California floods show the limits of man-made solutions

By Adam Minter

NOBODY should have been surprised when California’s Pajaro River burst through a levee this spring, flooding homes and dislocating thousands of people. Warnings that the levee system was inadequate date back decades. California’s recent drought, the worst in 1,200 years, dried out and weakened levees, heightening those concerns. But plans to act on them were still years from being executed when atmospheric rivers packed with rain surged water into the earthen works and cement channels designed to protect lives and property.

It was a human-made disaster, intensified by climate change. And California won’t be the only state to suffer. Across the country, hard infrastructure — from levees to jetties — is proving inadequate to the challenges posed by increasingly extreme weather. Instead, what often works best to control the onslaught is what engineers and architects long sought to replace: natural features and processes such as flood plains and wetlands. Nature-based infrastructure, as the concept is known, remains a relative niche compared with concrete, steel and earthen works. It needs to be a priority.

ENGINEERING TO THE RESCUE
For two centuries, the Army Corps of Engineers has played the lead role in building US infrastructure, from roads and bridges to canals and levees. For example, the once-wild and unruly Mississippi was turned into an orderly, navigable highway through locks and dams designed, built and operated by the Corps. Today, the river supports hundreds of billions of dollars in economic activity.

But the Corps’ works have also come with unintended side effects. Levees don’t just prevent flooding, they cause it. When water is squeezed into a levee, its flow rate and height rises. When a breach happens, or the water tops the levee, disaster ensues. But even if the levee is sound, a surge can cause a pileup of water outside the structure. Researchers estimate that significant flood risk has increased 20% on the Mississippi River over the last 500 years, with 75% of that risk attributed to engineering.

Climate change has just made everything worse. Extended droughts, such as the one that California just exited, weaken levees by drying out soil, causing cracks and accelerating land subsidence. Surging floodwaters then erode away what remains, setting the stage for disaster. That, and poor maintenance, likely combined to cause California’s disastrous Pajaro River breach.

NATURAL ADVANTAGES
In the 1960s, ecologists and landscape architects began to consider whether natural processes and features should play more of a role in infrastructure. Before levees, for example, water spilled into flood plains. Those floods could be a nuisance, especially if someone made the mistake of building on them. But they had the benefit of recharging groundwater and fortifying nutrient-rich soils. In that sense, they were multi-use infrastructure, even if some of those uses weren’t appreciated when they were cordoned off by levees and dams.

The Army Corps of Engineers in the 1970s began to view natural structures as potential components of traditional engineering projects. The military is a keen customer.

At Fort Hood, Texas, the largest active-duty armored post in the US, cycles of intense drought and flooding have repeatedly — and increasingly — stressed the base’s ability to manage stormwater, flooding and any associated contamination. So, as part of a plan to manage the surges, engineers and architects have installed vegetation that slows the intensity of water flows and increases groundwater retention, as well as wetlands that help to filter oil-contaminated water.

Far more ambitious nature-based projects are happening in the civilian sector. In March 2019, record-setting floods breached a levee in northwest Missouri, inundating 56,000 acres, destroying 121 miles of roads and flooding 156 homes. Rather than rebuild the levee as it was, the Corps, partnering with local government, moved portions of the levee away from the river channel so that the water can move more naturally through 1,000 acres of restored flood plain and 400 acres of restored wetland.

The roughly $100 million levee setback, completed during the summer of 2021, isn’t without its critics. Restoring flood plains typically entails acquiring private property and making it off-limits to future development (with a parallel hit to the local property tax base). But the improvements should not only reduce the risk of future catastrophic flooding, they’re already contributing valuable wildlife habitat and climate mitigation value.

Ultimately, that’s why other regions are looking at similar solutions, including the agencies in charge of California’s failed Pajaro River levee. Thanks to this year’s breach, a nature-based update is now on the fast track.

RAISING AWARENESS
Ensuring that other communities have the chance to fast-track their own nature-based solutions, especially as weather becomes more extreme, should be a national priority. Some progress has been made. The Inflation Reduction Act appropriated more than $8.7 billion to build nature-based solutions into transportation systems. But that’s a pittance compared with other infrastructure funding in the law. Meanwhile, policies at both the local and federal level continue to favor conventional infrastructure, while experts and crews trained and familiar with nature-based engineering remain scarce.

Ensuring that nature-based solutions receive a fair hearing requires reversing both those trends. For starters, the Corps and other federal agencies should develop certification standards and best practices for nature-based engineering and then require them in federal contracts. To raise awareness of nature-based engineering, the government should sponsor further research into their effectiveness, especially in large-scale projects. Meanwhile, federal permitting for infrastructure projects should be adjusted to give priority consideration to nature-based solutions.

There is no way to engineer the US out of the climate crisis. But a long-term commitment to leveraging nature’s ability to mitigate disaster will ensure a more resilient, less disaster-prone future. — Bloomberg Opinion