Efficiency of Sediment Settling Basins

Abstract

Design of sediment settling basins requires evaluation of sediment removal efficiency over a range of sediment particle sizes. Past studies analysing sediment settling and basin efficiency has been limited to rectangular basins, assuming uniform conditions across the full width of the basin. In practice however, expansion and contraction of the flow in the basin inlet and outlet zones, respectively, means that this condition is not always met. A numerical model is presented that evaluates settling of sediment in a settling zone with variable width. This model was used to compare basin efficiency with and without taking into account the basin inlet and outlet zones. This comparison showed that, depending on the size of the sediment particles, there could be a significant reduction in basin performance of up to 35% due to the inlet and outlet zones. This result highlights the importance of ensuring that the inflow to and outflow from settling basins are evenly distributed across the full width of the basin.