Sewer Line Design Based on Critical Shear Stress

A design chart and a simple design procedure have been developed for applying the critical shear stress approach for the hydraulic design of self-cleaning circular sewers. Studies indicate that the possible region of deposition is limited to the lower relatively flat part of the sewer and the average boundary shear stress can be used safely as the basis of design for partially full flow. Suitable critical shear stresses for design uses are suggested. The conventional minimum velocity approach tends to either overdesign smaller sewers or underdesign larger sewers. A numerical example is included to illustrate the application of the chart and the procedure.