Discussion of “Design Considerations for High-Speed Flow in Sewer Systems”

The discussers are happy to see that sewer hydraulics merits a state-of-the-art review in the Journal of Hydraulic Engineering; the discussers thank the authors for their initiative. Troubling phenomena, such as air pulsation, abrasion, abrupt pressurization, and even geyser flow, may characterize the operation of sewer structures with fast flows. The authors proposed a summary of the design criteria to prevent the occurrence of such incidents. Structural solutions, including the realization of specific manholes as a drop structure, were also reviewed. Among other issues, flow choking should be avoided in sewer conduits and manholes because it can strongly reduce their discharge capacity. Choking more likely occurs for supercritical flows in manholes than across sewer conduits because geometric and hydraulic changes provoke flow surface singularities (shock waves).