I am not sure exactly how the Crown Hydro project would lead to the entire collapse of the falls.
WM: There are 2.9 miles of tunnels under the river, along both east and west banks, and under Nicollet Island. There very existence serves to destabilize the river bed. The 1,100 ft. of remaining caprock is, by definition, unstable. It is the Corps of Engineers "skirt" under the falls which holds it in place; it is the tunnels which destabilize it. At the time of the Eastman tunnel cave in, it was determined, by the Corps, that adding another tunnel was beyond the ability of the riverbed to support. To create the barge locks, five small islands were removed from the riverbed.
The erosion of the falls occurred because of the softer sandstone and limestone beneath this hard layer.
WM: This is the same reason why Niagara Falls keeps moving upstream--or probably any other falls. St. Anthony Falls has reached it's last place. The caprock layer gets thinner behind the falls at the site of the falls.
The Hydro project water would move over this hard layer and fall through an existing tunnel that would likely be lined, sending it out the tailrace- No threat to the falls. Also, as the stone arch bridge is a historic landmark, I am sure the necessary precautions would be taken.
WM: I don't feel at all sure that there is no threat to the falls because the hydro project requires removing earth that has settled and supports the streambed. And "all necessary precautions" have seldom been taken before, so it is unwarranted to expect that it will be done now. Underestimated costs, unforseen problems, etc. virtually always cause higher costs and then someone(s) look for cost cutting measures.
I would like to see more localized power sources as well as an opened end expanded headrace.
WM: In a state that, except for the Dakotas, is probably the windiest in the nation, localized power sources are easily had.
WizardMarks, Central ________________________________
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