From Scientific American
As sea levels rise along US coasts, it may soon get easier for people and local governments to obtain federal permits to build what are known as “living shorelines,” natural or nature-based structures designed to protect communities and infrastructure from extreme storms and flooding even as they protect habitat. Should we start to look more closely at these ideas in the Channel Islands? There are already some good examples.
In the US, the Army Corps of Engineers is considering a new category to its nationwide permits that would allow speedier approval of living shorelines, which include wetlands with sea and marsh grasses, sand dunes, mangroves, and coral reefs. Currently, it’s much faster for property owners in many parts of the country to get a permit for sea walls, bulkheads and other so-called grey infrastructure than it is to get a permit for construction of nature-based systems. If the corps moves forward with the new category, though, permits to build living shorelines could be issued in as few as 45 days, instead of 215.
The move toward more natural coastline protection comes as federal agencies, state governments, and local and business leaders focus increasingly on the concept of resilience as they plan for how communities will adapt to climate change. The spotlight on dynamic systems is a major shift for agencies like the Army Corps, which in the past paid more attention to engineered solutions. Unlike with engineered solutions, there’s greater uncertainty with living shorelines. Researchers and engineers have less information about how they will respond to sea-level rise, storm surge and other extreme events. They’re learning to be more nimble.
Natural shorelines protect species, but what about homes?
Other federal agencies, including the National Oceanic and Atmospheric Administration, support living shorelines in places where they’re warranted. They work best in more sheltered systems with moderate wave energy, like the Chesapeake Bay, river systems, Puget Sound and even the Great Lakes.
A study by the Pew Charitable Trusts found that about 14% of the US coastline is what researchers described as “armoured.” A 2015 report from NOAA on living shorelines noted that if coastal populations continue to increase, and if so-called “shoreline hardening” continues at the current rate, nearly one-third of the contiguous US coastline could have sea walls or other grey infrastructure by 2100. The agency found evidence that shorelines with intact natural coastal habitats not only see less damage but bounce back more quickly from severe storms.
“Studies have shown that living shorelines host greater populations of fish and other organisms crucial for shorebirds and for recreation and commercial fisheries”, said Rachel Gittman, a postdoctoral research associate at Northeastern University’s Marine Science Center. Gittman, who spends much of her time in North Carolina, was asked by the Pew Charitable Trusts to analyse the effectiveness of natural shorelines compared to hard infrastructure. The work is part of the foundation’s climate adaptation efforts to improve flood readiness in US communities.
Bulkheads, sea walls and vertical structures with marginal structural complexity don’t provide the same habitat for marine organisms as natural shorelines, Gittman said.
“It’s not the same type of habitat. It’s a difference in the slope of the shoreline. A vertical wall is very different than the slope of the shoreline. We think it has to do with the wave dynamic, so how sediment is transported changes when you put in a wall.” She added “And we also just think it’s a simplification of that shoreline. So you go from a shoreline that might have lots of pools and crevices and rocks … to a wall. Organisms are not finding refuge along that shoreline.”
The biggest drawback to living shorelines so far has been the uncertainty about how well they’ll work, and whether they are truly less expensive than hard infrastructure.
Finding hidden economic savings
Some organisations are trying to quantify whether living shorelines cost less to build and can provide the same protection. The Nature Conservancy found a perfect opportunity in Miami-Dade County in South Florida.
There, the county’s aging wastewater plant was under orders to stop dumping waste into the ocean. The Nature Conservancy is studying whether marshes surrounding the low-lying plant can help protect it from storm surge and flooding. The marshes aren’t just protection for the plant’s $3 billion in upgrades—they’re a part of the massive federal Everglades restoration project.
The Nature Conservancy hopes that what it learns about the project will make it easier for other communities weighing similar projects to move forward with natural systems. Wetlands like the ones in Miami-Dade County also have benefits that can’t be captured in traditional cost-benefit analysis. For example, mangroves might be used on either side of a road that frequently gets washed out during high tides. That allows people to get to work and protects infrastructure. Those are more challenging metrics to capture but they are crucial for keeping an economy operational after a storm, and for minimising expensive damage to roads due to sea-level rise.
Jennifer Molloy, green infrastructure coordinator for US Environmental Protection Agency, said that the agency often is criticised for not giving enough weight to the complexities of operating and maintaining living shorelines. But hard structures also have operational and maintenance issues. Both need flexibility with climate change. “They’re not that different,” she said of green systems. “We ought to not see them as so different. We’re going to end up with combinations of both, and they function together.”
The traditional use of seawalls and bulkheads has slowly been hardening our coastline and destroying our marsh and wetland environments, which in turn damages the wildlife dependent upon them. A sensible and environmentally friendly alternative, the living shoreline, has been burdened by unnecessarily cumbersome scrutiny. The health of shores is integral to our fishing industry, our tourism appeal, and the coastal way of life
Despite the massive push for living shorelines, such natural systems may not be appropriate everywhere. But they do give communities options that might supplement hard infrastructure, Gittman said “I think it would be naive to say you shouldn’t modify your shorelines, because obviously we’ve built along our shores. We have a lot of infrastructure and communities that we need to protect.” “If you’re talking about a really urban area, you’re probably going to still need other structures for flood protection. Maybe there are places where a sea wall is the only option, maybe it’s a major port, so you really have to have a deep channel.”
“What it means is that we need to be more creative in how we stabilise shoreline, and I think we also need to learn a bit more from nature,” she said. “We should be thinking about how to incorporate natural shore protection components. Anywhere where naturally stabilising features can be incorporated—I think that’s what we need to be thinking about.”