Measurements of critical shear stress in sewers

Critical shear stress of sediment located in a grit chamber and in a sewer was determined in full-scale by a measuring device constructed in the laboratory of the Institute of Hydrosciences at the Federal Armed Forces University, Munich. The estimation of critical shear stress is actually based on the measurement of the corresponding critical water discharge. Incipient motion was recorded by a video camera and the recorded pictures were treated by an automatic image processing system. The measurement results were compared with data taken from the literature. A good agreement between measurements and literature data was obtained. The automatic image processing contributes to a more objective quantification of the sediment transport initiation.