Fewer Than 10% of Levees in the Greater Bay Area Have a Federal Flood Risk Rating

Atmospheric river-fueled storms have hammered the network of hundreds of levees in coastal counties near the San Francisco Bay — from the agricultural fields of Monterey County to urban places like San Leandro, Walnut Creek and Richmond to more rural parts of the North Bay. At least two major levees, in Salinas and Pajaro, have failed since New Year’s Eve.

The levee breach along the Pajaro River, which divides Santa Cruz and Monterey counties, left the entire town of Pajaro in a deluge of water. More than 3,000 residents could be displaced for several weeks. The disastrous flood submerged a significant acreage of agricultural land there, and the mostly lower-income Latino community now faces overwhelming economic and housing uncertainty.

The river valley has flooded twice before, in the 1990s. State and federal officials knew the levee could fail but didn’t fix it, although a plan was in the works to update the system beginning in 2025.

But the dozen atmospheric river storms this winter wouldn’t wait for that construction to begin.

“It’s a horrible tragedy, and now it’s happened again,” said Nancy Faulstich, executive director of Regeneración, Pájaro Valley Climate Action. “It feels like it’s exactly a case of environmental injustice that it was known that the levee would fail.”

Thirty minutes before water raced down his street, Andy Garcia and his 8-year-old daughter fled.

“We just grabbed a few blankets, clothes and some documents and left,” he said. “We had so many years without rain. They had the money but didn’t ever do anything to prevent this from happening.”

Garcia fears what he will find on his drowned street when the floodwaters recede.

“We probably lost everything,” he said. “I’m just hoping my house didn’t get flooded.”

Large gaps in the federal levee database

Levees are designed with a certain level of flood risk, and the U.S. Army Corps of Engineers rates how safe each levee is as part of the National Levee Database. But federal risk records are available for less than 10% of the coastal region surrounding the Bay Area. The agency was not available for an interview but did comment via email.

The database identifies 539 levee systems across 11 counties — Alameda, Contra Costa, Marin, Monterey, Napa, San Francisco, San Mateo, Santa Clara, Santa Cruz, Solano and Sonoma. Forty-one have a low-risk rating, 12 have a moderate-risk rating and 484 have no rating — either because that information doesn’t exist about the levee or the jurisdiction that maintains it hasn’t reported it to the federal government.

The state of federal levee records “is an extensive problem that we have been aware of and there won’t be overnight magic to solve this,” said Farshid Vahedifard, professor of civil engineering at Mississippi State University.

Levees outside the coastal range in California’s Central Valley — which play an integral part in the state and federal transport of water — also are at risk of breaching. This is where many miles of levees are on private land and are not subject to the same routine inspection and maintenance that state or federal levees undergo. During a recent storm on a farm in the Central Valley, workers filled a failed levee with two trucks piled with dirt.

The California Department of Water Resources proactively tracks levee incidents within the Central Valley as part of its state flood control plan but doesn’t for those outside it. Still, the state has sent assistance to both Salinas and Pajaro.

“We need to have coordinated work to improve our fundamental understanding gaps, to develop practice-ready tools to be able to better capture this evolving risk,” said Vahedifard.

The ratings from the Army Corps consider how much damage and loss of life could happen if a levee fails, along with its integrity.

The region’s 53 low- and moderate-risk levees in places like Alameda, Pajaro, Petaluma, Richmond and Walnut Creek help protect $63 billion of property, more than 450,000 people and more than 119,000 buildings

Vahedifard said all levees have the possibility of failing at some point, and climate change increases their fragility. “A low-risk levee does not mean it’s safe forever,” he said. “It’s no secret that California has a marginal levee system.”

He studies how repetitive droughts and floods — like the current multiyear dry spell with back-to-back atmospheric river storms within it — weaken and threaten the life of the state’s levees.

Because of climate change, atmospheric river-fueled winter storms could become around 30% wetter by mid-century, according to a study published in the journal Nature Climate Change.

On top of the severity of storms, Vahedifard said many of the levees are old. People constructed these aged levees with logs, dirt and anything else they could find during the 1900s for a climate that no longer exists.

Vahedifard said California has way more levees than the federal government has documented in its levee database.

“There are potentially 50% more levees in California that have not been documented,” he said, mostly of levees on private land with little or no maintenance records.

A lot to ask of a passive patch of dirt

While the levee breaks this year have been mostly on tributaries of rivers and creeks in rural areas, many of the levees at low or moderate risk in the region are in major urban areas like Alameda — during the atmospheric river storms in early January, a floodwall near a levee crumbled in a San Leandro neighborhood.

California’s population has ballooned over the past decades to nearly 40 million people, much more than when most levees were built. These piles of dirt of yesteryear are now tasked with several missions: to protect public safety, life, homes, businesses and highways while simultaneously being recreation paths, said Jay Lund, professor of civil and environmental engineering at UC Davis.

“It’s a lot to ask of a little passive patch of dirt stuck up on a steep slope,” he said.

Flood agencies must comply with state requirements that levees protect urban areas with a 200-year level of flood protection in any given year. That translates to a 0.5% probability of flooding annually. But as climate-fueled storms intensify, Lund said, cities should prepare for deeper floodwaters, even as much as a 500-year flood event with a 0.2% probability. But other levees in rural areas have different standards.

The thing is, most people don’t understand what these probabilities mean, Lund said. But he has an idea to help residents understand flood risk in neighborhoods near levees.

“Maybe on all the street lamp posts, there should be a painted blue stripe at the level of the 100-year flood [and so on],” he said.

While California has always experienced floods — it is a boom-and-bust state with cycles of droughts and floods — human-caused climate change has made these events more intense and severe.

Unfortunately, it often takes a tragedy to spur people into preparing for natural disasters like flooding from atmospheric rivers, Lund said.

The Pajaro River levee breach could be the moment the state needs to get serious about updating outdated levees.

“We have floods and droughts frequently relative to other parts of the world and we pay more attention to water,” he said. “Does that mean we’re perfect? By no means. But it means we can’t be complacent for very long.”

KQED’s Anna Marie Yanny contributed reporting to this story.