> My guess is dynamite blasting Exactly right! I was involved in a 'lake tap' project in Oregon where the concrete plug in the diversion tunnel was mechanicall

> My guess is dynamite blasting Exactly right! I was involved in a 'lake tap' project in Oregon where the concrete plug in the diversion tunnel was mechanically demolished down to the minimum safe thickness, then we came in and finished it off with explosives. A gate structure was first built farther down the tunnel, to allow the operators to again close off the tunnel or chose a given flow level and let me tell you, having to sidle sideways through that partially open gate to go place explosives into the remnants of the tunnel plug was an interesting experience. Here is a presentation put together on the project: https://ndiastorage.blob.core.usgovcloudapi.net/ndia/2005/triservice/track1/schlenker.pdf https://ndiastorage.blob.core.usgovcloudapi.net/ndia/2005/tr...