New Method Better than Stormwater BMPs, NC State Says
In a study comparing best management practices against alternatives on road stormwater runoff in western North Carolina, North Carolina State University researchers found an 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.
Rich McLaughlin, Ph.D., associate professor of soil science and one of the researchers, 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 Greg Jennings, Ph.D., professor and extension specialist in biological and agricultural engineering, found that natural fiber check dams (FCDs) enhanced with polyacrylamide (PAM), a chemical that causes sediment to clump together, works better. 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. 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. (Subscription required.)