Hi,
The error message you encountered will come if you have defined any external inflow to any of the junctions as Unit Hydrograph but the data need to be entered are missing.
In the junctions dialog box invert elevations are the sump elevations of manholes or junctions. Maximum elevations are the rim elevations/ground elevations of manholes/junctions. Initial elevations are the elevations of water if there is any water already exists in your manhole/junctions before the start of your simulation period.
The full form of IDF is Intensity-Duration-Frequency Curve. IDF curves are being used as rainfall inputs if you are using Rational/ Modified Rational as your hydrology/subbasin hydrograph method method.
Thanks,
Debajit Basu Ray
debajit@bossintl.com