Beneath Your Feet

Beneath Your Feet. An Underground Dam. "Colonel Farquhar said to me that, in his opinion, only eternal vigilance would keep the falls in existence...", William de la Barre, Water poured through the collapsed tunnel in 1869, undermining foundations of some buildings on Hennepin Island., Entrepreneurs had almost finished digging a 2,000' tunnel beneath the riverbed from Hennepin to Nicollet Islands when the tunnel collapsed in 1869, nearly destroying the falls. De la Barre studied how the city almost lost its waterpower:, "An attempt had been made to tunnel from below the falls to place a turbine on Nicollet Island, and vent the water it discharged below the falls, thus gaining the maximum available head and fall., "This tunnel, when partially constructed, collapsed, and disaster to the entire falls seemed imminent. The water in the river got under the limestone ledge forming the river bed and washed out the underlying soft sand stone formation, causing caves of considerable magnitude and breaks of the ledge above., "The federal government was finally appealed to, with the result that the government made various appropriations of money and the corps of engineers of the United States army took charge of preserving the falls, and under their direction a concrete curtain wall, 45 feet in depth, was built under the limestone ledge clear across the river bed, with the object of cutting off any seepage or communicating fissures or water passages between the water above and below the falls., "The scare and anxiety was still upon the public in 1878 and for years subsequent thereto, and at every period of high water in the river, some old residents might be seen standing upon the bank expecting to witness the destruction of the falls.", Building an Underground Dike, The concrete form just behind you caps the shaft used to build the dike beneath the river. This innovative and dangerous construction project was started in 1874 and finished in 1876., . The vertical shaft was dug and a hoist and stairway were installed., . A horizontal "drift" (tunnel) was extended just below the limestone/shale layer to hold a track and cars for removing excavated materials. "A crew of eight men, 4 picking and shoveling alternatively and 4 running cars, advanced from 8 to 10 feet in eight hours.", . The base of the drift was widened and extended to the east and west banks on the alignment of the dike., . Concrete was poured for the dike.