SkyscraperPage Forum - Newly rebuilt Oroville Dam spillway is back. And it may get its first test this week

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Crunch time may finally be here for Oroville Dam, which is expected to send water over the repaired concrete spillway this week for the first time since the structure partially collapsed in 2017 and engulfed the region in crisis.

State water officials, who manage the 770-foot-high dam, said storms this week will probably force them to open the floodgates to control water levels in the reservoir, which is brimming after several winter storms and heavy snowfall in the mountains . . . .

The dam’s main spillway failed so spectacularly during heavy rains in February 2017 that managers turned to an emergency spillway, which poured water over a mostly barren hillside that quickly eroded, as the deluge cascaded down the hillside.

A team of independent engineers blamed the failure on weakened concrete, poor drainage and a history of shoddy maintenance, including a failure to adequately review for problems. It raised concerns about the rest of California’s aging water infrastructure.

The department spent $1.1 billion rebuilding the complex’s two faulty spillways, pouring enough concrete to fill 372 Olympic-size swimming pools, reinforcing the concrete with 12.4 million pounds of steel rebar.

The half-mile-long main spillway, where the initial fracture occurred, is now as wide as a 15-lane freeway and averages 7½ feet thick compared with 2½ feet in the original 1960s version. It is capable of handling up to 270,000 cubic feet of water per second, way more than dam operators ever expect to release and nearly twice the capacity of the old chute, which could handle only 160,000 cubic feet per second.

The new 3,000-foot-long spillway has steel pillars anchoring the structure 15 to 25 feet deep into bedrock and a modernized drainage system. The old spillway had only 5-foot-deep piles holding it in place.

The work on the 50-year old dam, a primary source of drinking and irrigation water in California, was the biggest and fastest construction project in recent state history . . . .

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