Slope Equation for Self Cleaning Sewage Pipes

Question

Slope Equation for Self Cleaning Sewage Pipes

MatthewMansfield (Civil/Environmental)

(OP)

4 Jul 21 22:51

Hello all

I was wondering if someone could help shed some light on an equation I found regarding obtaining the slope of sewage pipes in the following paper:-

The equation that is quoted to obtain the slope (equation 13) is given as:-

S = 4.65 * N^2 * D^(-4/3) * (q/Q)^(-1/2) * v^2

I was wondering if anyone could figure out what the variables q and Q referred to as these variables are not defined in the paper.

I think Q = Flow Rate but no idea what q refers to.

Can anyone help?

Thank you.

3DDave (Aerospace) · Answer 1 · 2021-07-05 00:18:22

Q is given as the full flowing rate in equation 8. q/Q is the ratio between the flow rate and the full flow rate.

bimr (Civil/Environmental) · Answer 2 · 2021-07-06 18:34:59

This is the standard that most agencies use. Set the fluid velocity at 2 ft/sec and come up with a slope. Attached is a chart from Illinois with the same numbers.

https://files.engineering.com/getfile.aspx?folder=ea17606f-705d-4ef3-8b4c-e

GeoEnvGuy (Geotechnical) · Answer 3 · 2021-07-07 15:54:57

Self cleaning slopes are determined by the velocity required to clean off any accumulated solids which varies based on the intended build up. When the trend to low flow took of this really screwed up the systems and we now require more sewage line flushings. Below is the Ontario Canada guide. These are jurisdiction specific so you would want to know what local code applies.

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Slope Equation for Self Cleaning Sewage Pipes