Photo courtesy of the U.S. Army Corps of Engineers

The Manitoulin was the last big ship through the Soo Locks this month before the annual shutdown.

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By Tanda Gmiter | MLive

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SAULT STE. MARIE, MI - After nine months of heavy use raising and lowering ships big and small as they traveled between Lake Huron and the higher Lake Superior, the Soo Locks are now closed for their annual maintenance season.

But before the work could begin, the U.S. Army Corps of Engineers had to drain the locks so workers can inspect the interior and make needed repairs.

"The winter work season has officially begun for crews at the Soo Locks," the Army Corps said on social media this week. "The last boats passed through the Poe Lock January 15 and the next day workers began dewatering the lock."

Each year, the locks handle more than 4,500 vessels carrying up to 80 million tons of cargo. Iron ore, limestone and coal make up the bulk of what is coming through on the big freighters.

Of the Soo's four locks, only the Poe and the MacArthur locks are in regular use in the St. Marys River during the shipping season. Draining them means pumping out about 73.3 million gallons of water, the Army Corps said.

It takes about 22 million gallons of water to raise the level of the Poe Lock by 21 feet when a big ship comes through, the Army Corps said.

While a new lock is being built, the Army Corps has said it's imperative to keep the two frequently used locks in good repair.

The Poe Lock, which is 1,200 feet long, handles all the big lake freighters. The smaller MacArthur Lock is 800 feet long.

The Army Corps has shared a dozen photos of how they prepped the Poe Lock for a list of winter maintenance projects. It took workers about 17 hours to pump the water out of the biggest lock. In addition to the photos, they've provided descriptions to go along with the work being shown in each image.

So take a little trip through the Soo Locks, from a perspective few people get to see.

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Making a Temporary Dam

Workers secure a guide line to the lifting bar hook in preparation for setting stop logs to form a temporary dam at the upper end of the Poe Lock.

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Photo courtesy of the U.S. Army Corps of Engineers

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Easing the Stop Log into Position

Two workers handle lines as the stop log is eased into position, while another maintains communication with the lift supervisor on the barge.

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Photo courtesy of the U.S. Army Corps of Engineers

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The Final Stop Logs put in Place

One of the final stop logs is lowered into place at the upper end of the Poe Lock. These logs fit one on top of the other to form a temporary dam so the water can be removed from the lock chamber. Each log spans the entire length of the 110 feet wide lock and weighs 49 tons.

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Photo courtesy of the U.S. Army Corps of Engineers

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Checking the Depth

Using a marked, weighted line, a worker monitors the depth of the log as it is lowered into place.

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Photo courtesy of the U.S. Army Corps of Engineers

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Prepping a Hard Hat Diver

Tenders assist a hard hat diver preparing to enter the water. The Soo Area Office has a dive team made up of engineers, maintenance workers, electricians and lock a dam operators. This team with its diverse skills helps increase the self-sufficiency of the Soo Area Office allowing a great deal of flexibility in scheduling work and the ability to quickly address dive needs.

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Photo courtesy of the U.S. Army Corps of Engineers

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A Diver Enters the Water

A diver uses ladders built into the stop logs to enter the water to open valves on the lock floor. The surface water temperature was 32.4 degrees Fahrenheit.

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Photo courtesy of the U.S. Army Corps of Engineers

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Divers Open Valves on Lock Floor

On the surface, the dive supervisor maintains communication with the divers and records and records the camera feed from the their helmets as they open one of the valves on the lock floor.

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Photo courtesy of the U.S. Army Corps of Engineers

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Melting the Gate Ice

At the lower end of the lock, workers set up steam lines and insulating tarps to start melting ice on the gates. This ice, if left in place, would present a hazard to anyone working below.

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Photo courtesy of the U.S. Army Corps of Engineers

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Meet Crane Barge Harvey

The Crane Barge Harvey is set into place in the lower fore-bay of the Poe Lock. As the water is removed from the lock, the Harvey will settle on cribbing secured to its hull and provide crane support at the lower end of the lock. The dry lock will also serve as a dry dock for the Harvey for inspections and planned upgrades.

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Photo courtesy of the U.S. Army Corps of Engineers

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Tug Pushes Shut the Gates

Workers check the miter of the gates as the Tug Owen M. Frederick helps push the lower guard gates shut at the lower end of the Poe Lock. These gates form a temporary dam at the lower end of the chamber.

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Photo courtesy of the U.S. Army Corps of Engineers

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Meet the Owen M. Frederick

One of the many hard working tugs, the Owen M. Frederick.

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Photo courtesy of the U.S. Army Corps of Engineers

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Reaching Lock Bottom

At the bottom of the lock, workers lift a man hole cover to assist with drainage in the lower end of the Poe Lock.

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Photo courtesy of the U.S. Army Corps of Engineers

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The Empty Poe Lock

A view from the lower guard gates of the empty Poe Lock. It took about 17 hours to pump the lock down to the floor.

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Photo courtesy of the U.S. Army Corps of Engineers