Don't know the details of the projects but from the pictures posted (here and elsewhere) it seems that only topsoil was eroded. Yes, bedrock is not indestructi

Don't know the details of the projects but from the pictures posted (here and elsewhere) it seems that only topsoil was eroded. Yes, bedrock is not indestructible, it could get eroded from water, but it takes times. Plus it get eroded slowly over time. The main concerns was the use amount of water released by the failure of the spillway. For sure the water keep flowing over the collapse spillway would erode the bedrock lowering it, but at a slower pace...