rational flow in pipe is not match-SewerGEMS

Hello Hamid,

The reduced flow in the downstream conduit is due to flow attenuation. For example, if I reduce the length of conduit "CO-3" from 45.9m to 0.1m, then the flow in the downstream conduit "Pipe - (2) (STM)" is 200 L/s.

Please take a look at the following article.

Flow Attenuation - Why does flow or velocity sometimes decrease when moving downstream?

But, I have more than 100 pipes like this and client wants to see the correct number labeled there, I don't want to go throught the known flow as it is confusing for me. I want software calculate for me not enter manually.

please help me in this case.

The software appears to be calculating the flow correctly.

The flow at manhole "STM-MH5 (STM)" is calculated with the following method.

("System CA" at manhole "STM-MH5 (STM)") = ("Catchment CA" at catchment "CM-1") + ("Catchment CA" at catchment "CM-017")
System CA = 0.114 ha + 0.565 ha
System CA = 0.679 ha

The "Time of Concentration" for catchment "CM-2" is 10 min.
The "Time (Pipe Flow)" for conduit "CO-3" is about 2.51 min.
Therefore the "System Flow Time" at manhole "STM-MH5 (STM)" is 12.51 min (10 min + 2.51 min).

The intensity, corresponding to 12.51 min on the 5 year intensity-duration curve, is 94.1mm/h (labeled "System Intensity" in the manhole properties).

Q=(CIA)/360
Q= (0.679*94.1)/360
Q=0.177 cu.m/s = 177 L/s

This is also explained in the following help topics:
"System Time / Controlling Time / Duration"
"Flow Balance at Junctions"