Design Considerations for High-Speed Flow in Sewer Systems | Journal of Hydraulic Engineering | Vol 148, No 9

AbstractWith the development of urban areas, many municipalities are facing issues where the flow velocity in their sewer systems is relatively high at various locations. This is because of either geographical or local hydraulic conditions. Existing design guidelines generally include a velocity limit of 3  m/s. However, the rationale for this limit is not presented in these guidelines. This study explores the feasibility of higher allowable sewer velocities on municipal infrastructure. Potential issues that may be considered when increasing the velocity to a higher value of 6  m/s or even around 10  m/s are discussed, including capacity, air demand, and transient flow. Considerations as to system protection are then reviewed including the forces exerted on structures, cavitation, and presence of sediments. Design alternatives are also discussed including drop shafts and energy dissipators. Increasing the existing maximum allowable velocity of 3  m/s to a higher value may result in a decrease in pipe diameter and depth of cover, which would yield financial savings. A value for the maximum allowable velocity in sewer system design is not proposed in this paper given the complicated hydraulic features of high-speed flow and the significant gaps between research and actual engineering requirements.



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