Pipe sizing
Pipe sizing
(OP)
Hello all,
I am designing a sediment basin with a required detention time of 15 hours. I developed my hydrograph and determined the volume and required discharge. I need to know how to calculate the maximum discharge from a pipe of given diameter. The basin is designed to be 3.5 feet deep with the outlet pipe 6 inches of the floor. Consequently, the pipe could have a head pressure of 3 feet. Any help is greatly appreciated.
Scott
I am designing a sediment basin with a required detention time of 15 hours. I developed my hydrograph and determined the volume and required discharge. I need to know how to calculate the maximum discharge from a pipe of given diameter. The basin is designed to be 3.5 feet deep with the outlet pipe 6 inches of the floor. Consequently, the pipe could have a head pressure of 3 feet. Any help is greatly appreciated.
Scott





RE: Pipe sizing
Here is a link to FHWA's website:
http://www.fhwa.dot.gov/bridge/hydpub.htm
if you follow the software link to on that page you can dl HY8.
RE: Pipe sizing
(Ok if the pipe is very short, like only the width of a 8" wide concrete block retaining wall). The orifice equation is Q = 0.6*Ao*H^.5, where Ao = pi*.25^2 and H = (3.5-.25) so Q = 0.2 CFS. Of course, if the pipe end is projecting on the inside, the flow will be reduced, and if the inside pipe end has a nice bell, the flow will be increased. The analysis assumed a flat, sharp end. (The constant will change with your units.)
Best of Luck.....
Clifford H Laubstein
FL PE 58662
RE: Pipe sizing
Q=A*sqrt(2gH/1+Ke+KpL)
Where
Q = Flow Rate
g = Acceleration due to graviity 32.2 ft/sec
H = Head on the pipe
Ke = Entrance Loss Coefficient
Kp = Pipe Loss Coefficient
L = Length of Pipe
Ke = 1
Kp= 5087*n^2/d^(4/3)
Where
n = Mannings "n" for selected pipe
d = diameter of pipe
Is this even close to what I need?
Any help is greatly appreciated.
Scott
RE: Pipe sizing
Hello,
That seems to be what you need indeed, with A=section of your outlet pipe and H= 3.5feet minus 6inches minus pipe's diameter.
the constants may be different from what I know (working with meters).
Junction headloss: Ke#1/m2 with m flow coefficent gibfrog was talking about, m equals 0.6 for a standard sharp junction: Ke=1 is for a smoothed junction.
Linear headloss: Kp can be evaluated using colebrook formula (wich needs iterating) or an analog formula.
I hope this answers to you question...
David
RE: Pipe sizing