Stormwater calculations are complex and involve a lot of data. Civil 3D has a variety of tools available to help us track and begin to analyze that data. 

Using Stormwater Design & Analysis
In Civil 3D

You'll accomplish the following:

Create Civil 3D Labels to report your various stormwater parameters created by this workflow 

Calculate the Time of Concentration using a Civil 3D Flowpath 

Execute a Water Drop analysis and Surface Analysis to help you delineate a watershed/catchment