Brett Kelman

The Desert Sun

Six months ago, an unremarkable bridge on a desolate stretch of desert highway collapsed, severing one of the most important roads in the nation. A flash flood toppled the eastbound portion of the Tex Wash Bridge, which carried Interstate 10 across a dry riverbed near Desert Center. A motorist was nearly killed. The main route between California and Arizona was closed for five days, diverting travelers and truckers, costing millions in detours and repairs.

The collapse occurred on July 19, after nearly 7 inches of rain fell on the Chuckwalla Mountains south of the interstate, then flooded into the wash below. The storm was extremely rare and powerful, but its destructive force was magnified by critical flaws in the design of the bridge, according to an engineering expert's new study of the bridge failure.

The Tex Wash Bridge was built in 1967, as the I-10 slowly grew across the country, crossing the dry, dusty desert between the Coachella Valley and the Arizona-California state line. Dozens of short bridges were built in that stretch, but the Tex Wash was wide and delta-like, so it demanded a longer, stronger bridge. Instead, construction crews narrowed the wash, then built a short bridge with a shallow foundation. They also re-shaped the wash into a curve, which directed the full force of floods against the eastern base of the bridge.

Eventually, when the heavy rains finally came almost 50 years later, the pressure was too much. A flash flood pummeled the bridge's foundation until the concrete cracked and the asphalt tumbled into the rushing water.

"This was not good engineering,” said Abolhassan Astaneh-Asl, a UC Berkeley engineering professor, who visited the Tex Wash Bridge site in December. “In good engineering, you work with nature, you don’t fight against it.”

“Because the flood will always win.”

Astaneh is an internationally recognized expert on failed structures, who has studied some of the deadliest structural collapses in modern history. He speaks out frequently about his public safety concerns in a field where criticism is rarely aired publicly.

In 2001, Astaneh was hired by the National Science Foundation to study the collapse of the World Trade Center. In 2007, the professor made headlines when he attributed the collapse of the I-35 Bridge in Minneapolis, which killed 13 people, to undersized steel plating. A federal investigation later confirmed his findings.

More recently, Astaneh has turned his attention to the Tex Wash Bridge, which he studied with the help of Maryam Tabbakhha, another structural engineer at Berkeley. Together, they are preparing a research paper on the cause of the collapse, spotlighting four "fatal flaws" in the bridge design. The paper is expected to be made public later this month. Astaneh gave The Desert Sun exclusive access to his preliminary findings.

They include:

Narrowing the wash: First, the Tex Wash Bridge was built over a wide flood plain, shaped like a river delta rather than a stream. Construction crews could have spanned the entire flood plain, which had been done with another bridge in the past, but instead narrowed the wash by filling it with dirt, then built a shorter bridge. This design made construction cheaper, but it also forced storm runoff into a channel, creating a bottleneck that increased pressure on the bridge in the same way that a spray nozzle boosts the power of a garden hose.

Redirecting the water flow: Narrowing the wash created another problem too. The path of water, which once flowed straight through the delta wash, was now forced into a curve that put additional stress on the eastern side of the bridge. Rushing water now carved into the dirt berm around the base of the bridge, eventually digging up its foundation.

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No piles beneath foundation: The foundations on both sides of the bridge were built with no underground piles anchoring them into the soil. Instead, the foundation was just sitting in the dirt that had been used to narrow the wash, susceptible to rushing waters that whipped through the curved wash.

No walls to prevent erosion: Finally, the foundation of the bridge could have been further protected by a retaining wall that funneled water inward to prevent erosion on the curved wash. Instead, the wash was lined with protective boulders – called "loose riprap" – which were simply swept away by the flood.

Collapsed I-10 bridge given an A rating just last year

Despite Astaneh's criticism of the bridge, which allege a serious public safety risk, no response has come from the officials who are actually responsible for the Tex Wash Bridge. When reached for comment by The Desert Sun, the California Department of Transportation refused to discuss the collapse of the bridge.

CalTrans spent $8 million to build a replacement bridge, which restored the interstate to normal when it opened on Sept. 24. Astaneh claims the new bridge suffers from many of the same flaws as its predecessor, and is only slightly less susceptible to flash flood. Reconstruction did not change the configuration of the narrow channel and the curved wash, so runoff will still bottleneck at the bridge. Underground piles were added to the foundations of the new bridge, but there is still no retaining wall protecting the earth from erosion. Instead, CalTrans contractors buried the edge of the wash under even more boulders, which could wash away again, Astaneh said.

