In this study, the characteristics of sediment deposition with three levels of wastewater, different shear stress and initial sediment concentration were investigated in an annular flume. Sediment used for experiments was taken from Pirbalut dam reservoir, in south west of Iran. The velocity and the shear stress profiles were measured, using an Acoustic Doppler Velocimeter (ADV). The results showed that the concentration of cohesive sediment decreased as time passed and finally it reached an equilibrium concentration of sediment. The ratio of equilibrium concentration to initial concentration (Ceq/C) with a constant shear stress, for different initial sediment concentrations and different levels of wastewater were almost the same. The equilibrium concentration depends on the initial concentration sediment. Adding wastewater to the mixture causes the increase of threshold and full deposition shear stress. The critical shear stresses for full deposition for three wastewater levels of 0, 30% and 60% are obtained as 0.050, 0.081, and 0.084 N/m2, respectively.

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