ASABE Technical Library - Abstract

Abstract. Accelerated erosion and highly turbid stormwater runoff from construction sites are known to result in measurable environmental and economic impacts. In order to reduce turbidity and trap eroded sediment on site, research was conducted to evaluate ditch checks commonly used as sediment control best management practices (BMPs) on highway construction sites. Two active sites were chosen in South Carolina to represent clay subsoils commonly found in the Piedmont and sandy soils typical of the coastal plains.

Instrumentation was deployed at the inflow and outflow of runoff conveyance channels to measure the change to turbidity as runoff flowed through or over a series of check structures. Three ditch check configurations commonly used in linear construction (rip-rap, rap-rap with washed stone face, and excelsior wood wattles) were evaluated. Peak turbidity in addition to time and flow weighted means were calculated at each site for each event.

For the Piedmont site (Site A), rock ditch checks alone showed an increase in mean turbidity between inflow and outflow of channel by 282% to 497%. Final discharge turbidity values between 1635 to 3242 FNRU were observed. Rock ditch checks with washed stone showed an increase in average turbidity of 10% to 43%. Peak turbidity varied with average final peak turbidities ranging between 1163 to 2473 FNRU. For the coastal site (Site B), excelsior wood wattles showed a decrease in turbidity between inflow and outflow of channel by 43% to 73%. Peak turbidity between inflow and outflow decreased by 9.5% to 29% with peak downstream turbidity values between 713 to 1275 FNRU. Rock ditch checks with washed stone showed a decrease in mean turbidity between inflow and outflow of the channel by 39% to 98%, excluding one storm which did not result in a statistically significant change in turbidity. RDC-WS had average final discharge turbidities between 33 to 917 FNRU. Peak turbidity varied with final peak discharge turbidities ranging between 213 to 1591 FNRU. A variety of storm sizes, durations, and intensities were observed during these tests. The wide ranges in observed turbidities were attributed to storm variability and resulting runoff flow characteristics.