Game of Floods - Wastewater Plant
Bird Watcher / Nature Lover
Assignment: Read the role assignment and background reading below, then answer the questions at the end.
Role Assignment:
You are a bird watcher/nature lover who likes to walk and kayak in the marshy area near the wastewater treatment plant. You know how important marshes are for migratory birds. The marsh is so much smaller than it used to be decades ago, before the wastewater plant was built, and you are concerned that it will disappear entirely as sea level rises. You’d love to see restoration of the marsh. You think that buildings on the shoreline are eyesores, and should be torn down and replaced with natural habitat. It drives you CRAZY that people don’t understand the benefits of restoring natural habitats like marshes and dunes.
Background Reading:
Why you want oysters and a salt marsh between you and a hurricane
Adapted from an article by Anne N. Connor | Jun 3, 2019
More coastal towns are building “living shorelines” for storm and flood protection.
In September 2018, Hurricane Florence slammed into Beaufort, North Carolina, a town on the state’s inner banks that sits just 10 feet above sea level. The hurricane brought a 2.5-foot storm surge and sustained winds of 75 miles an hour that lasted some three days.
The living shoreline of cordgrass and oyster reef was built by NOAA to protect Pivers Island in Beaumont, North Carolina. | NOAA Fisheries
Florence was a big test for two different strategies for protecting the coast. While the areas with “hard” solutions — seawalls — sustained damage and significant erosion, a section of coastline with a “soft” solution, called a “living shoreline,” fared much better. According to the National Oceanic and Atmospheric Administration, the Beaufort Living Shoreline oyster reef and marsh was “intact after the storm, with minimal erosion.”
More and more communities are trying to stabilize and fortify their coastlines against future storms, flooding, and sea level rise. The more than 120 living shorelines around the country are showing that a combination of oyster reefs, oyster shells, rocks, marsh plants, and other natural materials can be an effective alternative to seawalls. They’re also far less expensive.
The Shortcomings of Seawalls, Explained
Seawalls are hard structures that block waves from approaching the shore. Some are located in the water, but many are built into the shoreline, replacing natural shorelines.
Seawalls are expensive to build and maintain, and do not stand up well to severe storms. When waves break on seawalls, they “scour” the bottom — their turbulence digs away at the sand at the base of the seawall. Eventually, as a hollow grows under the wall, it cracks and tips over, making seawalls more vulnerable to erosion than natural shorelines.
Vertical seawalls deflect waves, magnifying rather than dampening them. If you were to hold up a plate and direct your kitchen faucet at it, water would splatter back at you, because the dish is rigid. If your neighbor installs a bulkhead, waves will ricochet off the seawall and onto your property, increasing erosion.
Seawalls protect seaside homes in Ventura County, CA. 65% of the shoreline in Ventura County is armored. | Bryan Chan/Los Angeles Times via Getty Images
Many flood-prone cities, desperate for a solution, are spending massive amounts of money building seawalls, but the protection may be far less than residents hope. For instance, a $14 billion levee system recently completed in New Orleans is already sinking and is expected to be ineffective by 2023. The U.S. Army Corps Engineers acknowledged that it had not fully taken into account sea level rise when designing the New Orleans project.
Salt Marshes Act As Giant Sponges
Coastal habitats such as salt marshes, on the other hand, reduce the number of human lives and properties at risk from storm surge and sea level rise by half, according to a study in Nature. In early fall, at the height of hurricane season, marsh grass reduces wave energy twice as much as in early summer due to its growth phase. A salt marsh projecting just 15 feet from the shore can absorb 50 percent of incoming wave energy.
“Wetlands ... absorb floodwaters by acting as a natural sponge,” explains Kate Brogan of NOAA’s Fisheries Department.
Salt marshes prevented more than $625 million in direct flood damages during Superstorm Sandy in 2012, according to a 2017 study in Nature. Wetlands endure storms better than hardened shores; in one North Carolina study, 76 percent of bulkheads in the central Outer Banks were damaged during Hurricane Irene, compared with none of the coastal habitats studied.
Yet rather than protecting these natural sponges, we’re destroying them. The US loses 80,000 acres of coastal wetlands each year, largely to development, drainage, erosion, and pollution. “That’s approximately seven football fields every hour,” according to NOAA’s Office of Habitat Conservation.
Living Shorelines Are an Affordable Solution That Can Be Scaled
Living shorelines are easy to install, compared with seawalls, and cost far less; the average expense is $361 per linear foot, about a third the price of a concrete bulkhead. In some communities, volunteers install them at only the cost of the materials. Living shorelines also last indefinitely.
In contrast, a vinyl bulkhead averages about $686 per linear foot, a wooden bulkhead $652 per linear foot, and a concrete bulkhead $1,022 per linear foot. Most of these structures last 20 or 30 years (50 for vinyl), with a projected replacement cost of 120 percent of the original expense.
The sills of living shorelines — often made of crushed rock or bags of oyster shells, placed about 15 feet offshore — are positioned in front of wetlands. If existing marsh is sparse, plants may be supplemented by planting plugs of grass during the installation process. The marsh plants do the real work; sills just provide temporary tranquility in which they may take root.
Once marsh grass is established, it spreads into deeper water, capturing silt as it goes. The captured silt mixes with organic matter to become soil, and gradually extends the shore further into the sea. Living shorelines have been successfully deployed in Norfolk, Virginia, for example, as well as in the hurricane-vulnerable Outer Banks of North Carolina.
Often, marine life takes hold as well, and the sills turn into living reefs, teeming with fish, crabs, and other shellfish. A healthy salt marsh is marked by a profusion of salt-resistant plants, such as the cord grass Spartina alterniflora, succulent pickleweed, and bulrushes. The marsh attracts dragonflies; fly-catchers like the red-winged blackbird with its distinctive trill; and leggy wading birds, intent on the crabs and mummichogs below. Salt marshes are often punctuated by little channels, peaceful places to explore by canoe.
Living shorelines are not appropriate for every location; container ships can’t dock in a salt marsh, so shore hardening is necessary in major ports. Nor would they be appropriate at public swimming beaches, where people seek sand rather than silt. But for many towns, or for coastal homeowners, living shorelines could be an excellent alternative.
Questions:
1. What is a living shoreline?
2. What are two advantages of living shorelines over sea walls?
3. Why do sea walls sometimes fail in severe storms?
4. Answer this question in character as a nature lover/bird watcher (see the role description at the top). What would be the most effective way for the town of Resilient to protect its wastewater treatment plant from sea level rise? Explain your answer.
Once you have answered the above questions, move on to Part 2 here.
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