United States Department of Transportation
i
Evaluating systems to reduce road improvement impacts on mountain streams.
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2007-08-14
[PDF-2.09 MB]
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Edition:Final report; July 1, 2004-June 30, 2007.
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Abstract:Sediment is the most common pollutant affecting North Carolina’s waterways, impacting a range of aquatic organisms, reducing
reservoir capacity, and hurting their aesthetic value. Construction activities, including roadway projects, are a significant
contributor of state-wide sediment loading. The NC DOT program of widening and paving rural roads in the mountain region
provided an opportunity to evaluate new types of roadside erosion control BMPs with the goal of protecting the particularly
sensitive trout streams commonly found there.
Two roadway paving projects were each divided into experimental sections installed with either 1) the standard DOT BMPs
consisting of narrow sediment traps and rock checks, 2) the new fiber wattle check dams (consisting of a mix of straw wattles and
coir logs) with 100 grams of granulated polyacrylamide (anionic PAM 705) added to each, or 3) the new wattle check dams alone
(no PAM added).
The results suggest a significant advantage to the use of the new BMPs. At the first site, from June 2006 to March 2007, the
average turbidity values (in NTUs) for the stormwater runoff for were 4,198 for the Standard BMPs, 30 for the Experimental
BMPs with PAM, and 187 for the Exp. BMPs alone. The second site showed similar results with average turbidity values of 64
for the Exp. BMPs with PAM, as compared to 852 for the Standard BMPs. Sediment loading at both sites was similarly skewed
with dramatic decreases in sediment discharged off site from the new BMPs. At the first site, the Standard BMPs lost an average
of 944 lbs (428 kg) of sediment per storm event as compared to just 1.93 lbs (0.88 kg) for the BMPs with PAM and 6.53 lbs (2.96
kg) for the Exp. BMPs alone. At the second site, the Standard BMPs lost an average of 8.84 lbs (3.63 kg) per storm event
compared with 1.67 lbs (0.76 kg) for the Exp. BMPs with PAM.
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