Corps of Engineers envision nature-based flood control
The US Army Corps of Engineers is known for damming rivers and building dikes to keep waterways at bay. But a new initiative is seeking natural flood control solutions as climate change results in increasingly frequent and severe weather events that test the limits of concrete and steel.
It makes sense to use Mother Nature’s flood defenses as one of the tools to combat destruction caused by heavy rains in the middle of the country and storms and sea level rise on the coasts, explains Todd Bridges, who leads the Corps Engineering with Nature initiative.
The pieces are in place to make the change. In the Water Resources Development Act of 2020, Congress ordered the Corps to consider nature-based systems on a par with more traditional infrastructure. And the initiative was first directly funded last year with $ 12.5 million.
But the Corps is often constrained by its own rules and how the costs and benefits of its projects are assessed.
“The Corps has a lot of people who are used to doing things a certain way,” said Jimmy Hague, senior water policy advisor at The Nature Conservancy. “We are currently following some projects where nature-based solutions are almost an afterthought.”
In Missouri, the Corps recently completed a dike along the Missouri River after the existing dike was overrun and ruptured by flooding in 2019. Rather than simply repairing the dike, the Corps built a new section of 8 kilometers further from the river, opening up about 1,000 acres (405 hectares) of floodplain to help reduce future flooding while providing habitat for rare and declining species.
Dave Crane, the Corps’ environmental manager on the project, said the achievement was not easy. The Corps is required to repair the dikes at the lowest cost, and only extreme damage to the original dike made it possible to build a new one under its rules.
The Corps also likes to work quickly to repair dikes before another flooding occurs, and moving the dike took time to plan and acquire land. The local Dike District needed to buy millions of dollars in farmland that would no longer be protected. With help from The Nature Conservancy and buy-in from the local community, the Corps built the setback, but that’s far from the norm.
Bridges hopes that new 1,000-page international guidelines for nature-based systems, in preparation for five years, will push the Corps to take nature-based solutions more seriously. The manual was developed in collaboration with the Netherlands and the United Kingdom, among others.
The stakes are rising. In the past five years alone, weather and climate disasters have cost the United States more than $ 630 billion in damage, said Richard Spinrad, head of the National Oceanic and Atmospheric Administration, when the guidelines were released on the 16th. September.
“How we assess the benefits (of nature-based solutions) is the key question,” said Bridges. Giving a monetary value to their flood protection is a first step. Bridges also wants the Corps to recognize social and environmental benefits that are not traditionally considered.
For example, he said, a mangrove forest can provide wildlife habitat, fun for people who dive, fish or boating, and cleaner air and water. And while concrete flood walls crumble and need to be replaced, mangroves can grow, providing more protection over time.
“Florida today has 500,000 acres of mangrove forest providing billions of dollars in flood risk reduction. How do we maintain or even increase this advantage in the future? Bridges asked.
The Corps has rules beyond benefit assessments that complicate its adoption of such solutions.
In Port Fourchon, Louisiana, authorities want to use the dredged material to restore nearby marshes. But the Corps wants to pump the booty into the Gulf of Mexico, said Chett Chiasson, the port’s executive director.
This is because the money for the project comes from the Corps navigation fund, forcing the agency to dispose of the loot as cheaply as possible. It doesn’t matter that there is a separate ecosystem restoration fund for projects like the swamp, Chiasson said.
“Their money is in a silo and they can’t raise (funds) in a way that makes sense,” he said.
In northern California, near the state capital, Sacramento, the Corps built the Yolo Bypass nearly a century ago to divert flood waters. Its 59,000 acres (24,000 hectares) have also become habitat for native and endangered species, including chinook salmon and rainbow trout.
Rick Johnson, executive director of the Sacramento Area Flood Control Agency, wants to make the necessary improvements to the bypass while improving fish habitat. But the Corps, which has a flood control easement on the property, has rules that require it to own the property before doing ecosystem restoration work.
“We are currently in a position where it is difficult to build new infrastructure, so we have to take what we can out of what is out there,” Johnson said. “And we have to look at it through a multipurpose lens.”
Relatively little has been done to quantify the benefits of nature-based flood control, but a 2016 study estimated that coastal wetlands saved northeastern states from more than $ 625 million in damage during the super storm Sandy. According to researchers at the University of California, Santa Cruz, The Nature Conservancy, and the Wildlife Conservation Society, census areas with wetlands caused an average of 10% less property damage than others.
Researchers at a Corps lab in Vicksburg, Mississippi are trying to better quantify the benefits of mangrove forests with a simulation. An intricate network of PVC pipes mimics mangrove roots inside a nearly 65,000 gallon (246,000 liter) tank where a wave machine delivers a storm surge.
The Louisiana Coastal Protection and Restoration Authority spent billions of dollars restoring coastal wetlands and barrier islands after Hurricane Katrina to bolster the state’s defense against storms. Hurricane Ida was the biggest test to date, and the assessment is ongoing.
Nature-based systems do not attempt to recreate a past landscape, but rather to restore the function provided by a feature of the landscape. And they can’t entirely replace more traditional infrastructure, Bridges pointed out, noting that a barrier island can work with a wetland and dike to provide layers of protection.
“We need to rethink what the infrastructure looks like,” he said. “Managing flood risk is serious business. People are dying.”
This story corrects Chett Chiasson’s spelling.