I keep getting a negative flow continuity error % when I compute my SewerGEMS model. But from previous questions answered on this forum, I understood that flow continuity % error is an absolute value. Does the negative value indicate there is a serious error in my model?
Cecily,
Have you addressed all the user notifications that you're getting? Especially the red and yellow ones?
Mark
Cecily, this article explains how the continuity error is calculated as a mass balance from the inflow, outflow, volume change and overflow. If the absolute value of the continuity error is less than ~5% that generally indicates a stable run but spot checking is still recommended. If the number is high, it indicates that you may need to review your notifications, input data and advanced calculation options to achieve a more stable run. This article has more guidance: Troubleshooting unstable SewerGEMS and CivilStorm results using the Implicit solver
Regards,
Jesse DringoliTechnical Support Manager, OpenFlowsBentley Communities Site AdministratorBentley Systems, Inc.
I have cleared all but two errors that are yellow errors.
1) Node known flows and additional flows ignored by solver
2) IDF data is not supported my SWMM solver. The IDF event was not exported.
My model utilizes the Explicit solver and after viewing the profile, the flow is contained within the system without inundating the pipes or catch basins.
As long as my flow is contained within the system and the catch basins aren't being inundated is it safe to assume that the negative flow continuity error % is acceptable?
Hello Cecily,
While the Implicit solver just looks at the absolute value of the continuity error, the explicit solver does display the continuity error as positive or negative. However, that the continuity error is negative instead of positive is less important than making sure the value is relatively small and that the overall results in the model are stable. This link has information on the continuity error in general: What is the continuity error and what is a good value for it?
If there are areas of concern, you can use the Hydraulic Reviewer to dig a little deeper into it.
Scott
I'll check out the Hydraulic Reviewer.
Thank you!