SEDIMENT AND HEAVY-METAL ACCUMULATION IN DRY STORM WATER DETENTION BASIN

Amount, heavy metal content, organic content, and mass distribution of the bottom sediment in an 18 year old, single-purpose dry storm water detention basin were measured. The measured results were used to asse ss the effect of sedimentation on flood control capacity and the appli cability of recommended values for predicting amounts of sediment and heavy metal accumulation. The rate of sediment accumulation was measur ed to be 0.8 cm per year. Because of sedimentation, the flood control capacity of the basin was estimated to have decreased from that for th e 13-year storm to that for the 4-year storm. Both the soil erosion ra te and the suspended solid concentration recommended for predicting th e amount of sediment accumulation appear to be applicable for this bas in. However, recommended metal trap efficiencies, recommended concentr ations of heavy metals in runoff, or both appear to be too high for pr edicting the amount of heavy metal accumulation in this basin.