Tuesday, July 31, 2018

Nevers Dam, 80' Bear Trap Gate was the longest at the time

The dam was removed in 1955 after 1950 and 1954 floods made it a danger to fisherman and canoeists. So I can't provide a satellite image of it. According to John Weeks, it had a head of 17'.

I learned about this dam because it was part of a tour of dams taken by two of the engineers for the Chicago Drainage Canal (now the Chicago Sanitary & Ship Canal). They studied the 80' bear trap gate at this dam to refine their design of a 160' bear trap gate for the CS&SC control structure. [Building the Canal to Save Chicago by Richard Lanyon, p55]

The St. Croix River was like the Muskegon River in that a lumber industry used it to float logs from the forest down to saw mills. Another similarity is that the dams on the rivers use a bear trap gate to pass the logs over the top. When the Nevers Dam was built in 1889, it was the largest wooden dam in the world, and the 80' bear trap gate was the longest gate in the world.

The wooden piers were built on top of piles and filled with stone. The road built across the dam was the only road across the river in the region. The truss bridge spans the 80'x20' bear trap gate and the 13 other gates were 16'x24' Tainter gates. The builder, Robert A. Lang, was the inventor of the bear trap gate.

 I've seen numbers of 5000, 7500, and 9000 for the number of piles under the dam. They were driven 12' to 15' into the ground. This is a photo of a steam pile driver used during 1916 repairs.
J.R. Frawley Photo

J.R. Frawley Photos
J.R. Frawley was the manager of the dam for many years. Unlike the dams on the Muskegon River that were built to harness the river's flow to generate electricity, this dam was built to create a flow. Sometimes the river would not have enough flow to float the logs downstream. So they built this dam so that they could close the gates for two weeks to create a head of water and then open the bear trap gate to allow the logs to float downstream on a tidal wave of water. The sawmills would process that wave of logs during the next two weeks as the water and logs again built up behind the dam. The bottom photo shows that there was a significant leak at the bottom of the gate when it was closed.

By 1903 the logs were pretty well gone so the Northern States Power Co. bought it as a river control point for the hydroelectric power dam it planned to build 11 miles below at St. Croix Falls. The last log was sluiced through in 1912.

After 1955, the power company hired a two-man well-driller crew to take 100s of samples of the river bottom. But the results were that the sand and gravel extended down as far as 113' with sandstone beneath that. Northern States Power was evidently not aware of the Tumble Bays, long aprons, and pier keys used by the Midwest power companies to build concrete dams without a viable bedrock. For example, the Elkhart Hydro Dam.


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