Some of the most interesting historical structures in the region remain unknown and unseen by today’s visitors along the Mississippi River. They served their purpose well for 50 years, then disappeared into the depths of the river, reminding us of their existence with subtle fluctuations in the water surface.
These structures are wing dams, built with federal funds under the supervision of the U.S. Army Corps of Engineers during the late 19th and early 20th centuries. Some 1,900 wing dams and closing dams, both known as “river training structures” by the U.S. Army Corps of Engineers, were built as part of the first attempts to control the depth of the Mississippi River and maintain a navigation channel.
“Shortly after the Civil War, we were authorized to start looking at ways to provide a consistent water level,” said Brad Perkl, archeologist with the U.S. Army Corps of Engineers, St. Paul District. “I think the first wing dam was built about 1873, and the idea was to try to direct the water into the main channel.”
This process of constricting the river caused it to scour the bottom, moving sediment farther downstream until it encountered slower moving water along the banks in the spaces between wing dams and settled there. Similar river improvements had been used by German, French, and Dutch engineers on their rivers, according to John Anfinson in his book “The River We Have Wrought,” and the method used by the Germans featuring rock and brush dams seemed like a good match for the Mississippi River.
By the time Congress authorized a 4 ½-foot navigation channel in 1878, wing dams in the main channel and closing dams blocking side channels had become the standard means of achieving this, and the U.S. Army Corps of Engineers built them in many locations along the Mississippi River.
The demand for wing dams was great, so the Corps of Engineers contracted construction to companies such as Kirchner Contracting in Fountain City, Wis. The company, owned by Albert Kirchner, employed 120 men and is credited with building over half the wing dams between St. Paul and St. Louis, according to an Oct. 31, 1976, article in the Winona Daily News.
Another company, owned by Capt. V.A. Bigelow was awarded a $100,000 contract for building wing dams near Prairie du Chien, Wis., and between Dubuque and Savanna, and according to an Aug. 2, 1893, article in the Winona Daily Republican, Bigelow “will use his boat, the Jessie B, and a large crew of men will commence the work as soon as the necessary papers arrive from Washington.”
Constructing the dams was hard work. It involved moving enormous amounts of willow trees and rocks to each location, and carefully layering the materials.
“The wing dams are constructed by putting in what is called a mattress of willows,” explained Capt. Walter Blair in an article published by the Winona Republican Herald on Nov. 18, 1908. “These willows are cut in bundles, the requirements being that they shall not be less than twenty feet in length and the bundles are a foot in diameter.”
The bundles were loaded onto a barge and tied together to form a mattress about 100 feet long, 20 feet wide, and 2 feet thick, according to Blair. The barge was anchored in place at the site of the wing dam, and the mattress was slid off the barge into the water.
“Rock is then loaded onto it until it sinks, the great ropes attached to heavy steam capstans holding it against even the strongest current and controlling it until it settles, even in a swift current, and a depth of twenty feet or more, in the exact position the engineer desires,” Blair is reported as saying.
A second mattress, with the branches pointing upstream, was then lowered, but 10 feet upstream, onto the first mattress and stones. The downstream end of this mattress was then raised by the first mattress and formed the foundation for the wing dam. A second and third mattress and layer of stone were placed on top of the foundation, with the downstream end of each layer being higher and higher.
“Thus the force of the water is not directly against the dam, as it would be against a solid wall,” Blair explained. “Rather because of the upward incline of the structure, the force of the current has a downward effect, and instead of being against the dam, its tendency is to force the dam down and contribute to its holding powers.”
The wing dams were not evenly spaced, nor were they the same length or height, suggesting that their placement may have been more art than science.
“I expect that they put them in places where they realized they were having trouble with sediment and the navigation channel was getting filled up,” said Walt Bennick, archivist with the Winona Historical Society and author of “Upper Mississippi River at Winona.”
“By June 30, 1906, the Corps had established a minimum depth of 41/2 feet or more for much of the upper river during normal low flows,” Anfinson wrote. “Compared to the controlling depths of 16 to 24 inches between St. Paul and the Illinois Rivers originally present during low water, this represented a dramatic change.”
Deeper channel needed
Wing dams worked for some time, but as boats increased in size and depth, the need for a deeper channel forced Congress to mandate a 6-foot channel in 1907. Corps of Engineers crews and contractors were able to reinforce many of the existing wing dams and keep them functioning for the 6-foot channel.
However, boats and barges continued to expand, and in 1928, Congress created legislation for a 9-foot channel which is in effect today. That final act launched the construction of the lock and dam system in 1930. Raising the waters levels that much put nearly all the wing dams under water and left them as invisible historic monuments.
“They raised the water up in the various pools, so the wing dams became obsolete,” said Bennick. “If you are going up and down the river, and the water is a little low, you can actually see them because there will be a set of ripples along the sides where the wing dams are located.”
Perkl said that there is a long tradition of fishermen who search for those ripples of water and pools formed by the wing dams.
“Behind those dams, the fish congregate,” he said.
Those sunken forms have also drawn the attention of boaters who have learned that wing dams can cause problems.
“It doesn’t matter so much for canoes and kayaks,” Perkl said, “but for motorboats, they can be hazardous. If you get out in the main channel, depending on where the water levels are, you can run into those things. They will tear up your boat, especially the prop.”
Perkl said the Corps of Engineers has river navigation charts showing the location of all wing dams. These charts can be found in many public libraries as well as on the U.S. Army Corps of Engineers, St. Louis District, website at www.mvr.usace.army.mil/Missions/Navigation/Navigation-Charts/Upper-Mississippi-River.