We don't have many damns like that around here, so I'm not familiar with the process. Thanks for that information, another bit of "matter" I have learned on FR!
It also gives details on how they built Hoover Dam and really explains how they were able to cool the cement to keep the projects moving ahead. It's wierd, but it really fascinates me....
In the Spring of 1983 we had a particularly wet Spring and all out dams started overflowing, they had to open the penstocks to let the water out quickly at Powell (and Mead, and Havasu, etc.) and the water going through the bypass tubes started spitting out dirt and rocks and they did come very close to losing the dam...
It took a couple of years to repair the damage and one thing they did was inject air into the tubes so that in the future (if we ever get rain and fill our lakes again) the water will actually ride on air instead of cavitating and tearing up the cement in the tubes. They say this method has been incorporated in a lot of large dams as a preventative.
I know more info than you wanted