The Hennepin Iceland Tunnel was a 2500 feet ( about 760 m) long tunnel in Saint Anthony (now part of Minneapolis ), which was dug 1868-1869 under the river bed of the Mississippi River to a drainage channel for water power extraction for sawing and to create flour mills were located above the Saint Anthony Falls. The tunnel ran from Nicollet Iceland downriver under Hennepin Iceland through and had its output below the waterfalls.
During the tunnel construction, the river broke out on October 5, 1869 by the thin blanket of limestone that separated the river bed of the tunnel. The river swept through the tunnel hollowed parts of Hennepin Iceland and caused the collapse of the supporting soil on the upstream side of the falls. There were serious concerns that the river bed crumble and the Saint Anthony Falls would be converted to a long series of rapids. Within a few weeks dams were built to keep the river and thus to stop the flushing of the cases. The measure, however, was only temporary, because the spring floods in 1870 damaged some of the new dams and still wegspülten larger parts of Hennepin Iceland. By the autumn of 1870 the riverbed and banks were stabilized further and built a wooden weir above the falls. As a direct result of the collapse of the Saint Anthony Falls, were awarded the concrete weir, which created an artificial waterfall, the only major waterfall on the Mississippi River.
The former tunnel is about 1650 meters upstream of the collapsed in 2007 -35W Mississippi River bridge.
( † about 1705 * May 12, 1626 ) was named Hennepin Iceland was for the discoverer, Catholic priest and Franciscan Louis Hennepin. The entrepreneur William W. Eastman and John L. Merriam had 1865, the neighboring island, Nicollet Iceland bought, because they had the idea to dig a tunnel under Nicollet Iceland from the Saint- Anthony Falls through to the profit the various flour mills and sawmills, which were located above the falls, to provide a Mühlkanal available. The tunnel should be a part of a system of hydraulic engineering facilities, for the benefit of industrial enterprises, of which the growth of Minneapolis ' was dependent. The project was intended to allow the hydropower Other industrial operations on Nicollet Iceland.
The Saint Anthony Falls consist of a hard limestone cap sitting on soft sandstone. Even 10,000 years ago, the falls were there, where Fort Snelling is today, at the mouth of the glacial River Warren. During the ensuing millennia the river has eroded the sandstone and thereby undermine the sitting thereon limestone, making the waterfalls are slowly migrated upriver until they arrived at their present location.
The workers began in 1868 to dig a 2500 foot long tunnel under the river bed, the downstream under Hennepin Iceland led through under Nicollet Iceland and below the waterfalls should come to the fore again. For a period of one year, the workers dug through the soft sandstone, which lies under the thin layer of limestone, through which the river bed is formed. Then, in October 1869, the water from above began to seep into the tunnel.
On 5 October 1869, the river broke through the thin layer of limestone. The rushing current swept through the tunnel, brought parts of Hennepin Iceland to give way and caused the collapse of the soil that embeds the Saint Anthony Falls. There was immediate concern that the river bed could crumble and thus the waterfalls would be transformed into a long series of rapids. A witness remembers,
" Shop owner rushed to the falls, took their sellers with itself; the baker left their stoves, wood workers were sent from the mills, the barbers were unshaven their customers; Craftsmen dropped their tools; the lawyers closed their books and listened to, to make entries on the court; doctors leaving their practices. In the streets we saw hundreds on their way to the waterfalls in haste. "
At present, work began to clog the tunnels and hundreds of volunteers used wood and stones for it. The river washed away but this without any problems. After a few weeks, the situation improved and dams were built to divert the river and prevent the washing away of the falls. The repair was only temporary, because the spring floods in 1870 tore up some of the new dams and still more soil washed away from Hennepin Iceland. In addition, the ground collapsed under the Summit Grain Mill, Moulton's a mechanical slicer and a granary and these buildings collapsed into the river.
By the fall of 1870, the river bed and the river banks, however, were stabilized and a wooden military protected the troubled Saint Anthony Falls against further headward erosion. The weir covered the jagged rocks of the cases and tamed the Prancing water.
The extensive damage that was caused by the collapse of the Hennepin Iceland tunnel, brought litigation and calls for policy changes. A central question in this case was at that time that the local taxpayers have to pay for repairs, only bring the wealth of entrepreneurs on the river bank with them. The collapse of the tunnel was ultimately one of the factors that caused the 1872 merger of St. Anthony and Minneapolis. To facilitate the local population, the United States Army Corps of Engineers led the repair work under the assumption that this will ensure the navigability on the river and federal funds used for this purpose. Seven years after the tunnel collapse, 1876, the waterfalls were secured with an underground dam and other low dams, which are still present above the Stone Arch Bridge. By 1880, the Army Corps of Engineers has installed a concrete weir and even helped create the now man-made waterfalls. The federal government spent 615,000 U.S. dollars on these efforts, the two cities of St. Anthony and Minneapolis paid 334 500 dollars in costs.