The emergency spillway is around 30 feet high, the dam itself is 770 feet high. The amount of water released from a failure of the emergency spillway will be enormous, but still much smaller than the amount of water released by a complete dam failure.
Excellent link, thanks. I found the following comment sobering:
"Countryman: It’s not going to be the (main) embankment failure, but it’s a failure. If it does happen, there’s nothing saying that the ground is going to stay where it is. That force of water will start tearing that hill apart, and it could eat back into the reservoir and drain the reservoir."
