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