Crews Dewater Locks for Winter Maintenance Projects

By Mrs. Samantha Heilig (USACE)April 6, 2016

Mississippi River Lock 13 Dewatered
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Inspecting Stand-pipes at Lock 13
2 / 4 Show Caption + Hide Caption – Civil Engineer, Stefan Flynn, inspects the stand-pipes that were installed in the floor of Lock and Dam 13 during the winter dewatering project. These pipes reduced the flow of water and eroded soil entering the chamber through weep holes in the conc... (Photo Credit: U.S. Army) VIEW ORIGINAL
Filling Valve
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Lock 13 Lower Gate Dewatered
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Keeping navigation possible on the Upper Mississippi and Illinois rivers is one of the primary missions of the Rock Island District. For more than 80 years, crews have been performing routine maintenance and repairs to keep the aging lock and dam system operational. Major maintenance projects have also become a necessary part of the maintenance process and are typically scheduled during winter months to reduce impacts to the river transportation industry.

This winter the Rock Island District performed winter maintenance at Locks 13, 14, 17 and 21 on the Mississippi River. Two of these locations, Locks 13 and 21, required removing the water from inside the lock chamber in a process known as dewatering.

According to Aaron Dunlop, operations manager for the Mississippi River Project, the lock dewatering process has become routine for many of the crew members working on the river system. First, bulkheads are installed at each end of the lock which serve as temporary walls to keep the river out when the lock chamber is emptied. Then large pumps are lowered into the chamber and crews begin removing the water by pumping it to the main river channel. Removing the water took about 24 hours and depends on the water level of the river at the time of the dewatering. When all the water is out, stair towers are installed along the sides of the lock to give workers access to areas that may not have been seen in decades.

"Dewatering is an essential part of keeping the lock and dam system repaired and maintained," said Dunlop. "It gives us a chance to evaluate the condition of the lock, make needed repairs and visually inspect areas that are normally underwater."

This year while crews were dewatering Lock 13 near Fulton, Illinois, they ran into a unique situation that prevented the lock from being completely dewatered. While pumping the water out of the chamber crews found excessive amounts of water seeping through the floor. Small holes in the concrete allowed the unwanted water into the space.

"The holes, known as weep holes were originally added to the the lock to decrease pressure on the concrete," said Dunlop. "Not every lock is like Lock 13; only the ones without a bedrock base have a need for the concrete floor."

To address the issue of the unwanted water, which was also carrying eroded soil from beneath the lock, crews installed plastic tubes called stand-pipes in the weep holes to balance the pressure. These stand-pipes did not stop the water from coming through the floor but reduced the overall volume and prevented most of the soil from entering the lock. Water that did make its way through the stand-pipes was continually removed from the chamber with 12-inch pumps.

"The crews did a great job of coming up with a solution in a timely manner," said Matt Thurman, chief of the Mississippi River Project's Maintenance Section. "Once the water level was managed, crews were able to stay on task and completed the maintenance work as scheduled."

Work completed during the Lock 13 dewatering included installation of a bulkhead sill beam which is necessary for future dewatering projects, replacement of filling valve cables and grease lines and repair of a bubbler system that keeps lock gates free of ice and debris. Crews also evaluated the lock floor system and made needed repairs to damaged weep holes. Something that was not anticipated but was found during inspections of the underwater lock features was a damaged mounting point on one of the filling valves. Because the lock was not in use, crews were able to pull the valve from the transfer tunnel, make needed repairs and replace it in time for the main navigation season to begin.

Much of the same type of work performed by the maintenance crews at Lock 13 was also completed at Lock 21 in Quincy, Illinois, during this past winter. Several members of St. Paul District's maintenance team traveled to Rock Island to support the regional effort of getting the river back open for navigation.

"It was nice to have additional people helping with the maintenance efforts," said Thurman "These projects are a lot of work and the more skilled people we have on the job, the more efficient we are at getting it finished."

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Rock Island District