How TVA dams and locks make navigation possible
Quick! Name some ways TVA dams benefit people in the Tennessee Valley.
Flood damage reduction, power production, recreation—those are the ones that come to mind first.
But “promoting navigation” was actually the very first purpose mentioned in the TVA Act of 1933, which spelled out exactly how the new agency was to manage the river. Navigation has been important to the welfare of the Valley ever since.
If it weren’t
for those barges moving up and down the river, we would be paying
more for all kinds of products. Anything made from materials shipped
in large quantities—grain, stone and gravel, iron and steel,
lumber, coal, and chemicals, for example—would cost more. Why?
Because they’d have to be shipped by rail or truck, which would
cost over $550 million a year more than moving them by barge.
One barge can carry as much stuff as 60 trucks, so there’d be a lot more 18-wheelers on the road, too. Using barges helps keep our highways safer and reduces fuel use, air pollution, and the number of tires going to landfills.
A river highway
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TVA built nine dams along the main Tennessee River to create a 652-mile long river highway. TVA operates these dams to make sure the water all along the way is at least 11 feet deep—enough to float even the heaviest barge.
Before these dams were built, the water was too shallow for barges to travel very far up the Tennessee River. In fact, in dry years, you could cross the river near Muscle Shoals, Alabama, without even getting your feet wet—if you didn’t slip off the rocks!
The main-river dams form a “staircase” of quiet, pooled water and controlled current along the entire length of the Tennessee River. But how do boats get around the dams?
Every dam has a lock—a canal for raising and lowering boats—which allows boats to pass around the dam and to deal with the difference in elevation between Knoxville, Tennessee, and Paducah, Kentucky. Paducah is 513 feet lower than Knoxville.
How does a lock work?
A lot like an elevator—only slower! When a barge or other
boat enters the lock, the gates close and the water level inside
the lock is raised to the upstream level or lowered to the
downstream level, depending on which way the boat is moving.
The locks are filled and emptied by gravity—no pumps are used. If the boat is going downstream, the water level in the lock is lowered by opening the downstream valves so the water can drain out. If the boat is moving upstream, the downstream valves are closed and the upstream valves are opened. This allows water from the upstream side to flow into the lock, filling the chamber to the upstream water level.
In about 45 minutes, when the water level inside the lock is equal to the level of the next reservoir, gates at the other end of the lock are opened and the boat can continue on its way.
You can see a little movie of how a lock works here.
