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http://www.water.ca.gov/oroville-spillway/pdf/2017/Lake%20Oroville%20events%20timeline.pdf

February 7: As water releases from the flood control spillway ramp up to 54,500 cubic feet per second (cfs), in anticipation of inflows expected from rainfall, DWR employees notice an unusual flow pattern. Spillway flows stop for investigation. Engineers find large area of concrete erosion.

[Repeal The 17th]

Copy/past from your link:
➊ February 7:
As water releases from the flood control spillway ramp up to 54,500 cubic feet per second (cfs), in anticipation of inflows expected from rainfall, DWR employees notice an unusual flow pattern. Spillway flows stop for investigation. Engineers find large area of concrete erosion.
➋ February 8:
DWR begins ongoing consultation with FERC and other dam safety agencies. DWR runs test flows down the damaged spillway, monitoring further erosion, and prepares for possible use of emergency spillway. 24/7 emergency interagency operations centers activate to study and implement response to flood control spillway and related structures, with careful study of weather forecasts.
➌ February 11:
Inflow to Lake Oroville brings lake level above 901 feet. This engages the emergency spillway for the first time in the history of the facility.
➍ February 12:
Anticipated erosion begins to progress faster than expected at the base of the emergency spillway. The Butte County Sheriff’s Office issues mandatory evacuation orders for the Oroville area. To ease pressure on the emergency spillway, the flood control spillway outflow is increased to 100,000 cfs. After several hours, inflows decrease and overflow stops at the emergency spillway. Erosion to the emergency spillway hillside is assessed.
➎ February 13:
DWR crews begin working around the clock to repair the emergency spillway. Evacuation orders remain in effect.
➏ February 14:
As the lake level continues to drop, the mandatory evacuation order is modified to an evacuation warning. Crews continue working around the clock to repair the emergency spillway. An elevation of 850’ is targeted for lake level.
➐ February 16:
Flood control spillway flows are reduced below 100,000 cfs to facilitate the clearing of debris from below the spillway. Lake levels continue to drop. Construction to armor the emergency spillway continues.
➑ February 18:
Lake level down to 854 feet. Flood control spillway flows are reduced to 55,000 cfs. Barge construction begins in order to remove debris from the diversion pool beneath the spillway.
➒ February 20:
Lake Oroville elevation reaches 848.95 feet at 11 a.m. Repairs and preparations continue around the clock.

[Jim W N]

February 7: As water releases from the flood control spillway ramp up to 54,500 cubic feet per second (cfs), in anticipation of inflows expected from rainfall, DWR employees notice an unusual flow pattern. Spillway flows stop for investigation. Engineers find large area of concrete erosion.

Nice graphic. A few of more questions:

1) Do you know when prior to Feb 2017 the spillway outflows were significantly greater than 50,000 cfs? Did they ever previously run the outflows at full capacity of 150,000 cfs?

2) Any educated guesses as to why there was damage at 50,000 cfs now and not after outflows were significantly greater? (Maybe the one-two punch of first weakening and then later, final breaking - and/or - the constant battering of hot/cold expansion/contraction pressure on the concrete over about 50 years?)

3) I've heard some experts call this one of the greatest engineering failures in history. Maybe that's too much, I don't know, but how do you rate the failure of the spillway after it ran for 24 hrs at about one-third capacity its planned capacity?