What is the best method for computing small site pre development and post development rational method calculations using AutoCad C3D? I have used SSA and Hydraflow Hydrographs and pencil and paper.
If you are using rational you are sizing pipes and the Storm Sewer program works well.
I start with drawing the poly lines to determine the catchment area. I use the parcel function to measure and label the areas.
I haven't had much luck with the catchment function as you can't merge areas
I use bpoly to determine how much of the drainage area is impervious, etc.
I have spreadsheet to determine CA values and another for time of concentration.
Did you have a more specific question?