You are a member of a very large club. Everyone is confused , and most don't even understand what happened to the dam. It wasn't lack of maintenance at all.
Didn't they build flood gates into this damn so that they can open them to release over flow?
The water for the turbines runs under the dam, and comes out further down the river.
There is the main spillway, which is where the 'flood gates' would be. There is also an emergency spillway.
The problem was that they didn't release ENOUGH water EARLIER, because they was so concerned with filling the lake TO THE TOP, in an effort to make up for the lack of water during the previous drought period.
Once it got near the top, they started draining off water via the main spillway. Normally (meaning if the lake wasn't filled almost to the top), they could have released water at a nominal rate, and everything would have been OK.
BUT, they had to release the water at a VERY HIGH RATE due to the impending water level that was threatening to reach the 'emergency spillway'. They released the water at such a high rate that the water flowed OVER THE SIDES of the main spillway, and eroded the ground UNDERNEATH the spillway, which then caused the collapse of part of the main spillway, because it no longer had any support.
SO,,, they had to cut down the water rate going through the main spillway. This led to the lake level continuing to rise rapidly, and eventually, it overflowed the EMERGENCY SPILLWAY and started eroding away pretty much everything downhill from the emergency spillway.
They gambled on trying to get the lake FULL and they almost LOST...everything.
But that was just the first hand, and the poker game isn't over yet. Mother Nature deals the cards for the next hand.
The spillway failure you describe failed long before the water went over the emergency spillway.
50,000 cfm is no where close to the maximum rate quoted of 150,000cfm at the time the spillway cratered. If the flow was able to jump across the side barriers of the spillway with no prior defect and well below the maximum rated discharge, what you’ve described sounds like a design flaw.
Inspection reports reference water movement over time eroding underneath the spillway, leading up to a repair in 2013. Is this what you are referring to?