Age, drought, rodents and neglect weaken California levees, increasing flood risk

The levee breach that left an entire California town under water this weekend highlights how the state’s vital flood control infrastructure is weakened by age, drought, change climate, rodents and neglect, leaving dozens of communities at risk.

On Friday night, the swollen Pajaro River burst through the worn levee, flooding the entire town of Pajaro and sending its roughly 3,000 residents into what authorities now believe will be a months-long exile. A second breach was reported on Monday.

For decades, the levee was ignored by the federal government — never achieving project-worthy-fix status — despite repeated appeals, violations, flooding and even two deaths.

“Yeah, the money wasn’t there because the prioritization wasn’t there,” said Mark Strudley, executive director of the Pajaro Regional Flood Management Agency.

And as communities and local government agencies pleaded for help and funding, the levee aged, eroded and, in some places, sank.

The situation is by no means unique to Pajaro. Experts say similar weaknesses affect levee systems across California and the country.

As climate change threatens to intensify and exacerbate extreme weather events – such as flooding and even drought – the unease and desperation of residents and emergency responders in communities near these crumbling systems increase.

“We all know there are a lot of economically disadvantaged communities that are built in areas that are prone to natural disasters,” Strudley said. “It’s just the very unfortunate way the planning and development process has worked for the past 100+ years in the United States.”

Throughout Northern California, the Central Valley, and the Sacramento-San Joaquin River Delta, there are more than 13,000 miles of levees designed to protect drylands from flooding, provide drinking water, and protect communities. homes, businesses and agriculture from flooding.

According to the work of Farshid Vahedifard, professor of civil engineering at Mississippi State University, a high percentage was built by settlers in the mid to late 19th century to protect farmland from flooding.

“And they got worn out, like anything else,” Strudley said. “They have a limited lifespan.”

In most cases, Strudley and Vahedifard said, the levees were built with poorly compacted, unengineered mixtures of sandy, clay and organic soils, materials “that were scraped from the river bed and used as backfill for build the levees,” Strudley said.

Additionally, they have endured the wear and tear of time, rodents, seismic events, and drought.

“These things leak long before they’re overrun,” Strudley said, noting that one of the biggest problems is digging animals.

In 2011, the California Department of Water Resources reviewed Northern California’s levee system. The assessment considered around 1,800 miles of earthworks in the Sacramento and San Joaquin river basins and found that more than half of the levees were what they considered ‘high risk’ – indicating that they were in danger of breaking down in an earthquake or flood.

And that was before the mega-drought, which dried out the soils inside the levees and below, causing structures to weaken and lose strength, Vahedifard said.

Drought also accelerated subsidence as districts and water users siphoned water from underground aquifers, depressing and sinking the land above.

But until recently, the federal government and the US Army Corps of Engineers did not consider these systems a priority, especially if they were in marginalized or economically disadvantaged communities.

“The federal funding system for levees and other life protection systems completely disadvantages disadvantaged communities at the federal level, systemically,” said Zach Friend, a Santa Cruz County Supervisor whose district includes Watsonville and the north side of the Pajaro river valley.

He said what happened to the Pajaro seawall could have been avoided if resources had been provided to the community to rebuild the seawall – something they had been asking for since the 1960s.

“The storms that blew the levee…are a five to seven year interval storm,” he said. “So if our infrastructure can’t even hold back what is really a relatively regular storm, climate change – what we’re seeing in the future and what it’s going to do for disadvantaged communities – is something unbearable. .”

He said the cumulative effect of these storms and the “weather whiplash” between severe drought and severe storms “really tests the possibility of how you even build and plan for that level of resilience to communities that have been underinvested in the last 100 years and which begin with a net negative reconstruction.

The levee failure on the Pajaro River indicates greater risks that California has yet to address in many areas where communities are vulnerable, said independent water advocate and researcher Deirdre Des Jardins.

“Pajaro is just the beginning,” Des Jardins said.

For years, Des Jardins has urged state and local authorities to invest in flood protection infrastructure in at-risk areas, and she suggested that an effective climate adaptation strategy should focus on “measurable goals and achievable for the protection of vulnerable populations”.

“You look at where to invest money to protect lives. And we don’t. We don’t have quantifiable goals around protecting lives and protecting these vulnerable communities,” De Jardins said.

In addition to rural communities like Pajaro, she said Stockton and nearby towns face major flood risks due to their reliance on inadequate levees with known seepage issues.

As the federal government continues to reassess how it invests in major infrastructure projects in economically disadvantaged communities, the cost of inaction will continue to rise.

“What is the risk of flooding in California? A lot. The reason is quite simple,” said Jeffrey Mount, senior fellow at the Public Policy Institute of California. “The economic consequences of even a modest flood are quite significant.”

He said that’s especially the case in the Los Angeles Basin, where the increasing likelihood of major flooding overlaps with the rising value of surrounding properties.

“There is a long legacy of very poor flood management and land use choices along the LA, San Gabriel and Santa Ana rivers,” Mount said. “It’s a high-risk equation because eventually a flood will happen and the economic costs will be immense.”

Local, state and federal officials have improved flood control infrastructure in the Sacramento area over the past two decades, which has reduced risk in the area, Mount said.

Yet many low-lying communities in the Central Valley face significant flood risk. And many farms in and around the delta are below sea level, requiring levees to keep water out, Mount said.

“Our flood infrastructure is old,” Mount said, “and is designed for the hydrology of the past, not the future.

“This is going to be a major challenge going forward, particularly because we have increased the potential economic costs of flooding by our land use choices.”

In January, when levees broke along the Cosumnes and Mokelumne rivers and caused deadly flooding, Mount said those breaks indicated greater risk. “There are two types of levees: those that have failed and those that will fail,” he said.

Mount said he is now particularly concerned about the immense amount of snowmelt runoff expected from the central and southern Sierras this spring.

Times writer Hayley Smith contributed to this report.

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