Hi,
I'm trying to calibrate an existing Waste water collection network which is a combination of several conduits, manholes, pumping stations with wet wells, pumps and pressure pipes. etc., and had following concerns.
1. While running the analysis and computing the model, the results showed up with a continuity error of 9.2 (which is >5% and considered abnormal as per several power users of SewerGEMS as i observed from queries on Bentley communities). A few support sections suggested removing complex attributes from the model which is making the mass balance cumbersome during computation but I would like to save it as my last action.
I'd like to know if there any alternate methods to minimize it, and i'm happy to share the model file if needed.
2. The 'Total system overflow volume' in computation summary doesn't match the sum of 'Overflow volume' that I got through Hydraulic review on several nodes where overflow is experienced.
3. All the manholes & wet wells experiencing overflows are just downstream of any pumping arrangement within the model. Is removing the pumping arrangements and adding the resulting flow as inflow on these manholes the only solution i'm left with? suggest alternate solutions if any.
Hello Jasti,
The continuity error is the a measure of the difference of what is coming into the system versus what is coming out of it. We usually recommend getting as low of a value as possible.
The first step we usually recommend is making sure the setup of the model is correct. Look at any user notifications after validating or computing the model. With the Implicit solver, things like very short pipes or large slopes can sometimes have an impact on the stability. It is possible that simplifying complex situations can also stabilize the results without having a large impact on the results, as you mention above.
I would suggest taking a look at this wiki: Troubleshooting unstable SewerGEMS and CivilStorm results using the Implicit solver. This includes some of the troubleshooting steps mentioned above, but also has some adjustments to the calculation options that may help with the overall results. Another option could be to use the Explicit solver. This link has information on the different solvers available in SewerGEMS.
Regards,
Scott