Astaneh claims the replacement bridge has also introduced a new problem – it will float. The bridge is built from long, hollow concrete boxes, and similar bridges have floated off their foundations during the extreme flooding after Hurricane Katrina, Astaneh said.

“They built a boat,” he said while inspecting the new bridge. “If the 500-year flood comes, the analysis shows that it will very likely lift this and carry it away."

A flood that could lift the new Tex Wash Bridge would need to be larger than the flood that struck in July, but it is not impossible.

Meteorologists said a storm of this size is extremely rare – predicted to fall in this spot less than once every 1,000 years. However, the Tex Wash carries runoff from the Chuckwalla Mountains to the south, so any major storm on the northern half of the mountain range would send water flowing towards the bridge. A similar storm in a different spot still could flood the washes near Desert Center.

“Sure, it could happen again,” said Valerie Meyers, a meteorologist in Phoenix. “Just because we are saying this is a 1000-year storm, doesn’t mean it’s only going to happen once in one thousand years. We are just describing the rarity of the event. It could happen next week. It could happen 5 miles down the road. It could happen tomorrow.”

Terri Kasinga, a CalTrans spokeswoman, said the agency would not respond to Astaneh's findings because his research had not yet been published. Kasinga added that CalTrans was unwilling to discuss or explain the failure of the bridge because a claim for damages was likely to be filed over the collapse.

That claim is expected from Bryan Castor and Scott Meyn, a driver and passenger who were injured when their vehicle was smashed by the tumbling bridge. Meyn escaped with a fractured sternum, but Castor was pinned in the crushed vehicle, surrounded by rushing water, with busted knee caps and broken ribs. He likely would have died, if not for an award-winning rescue by local police and firefighters.

Castor and Meyn each plan to file claims against CalTrans by the end of the month, said their attorney, Dane Wood. However, Wood said that is no excuse for CalTrans to remain silent on the collapse.

"Considering the public interest and the public safety involved, one would think CalTrans would be more willing to share at least some basic information about their findings," Wood said. "If and when there is a lawsuit, they will have to provide that information to us anyway. So why wait until then?"

Although CalTrans won't talk about the bridge, public records show the agency's engineers have come to at least some of the same conclusions as Astaneh.

One day after the collapse, CalTrans engineer Terence Cheung determined that the narrowing of the channel and the bend in the wash were responsible for the flood damage.

"Although the channel bed appears to have stabilized, further degradation may be cause for re-evaluation, so the channel needs to be monitored," Cheung wrote in a July 20 inspection report.

CalTrans inspectors had previously given the Tex Wash Bridge far more positive reviews. In 2015, the bridge received a grade-A "sufficiency rating" – 91.5 out of 100 – and one of the highest possible flood safety ratings. Forty-five other Riverside County I-10 bridges had received lower ratings, and seven of those were deemed "functionally obsolete," meaning they were too small or poorly suited for modern-day traffic.

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The Desert Sun also spoke to three additional California engineers who said the narrowed channel and the curved wash likely contributed to the Tex Wash Bridge collapse, but they were unwilling to be interviewed in detail because they had not studied the bridge personally. However, one of those engineers said the July flood was so large that, even if the Tex Wash had been left wide and straight, the bridge may have been destroyed anyway.

To counter that point, Astaneh points to a neighboring bridge – the Ragsdale Bridge – which spans the same wash as the collapsed bridge but tells a very different story.

The Ragsdale Bridge carries an access road across the Tex Wash about 200 feet north of the collapse site. The wood bridge was built in 1931, so it is both older and – in theory – weaker than its concrete cousin. Yet, when the heavy rains came in July, the Ragsdale Bridge survived the flood.

The difference lies in the design, Astaneh said. Unlike the collapsed bridge, the Ragsdale Bridge’s foundation is anchored by underground piles and protected by diagonal walls, which funnel flood waters inward to prevent erosion. The bridge was built before the wash was narrowed, so that it is nearly three times longer than the Tex Wash Bridge. Flash floods can pass beneath without being compressed into a channel.

In short: Everything that Astaneh says the builders of the Tex Wash Bridge did wrong, the builders of the Ragsdale Bridge did right.

“This is the bridge they should have built,” Astaneh said, smiling, as he marveled at the sturdiness of the wooden structure. “All you have to do is change the timber to concrete or steel and you are done.”

Desert Sun Reporter Brett Kelman can be reached by phone at (760) 778-4642, by email at brett.kelman@desertsun.com, or on Twitter @TDSbrettkelman.