Manning's equation usage in CivilStorm

Dear sir / madam,

I am having a problem in CivilStrom regarding pipe losses calculation. I have a sewer system that is running full (pipe are always 100% full) because this system drains to a pond that has a water level higher than the pipe crown level. Pipes are running flat with no slope.

The issue I am facing is that the pipe losses calculated in CivilStorm using the Implicit (SewerGEMS Dynamic Wave) solver differs dramatically from the losses I calculate manually using manning's equation for the same flow and roughness coefficient. I am assuming that a 100% full pipe is designed as a pressurized pipe and I have already chosen in the Calculation Options Manning's equation to be used as the "Pressure Friction method".

I have attached:

1- a PNG file with my question rephrased in more clarity

I have tried to load the CivilStorm files but failed to do that because of their size exceeding the maximum allowed. If there is another way to upload the files, please let me know.

Thanks in advance for your support,

Regards,

Amr

Can someone help me figuring out why CivilStorm pipe losses do not match the manually calculated ones using manning head loss equation? I am really confused !