Oxbow Lake: History of Oxbow Lake's Construction
A river naturally winds through the landscape, changing
its course over time to follow the path of least resistance. In
the mountains, river routes are usually tightly constrained by steep
hillsides, but in flatter parts of the country a river turns into a
sinuous snake. These looping curves, known as meanders, are a
natural result of erosion and deposition.
Erosion
lengthens even the smallest curve as water rubs up against the outside
bank. If you imagine cars passing each other on a curving
racetrack, you will realize that the car (or water) on the outside of
the curve must travel much faster than the one on the inside of the
curve to reach the straightaway at the same time. Just as the
faster race car would cause more damage if it ran into the wall of the
track, quickly moving water has a greater ability to cause
erosion. The water on the outside of the curve carries away soil
and gravel that was once part of the curve's outside bank.
Meanwhile, the
water on the inside of the curve dawdles, taking its time to reach the
straightaway. As water slows down, it can no longer hold as much
silt and gravel, so the slow-moving water drops dirt and debris out of
its grip. A sandbar forms on the inside of the curve, then trees
colonize the area and new land is formed. The combined actions of
the eroding water on the outside of the curve and the depositing water
on the inside of the curve results in a river bend that may be a mile
or more long. Over time, a river that was once nearly straight
turns into a winding snake.
The next step
in an oxbow lake's construction often comes during a flood.
Raging waters back up as they push their way around a curve, and
suddenly the water is high enough to bypass the curve and make an
overland shortcut to rejoin the river further downstream. Once
water has flowed across the shortcut, it becomes the path of least
resistance --- why would any water take the long route through the
sinuous curve when it could just barrel on through the shortcut and be
downstream that much faster?
The old curve
of the river is now a lake of still or slowly moving water. The
so-called oxbow lakes are named from their resemblance to the U-shaped
yoke once put around an ox's neck to harness it to a plow or
wagon. Although oxen are seldom harnessed in today's society,
oxbow lakes remain a common feature in our landscape.
Despite sharing
its name with these natural oxbow lakes, St. Paul's lake is a special
case. Oxbow Lake wasn't created by flooding, though its creation
was spurred by a massive flood in the early 1980s. After
receiving extensive flood damage, the town of St. Paul chose to
re-route the Clinch
River to bypass their buildings, giving the town a bit of
protection from later floods and forming a man-made oxbow lake from the
discarded portion of the river.
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