SewerGEMS: Why I have zero overflow volume (Hydraulic Reviewer manhole table) in manholes that show "True" in the "Is ever overflowing" field? I'm using the explicit SWMM solver and I don't have bolted covers. Thank you very much.
Hello Ana,
Are you using any surface storage like ponded area for manholes? Is it a free outfall or tailwater elevation is defined?
In case of explicit solver overflow is determined by the total inflows minus the total outflows which is based on the enforced node elevation.
Do you see any flooding in SWMM calculation summary reports as below?
How do the dynamic solvers calculate overflow from a catchbasin or manhole?
If required you may upload model files for our review, Sharing model files.
Regards,
Sushma Choure
Bentley Technical Suppport
Hi Sushma,
We have "No storage" in the "Surface storage type" field for all of our manholes.
All the outfalls are "Free outfall" type
I see flooding in SWMM calculation summary report, but it is not equal to the overflow volume reported in the Hydraulic Reviewer:
The model is uploaded here: https://drive.google.com/file/d/11UH8ob_L3i-ZmMBSg7XsZd_y65QBi0DC/view?usp=sharing (I tried to upload it into the message but it showed some kind of error). The scenario I'm reviewing is Escenario11_Usuarios30_IDF2021_TR10_HuffLocal.
Thank you very much!
Ana Maria,
Try the following calculation options:
With this, the %non-convergence is 3%, the Flow Continuity Error is 0.4% and the overflow volume in the calculation summary matches pretty close to the sum of the overflow volume in the hydraulic reviewer. Also, I was only able to find a few manholes with "is ever overflowing?" set to True, without overflow showing in the overflow graph (8576963, 6066226, 6066059, 6060055, 6065070)
Jesse DringoliTechnical Support Manager, OpenFlowsBentley Communities Site AdministratorBentley Systems, Inc.
I was able to further improve the results by reducing the SWMM Output Increment to 0.1 minutes. With this, I was able to view positive values in the overflow graph for all elements with "is overflowing ever?" set to True.
I have updated this article based on the outcome of this conversation.
Hi Jesse. I tried the calculation options you proposed and the results are very good. The surcharge method "Slot" is the Preissman Slot? What is the difference between Preissman Slot method and Extran method?
Thank you very much!!!!! Very helpful advice!!!
The Preissmann slot method is used for simulating pressure or surcharged flows for gravity conduits, by adapting the conceptualization of pressurized flow to fit a free surface model. The slot extends vertically from pipe crown to infinity and over the entire length the pipe, and the width of the slot is usually 1% of the characteristic pipe dimension (diameter for a circular pipe) but not large than 0.02 ft. Read more about this in help documentation - search for "Pressure (Surcharged) Flow and Overflow (Street Flooding)".
EXTRAN is the original SWMM method to simulate pipes under pressurized conditions. When the nodes at both ends of a pipe have a water stage higher than the top of the pipe at that node, EXTRAN switches to equations for pressurized pipe flows.
Also you can read more about the comparison in this below discussion on SWMM forum.
Surchage method.
Thank you very much for the explanation, Sushma!!
We have added this information in the form of wiki which can be beneficial for other users in future.
What is difference between surcharge methods - Preissmann slot method and Extran method?