Notification Error at Sewer Cad!

Here is the support solution , which would help you understand it.

communities.bentley.com/.../17095.manhole-hgl-is-greater-than-pipe-crown-at-pressure-to-gravity-transition.aspx

Sushma,

Thanks for the information.

I have extracted from that Tech Note this statement "It's a way to indicate that the pressure network flows may be overestimated". What this statement means?

Also this statement "There is no real 'fix' for this in SewerCAD - it's just an assumption that you have to accept when dealing with surcharged gravity pipes. It often doesn't have a big impact on results."

Reason why I am asking these, is because I am modeling a existing network and I am getting this notifications. Can I still rely on the results of my Sewer Cad?

Regards,

June

June,

In the "Reason" section of that article, it explains why the flows might be overestimated:

"Because SewerCAD assumes the HGL at the downstream end of the pressure network is 172.2m (i.e. equal to the pipe crown), when it should actually be more like 173.8m  (based on the SewerGEMS results). As the downstream HGL is slightly lower in  SewerCAD, the flow through the pump is slightly higher. In other words the pressure network flows are overestimated."

Basically if the pump were to add enough head to overcome the high tailwater at the gravity transition, it would consequently add less flow as it shifts on the pump curve.

Regarding "Can I still rely on the results of my SewerCAD" - this is an engineering judgment you will need to make. Based on the assumptions discussed, you'll need to decide if the ultimate decision that your model is helping you make will be impacted by this or if you need to consider another approach. I added a few more notes to the Support Solution article, which might help.

communities.bentley.com/.../17095.manhole-hgl-is-greater-than-pipe-crown-at-pressure-to-gravity-transition.aspx