Calculate Minimum Sewer Slope
Calculate Minimum Sewer Slope
(OP)
Hello All,
I am trying to develop a spread sheet that will help calculate the minimum slope for sewer pipes. I would like to be able to go in either direction with my calculations but am not sure of what version of Manning's equation to use to solve for the following.
1. Calculate the minimum pipe slope given flow rate (cfs) and velocity (ft/s).
2. Calculate velocity given flow rate (cfs) and slope (ft/ft).
Any help is appreciated.
I am trying to develop a spread sheet that will help calculate the minimum slope for sewer pipes. I would like to be able to go in either direction with my calculations but am not sure of what version of Manning's equation to use to solve for the following.
1. Calculate the minimum pipe slope given flow rate (cfs) and velocity (ft/s).
2. Calculate velocity given flow rate (cfs) and slope (ft/ft).
Any help is appreciated.





RE: Calculate Minimum Sewer Slope
RE: Calculate Minimum Sewer Slope
RE: Calculate Minimum Sewer Slope
8in - 0.40
10in - 0.28
12in - 0.22
14in - 0.17
15in - 0.15
16in - 0.14
18in - 0.12
21in - 0.10
24in - 0.08
27in - 0.067
30in - 0.058
33in - 0.052
36in - 0.046
39in - 0.041
42in - 0.037
RE: Calculate Minimum Sewer Slope
RE: Calculate Minimum Sewer Slope
Richard A. Cornelius, P.E.
WWW.amlinereast.com
RE: Calculate Minimum Sewer Slope
The Manning equation:
Q = (0.463/n) * D^8/3 *S^1/2 (US customary units)
Q= cubic feet/second
D = pipe diameter in feet
S = slope of energy grade line (ft/ft)
n= coefficient of roughness
See McGraw Hill Series Wastewater Engineering Collection and Pumping of Wastewater
RE: Calculate Minimum Sewer Slope
It kind of takes some of the engineering out of the work but the regulators like to regulate.
RE: Calculate Minimum Sewer Slope
"Generally, Manning's n for a given sewer, after some time in service, will approach a constant which is not a function of the pipe material but represents the grit accumulation and slime build -up on the pipe walls. This n
will be on the order of 0.013. A coefficient which will yield higher friction losses should be selected for sewers where disturbing influences are known or anticipated. Because of the empirical nature of each formula, conservative design is prudent."
While many contemporary piping materials and linings etc. including pvc have exhibited in clean water flow coefficients very close to the smooth pipe curves, beyond this pvc and pipe thereof is also known to be a rather "oleophilic" material in some long-term service (see e.g. page 63 of the document at http://ww
RE: Calculate Minimum Sewer Slope
Q = V A
V = (1.46/n) H<2/3 x S<1/2
RE: Calculate Minimum Sewer Slope
V = (0.590/n) * D^2/3 *S^1/2 (US customary units)