Experimental Study of Wastewater Effect on the Critical Shear Stress in Cohesive Sediment Deposition

Due to adhesion properties of fine sediments، chemical physics factors of fluid can cause changes in the behavior of sediments. In this study، the characteristics of sediment deposition with three levels of waste water، different shear stresses and initial sediment concentrations were investigated in the annular flume located at Hydraulic Laboratory of Shahrekord University. Sediments for experiments were taken from the Pirbalut dam reservoir. The velocity and the shear stress profiles were measured using an Acoustic Doppler Velocimeter (ADV). The results showed that the concentration of cohesive sediment was decreased with time and finally it reached an equilibrium concentration of sediment. The equilibrium concentrations to initial concentration (Ceq/C0) in special shear stress، for different initial sediment concentrations and different levels of waste water were almost the same. Equilibrium concentration was dependent on the initial concentration sediment. Threshold and full deposition shear stresses were increased in waste water. Shear stresses of full deposition for 0، 30 and 60 % wastewater were 0. 053، 0. 075 and 0. 070 N/m2، respectively. Also، for specified levels of waste water، the values were obtained 10، 15 and 17، in which the suspended sediments would remain.