Purging and Flooding of Pipeline Sewage Outfalls
Publication: Journal of Hydraulic Engineering
Volume 123, Issue 1
Abstract
The effluent discharge from most ocean outfalls is periodic while some others discharge only intermittently. When the rate of discharge falls below a critical level, seawater commences to flow into the deeper end of the diffuser forming a salt water wedge in the bottom of the diffuser section of the outfall. The paper examines two aspects of this phenomenon: the purging of seawater from a simple multiport pipeline outfall at start-up or after partial intrusion of seawater, and the flooding of the outfall following cessation of effluent discharge. Mathematical models are developed that describe each of these processes. It is shown that a certain minimum discharge is required before all ports on a sloping diffuser will be utilized. The flooding of a pipeline is described in terms of the volume fraction of the diffuser section that is flooded and a normalized time parameter. Two programs of hydraulic model testing provided verification for the mathematical models of the flooding and purging processes.
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References
1.
Brooks, N. H.(1988). “Seawater intrusion and purging in tunnelled outfalls: a case of multiple flow states.”Schweizer Ingenieur und Architekt, 6(2), 156–160.
2.
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3.
Munro, D. (1981). “Seawater exclusion from tunnelled outfalls discharging sewage.”Rep. 7-M, Water Resour. Ctr., Stevenage Laboratory, Stevenage, U.K.
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Sharp, J. J., and Wang, C.(1974). “Arrested wedge in a circular tube.”J. Hydr. Div., ASCE, 99(7), 1085–1088.
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Wilkinson, D. L.(1988). “Avoidance of seawater intrusion into ports of ocean outfalls.”J. Hydr. Engrg., ASCE, 114(2), 218–228.
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Copyright © 1997 American Society of Civil Engineers.
History
Published online: Jan 1, 1997
Published in print: Jan 1997
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