After you define your 'rivers', you then get to assign river properties such as overbank locations and mannings values for the channel and left and right overbank areas. With ARD HEC-RAS you can also easily establish ineffective areas, obstructions and skewed sections for export to HEC-RAS.
The information is passed into a file for import into HEC-RAS at the click of a button.
You then import the river geometry and do your channel analysis in HEC-RAS.
After creating an output from HEC-RAS, you can immediately import the results back into the drawing - you will get 3D polylines representing the channel extents, as well as 3D polylines perpendicular to the channel centreline representing the cross section of the top water surface. From this you can readily construct a digital terrain model and generate immediate outputs (volumes, sections, elevation differences, long sections, etc).