The Hennepin Island Tunnel, Minnesota
The Hennepin Island tunnel was an unfinished 2,500-foot-long underground tunnel in Saint Anthony, Minnesota, dug beneath the Mississippi River riverbed between 1868 and 1869. The passage was created as a spillway for industrial businesses located upstream, but during construction of the tunnel, the river broke through the limestone between the riverbed and the newly constructed tunnel walls. The Mighty Mississippi flooded the tunnel and caused parts of Hennepin Island and the St. Anthony Falls waterfalls to cave in. The tunnel collapse caused legislative policies regarding tax payers’ responsibility for failed public works to be enacted and a was a major factor in St. Anthony merging with Minneapolis to create a metropolitan area in 1872.