Study finds better way to
protect streams from construction runoff
Friday, April 17,
2009
Researchers at North Carolina State University have found an
exponentially better way to protect streams and lakes from the
muddy runoff associated with stormwater around road and other
construction projects.
The alternative is lower or comparable in cost to commonly used
best management practices (BMPs) around construction sites, yet
much more effective at keeping streams and lakes free of runoff
sediment that pollutes water and harms aquatic life.
In a study comparing BMPs against alternatives on road stormwater
runoff in western North Carolina, the NC State researchers found
the alternative method kept local streams that received the runoff
cleaner, and helped reduce the amount of sediment loss inside
ditches near roads. Sediment and muddy water are among the most
common pollutants of streams and lakes.
Dr. Rich McLaughlin, associate professor of soil science at NC
State and one of the researchers involved in the project, says that
the current BMPs used in controlling erosion and sediment involve
using so-called "sediment traps" along with rock check dams in
ditches. Sediment traps collect water with the heavier sediment –
like dirt and other larger, heavier particles – settling to the
bottom and the "cleansed" water moving through rock check dams, or
piles of rock that are intended to slow the flow of water through
the ditch. Water then travels out of the ditch through a pipe to
streams, rivers or lakes.
In the study, McLaughlin and NC State colleagues Scott King,
extension associate in soil science, and Dr. Greg Jennings,
professor and extension specialist in biological and agricultural
engineering, found that the BMPs don't hold a candle to the
alternative – natural fiber check dams (FCDs) enhanced with
polyacrylamide (PAM), a chemical that causes sediment to clump
together. FCDs use natural fibers instead of rocks as a type of dam
to slow the flow of water in ditches.
The researchers found, in a measure of the "muddiness" of road
runoff, that the BMPs yielded 3,813 nephelometric turbidity units
(NTUs) in testing, equating to some rather muddy water, McLaughlin
says. Fiber check dams with PAM yielded averages of 34 NTUs, a
veritable drink of Perrier in comparison, McLaughlin adds.
Further, the study showed that after a storm, sites that used
standard BMPs lost an average of 944 pounds of sediment compared
with only 1.8 pounds of sediment lost at sites utilizing FCDs with
PAM.
McLaughlin says that these results are so convincing that North
Carolina's Department of Transportation is in the process of making
FCDs with PAM the new best management practice around road and
construction sites. McLaughlin's group is also training engineers
and installers around the state and nationally in the use of this
system.
A paper showing the study results appears in the March/April
edition of the Journal of Soil and Water Conservation.
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North Carolina State University
Thanks to North Carolina State
University for this article.