Why is the flow in the system more that I expect? 

If the flow in your model is more than what you expected, base on quantity of loading from Flow Files, there are a few possible reasons for it.

Redundant Flows

Perhaps you selected more Flow Files than you meant to.  For example, you may have 2 sanitary Flow Files, one for the year 2000, and one for the year 2020.  If you accidentally selected both, you would probably have more than twice the amount of sanitary flows in your system.

Flows from “Point Flow” injections 

It is possible there is more flow entering the collection system than is represented by Flow Files.  Additional flow can be entered at the SY_CMD field, and these flows will be a part of every analysis until you remove them.  Also, if you have used the INF Command for infiltration, this infiltration may be injected for other pipes in the system, depending on how you input the data.

Hydrograph Time-Step Considerations

There is a discussion of the affect of setting attenuation to “preserve peak” vs “preserve volume” in the Hydra® 6 User Manual (Oct 2000) update on page 165.  This is also in the Help file topic “Setting Hydrograph Attenuation to Preserve Peak or Volume”.  This analysis setting affects flows when you have pumps or reservoirs in your system, and may seem to “create” flow in your system.

To review your existing analysis runs, to see which settings were used, you can look in the command file for each run.  These will
be called [RunName].CMD and you can look at them with a text editor.  Near the top of the command file, you will see the Settings command having to do with how Hydra added the hydrographs together.

You will see: SET ADD PEA (for preserving peak)
or
SET ADD VOL (for preserving volume)

Check units.  Did you input flow data using the wrong unit?  Did you use the wrong unit for pipe diameter?