El Nino could mean trouble for California bridges

LOS ANGELES (KRON) – Construction crews worked Wednesday in the Southern California desert to fortify a bridge that a surge of floodwater damaged, their goal to reopen the main route connecting Los Angeles and Phoenix by Friday.

Resuming even a limited flow of traffic on Interstate 10 was expected to have taken weeks, but the California Department of Transportation announced Tuesday that the highway will handle traffic again far sooner than originally expected.

The flash flood eroded land around several bridges, with the hardest hit crossing Tex Wash, a normally dry gully that swelled with rainfall Sunday amid the kind of sudden, intense storm that can reshape the desert floor.

The fast-moving water severely eroded soil under the concrete that anchors one side of the interstate’s westbound span, making it unsafe.

The eastbound span fared worse, buckling into the gully. One driver was seriously injured when his truck partly fell off the roadbed toward the raging water below.

In light of the damage, some outside engineers said Caltrans may need to adopt tougher design and protection standards for highway bridges, particularly with heavy rains possible in the coming months due to the ocean-warming phenomenon known as El Nino.

While El Nino comes and goes periodically, the general warming of the Earth could have longer-term implications for bridges over desert washes. According to the 2014 U.S. National Climate Assessment, a trend toward “increased heavy precipitation events” will continue, even in the Southwest, where rainfall is expected to decrease overall.

I-10 typically sees 54,000 vehicles a day in the area of the washout, about 50 miles west of the California-Arizona line, according to Caltrans. That traffic has been taking a detour of several hours over smaller desert highways.

The faster timetable emerged even as inspectors found that two bridges near Tex Wash also suffered erosion. Those repairs were completed Tuesday, Caltrans said.

On Sunday, flooding touched off by unusually intense July rainfall of nearly 7 inches washed away boulders that Caltrans had placed along the gully’s bank to protect against erosion. Once that “armor” was gone, the water made quick work of the soil beneath the abutments where the bridge connected the road bed to solid land.

The bridge over Tex Wash was built in 1967 and easily passed a March safety inspection. The inspection report recorded no erosion concerns.

Caltrans had been aware that water could focus its full force on the eastern bank of Tex Wash, as it did, rather than the middle of the channel.

As part of statewide assessment of bridges that might be susceptible to serious erosion, inspectors noted in 2001 a “potential vulnerability” due to the angle of incoming water, according to Kevin Flora, a Caltrans bridge engineer.

At the time, there were no signs of past erosion, according to the report Flora reviewed. The protective sheathing of boulders seemed to be working.

As a result, inspectors did not add Tex Wash to 67 other bridges on the state’s “scour critical” list, which would have meant closer monitoring and possible reinforcement. Speaking by phone from the scene of the collapsed bridge, Flora described that as a “judgment call.”

Any decision on whether to change the protection or maintenance of bridges over desert gullies will come later, according to Caltrans spokeswoman Vanessa Wiseman.

Armin W. Stuedlein, an engineering professor at Oregon State University who studies how structures such as bridges interact with soil, said there may be “room for improvement” in bridge design and protection standards.

He noted that this stretch of I-10 has several dozen similar bridges.

“Any one of those gullies on any given storm event could be the bad actor,” Stuedlein said.