Need to find drainage area using LIDAR

[spbLCVEJ]

I'm working to find the drainage area of an area that contributes water to a certain point (a culvert underneath a highway leading into our site). I was looking for ways to find the drainage area at this specific point, but when I try to find the catchment area for the point of the culvert inlet, it only goes so far out (See attached picture). I've been told that usually we find the drainage area by hand, but I feel like if we have LIDAR, we should be able to find a rough idea of the drainage area using Civil 3D. 

I'm using AutoCAD Civil 3D 2021, using LIDAR made with LAS files. Let me know if you need any more information.

[KirkWM]

It's possible that you are getting the correct answer (or close to it) but some other ways to check is use the raindrop tool and a more robust way is to make a surface style with "watersheds" and "slope arrows" displayed, this will likely take a while with a large surface but you could crop the surface where you are looking and maybe that would go faster. A bit more extreme option is taking the surface into Infraworks and use the watersheds tool but that may take tokens if it's really large area. Hope this helps.