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In Stream Gravel Mining May Worsen Effects of Flooding
January 2011
Beech Fork Creek has been modified over the
years to control water flow, but dredging a stream could lead to
increased downstream flooding and problems with bank erosion.
In the spring of 2010, the Scioto Brush
Creek Watershed was hit with two significant rainfall events
resulting in flash floods along several streams in the drainage
area, causing significant damage to private property and public
roads.
After serious flooding events such
as these, landowners consider methods of controlling floods and
many conclude that gravel removal is an effective solution.
In spite of the landowner’s attempt
to control the flooding problem, however, altering the stream
does little to solve the issue and can worsen the effects of
flooding and erosion.
Channel straightening is a common practice
landowners will apply to address flooding problems, but
modifying a stream by straightening its course may create more
problems for the property owner and seriously impact his
downstream neighbors.
Although straightening the channel
allows water to pass through a landowner’s property faster,
downstream properties will experience higher water levels during
heavy rainfalls, which may increase flooding problems for those
landowners.
The increased velocity of the water
will also generate more force as it flows through the
straightened channel, increasing erosion forces that may cause
damage for the property owner and his downstream neighbors.
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Gravel removal also seems like a
simple way to address flood issues, but unintended
consequences may result from the practice.
Removal of material from the
streambed will damage riffles, pools, and vegetation
that reduce the speed of flowing water. Dredging removes
this natural structure, replacing it with a uniform
stream bottom that does not slow the flow of water,
again, increasing erosion forces.
Widening the stream will
have the opposite effect on the stream, but another
unintended result.
A wider channel will slow
the movement of water so the stream is unable to move
sediment.
Gravel and sand will be
deposited in the widened channel, filling the waterway
and forcing water outside the stream’s banks. |
 Vegetative cover along the stream's
edge and a natural structure at the bottom of a stream
will help slow the velocity of water and alleviate the
effects of low-level flooding. |
Removing gravel bars will also prove to be
a fruitless effort to control floodwater.
Gravel bars form naturally in
streams when the flow of water slows, causing the material
carried by the current to drop.
Often, these features are found on
the inside bank of a stream meander, where sand and gravel
accumulate as the water slows.
Removing the gravel may be a
temporary solution, but will not resolve flood issues.
After the next high flow event, the
gravel bar is likely to return, making it a waste of the time,
energy, and money spent to remove the material.
What can a landowner do to prevent
flooding?
Floods are a natural phenomenon, and
unfortunately, little can be done to stop flooding.
Maintaining a forested buffer along
the stream’s edge and establishment of wetlands will slow flood
waters during periods of heavy rain to prevent low-level
flooding.
Still, in the event of a major flood
event, these practices will have an insignificant effect on
flood control.
Water will continue to choose its
own course, whether people like it or not.
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