The U.S. Army Corps of Engineers, St. Paul District recently, dewatered the lock chamber at Lock and Dam 4, near Alma, Wisconsin, for routine inspection, maintenance and repairs.
Locks are dewatered on a 20-year cycle. The dewatering is accomplished by placing large bulkheads at the upstream and downstream ends of the lock chamber to prevent the flow of water into the chamber. The dewatering takes between three to four days.
When in normal operation, it takes about seven minutes and 6.2 million gallons of water to fill the lock chamber from the lower pool level to the upper pool level; the difference between the lower and upper pool levels is 6.5 feet.
The lock was dewatered to perform maintenance and repairs, at a cost of about $4.5 million dollars. Maintenance and repair was performed by 60 people including 53 people from the St. Paul District maintenance and repair section and seven seasonal lock and dam staff.
“We’re able to do this with all St. Paul District staff, and it provides jobs to staff who may otherwise be laid off during the non-navigation season,” Jim Rand, chief of locks and dams, said.
The worksite was active 24-hours a day to meet the deadline of reopening in March for the 2021 navigation season.
Joe Schroetter, project manager, said, “We have a luxury here in St. Paul. Because the river freezes up here, we have a pause in shipping traffic where we can perform this necessary maintenance and repair. Down south from us, they don’t have that luxury.”
Work included sandblasting and repainting the miter gates, concrete repairs and updating the bubbler system used to prevent ice buildup in the lock chamber. Sandblasting will occur overnight to maintain the schedule. Chris Stai, St. Paul District chief of maintenance and repair, said, “It’s cold work. They’re out there at night in the Wisconsin winter, and they can’t use heaters because it could cause rust.”
Maintenance is important to keep the lock and dam running. Schroetter said, “It’s like doing maintenance on your car. If you don’t change your oil and check the fluids, your car will not run. This lock and dam is almost 90 years old and we want to make sure it keeps running for many more years.”