Locks and Dams 3 through 10 have auxiliary chambers. Each auxiliary chamber has only a single set of miter gates that could pass shallow draft navigation traffic if the lock chamber was out of operation and the upstream and downstream pools were equalized. At each site, the U.S. Army Corps of Engineers only installed one set of miter gates. An auxiliary lock chamber was never authorized by Congress, which would have included a second set of miter gates. Since installation, the auxiliary emergency gates have never been used, and the gate operating machinery was never installed.
The project involves Locks and Dams 4, 5, 5A, 6, 7, 8, 9 and 10.
The Corps performs periodic inspections of all its sites. Recent periodic inspection reports for these sites have raised concerns about the condition of the auxiliary miter gates because they constitute a non-redundant portion of the damming surface that cannot be properly inspected and maintained. Deterioration and failure of the auxiliary miter gates could result in a loss of pool and disrupt navigation on the Upper Mississippi River.
At each site, the Corps plans to install a double-walled sheet pile structure upstream of the auxiliary gates. The sheet pile structure will act as a redundant damming service and a walkway. If removed, the structure would not interfere with the function of the auxiliary gates.
Construction for Locks and Dams 5 and 5A were completed in 2020. In 2019, the Corps completed designs related to Auxiliary Lock Closures at Locks and Dams 3, 4, 6, 8, 9, and 10. In April 2022, the Corps awarded a construction contract for sheet pile installation at Locks and Dams 6 and 10 and advertised for construction at Locks and Dams 4 and 8 in July 2022. Project work at Locks at Dams 6 and 10 is expected to be completed in summer 2023.
Congress authorized the Upper Mississippi River 9-Foot Channel Navigation Project as part of the River and Harbor Act, approved July 3, 1930.
Design and construction of the sheet pile at the auxiliary locks are completed with 100% federal funds. In fiscal year 2018, construction contracts at Locks and Dams 5 and 5A were awarded for $2,272,000 and $2,950,000, respectively. In April 2022, Locks and Dams 6 and 10 were awarded for $6,869,867.