Maximum allowable velocity in sewer for stormwater drainage
Published on by Yongseok Choi, Senior Manager at GS E&C in Technology
When we design sewer for storm water drainage, there will be a design standard as for the allowable maximum velocity in sewer in each country. For example, the one is 3.0 m/sec in South Korea.
However, when installing sewers for storm drainage in steep slope terrain, it often causes the increase of excavation volume due to gentle slope of sewer to meet 3 m/sec (allowable maximum velocity, design standard). And temporary soil retaining wall will be used according to the site situation.
Someone sent me "Urban Drainage 2nd Edition" and there is a statement for the following and Hong Kong design standard allows the maximum velocity up to 4.5 to 6.0m/sec if using abrasion resistant pipe or interanal lining is chosen.
Historically, many sewerage systems were designed so that velocity would
not exceed a specified maximum. This was no doubt a sensible criterion for
early brick sewers with relatively weak lime-mortar joints. However, research
has shown that abrasion is not normally a problem with modern pipe mater-
ials. Perkins (1977) has suggested that no fixed maximum limit is required,
but where velocities are high (>3 m/s) careful attention needs to be given to:
So I'd like to gather some information about the exceptional cases in other countries. It will be very appreciated you share your experiences or let me know exceptional design standards in your countries.
Thank you.
Best regards,
Yongseok CHOI
Taxonomy
- Hydraulics
- Sewer Networks
- Hydraulic Engineering
6 Answers
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Agreeing with Arturo Constante -- For developing countries viz India, even Pressurised system needs to have extra safety margin, as most times,
Systems are functioning with no power, hence be safe on flows.
At best it would be 0.5 m per sec, with 5% slope of flow pipe.. or have sunken trenches with extra HRT in pipes and system..
Well wishes.
Prof Ajit Seshadri. India .
1 Comment
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Dear Ajit Seshadri,
it's not for pressurized system but gravity sewer.
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@ YIANNIS Tzeranis , @ Alejandro Gomez
Could you send the design standard you mentioned to my e-mail?
My e-mail address is yscatfish96@gmail.com or yscatfish@hanmail.net
Many thanks to you in advance.
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If the velocity becomes unacceptably high, you can install drop structure to dissipate the energy. Here is a link that discusses how to model it. https://communities.bentley.com/products/hydraulics___hydrology/w/hydraulics_and_hydrology__wiki/13308/what-is-a-drop-manhole-and-how-do-i-model-one
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Hi, in Colombia, South América the National Code recommends a maximum velocity of 5 m/s unless you are using plastic pipes then you can use 10 m/s. Anycase, structures of the system must be protected for velocities over 4 m/s.
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I ever considered 3 m/s as pressure system; you can refer to pipe engineering or calculate directly from pipe specs sheet about permitted ft/s for the whole area
for non pressure sewage system is considered since 0.5 m/s with 3% to 5% length slop; the effective sewage area segment is the standard minimum chord; hope it helps
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Hi
In Greece is also max=6m/sec without any specification for pipes