Why am I getting random spikes in flow?

Sometimes when I run my model in SewerGEMS, I will get large spikes of flow that seemingly come out of nowhere. This spike is not in the upstream pipe, and it attenuates slowly downstream. The spikes are usually near the outskirts of the model where flows are lower and there are some steeper pipes. Sometimes when I run the model the spikes will go away, without changing anything. My model has a less than 1% continuity error. These spikes are negatively affecting my model calibration. Any advice on how to make them to go away? 

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  • Just an update on this. The Explicit solver appears to have more stable results, though the continuity error is higher. Try using the Explicit solver with a Routing Time Step of 1 second and an output increment of 0.1 hours to see if the results appear more stable. I also tried setting the Surcharge Method to "Slot." This lowered the "Not Converging" percentage, but increased the continuity error. The results still looked relatively stable, at least for the conduits I looked at.

    The link provided earlier on troubleshooting the Explicit solver has additional settings you can consider in troubleshooting the model.

    Regards,

    Scott

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