When did this spillway graduate to be the "primary" spillway?
As I understand it, it has always been the emergency spillway, not used for decades.
Which is it? The primary (main) spillway is off to the left as the site has been shown in most photographs.
The article talks about the numero uno spillway.
It’s confusing. The primary (or main) spillway, sometimes less ambiguously known as the concrete spillway, is the one to the right in the top photo above. It’s the one that’s suffered the most damage. A giant crevasse has been carved into the hillside to its right. That hillside, between the concrete spillway and the main dam is what holds up the main dam. If you allow enough of that hillside to erode away, then the whole 900 foot dam comes crashing down. Millions of people would be affected. Perhaps hundreds of thousands would die. DWR says that’s not happening. I think they are totally incompetent and full of crap. Look at that gash! If it enlarges much more, that hilllside, and the main dam, is coming down.
Now, the “emergency” spillway is to the left of the concrete spillway, and is nothing more than a bare earthen hillside. It has not been reinforced or improved in any way. It has never been used in its 50 years of existence. It is 1,700 feet wide and holds back Oroville Lake at the shallow end. DWR always considered it to be sufficient as it would probably never be needed, despite the engineers who have been arguing for 20 years or more that it’s a disaster waiting to happen. Well, now we know how wrong DWR was — again. When the concrete spillway was blown to smithereens by the incredible volume of water flowing over it, DWR shut it down and decided to let the emergency spillway handle the overflow. But within a few hours of water rushing over the emergency spillway, it was apparent it was rapidly eroding away and was in danger of collapsing — and the shallow end of the dam with it. So they had to evacuate 200,000 people. Total incompetence.