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Changing the Locks

Though modern Americans mostly think of shipping in terms of Ice Road Truckers and FedEx freight terminals, billions of dollars in goods still travel by river every year. There’s just one problem: The infrastructure is nearly as old as the country itself. The locks and dam that are being replaced at Olmsted, near the confluence of the Ohio, Mississippi, Tennessee and Cumberland rivers, still have their original, wooden pieces. A planned overhaul will update Olmsted, shaving five hours off a ship’s journey and reducing the price of goods that make the trip by up to $700 million. To pull it off, engineers will build parts of the dam on land, hoist them onto a barge with an enormous rectangular crane, float them out to the middle of the river and then sink them into position. As it turns out, that’s a little harder than it sounds.

Author JACQUELINE DETWILER

OLMSTED, ILL.

1 When making a lock or dam, engineers usually construct a temporary box around the area where they want to work, then pump the water out and build the dam on dry ground. This time, the US Army Corps of Engineers is using a new, more efficient method: assembling the dam on the riverbank and later sinking it. To lift the enormous dam pieces once they’re built, workers will use one of the biggest cranes on earth, the 5,304-ton-capacity, rectangular Super Gantry.

2 According to project manager Larry Bibelhauser, the most complicated part of sinking the dam is the river itself. Once a piece is on the barge, rising water levels, changing speed and even wake from passing boats can knock it out of position before it can be lowered. To compensate, the captains carefully balance two sets of winches: Mooring winches anchor the barge to the riverbed, and snubbing winches adjust the position of the dam in relation to the barge — just in case.

3 The dam shell has to be set perfectly on the river bottom — to within a single inch of the right spot on the blueprints. To pull this off in the shifting, muddy waters of the Ohio, engineers use specialized, hyperaccurate GPS to locate all four of the section’s corners underwater. Then technicians at the base spend eight hours maneuvering each corner into a bull’s eye on a computer system that functions much like a video game. Once the corners make it into the bull’s eyes, the piece is lowered.

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