First, a short introduction. A river flows downhill towards the sea or a lake. In flat terrain, it flows slowly, and, provided water depth is adequate, vessels can traverse both upstream and downstream. But, as the terrain becomes steeper, a vessel has more and more trouble moving upstream because of the increasing current. Therefore, to aide navigation, engineers build dams across the river to create a series of lakes or pools. The river ends up looking like a series of terraces with dams marking the lower (downstream) edge of each pool. To let ships pass, a lock or boat lift must be built at each dam. Locks are also used to bypass an area of dangerous water, such as cataracts or waterfalls.
Click the link for an excellent Corps of Engineers brochure on Upper Mississippi River locks and dams. "The Upper Mississippi River – Illinois Waterway System includes 37 locks and 1,200 miles of navigable waterway in Illinois, Iowa, Minnesota, Missouri, and Wisconsin. The 9-foot Channel Navigation Project was largely constructed in the 1930s and extends down the Upper Mississippi River from Minneapolis-St. Paul to its confluence with the Ohio River and up the Illinois Waterway to the Thomas J. O’Brien Lock in Chicago. "The maintenance needs of the aging infrastructure are increasing at a rate much greater than the operations and maintenance funding provided for the system." This is a polite way of saying that Congress has been grossly underfunding maintenance for decades. It is a symptom of our race to the bottom.
"9-foot Channel Navigation Project" means that barges with a draft of 9 feet can transit the system. In the south, the 9-ft channel begins at Baton Rouge. Ocean-going ships can travel up the Mississippi as far as Baton Rouge, but further north, cargo must be transferred to barges. I do not know haw a depth of 9 ft was selected in the 1920s, when the ambitious project was conceived.
In the first photograph, the template for the bed is made of wood. Fifty years later, the construction process was almost identical, except that the templates were cut from aluminum.
This was the era before electronic computing machines, and all observations were recorded manually on graph paper. We built much of the nation's infrastructure like this, based on sound engineering by hard-working engineers, scientists, and technicians. And we are letting it crumble away through neglect, political infighting, corrupt politicians, and national stupidity.
Morang, C.N. 1937. The Effect of Symmetrical and Unsymmetrical Roller Gate Operation on Discharge Coefficients. M. S. thesis, State University of Iowa, Iowa City, IA, 68 pp.
Photograph No. 1 is from the Library of Congress:
TITLE: Mississippi River dam #15, general view of completed dam, view from top of Clock Tower building
SUMMARY: Photograph shows dam across the Mississippi River and Davenport, Iowa. The Government bridge, which carries railroad, automotive, and pedestrian traffic, is in the foreground. The Davenport city skyline is in the background.
DATE: 20 March 1934
This image is available from the United States Library of Congress's Prints and Photographs division under the digital ID ppmsca.17351