Some 6 million tons of commodities passed through the lock and dam along the Mississippi River in Hastings in 2023, and with navigation season at a pause, crews this winter have undertaken the herculean task of draining the lock chamber to inspect and repair the 90-year-old concrete walls that are typically submerged by river water.

The U.S. Army Corps of Engineers on Wednesday continued work on the $3.5 million project on Lock and Dam No. 2. Work began in December, the first time in more than 15 years that this lock chamber has been drained.

Referred to as “dewatering,” a simple definition is to remove all of the water from the lock chamber. In practice, it’s anything but simple. It involves draining billions of gallons of water from the 600-foot-long, 110-foot-wide and 40-foot-high lock chamber that regulates the height of the Mississippi River at Lock and Dam site No. 2.

Once the water is held back and the river floor is in view, workers can begin to diagnose possible repairs. Each lock is scheduled to be dewatered every 15 to 20 years. Hastings’ Lock and Dam No. 2 was last drained in 2007.

Stairways for boats

There are 29 locks and dams along the Mississippi River, stretching from Minneapolis-St. Paul to just north of St. Louis. The Corps of Engineers refer to the lock and dam system as a “stairway for boats,” as the locks and dams pool the water, raising it and lowering it, in order to create a consistent, nine-foot channel of traversable water for large boat traffic.

The lower portion of the Mississippi does not need a lock and dam system as it becomes deep enough to more easily allow barge traffic.

When the Hastings lock is full of water throughout the year, divers can attempt to diagnose potential issues, but the drawdown gives Corps officials a chance to truly understand the quality and condition of the concrete, said Steve Heidbrider, lockmaster at Lock and Dam No. 2.

Since workers only have a few months to review what rests beneath, and then make needed repairs, work begins quickly and continues at a consistent pace, a busy construction site now taking place where barges usually float by.

Workers also take the chance to clean the area of zebra mussels and complete other minor repairs, like cleaning and resealing a crossover pit that holds conduit for other lock and dam operations.

How it works

With the Highway 61 bridge at Hastings in the distance, workers continue inspection and repair of Lock and Dam No. 2 on the Mississippi River. (John Autey / Pioneer Press)

To begin the dewatering drawdown, crews start by placing huge steel bulkheads at each side of the lock chamber. With the pieces eventually measuring some 40 feet, they begin pumping the water out at a measured pace. It takes about 30 hours to drain the chamber.

With the chamber empty and the bulkheads holding the water at bay, pumps are set up to handle the relatively small amount of water squeezing through, keeping the floor of lock No. 2 from refilling.

Planning for the dewatering process began a year in advance, said Billy Thomson, a project manager with the U.S. Army Corps of Engineers.

On Wednesday, workers took to hydraulic lifts to inspect the lock’s 40-foot steel gates. The more than 200,000-pound gates were installed in 2021, and this gave officials the first look in dry conditions to see how the doors were handling the environment.

Crews are also replacing four valves at Lock and Dam No. 2 that are believed to be original to the 1940s.

Lock and Dam No. 2 first went into operation in 1931, but the original lock was soon replaced due to poor soil. The lock walls settled and tilted, causing the need for the current lock, which was completed in 1948.

Much of the concrete is original to that time, and crews on Wednesday morning identified small portions that need to be replaced.

Corps officials like Branden Johnson were generally pleased with the channel’s overall condition considering the repeated freeze-thaw cycles and water submersion. Johnson, a master tender with the Corps, has been part of 10 different lock and dam dewaterings up and down the Mississippi River.

“Just think about how concrete heaves, think about what happens to some driveways or sidewalks. And then look here,” Johnson said. “Everything is sound.”

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