River project where a section of marsh lies between a line of riprap and the water’s edge.
Advocates for living shorelines like Rogerson also note that it’s about four times as expensive to build a bulkhead than a living shoreline, and with none of the ecological benefits.
At Seagrass Plantation, a community of about 200 homes on the south side of Indian River Bay, a new living shoreline project has slowed the erosion of a marsh and a beach, and the environment is already showing improvements since it was completed in November.
The marsh is protected by a line of some 3,300 shell bags stretching around 350 linear feet, and is designed to halt erosion of about 3-4 feet a year, said Douglas Janiec, Natural Resources Program Manager for Sovereign Consulting, an environmental engineering firm that built the living shoreline.
Janiec said the community opted for a living shoreline rather than a hardened structure because of concern for the natural environment. The project is one of Delaware’s largest living shorelines, he said.
The option of a hardened shoreline “wasn’t even a consideration” for the community, Janiec said. “It wasn’t ecologically beneficial, it wasn’t aesthetically beneficial, it just wasn’t what they wanted.”
By contrast, the new living shoreline sustains the link between land and water. “If you put in a hard shoreline you are blocking the interchange between the water and the adjacent land. When you do a living shoreline project, you keep that connection,” he said.
Despite the attractive cost differential and ecological benefits of living shorelines, hardened shorelines are much more common around the Delaware coast and nationally, scientists say. The National Oceanic and Atmospheric Administration projects that 33 percent of U.S. shorelines will be hardened by 2100.
Still, there’s increasing interest in living shorelines as people understand more about their advantages, said Marianne Walch, Science and Restoration Coordinator at the Delaware Center for the Inland Bays, an environmental nonprofit that advocates for living shorelines.
“We’re getting quite a lot of calls from people who have waterfront property, asking, ‘How can I learn more about this, and how can I have someone come out and look at my shoreline?’” Walch said. “The majority of developed property has hardened shoreline but the attitude is changing over time. We really do have a lot of optimism that the picture is changing.”
To spread the word about living shorelines, Walch and her colleagues give special attention to educating contractors who are usually more familiar with hard shorelines, and can more easily price them than quoting for the alternative.
That’s why for the last four years, Center for the Inland Bays has been offering two-day workshops for contractors to educate them on how to evaluate different sites for living shorelines, and recommend the right type to their clients.
“They need to have these living shoreline tactics in their tool box, to understand them and be able to educate property owners,” she said.
Although the idea of living shorelines has been around for decades, it’s getting new attention as sea-level rise is forcing coastal landowners to look more seriously at ways of defending their properties, Rogerson said.
“Thirty years ago, people said ‘you can try this’ but now we are really feeling this urgency with sea level rise, and an exacerbated rate of erosion that we didn’t see 30 years ago,” she said. “As erosion and sea level rise becomes a bigger problem people are looking for options.”
Details can be found at https://www.delawarelivingshorelines.org/