computing pre development calculations

[bf]

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.

[bf]

and my help doesn't populate from either the question mark or the pull down menu. Any Help?

[annw2]

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?