A plan to build a $ 1.1 billion seawall around much of downtown Charleston relies on concrete structures, although many would like to see the US Army Corps of Engineers include less solutions. intrusives such as living shores and improved marshes.
The Post and Courier of Charleston obtained public comment through a Freedom of Information Act request. These comments show that residents, nonprofit groups, and even the South Carolina Department of Natural Resources all want to include more natural features.
“I am seriously concerned that a more naturalistic approach is not the result of this study,” wrote a resident in September.
The 8-mile (12.8-kilometer) project would include a wall rising 8 feet (2.5 meters) above tide levels. The plan includes dozens of gates that would close and block roads, streams and walkways as a storm approaches. The pumps would expel the water when the valves closed.
Jaclyn Pennoyer, the Corps’ Charleston District spokesperson, wrote in an email that the agency is considering three nature-based protections for the city – building living shores of oyster reefs, adding sediment to swamps existing and discover long tidal coves filled.
But neither of these options would protect Charleston against a hurricane wave of several meters, she wrote. This is the body’s protection mandate. Some oyster reefs are included in the most recent version of the plan. But they would run parallel to sections of the surge wall, not replace it.
Reefs, improved marshes or improved streams “as a self-contained perimeter protection do NOT appreciably reduce the risk of damage from coastal storm surges,” Pennoyer wrote. “Additional nature-based solutions could be included and funded by the City of Charleston to address precipitation and tidal flooding.”
University of West Carolina professor Robert Young said it was true that a reef would be drowned by a strong storm surge. But he said greener strategies would add environmental benefits. And he said the storm surge isn’t the only challenge for Charleston. Rising sea levels are already causing more frequent but less severe tidal flooding.
“It’s better to create some sort of tiered approach to gray infrastructure than to just build a sea dang,” Young said.
Live shorelines work best to protect the edge of a swamp or high ground from erosion. South Carolina now allows landowners to install their own versions to protect property or marshes.
In recent years, researchers have started deliberately placing oyster shells and other products to protect the marshes, said Peter Kingsley-Smith, senior marine scientist in the state’s Department of Natural Resources. Bags of seashells, “cement castles”, coir logs and even crab traps have all been tried, Kingsley-Smith told the newspaper.
These methods can preserve marsh grasses, which are important wildlife habitats and absorb carbon dioxide.
The Coastal Conservation League has commissioned an alternative plan from Charleston that features oyster reefs to slow the waves, earthen dikes and man-made wetlands in different sections of the city.
Outgoing Executive Director Laura Cantral admitted that this was not enough to stop the storm surges. But she argues that the wall would work better with these features.
“The Corps mandate is to fight storm surges, we get that,” she said. “We also believe that many of these nature-based solutions make the overall purpose of the wall … more effective.”
One of the problems is that the Corps calculates a cost-benefit ratio to determine which projects are worth paying for. That ignores the benefits of greener options, said Natalie Snider of the Environmental Defense Fund. Congress has asked the Corps to consider incorporating these elements into plans in 2018 and 2020, she said.
“We just saw the Corps being slow to develop and rely on these features,” Snider said.
The cost-benefit ratio of the Charleston project as it is now designed is over 10 to 1, making it one of the most attractive for the federal government to fund in the Southeast.