Autodesk Civil 3D Surface Comparison Hydro colorationWe often have to verify the condition of Stormwater basins for our clients. In the example today, I was requested to evaluate the volumes of a past as-built, and compare it to a recent version.


While there were difference in volume, the problems lied in the inability to visually evaluate where those differences had occurred. EG Contours are shaped similarly, and spot grades are located differently. Also, I was given half an hour to delineate the differences.


I have the 2 Grid volume surfaces that establish storage volume to the outfall elevation. What I need now is a Volume surface that compares the EG surfaces of the two pond bottoms.  

Create a Grid surface and compare the old surface to the new surface. Refer to the steps and images below.

  • Create Surface
  • Choose a volume surface, Grid or Tin

Autodesk Civil 3D Surface Type

  • Add all the pertinent information as usual such as name, layering, style, etc.
  • Choose the two surfaces to be compared
  • Specify the spacing size if Grid was selected. 25′ is the default, but I was hunting minute changes, so I went tight with 1′. Use just enough to capture the precision you are concerned with. Too tight is a bad thing, trust me.

Autodesk Civil 3D Surface Create    Autodesk Civil 3D Volume Surface  Result

Once created, all we need to do is to adjust the Surface Style to visually delineate the differences.

Autodesk Civil 3D Surface Analysis Style  Autodesk Civil 3D Surface Style Display

Then I added spot grade labels to help the Project Manager complete the evaluation.

Autodesk Civil 3D Surface Spot Grades   Autodesk Civil 3D Surface using Land coloration

Nothing to it. There is no shortage of power using the tools in Civil 3D. Remember that you have to think beyond the labels given to the tools, and look to what the combination of the tools can do for your needs.