Hello,
I have a plot which is divided into sub areas, 10 to be specific, with individual outfalls. All outfalls are "Free Outfall". Each sub area is a gravity drained system served by catch basins and underground piping connecting to the respective outfall. All catch basins are subject to same rainfall intensity, ie. same time of concentration and same runoff coefficient. I am running this in GVF environment.
after running the model i noticed that in some, 5 to be precise, of the outfalls, the product of "System CA" and "System Intensity" matches "Flow (Total Out)" but in other cases it does not. It can vary almost by 100%.
I looked at a previous forum answer on flow balance at junctions in GVF, which does not seem to explain this situation because why would some outfalls, the product would match and not on the others. Secondly, the Tc at the outfall and the individual catchment areas is within a few percentage point, so intuitively the discharge rates should be similar.
what could explain this difference?
thanks
KP
Hello Kanwarpreet,
Can we have a look at the model files to understand this better? See the below link for details;
Sharing Hydraulic Model Files on the OpenFlows | Hydraulics & Hydrology Forum
One thing to consider here would be the conduit travel time. If you have currently set "Include Conduit Flow Travel Time in Design" to "True" it might be that the reported System CA values would be different. Check if the values are changing and as per your requirements when you set this to "False". See the below article which explains this in detail;
Reported system CA at the outfall element is not correct
Another article which can help you to understand how System CA is calculated;
In StormCAD (GVF-Rational Solver), how is the conduit property "System CA" computed?
Let me know if this helps.
Regards,
Yashodhan Joshi
Yashodhan,
just sent the files to you. i may have ended up sending them twice, as i did not see any message confirming the delivery. Please let me know if you have not received the files.
i checked and found that the "Include Conduit Flow Travel Time in Design" was set to False.
Also, it appears i have figured what it is doing but i am still unsure of why it is doing. I found that if an outfall has multiple conduits coming to it, the quantity "Flow (Total Out)" reports only the highest.
any help you can provide in answering as to why it is doing this would be helpful.
Thanks for sending the model. This was a known issue in the older version that you're using (10.00.00.45). It was first reported in 2016 in this thread, and fixed in 2018. The latest available version (10.02.02.04) does not have this problem, and the Flow (Total Out) for outfalls with multiple incoming pipes is reported correctly (for example 3.03 CFS for outfall O-LS4 in your model.)
Please see the following article from our Wiki for information on upgrading: Downloading OpenFlows Software
Jesse DringoliTechnical Support Manager, OpenFlowsBentley Communities Site AdministratorBentley Systems, Inc.