EFFECTIVENESS OF SEDIMENTATION BASINS THAT DO NOT TOTALLY IMPOUND A RUNOFF EVENT

Abstract

Twelve simulated 35–mm, 2–yr, 24–hr runoff events from a denuded 0.4–ha construction site in Pennsylvania were introduced into a 51–m 3 sedimentation basin. Each event consisted of a 100–m 3 inflow hydrograph that contained a sedigraph with 454 kg of soil. The basin’s sediment–capture ability was evaluated during four sediment removal/dewatering control treatments, each designed to dewater the basin in 24 hrs. Additionally, these small–basin sediment capture results were compared to those obtained from a 142–m 3 large basin previously charged with identical hydrographs and sedigraphs. The perforated riser treatment in the small basin discharged 37.5 kg of the injected 454 kg of soil through the combined principal and emergency spillways, in comparison to 31.8 kg discharged from the large basin, where only the principal spillway was used. The skimmer treatment in the small basin discharged 26.4 kg of the injected 454 kg of soil through the combined principal and emergency spillways, in comparison to 15.0 kg discharged from the large basin. On average, the small basin discharged 150% more sediment than the large basin. The addition of trenched–in geotextile barriers oriented perpendicular to the primary flow direction in the basin did not cause a significant improvement in the capture efficiency of either basin or for either of the principal spillway configurations.