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Effect of Pipe Sags on Wastewater Collection System Performance
Author(s) -
Sever V. Firat,
Foust Henry
Publication year - 2011
Publication title -
water environment research
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.356
H-Index - 73
eISSN - 1554-7531
pISSN - 1061-4303
DOI - 10.2175/106143010x12780288628778
Subject(s) - wastewater , flow velocity , flow (mathematics) , volumetric flow rate , pipeline transport , pipe flow , environmental science , nominal pipe size , flow conditions , engineering , geotechnical engineering , environmental engineering , mechanics , materials science , meteorology , geography , turbulence , physics , composite material
Sagging of pipelines is a common problem in centralized wastewater collection systems. Wastewater flowing through sags experiences several changes of slope, and the flow through flat and negative slope sections is prone to a significant reduction in mean velocity. The objective of this study is to determine when pipe sags would result in significant velocities below design conditions, which also would increase the risk of a sewer backup. A sagged pipe configuration that could be encountered in sanitary sewer systems was depicted; thereby, analyses on uniform and gradually varied flows were conducted to determine velocity profiles through different segments of the sagged pipeline setup used for the study. The results indicate that there are significant occurrences when either the velocity in the pipe sags goes below minimum, as recommended in the Ten States Standards (Health Research, Inc., 2004) (0.61 m/s [2.0 ft/sec]), or flow depth rises to pipe diameter (full section flow). Additionally, velocities along a sagged pipe were calculated for temporal flow rates to account for daily and seasonal flow rate changes in a typical wastewater collection system. Results of the temporal flow rate analysis suggest that, for a 200‐mm (8‐in.) diameter sagged pipe segment with full‐section (wet weather) flow, 75% of the mean velocities would be below the minimum velocity recommended as a Ten States Standard.