The interstate bridge that washed out in the desert between Los Angeles and Phoenix easily withstood its daily load of thousands of cars and trucks, but it failed when the pounding of a powerful flash flood scoured away land where the bridge was anchored, officials said Monday. The flood severed a highway vital to the movement of people and commerce between two of the nation’s largest cities. On an average day, Interstate 10 carries about 27,000 vehicles in either direction where the bridge failed.
Water rushing through a normally dry desert gully eroded the land around the bridge, causing one side of the eastbound span to collapse and forcing the closure of the westbound span.
While the bridge should have been fine if the flood came straight down the gully, this time it swept through at an angle that pushed the water to one bank, digging away the soil at the gully’s edge where the bridge reconnected with the road bed, California Department of Transportation spokeswoman Vanessa Wiseman said.
Nine inspectors fanned out Monday to check all 44 bridges along a 20-mile stretch of I-10 after a second bridge showed signs of damage following the storm Sunday, according to Caltrans. They also planned to inspect bridges across the large swath of Southern California where the remnants of a tropical storm off Baja California dumped unusual deluges this month.
Late Monday, Caltrans concluded that the westbound span about 50 miles west of the Arizona state line could have a limited reopening within weeks. Work crews plan to shore it up — footing that once rested on ground had the soil swept from under it — and eastbound traffic could then use one of its two lanes, agency spokesman Will Shuck said.
While he did not have an exact time-frame for the limited reopening, he said, “we’re certainly not talking about months.” Rebuilding the eastbound span would take longer.
When inspectors visited the bridge in March, they found no structural issues, according to Caltrans. The inspection report shows that the bridge had minor cracks. The only work recommended was to upgrade the railing, and that was done several years ago. The span’s rating was a 91.5 out of 100, according to data from the Federal Highway Administration. It was deemed “functionally obsolete,” a label Caltrans spokeswoman Wiseman said reflected not its strength or durability but the fact that its 1967 construction style requires motorists to slow as they approach.
Many motorists speeding through the desert might cross the bridge without knowing. It spanned a shallow desert gully, just 40 feet wide. Such washes, as they are known, streak the desert floor and flash to life as rains are funneled into them much like tributaries can swell a river.
The bridge washed out as rain was falling at a rate of 1.5 inches an hour. A total of 6.7 inches fell Sunday in Desert Center, said National Weather Service forecaster Ken Waters. Showers and thunderstorms in drought-stricken southern and central California set rainfall records in what is usually a dry month.
The rainfall was unlikely to offer much benefit for the drought-stricken state’s water supply, most of which originates far from the desert, in the Sierra Nevada and Rocky mountains.
One driver had to be rescued Sunday from a pickup that crashed in the collapse and was taken to a hospital with moderate injuries, the Riverside County Fire Department said.
Source: Huffingtonpost.com
