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How to calculate flow in a pipe from water level masurements

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Hello,

I need to calculate flow in a pipe from water level masurements taking in the upstream and downstream manhole. It is important that especially single loss of energy in both inlet and outlet of the manhole is taking into account.

Some of the manholes have sewer overflows and thereby an edge, which should make single loss zero, but not all of them.

I first tried with the asumption that the pipe had full pipe flow with:
eq1_rw4qcn.png


But that assumption was not accurate. Moreover the equation did not take into account the energiloss.

Then I tried using the following equation:
eq2_uqlujr.png


This is not really correct either eventhough it is closer. But I do not know how to make a better estimation of the flow between two manholee whith the waterlevel measurements.

Edited: Now with pictures of the equations instead of equation code.
 
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Have you got a sectional drawing with levels?

How far apart are the manholes?

Is this open channel flow? That code you've listed makes no sense to me as I can't follow it. Open channel flow is very well understood so you should have no issue finding a good equation to use.

Also this forum is normally for high pressure hydraulics.

You would get better response in the water treatment and distribution forum...

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.
 
Hello,

Thanks for your response, and your guidance, as this is my first time on the site.

I have placed about 50 measurement point in my sewer system, so the specific information will vary. The points are either placed: (1) in a manhole that recives combined wastewater, and let it out to a combined pipe. (2) in a manhole, that recives combined wastewater and if the water level reaches the overflow edge, lets it out into the rainwater pipe. (3) in a manhole, that somtimes recives combined wastewater but otherwise just handle rainwater.

But to use a simpel example:
Sectional_drawing_with_levels_xe9kvw.png


In regards to the open channel flow, I do not know which assumption is best, as I want to use my flowrates to validate my hydraulic model. There are (almost) always water in my pipes, so open channel makes sense, but when it rains, there is a chance that the pipe will be full flowing. That of cource depends on the rainfall and the diameter of the pipe. So I do not know which assumption makes the most sense open channel or full flowing or if I need to combine the two. I have attached the "best" try I got in calculating a flow - but I do not think it is very realistic. It can also not handle if the downstream water level becomes higher than the opstream water level, but that could happen in real life, so I also need to take that into account somehow.
 
OP,
I agree with Littleinch that you will likely receive a better answer in a civil forum. When I say "better", I mean civil formulas are typically better refined for use case such as yours. From just a fluid dynamic aspect, I am going to do a mass and energy balance of the system, i.e. put a box around it. When I do that, I can make the statement if D1 and D2 are steady state then Qin=Qout. If this is true, then I can apply the Manning formula to determine velocity and flow with the hydraulic head determined from D1 and D2 plus the known basin elevations. I think the attached is what you are looking for, with sheet 1 giving full pipe flow and sheet 2 partial full pipe.

Disclaimer This is how I would do it after spending 15 minutes looking at this. I would run this by a civil/environmental to confirm your approach before proceeding too far.
 
 https://files.engineering.com/getfile.aspx?folder=447e18dd-8aa6-41c8-87bc-3ce93a3ae0bb&file=pipe-flow-depth-and-velocity.xls
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