Eastman tunnel

1869 Hennepin Island tunnel collapse near St. Anthony Falls.

Hennepin Island tunnel was a 2,500-foot-long underground passage in Minneapolis, Minnesota dug beneath the Mississippi River riverbed between 1868 and 1869 to create a downstream spillway for hydroelectricity power plants, milling and lumber business located upstream of St. Anthony Falls. The tunnel ran downstream from Nicollet Island, beneath Hennepin Island, and exited below St. 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 St. Anthony Falls to collapse upstream. There was serious concern that the riverbed would crumble and reduce St. Anthony Falls to a long set of rapids. However, within a few weeks, dams were built to divert the river and stop St. Anthony Falls from being washed away. The fix was temporary and the 1870 spring floods tore up some of the new dams and swept away more of Hennepin Island. By the fall of 1870, the riverbed and banks were stabilized and a wooden apron cap St. Anthony Falls to stop the upstream progress of the collapsing falls. As a direct result of the collapse of the Hennepin Island tunnel, St. Anthony Falls received a sloping concrete apron to create an artificial falls that are held out as the only major waterfall the Mississippi river.

History

Hennepin Island was named after explorer, Catholic priest, and Franciscan missionary Louis Hennepin (12 May, 1626 – c. 1705). In 1865, entrepreneurs William W. Eastman and John L. Merriam had bought its sister island, Nicollet Island, with the idea of creating a tunnel from Nicollet Island under St. Anthony Falls to provide for-profit spillway services to the many milling and lumber business located upstream of St. Anthony Falls. The tunnel was to be part of a system of waterworks that supported the industries driving Minneapolis' growth. The project was designed to create more industry on Nicollet Island through the waterpower.

St. Anthony Falls are made up of a hard limestone cap over soft sandstone. The falls had at one time been located in Fort Snelling, Minnesota near the mouth of Minnehaha Creek. However, the river had been washing away the sandstone and undermining the limestone lip of St. Anthony Falls, causing the falls to slowly retreating upriver for 12,000 years.

In 1868, workers began to dig a 2,500-foot-long tunnel beneath the riverbed from Nicollet Island downstream under Hennepin Island, exiting below the falls. For the next year, workers dug in the soft sandstone beneath the thin layer of limestone that forms the river's bed. However, by October 1869, water began seeping into the tunnel from above.

Photo taken shortly after the Hennepin Island tunnel collapse. The scene is of a group of men sorting logs on Nicollet Island looking toward St. Anthony Falls. A barge can be seen in foreground and St. Anthony buildings are in the background.

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 St. Anthony Falls to collapse upstream. There was immediate, serious concern that the riverbed would crumble and reduce St. Anthony Falls to a long set of rapids. One witness remembered,

"Proprietors of stores hastened to the falls, taking their clerks with them; bakers deserted their ovens, lumbermen were ordered from the mills, barbers left their customers unshorn; mechanics dropped their tools; lawyers shut up their books or stopped pleading in the courts; physicians abandoned their offices. Through the streets, hurrying hundreds were seen on their way to the falls."

Work started immediately to plug the tunnel and hundreds of volunteers used timbers and stones. However, the river easily washed these out of the tunnel. Within a few weeks, the plug held and dams were built to divert the river and stop St. Anthony Falls from being washed away. The fix was temporary and the 1870 spring floods tore up some of the new dams and swept away more of Hennepin Island. In addition, the earth support below the Summit flour mill, Moulton's planing mill and a wheat storehouse were undermined and each of these was tipped into the river.

By the fall of 1870, the riverbed and banks were stabilize and a wooden apron cap St. Anthony Falls to stop the upstream progress of the collapsing falls. The apron buried the falls jagged rocks and large waterfall cataract and tamed the fall's tumbling water.

Aftermath

The tremendous damage caused by the Hennepin Island tunnel brought lawsuits and demands for political change. A central issue at that time was whether local taxpayers should pay for repairs that would enrich riverfront industrialists. To the relief of the local population, the United States Army Corps of Engineers made the repairs using federal money on the pretext that it was protecting navigation. Seven years after the tunnel collapse, by 1876, the falls were stabilized with an underground dike and low dams that largely are still in place upstream of Stone Arch Bridge. By 1880, the Army Corps of Engineers had covered the face with a sloping concrete apron, creating the artificial falls that presently reside as St. Anthony Falls and are held out as the only major waterfall the Mississippi river. The federal government spent $615,000 on this effort, while the two cities spent $334,500.

In November 2006, John Anfinson, a historian with the National Park Service and an expert on the Mississippi's gorge and only major waterfall, gave a lecture on the details of the 1869 collapse of the Hennepin Island tunnel.

See also

• Hennepin Avenue Bridge
• Hennepin Avenue
• Hennepin Island Hydroelectric Plant
• History of Minneapolis, Minnesota
• Louis Hennepin
• Mill Ruins Park
• Mills District, Minneapolis
• North Star Woolen Mill
• Northwestern Consolidated Milling Company
• Pillsbury "A" Mill
• Washburn "A" Mill

References

• Kane, Lucile M. (1966). The waterfall that built a city: The Falls of St. Anthony in Minneapolis. Publisher: Minnesota Historical Society. ASIN B0007DN9Z8

External links

• U.S. Army Corps of Engineers St. Paul District: Upper St. Anthony Falls
• U.S. Army Corps of Engineers St. Paul District: Lower St. Anthony Falls
• Engineering the Falls: The Corps Role at St. Anthony Falls - an article on the U.S. Army Corps of Engineers website covering the history and geology of St. Anthony Falls.
• Minneapolis' official promotional site for the riverfront district

44°58′54″N 93°15′31″W