The Effect of Wastewater on the Non-Settling Velocity and Shear Stress of Cohesive Sediments

Sedimentation in open channels is one of the basic problems in the management of irrigationnetworks. Complexity of behavior of cohesive sediment transport makes determination of the criteriafor open channel design to be difficult. The purpose of this study is to determine non-settling velocityand non-settling shear stress for open channel flow containing wastewater and suspended cohesivesediment. Experiments were carried out in an annular flume located in the hydraulic laboratory ofShahrekord University, Iran. The sediment samples were taken from Pirbalut dam reservoir, locatedupstream of Northern Karun basin. The result showed that wastewater content in flow causes thesuspended sediment deposition and flocculation to be likely increased. It also caused the threshold ofnon-settling velocity to be increased at a rate of 10% compared to pure water. A similar result was alsoobtained for threshold of shear stress. The results obtained from this study were compared and theresults showed that the empirical methods were not capable in calculating non-settling velocity foropen channel flow containing waste water and suspended cohesive sediments. The results also showedthat the Froud number should be more than 0.47 for non-settling condition of suspended cohesivesediments.