calculating flow capacity in a stormwater downpipe
calculating flow capacity in a stormwater downpipe
(OP)
Hello all,
I have been tasked with designing a stormwater drainage plan for a single residential home. I am hoping you guys can help me figure out the flow capacity of different downpipe diameters. It has been a long time since I have done Fluid Mechanics in school.
Now I realize this problem will vary with change in pressure, storm intensity etc... I am hoping I can find something reasonably simple (rule of thumb) to find a flowrate at maximum capacity.
There is a local supplier who has rectangular downpipes at 100 x 75mm and claims these have a flow capacity of 4.4L/s. I could base my number of downpipes on this value, but I would like to see if I can use a few less (bigger) downpipes to please the architect as the lot is quite big (1200m2).
Thanks for your help!
I have been tasked with designing a stormwater drainage plan for a single residential home. I am hoping you guys can help me figure out the flow capacity of different downpipe diameters. It has been a long time since I have done Fluid Mechanics in school.
Now I realize this problem will vary with change in pressure, storm intensity etc... I am hoping I can find something reasonably simple (rule of thumb) to find a flowrate at maximum capacity.
There is a local supplier who has rectangular downpipes at 100 x 75mm and claims these have a flow capacity of 4.4L/s. I could base my number of downpipes on this value, but I would like to see if I can use a few less (bigger) downpipes to please the architect as the lot is quite big (1200m2).
Thanks for your help!





RE: calculating flow capacity in a stormwater downpipe
You'll want to model like a horizontal orifice, to ensure your desired head doesn't exceed the gutter or parapet depending on roof type.
RE: calculating flow capacity in a stormwater downpipe
Do you have a model I could follow to calculate flow capacity based on the pipe diameter?
RE: calculating flow capacity in a stormwater downpipe
Hydrology, Drainage Analysis, Flood Studies, and Complex Stormwater Litigation for Atlanta and the South East - http://www.campbellcivil.com
RE: calculating flow capacity in a stormwater downpipe
Unless the gutter is fairly deep or the downspout is quite small, I doubt you would ever get orifice flow conditions. I would use the weir equation with a sizable factor of safety to account for clogging and for air slug flow to determine the capacity of a downspout.
A couple of references for slug flow:
https://dspace.mit.edu/bitstream/handle/1721.1/614...
http://www.thermopedia.com/content/38/?tid=104&...
RE: calculating flow capacity in a stormwater downpipe
Richard A. Cornelius, P.E.
WWW.amlinereast.com