In another sign that the drought is ending across much of California, state water officials planned to open the floodgates at Oroville Dam on Friday to let water out of the state’s second-largest reservoir to reduce the risk of flooding to downstream communities.

“After three years of drought and low lake elevations, it’s really good to see the lake rising,” said Ted Craddock, deputy director of the state Department of Water Resources.

On Friday, Oroville reservoir was 75% full — or 115% of its historical average for early March. It has risen 180 feet since Dec. 1, and continued to expand steadily with millions of gallons of water pouring in from recent storms.

Devastating storms in February 2017 caused the spillway at Oroville, whose 770-foot tall dam is the tallest in the United States, to crumble, which prompted emergency officials who feared a potential dam collapse to evacuate 188,000 people downstream.

Investigators later found that the spillway, built in 1967, had corroded rebar and a failed drainage system. Construction crews overseen by a national team of independent dam safety engineers rebuilt the spillway in a $1 billion project by 2018. Friday’s event will mark the second time the new spillway has been used since then. It was used once before, in April 2019.

The new spillway is a colossal chute more than 3,000 feet long and as wide as 15 lanes of freeway. Its concrete is 7 feet thick, and contains 13 million pounds of reinforcing steel.

Craddock said Friday that dam safety engineers were on site for the scheduled noon opening of the gates atop the spillway, and have been performing regular inspections. The new spillway also has instruments to measure pressure, drainage and other factors. Craddock said it performed well in the 2019 release and he expected it to perform well again.

“It’s a very robust structure,” he said.

Lake Oroville, built on the Feather River about 70 miles north of Sacramento by former Gov. Pat Brown in the 1960s, is the linchpin of the State Water Project, a system of dams, canals and pumps that provide water to 27 million Californians from the Bay Area to Los Angeles. The purpose of the dam is not only to store water, but also to provide flood protection to communities in the Sacramento Valley.

In wet years, dam operators draw down the reservoir in winter when its level gets too high. The purpose is to create enough space in …read more

Source:: The Mercury News


Oroville Dam floodgates opening as storms fill massive reservoir

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