Redding (Calif.) Record Searchlight

REDDING, Calif. — Lake Oroville reached an important goal Monday: The reservoir measured 50 feet below capacity as of 6 a.m. PT.

Levels of the California lake, whose spillways were began to erode and alarm water officials after the reservoir began reaching capacity earlier this month, were at 849.4 feet, said Chris Orrock, a spokesman for the California Department of Water Resources. State water officials have said the 850-foot mark is important so crews can have more flexibility on releasing water during coming storms.

"It allows us to lower our outflows from the dam, so we can start working on the diversion pool," Orrock said.

The diversion pool at the base of the country's tallest dam now is filled with cement, trees, earth, and debris that tumbled down the emergency spillway as water rushed out of the lake as strong as 100,000 cubic feet per second. A pool of water has collected in that area, creating a levy that is blocking the flow of water, Orrock said.

► Related: Rivers in the sky causing widespread chaos in California

The incoming storms will raise lake levels about 5 feet, and at the height of the storms the inflow of water to the lake will be 100,000 cubic feet per second to 120,000 cubic feet per second. That is expected to taper off by Wednesday.

Outflows from the dam will remain at a constant 60,000 cubic feet per second.

In comparison, the Mississippi River at St. Louis, which has a larger riverbed and more capacity, is now flowing at about 187,000 cfs, according to the U.S. Geological Survey.

► Related: Battered Northern California blasted by new storm

But in the 2015 water year, the most recent information available, the average flow for the Feather River below Oroville Dam was 1,198 cfs, and the most it ever flowed that year was 2,230 cfs. The most that the river below Oroville Dam ever has flowed since the dam was completed in 1968 was 161,000 cfs on Jan. 2, 1997.

Next, crews will work to reopen a hydroelectric plant at the dam.

The National Weather Service in Sacramento forecasts 2 to 3 inches of rain over the next two days for Chico, Calif., about 25 miles northwest of Lake Oroville.

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Timeline of events

• Feb. 7. California Department of Water Resources officials identify a hole in the main spillway of Oroville Dam, the nation's tallest dam, and stop the release of water for a time down it.

• Feb. 9. Water officials say they know of “no imminent or expected threat to public safety or the integrity of Oroville Dam.”

• Feb. 10. Reservoir operators determine if releases from the nearly full reservoir can be maintained, the lake might not rise to the point where the emergency spillway would be used.

• Feb. 11. Water from Lake Oroville tops 901 feet above sea level, begins flowing for the first time in the dam's nearly 50-year history down the emergency spillway.

• Feb. 12. Water officials discover the emergency spillway's erosion problems and begin sending water over the damaged main spillway again. In late afternoon the Butte County sheriff declares mandatory evacuation of area below dam affecting nearly 200,000 residents.

• Feb. 14. Officials allow evacuees to go home but say the situation could change quickly as new storms dump more rain. President Trump OKs disaster relief for the area.

• Feb. 20. After continued releases of water from Lake Oroville in anticipation of the rain, water officials say they have reached their target lake level of 850 feet above sea level.

Related:

► Alabama: Alabama has the biggest dam problem in the U.S.

► California: Environmental groups warned of dangers at California dam more than a decade ago

► California: Beyond Oroville: Dam inspections in California are behind schedule

► Colorado: How safe are northern Colorado dams?

► Florida: Lake Okeechobee dike safer, but work remains

► Kentucky: Dozens of risky Kentucky dams in poor condition

► Michigan: No pending Oroville, but Michigan's aging, crumbling dams pose a risk

► Nevada: High hazard Nevada dams lack emergency plans

► New Jersey: A third of N.J.'s most critical dams need repairs

► New York: After Oroville, attention turns to New York dam safety

► Ohio: Officials: Dam 'hazard creep' a local problem

► Oregon: 7 Oregon dams in 'unsatisfactory' condition

► Pennsylvania: Big dam failures unlikely in Central PA

► Pennsylvania: What's the status of Indian Rock Dam?

► South Carolina: Risky dams face long inspection gaps

► Tennessee: Threats found in major dams in Tennessee