Downstream analysis (watershed?)

[Chaznsc]

So I need to perform a simple dosntream impact analysis for an area downstream of my site. Can C3D delineate a basin by pikcing a study point within a defined basin? 

[jameshitt]

I'm not aware of a way of doing that in out-the-box Civil 3D. The only workaround I've found is using the WaterDrop command and sort of uncovering the boundary high points that way (clicking a bunch of water drops all over).

There may be third party applications that can do that, or even better, maybe a dynamo script that someone might possibly have made?

[fcernst]

It does, and can be helpful to analyze your proposed grading, but it appears to not have any terrain sink/fill preprocessing routine so it fails on analyzing DEM/LiDAR existing condition terrain..