Four years earlier in 1865, four partners, the most prominent of whom were William W. Eastman and John L. Merriam, bought a large portion of Nicollet Island from Hercules Dousman. With the property came long-ignored water rights that the partners wanted to use.
They brought suit against Saint Anthony Falls Water Power Company, which claimed it controlled all water power on the east side of the falls. Eastman, Merriam, and their partners asked that Saint Anthony Falls Water Power Company remove or lower its existing dam so that Nicollet Island water could be used for new development.
A heated court battle followed. Eventually, the parties reached a compromise that preserved the power company’s existing dam but allowed Eastman, Merriam, and their partners to dig a tunnel under Hennepin Island and the Mississippi River to the tip of Nicollet Island, to create a tailrace.
Digging began in September 1868. Similar tunnels had been dug through the sandstone on the west side of the river and under Main Street in St. Anthony, so the 1868 project was considered feasible. However, none of the previous projects had excavated under the river.
The tunnel under the river was six-feet square, and work progressed without difficulty for a year, until October 4, 1869. That morning, workers returning from the weekend found water seeping into the tunnel. They thought it would be an easy fix and continued work. However, by noontime, the seep had become a flow, and the workers were forced out of the tunnel with all of their tools, never to return.
The next morning, Tuesday, October 5, the river broke through and the top of the tunnel collapsed. Water scoured the tunnel wider and deeper until the resulting hole was sixteen-and-a-half feet deep and as much as ninety feet wide. By this time, all of the falls were in danger of collapsing into rapids. With them would go all of the region’s water power.
By October 5, everyone in the area knew of the growing disaster at St. Anthony Falls. Hundreds of men volunteered to help fill the gaping hole in the rock wall of the falls. First, they threw rocks, dirt, and logs into the hole, only to see them swept away. Next, they constructed two cribs (rafts of logs), weighted them down with rocks, and sunk them into the hole. These worked briefly but eventually were swept away and made the damage worse.
Finally, under the direction of businessman and civic leader George Brackett and the Minneapolis Fire Department, volunteers built three cofferdams to block off the area of the break. Work on these cofferdams continued day and night for weeks until the water was diverted, the break sealed off, and the sandstone erosion lessened. The falls were saved, for the short term.
Further breaks in the sandstone under the falls required more work during the next few years. Eventually, the United States Army Corps of Engineers intervened. The Corps built a full concrete curtain wall and a protective apron before the falls were fully stabilized.
For more information on this topic, check out the original entry on MNopedia.