[steve86]

Remember, the depth of reservoir water at risk of a rapid, uncontrolled release is basically only 30-50 feet (down to “good” badrock on the sidehill). I am not minimizing what that amount of water can do in terms of flooding - death and property damage - but it is far from the entire contents of the lake. If the more solid bedrock is deeper yet than the water release could be bigger.

[metmom]

I found this. This explains everything and it seems to me that if the emergency spillway goes and the main one through erosion, the whole dam could go.

[metmom]

Here is another image that helps understand the whole situation.