Jack in VA has been showing what appears to be water underneath the new spillway. That rock in that area is not good bedrock.

If you read about the St Francis Dam failure in 1928, it was a big cement dam, but they didn't know about the faults in the rock to the sides. There had been ancient landslides and the rock was not solid as it appeared. First time they filled it, water began to move through the rock on the sides, the abutments where the cement was hooked in, and it created hydraulic uplift. That is, in more simple terms, water pressure lifting up whatever is on top, in this case rock and cement. Hundreds of people drowned when the dam failed, and it failed very quickly, like in a few hours.

People can't picture the power of water. You can't imagine water forcing up a cement dam or the rock above. But it can. Hydraulic uplift was not well understood 90 years ago but it is now, and it is scary.


Cahill and Robert Bea, the disaster guy from Berkley, both think water is moving through rocks under the gates, which is rock to the side of the dam itself. The spillway is off to the side. Can hydraulic uplift make the new spillway, which is well bolted into the rock, go up? Maybe not. But if it is starting to move underneath and fissures widen, it could bring down the lake to whatever depth it erodes. I remain very concerned. I wish they would lower the water as much as possible and reduce water pressure on any seepage in the rocks....or into that green spot.