Sediment pollution from construction sites has been of increasing concern since the impacts on nearby streams can be severe. Controlling erosion is the most effective approach to reducing sediment loads, but construction sites typically have large areas of exposed soil during the active phase of clearing and grading. As a result, sediment traps and basins are required to capture eroded sediment on most of these sites. The purpose of this research was to determine the trapping efficiencies of sediment basins of various designs installed on active construction sites. One trap and one basin were monitored in the Piedmont of North Carolina located on a highway construction site in Johnston County. Automatic samplers were installed to measure flow and to obtain representative samples during storm events. The basins were surveyed after storms to determine the change in volume after repeated surveys. Trapping efficiency was calculated from the sediment accumulation within the trap and basin and the amount of sediment discharged, the sum of which was the total sediment entering the device. The standard trap (sized for a 10-year storm event) with a rock outlet was found to have 35% trapping efficiency while the basin (which was sized for a 25-year storm, including coir baffles, a skimmer outlet, and 2:1 sloping walls established with vegetation) had an overall 99% efficiency. This suggests that the less efficient design of the rock outlet is releasing more coarse materials which are likely to settle in nearby streams and ponds. While these sites were highly variable and constantly changing, the data indicates that sediment capture rates can be >90% through sizing and design changes.
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