Sedimentation basin retention efficiencies for sediment, nitrogen, and phosphorus from simulated agricultural runoff

Simulated agricultural runoff, amended with sediment, nitrogen, and phosphorus, was passed through an experimental sedimentation basin. A series of six sequential runoff events was run through the basin for each of two treatments. The treatments consisted of one-day and three-day detention times, created using a perforated riser outlet structure. Effluent concentrations were monitored for total suspended sediment and various forms of nitrogen and phosphorus. For all runs, an average of 94% of the sediment, 76% of the nitrogen, and 52% of the phosphorus added to the inflow were retained by the basin. The three-day treatment retained significantly more sediment than the one-day treatment (p = 0.02). The majority of the sediment, nitrogen, and phosphorus was released within the first 12 h during the three-day runs and the first 4 h during the one-day runs.