TIL the Oroville dam is the highest in the USA, 44 feet higher than the Hoover dam. It's kinda mind boggling that it could actually fail tonight (though the latest reports indicate that the situation is improving).
If it fails, it will be a double disaster, many people will lose property, and California will lose some or all of the water in its largest reservoir. The challenge is going to be keeping ahead of it through to the next storm.
"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."
Lake Oroville is actually the second largest reservoir and one of six reservoirs with a storage capacity over 1M acre feet of water: http://cdec.water.ca.gov/cgi-progs/reservoirs/RES
The largest is Lake Shasta: http://cdec.water.ca.gov/cgi-progs/stationInfo?station_id=SH... with a storage capacity of 4.3M acre feet of water, approximately 800,000 more acre feet than Lake Oroville.
No, it's not. The local geology is fairly solid rock. The overflowing water will wear down the overlying soil and loose Earth, but should be sustained by the rock formation. It is a risk, certainly, but such a site is chosen because of the suitable foundation.
The issue right now is to see how the spillway fares over the night. If it handles the increased flow, then it should be able to continue to relieve the situation.
To be fair, I think it is a little ethically troubling to refer to the emergency spillway as anything other than that (e.g. auxiliary spillway), but it is designed to function in an emergency, not just fail catastrophically.
Where did you find the info on the area being solid rock?
That would go a long way to giving an idea as to how bad any increased failure might be.
There's definitely worries about the erosion on the main spillway moving back upstream towards the dam, but that is something folks are going to have to look at and consider over the remaining duration of the water season, unlikely to be a danger tonight.
I don't know enough about the geology of the area to know how likely it is to happen. But history does show that dams can go very quickly once erosion reaches the dam/reservoir, so alarm isn't exactly unwarranted.
However, my original comment was still substantially correct. See http://www.sacbee.com/news/local/article132356269.html
"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.