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Tale of 2 dams illustrates U.S. infrastructure problem

Michael R. Blood
Associated Press

Los Angeles — Twelve years ago, widespread destruction from Hurricane Katrina on the Gulf Coast helped compel federal engineers 2,000 miles away in California to remake a 1950s-era dam by constructing a massive steel-and-concrete gutter that would manage surging waters in times of torrential storms.

The nearly $1 billion auxiliary spillway at Folsom Dam, scheduled to be completed later this year, stands in contrast to the troubles 75 miles away at the state-run Oroville Dam, where thousands of people fled last week after an eroded spillway threatened to collapse — a catastrophe that could have sent a 30-foot wall of floodwater gushing into three counties.

Together, the two dams illustrate widely diverging conditions at the more than 1,000 dams across California, most of them decades old. The structures also underscore the challenge of maintaining older dams with outdated designs.

“Fifty years ago, when we were evaluating flood risk, the fundamental assessment was the climate was stable, not changing. We now know that is no longer true,” said Peter Gleick, chief scientist with the Pacific Institute, a California-based think tank specializing in water issues. “We need to look at the existing infrastructure with new eyes,” he warned.

State officials face questions about maintenance at Oroville Dam, the nation’s tallest at 770 feet, and why a decade ago they dismissed warnings from environmentalists that more needed to be done to strengthen its earthen emergency spillway.

When water gushed onto the spillway, the ground began eroding, and it was feared the intake lip could collapse and water would surge down the hill.

An investigation into what went wrong could take months.

John France, vice president and technical expert on dams for the engineering consulting firm AECOM, said the problems at Oroville should raise alarms.

“Most of the dams in the United States are over 50 years old, when we didn’t understand floods as well as we do now. So we have a number of dams in the U.S. that have spillways that aren’t large enough for the floods that they should be designed for,” France said.

At 340-foot high Folsom Dam, the huge concrete-and-steel chute being constructed by the Army Corps of Engineers is expected to add as much as 40 percent capacity to the main spillway. It’s designed to allow safer releases during times of high water, precisely the challenge that led to fears of catastrophic flooding at Oroville.

Rick Poeppelman, chief of the Army Corps engineering division in the Sacramento district, said extensive data about probable maximum flood levels, not available decades ago, helped prompt the decision to build the auxiliary spillway at Folsom Dam.

When completed, the spillway can act like a second dam, allowing operators to release water through a series of gates and lower the reservoir level when a major storm is approaching.