ute, rated to handle 250,000 cfs, broke open Feb. 7 with a relatively modest 55,000 cfs pouring down.
Some, including Tullis, point to a phenomenon known as “cavitation,” in which the blast of tiny water bubbles gushing down the chute at 50 mph effectively jack-hammered holes in weakened sections of concrete. Others, such as Robb Moss, a professor of geotechnical engineering at Cal Poly San Luis Obispo, speculate that roots from trees growing along the chute expanded weaknesses in the concrete.
Rogers, the dam failure expert from Missouri, said the spillway may have had cracks that weren’t properly patched. He also theorized the failure may have been tied to California’s five-year drought: The aging spillway could have weakened as it underwent contractions due to the sudden heavy soaking following years of dry weather.
Whatever the cause, the experts say, problems at Oroville should serve as a wake-up call on the state of America’s aging dams. At 48 years old, Oroville is actually slightly younger than the average American dam. According to the American Society of Civil Engineers, the average age of the 84,000 dams in the country is 52 years.
“The aging issues are without precedent,” Rogers said. “You’re going to see failure modes that you haven’t commonly seen before.”