AutoCAD Civil 3D

[#1]

is the catchment area tool like the water drop tool except backwards? if i pick a point on my suface i would think it would give me the area that's flowing to it, like a watershed. it does this somewhat but it's not giving me what i think should be an acurate pline around the area. when i pick a point it should cover the whole side of a hill but it gives just a small area. i've picked a lot of places on the hill but the results are the same. i can't find any settings to maybe tweak the output.

[#2]

I'd look at the triangles of the surface to see if there are any flat spots that are causing the catchment tool to not make it up the hill. Maybe put a slope label on the triangle to see if it's flowing the correct direction towards the low point.

Christopher

[#3]

i'm sure there a bunch of flat spots. it's quite a large site and the contours are derived from contour polylines. i was hoping there was a setting somewhere. i'm trying to find the top of the basin that's draining to our road. i just used the waterdrop tool and defined the ridge that way. my computer isn't powerful enough to use the watershed surface display. thanks anyway.

[#4]

If you review the user assistance, it is recommended that you use the water drop together with the catchment area to define the overall area.  

[#5]

Turn on the flow arrows of your surface to review the catchments area; if your surface definition has any vaugaries in it the catchments will pick them up. As Matt mentioned the tool works in conjunction with the water drop.

[#6]

"If you review the user assistance, it is recommended that you use the water drop together with the catchment area to define the overall area. " 

For years, this has been a tedious and very unelegant workflow suggestion. It is sophmoric and crude...

We need better basin analysis tools that think like an engineer and can see the drainage basin picture. We need surface drainage tools that allow the engineer to quickly achieve the level of basin discretization that the engineer is needing to achieve for the situation.

Usually this is aggregating the surface slivers these C3D surface routines typically produce for us, and expanding outward like the OP suggested.

Back to the drawing board for C3D programming...quickly get a surface algorithmist on this who understands what we have been frustrated with for years...