Eastman tunnel | |
 1869 Eastman tunnel collapse near Saint Anthony Falls | |
| Location | Minneapolis, Minnesota |
|---|---|
| Built | 1868 started |
| Built by | W. W. Eastman |
| Part of | St. Anthony Falls Historic District (ID71000438) |
The Eastman tunnel, also called the Hennepin Island tunnel, was a 2,000-foot-long (600 m) underground passage in Saint Anthony, Minnesota (now Minneapolis), dug beneath the Mississippi River riverbed between 1868 and 1869 to create a tailrace so water-powered business could be located upstream of Saint Anthony Falls on Nicollet Island. The tunnel ran downstream from Nicollet Island, beneath Hennepin Island, and exited below Saint Anthony Falls.
During construction of the tunnel on October 5, 1869, the river broke through the thin layer of limestone separating the river's bed from the tunnel. The rushing river scoured the tunnel, caving in parts of Hennepin Island and causing the earth supporting Saint Anthony Falls to collapse upstream. There was serious concern that the riverbed would crumble and reduce Saint Anthony Falls to a long set of rapids. Within a few weeks, dams were built to divert the river and stop Saint Anthony Falls from being washed away. The fix was temporary as the 1870 spring floods damaged some of the new dams and swept away more of Hennepin Island. The final fix for the tunnel disaster was a concrete dike constructed by the United States Army Corps of Engineers. The Corps also built a protective sloping wood timber apron to create an artificial waterfall which remains the only major waterfall on the Mississippi River.
The Eastman tunnel is a contributing resource to the St. Anthony Falls Historic District. The District is on the National Register of Historic Places.[1]
The site of the tunnel is about a mile upstream from the site of the I-35W Mississippi River bridge that collapsed in 2007.
- ^ Nomination 1971, pp. pdf 83–84.