Strong El Niño could cripple more I-10 bridges

If a potentially historic El Niño brings powerful floods to Southern California this winter, Sunday’s rain-induced bridge collapse could be a preview of highway hazards to come.

Across California, state officials list about 450 bridges as potentially unstable during intense floods. Five of those bridges are in the Coachella Valley, including two in Indio and two on the Interstate 10 in Whitewater. The latter are among the most highly trafficked of the at-risk bridges, seeing 80,000 drivers per day.

Officials call those bridges scour critical, meaning there’s elevated risk of a flood eating away at the dirt that holds their foundations in place. That’s what happened Sunday, when five inches of rain caused the Tex Wash bridge on the I-10 to collapse, severing the main artery between Los Angeles and Phoenix.

That storm was the latest sign a strong El Niño weather pattern is brewing in the Pacific Ocean. If the pattern holds, the Coachella Valley could see intense storms and floods, potentially crippling more bridges.

“It could lead to more active river systems, which could affect your bridges,” said Jeff Johnson, co-founder of Watershed Science & Engineering, a Washington-based firm that has analyzed bridge scour.

On Indio Boulevard, the eastbound and westbound bridges over the Whitewater River, just west of Clinton Street, are at risk. So are the eastbound and westbound I-10 bridges over the Whitewater River, as well as a smaller bridge just off the freeway.

Experts caution that just because a bridge is scour critical doesn’t mean it will collapse during a major flood. And even if a bridge has a good scour rating — like the Tex Wash bridge did — it doesn’t mean there’s no risk.

Transportation officials are required to monitor scour critical bridges closely, or to take preventative measures to lower the risk of a collapse. Those measures vary from bridge to bridge, experts and state officials say.

“There are so many different factors — every bridge is a different animal unto itself,” California Department of Transportation spokeswoman Vanessa Wiseman said. “If something is rated as scour critical, we have a plan of action about what we’re going to do about it.”

In Indio, city officials have received federal funding for a $3.2 million project to reduce flood risks on the at-risk bridges. But that funding is contingent on unfinished environmental reviews, so it’s unclear when work will begin.

“They are safe and passable, and if we feel in any way shape or form that they’re imminently unsafe, we’ll close them. We don’t take any chances with these things,” said Timothy Wassil, Indio’s public works director. “It’s just like all things — anything can happen. But in our analysis, they’re safe, and we’re trying to make them safer.”

Riverside County plans to replace or repair its scour critical bridge just off the I-10 in Whitewater, according to Juan Perez, director of the county’s transportation and land management agency. Caltrans didn’t immediately provide its plans for dealing with the heavily trafficked scour critical I-10 bridges.

Cash-strapped local governments often have trouble prioritizing slow-burning problems like scour risk at bridges, said Martin Teal, a water resources engineer at WEST Consultants in San Diego. Even if they do a good job of monitoring those bridges, he said, flash floods like the one that hit the Tex Wash bridge can be difficult to predict.

“Those things come and go so fast. By the time you know the water’s coming up, it’s probably there and gone,” he said.

If El Niño hits California as hard as some meteorologists say it could, flash floods could be a major problem.

In 1997-98, a major El Niño brought heavy rain and massive flooding, causing about $300 million in damage to the state highway system, according to the Federal Highway Administration. Much of the damage was in Northern California, and experts still aren’t sure how this year’s predicted El Niño will impact Southern California.

Sammy Roth writes about energy and water for The Desert Sun. He can be reached at sammy.roth@desertsun.com, (760) 778-4622 and @Sammy_Roth.