How Mississippi Locks and Dams Work

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Sixty percent of exported grain in the U.S. moves on the Mississippi River. Barges heading up and down have to go through the locks and dams of the nation.

Every day about five to six tows go through Lock and Dam number 15 on the Mississippi River.

Chief of Operations for the Army Corps of Engineers Michael Cox points out a tow entering into the lock, when the gates open, the water is equal to that side of the river, “This is a downbound tow. When the tow gets in here and gets tied off, they’ll close the gates as you saw. And then the lock operators will make sure that everything’s ready to go and then they’ll open up the lower valve. And then by gravity flow, they’ll empty the water out of the lock chamber until it equalizes with the water levels at the lower end.”

The way lock systems are designed, there’s no pumps needed to move that level, it’s all done by gravity.

Cox says going south from Minneapolis to the Gulf of Mexico, there are 39 lock and dams, “You can consider it almost like a stair step system. Because the topography of the river increases more the further upstream you go. So in order to have a navigable pool, where barges and heavy cargo like this can transport, we have to flatten the water out a little bit.”

When the water is level, the bridge opens up.

“We need significant water depth all the way through the system to allow nine foot draft barges and large tows like this to navigate up and down the river.” Cox says, “The other reason is to somewhat slow down the flow so tows can navigate a little bit more safely.

A swing bridge carrying trains, cars, and bikes opens up to let the tow through. Then, the tow heads to the barges.

Cox explains the process, “So now this towboat, he flanked, he’s maneuvering away from the wall so he can get himself positioned and he’s going to go into the center of the face of the barges there.”

Even though they’re called tow boats, they actually push the barges. Cox points out a three by four group lashed together. They are 800 feet long and a 105 feet wide.

That’s a tight fit according to Cox, “So when a tow boat operator has nine or in many cases, 15 barges ahead of him, and he has to take that 105 foot width and squeeze it in through the 110 foot lock chamber it takes a lot of maneuvering power.”

The tow then heads to the next lock and dam.