EXPERIMENTAL EVALUATION OF SEDIMENTATION BASIN PERFORMANCE FOR ALTERNATIVE DEWATERING SYSTEMS

The effectiveness of four sediment removal/water control treatments, e ach designed to dewater the 155-m(3) sedimentation basin in 24 h, was evaluated using 100-m(3) inflow hydrographs (35-mm, 2-yr runoff events ) from a 0.4-ha denuded construction site containing 454 kg of sedimen t. The treatments were a perforated riser alone that discharged 26.1 k g of sediment and had an overall sediment retention efficiency of 94.3 %; two internal barriers designed to trisect the basin's volume with a perforated riser significantly reduced the sediment loss below that o f the perforated riser alone to 20.4 kg; a skimmer alone discharged th e least total sediment at only 14.3 kg; and trisecting the basin with barriers, with the skimmer did not improve the capture efficiency of t he basin over that of the skimmer alone. All treatments removed 100% o f soil particles and aggregates larger than 75 mu m. Th basin sediment was completely mixed during the entire inflow/dewatering event and th e effluent particle size distribution was the same as that observed fo r the influent sediment smaller than 75 mu m. Particle sizes retained between 0.1 and 75 mu m ranged from 77 to 100% with the poorest retent ion in the 6 to 12 mu m range.