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I'm working with SewerGEMS for the first time ever and am having an issue with the EGL dropping upstream (or jumping downstream) at a manhole structure. Can anyone explain this? For reference there is a large basin discharging roughly 80 cfs into this same manhole at this period in time. I would appreciate any help.
Can you clarify where in the screenshot you are referring to? Which numerical solver are you using? (Implicit, Explicit, GVF-Rational or GVF-Convex)
If the element between stations ~250 ft and ~750 ft is a pond, the velocity in a pond is zero hence the velocity head is zero.
Energy grade discontinuity can be seen with the GVF-Rational solver as mentioned in this article but I do not think this is what you're referring to.
If you're referring to the element at around station 1300 ft, check the velocity result fields in that element and the adjacent conduits.
If this does not help, please send a copy of the model for review: Sharing Hydraulic Model Files on the OpenFlows Forum
Jesse DringoliTechnical Support Manager, OpenFlows ProductsBentley Communities Site AdministratorBentley Systems, Inc.
Thanks for the quick response. I meant to include more detail in my post but had to rush out of the office. My model is using the Implicit numerical solver, it was the default when I created a new model so I left it. I was indeed referring to the element around station 1300 ft. I compared velocity in and velocity out at the peak time step and it shows 19.5 ft/s in and 22.3 ft/s out. I'm not convinced my model is functioning the way it should be so I will send in a copy for review.
Kevin Desjardins said:When you say you modeled it with a "timestep of 0.025 hours" are you referring to the Routing Time Step or the SWMM Ouput Increment? They are currently set at 5.0 sec and 0.250 hours, respectively.
I had set the SWMM Output increment to 0.025 hours in my testing.
Thanks Jesse. Can you provide any insight into the different routing methods available within the Explicit numerical solver? There is Dynamic Wave, Kinematic Wave, and Uniform Flow. I want to be sure the model is taking into account the backwater effects from downstream.
Hi Kevin, our Wiki is a good resource to search through for information like this. Here is an article that should clear this up:
What is the difference between the kinematic wave option and the dynamic wave option in the SWMM solver?
Thanks Jesse, that cleared things up. Looks like the dynamic wave option is the one we want.
Thanks again for all your help, we are much more confident with our model outputs than we were before. I will let you know if I have any other questions.
Glad to help - good luck with your project!