Settling basins, sediment removal efficiency and applications in Turkey

In recent decades, pressurized pipe irrigation networks have been started to be used in Turkey instead of widely applied open channel networks as done all over the world. In order to switch to high pressurized pipe irrigation networks, it is economical to use existing open channel irrigation networks and therefore necessary to lower the amount of sediment transported with the flow in open channel networks down to the limits required by pipe networks. It is hence necessary to determine and re-evaluate the sediment removal efficiencies of present settling basins. In the frame of this study, several formulas in literature developed for the estimation of sediment removal efficiency of settling basins were reviewed, field measurements and laboratory analysis of collected field data were carried out for two settling basins in Turkey and their sediment removal efficiencies were estimated. Those measured and computed values for sediment removal efficiencies of these two basins were compared. It is found that the sediment removal efficiencies showed large discrepancies from those obtained from field data. The reason for these large discrepancies can be explained by heterogeneous and very fine sediment load, flow still being turbulent, non-uniformity of flow, sediment deposition during operation affecting parameters such as flow depth, velocity profile and magnitude etc., cross-sectional differences from experimental flume and ratio of settling basin to flow depth.Key Words : Settling basin, settling velocity, sediment deposition, removal efficiency