Inflow and outflow hydrographs are overlayed by default for reach and pond nodes. I believe one would have to show pre and post as side-by-side comparisons, or export the tabular hydrographs to another app (spreadsheet) to display them overlayed.
You can export the hydrograph data to a CSV (spreadsheet) file by clicking the Export button on any tabular hydrogrpah. You can also have the data exported automatically for all rainfall events by using the options on the Settings|Export screen.
