basic question re. sewer pipe sizing
basic question re. sewer pipe sizing
(OP)
Hey everyone,
I'm trying to determine the rule of thumb for sewer pipe sizing. I know that for water pipes, sizing is usually based on Max Day Demand (gal/day converted to gpm), which is double Average Day Demand (the average day over the year).
Are sewer pipes also sized for Max Day flow, or in other words, a peaking factor of 2 over the average day flow? Or are they sized based on Peak Hour flow, which is double Max Day flow, => max day x 2, => average day x 4?
I hope my question makes sense to someone reading it.
Thanks,
entp
I'm trying to determine the rule of thumb for sewer pipe sizing. I know that for water pipes, sizing is usually based on Max Day Demand (gal/day converted to gpm), which is double Average Day Demand (the average day over the year).
Are sewer pipes also sized for Max Day flow, or in other words, a peaking factor of 2 over the average day flow? Or are they sized based on Peak Hour flow, which is double Max Day flow, => max day x 2, => average day x 4?
I hope my question makes sense to someone reading it.
Thanks,
entp





RE: basic question re. sewer pipe sizing
RE: basic question re. sewer pipe sizing
In summary...check with your local regulations.
RE: basic question re. sewer pipe sizing
The devil is of course in the details. In this regard, there may be a sort of rule of thumb I’ve seen presented in the USA that might be helpful in some cases i.e. that roughly 70%-80% of a community’s domestic and industrial water supply returns as wastewater; however, it is obvious that much more water than this has gotten into many working sewer systems in the past (as a result of original “combined” storm and sanitary designs, all manner of infiltrations for various reasons and from whatever source/path including poor quality manhole and pipes/joints etc. into various parts of the systems, and even illegal connections etc.) that in general along with rainfall/flood events and other factors are probably some reasons for higher apparent per capita usage and/or high multiplicative “peaking factors” being used in some areas. The ASCE MOP previously mentioned also devotes quite a bit of copy to designing for “future” (e.g. 50 year or more) population and industry flow trends. I suspect, as also may be the case to some extent with hydrology, to do this right requires quite prescient judgment (or an accurate crystal ball!) if there are not to be future overflows/floods (in the case e.g. of near exponential development in many areas)!
RE: basic question re. sewer pipe sizing
The design process we go through in this region:
1. Determine the type of contributing flows (residential commercial, industrial, recreational, etc.) Sometimes there is a combination of any or all of the above.
2. Determine the average daily flow from these uses(should be given in design standards of the agency).
3. Apply a Peaking Factor (Qave x factor = peak flow) add this to Qave.
4. Determine I/I (Infitration & Inflow). Agency should have a factor for this too.
5. The sum of 2-4 above = Q design
6. Based on the design Q, use Manning's formula to determine pipe size and slope.
Generally speaking, pipes with a minimum velocity of 2 feet per second carry these flows:
6" pipe @ 0.0050 = 0.26 MGD
8" pipe @ 0.0033 = 0.45 MGD
10" pipe @ 0.0025 = 1.2 MGD
RE: basic question re. sewer pipe sizing
h
RE: basic question re. sewer pipe sizing
Teddy
RE: basic question re. sewer pipe sizing
Teddy
RE: basic question re. sewer pipe sizing
At population of 10,000, the ratio is 3.0
At population of 100,000, the ratio is 2.0
The chart is published in Water Supply and Wastewater Disposal by Fair and Geyer.
RE: basic question re. sewer pipe sizing
Teddy
RE: basic question re. sewer pipe sizing
Thank you all for the good information.
I do realize we have to check with the local agency before the design gets too detailed, was just looking for some planning ballpark estimates. Thanks also for the population based peak factors, and the references, those are very useful.
I have another question about wet well sizing, so I'll start another thread for that.
Thanks,
entp