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.
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?
Regards,
Sushma Choure
Bentley Technical Suppport
Thank you very much for the explanation, Sushma!!
Hello Ana,
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.
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!!!
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.
Jesse DringoliTechnical Support Manager, OpenFlowsBentley Communities Site AdministratorBentley Systems, Inc.