Purpose
Locks and Dams (LDs) 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 (USACE) installed only 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.
Location
LDs 4, 5, 5A, 6, 7, 8, 9 and 10.
Description
USACE 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 nonredundant 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 all sites except LDs 3 and 9, the USACE design solution is 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.
Status
Designs for LDs 5 and 5A were completed in 2018, and construction was completed in 2020. In 2019, USACE completed designs related to auxiliary lock closures at LDs 3, 4, 6, 8, 9 and 10. In 2022, USACE awarded a construction contract for sheet pile installation at LDs 6 and 10 and advertised for construction for LDs 4 and 8. Project work at LDs 6 and 10 was completed in 2023. Project work at LD 4 was completed in 2025; work at LD 8 is planned to be completed in 2026. LD 3 and 9 bulkhead slot installation was advertised for construction in 2023, with contract awarded in February 2024. Work at LDs 3 and 9 was completed in 2025.
Authority
Congress authorized the Upper Mississippi River 9-Foot Channel Navigation Project as part of the River and Harbor Act, approved July 3, 1930.
Funding
Design and construction of the sheet piles at the auxiliary locks will be completed with 100% federal funds. The construction contracts for LDs 5 and 5A were awarded for $2,272,000 and $2,950,000, respectively; the construction contract for LDs 6 and 10 was awarded for $6,869,867; the construction contract for LDs 4 and 8 was awarded for $9,041,572; the construction contracts for LDs 3 and 9 were each awarded for $2,344,625.