Experimental Evaluation of Novel Floating Risers for Sedimentation Basin Dewatering

Abstract

The effectiveness of two novel sediment removal/water control treatments, each designed to dewater a 155-m3 sedimentation basin in 24 h, was evaluated using 100-m3 inflow hydrographs (35-mm, 2-yr runoff events) which simulated runoff from a 0.4-ha denuded construction site containing 454 kg of sediment. The novel sediment removal/water control treatments used were modification of the floating riser, or Faircloth skimmer designed to minimize the outflow from the basin during the inflow event. The first device, called the Skimmer-Chute-Tube, was a skimmer with an elongated arm and a tube perpendicular to the arm, which alternated flow, discharged 15.7 kg of sediment and had an overall sediment retention efficiency of 96.5 %. The second device, called the Skimmer-Chute, was a skimmer with an elongated, parallel, second arm which permitted flow at low water depths, discharged 15.6 kg of sediment and had an overall sediment retention efficiency of 96.6 %. The two novel designs produced unique outflow characteristics, but the specific devices evaluated were not able to retain more sediment than the unmodified Faircloth skimmer (14.7 kg, 96.8% efficiency). It was concluded that, because all of the devices were of the skimmer type, any modification that increases the cumulative outflow during the initial outflow period, as the modified devices had, would not yield increases in sediment retention.