Hello,
Just noticed that sum of two conduit flows do not match the flow in conduit after the connection of previous two.
As it is shown in the scheme of the model, there is two conduits with flow of 133,4 L/s and 51,09 L/s, that connects in the same manhole. If I sum those flows mathematically, I get flow of 184,49 L/s which is bigger than the flow after the connecting manhole, which is 176,11 L/s.
How to interpret this situation? Why the numbers do not match?
I am using GVF – Rational Calculation Solver. Runoff Method – Rational Method.
This is because of flow attenuation. The GVF-Rational Solver depends on system time for peak flows. It does not simply add the upstream flows to calculate peak flow but rather considers the decrease in peak intensity as the flow moves downstream. See the below article which explains this in detail;
Flow Attenuation - Why does flow or velocity sometimes decrease when moving downstream?
Hope this helps.
Regards,
Yashodhan Joshi
Answer Verified By: Jesse Dringoli
Thank you.