I'm getting a zero elevation for the surface I create when I compare surfaces to get volumes. What am I missing?
Zero elevation is where the two surfaces intersect in a volume surface comparison.
Did you accidentally select both surfaces as the same surface?
Post your drawing and we may be able to spot the issue.
The elevations of a volume surface reflect the difference in elevation between the two selected surfaces. Where there is one foot difference, you would see an elevation of 1.00 (or -1.00 depending on which surface was higher). For example, typical elevations for a volume surface might be between +10' and -10'. A zero elevation, as Mr. Ernst pointed out, would be where the two selected surfaces had the exact same elevation.
This is not unusual and should indicate that you have done the volume surface correctly.
I'm trying to get an area in cuyd to calculate the volume of water a dentention pond will hold before it goes over the spillway. So yes both surfaces I'm comparing have a common elevation. I have a base surface built using the bottom of the pond points and the crest points ie. the existing or asbuilt pond. My comparison surface was built using the first continous contour line at the elevation closest to the spillway elevation. I have built this surface using both the extracted contour line and the bottom of pond points, as well as just the contour line. What am I still missing? This should be an easy task that so far is not.....
Thanks so much for the great responses so far!
Kim
I'm still not sure what you are asking. Your first post said you had a zero elevation in your volume surface, which is perfectly normal. Your last post simply asked, "What am I missing?"
Are you getting zero cubic yards for your volume comparison? Is that your problem?
I'm not sure about what you're specifically describing here, either. For pond volume (not area), you would have a base surface created probably from elevated polylines (contours) that describe the pond from bottom to top. This top may be the same elevation as your water surface or could be higher. The comparison surface would be created from just the water surface elevation polyline.
You'll also need to be aware of the extents of the volume surface and how that can affect the net volume. The extents of the volume surface (and therefore the extents of where "cut/fill" is calculated is the outermost, overlapping boundary - ie, the outermost boundary that is still contained within both compared surfaces.
HTH
I'm trying to get an area in cuyd to calculate the volume of water a dentention pond will hold before it goes over the spillway.
There is a much bigger problem here from a liability standpoint than figuring out how to use the appropriate Civil 3D tools.
Your proposed analysis approach for delivering the above, is incorrect.
It really helps to look at the right pond design drawing when doing asbuilt drawings. I kept getting the same volume results that were not even close to what the design drawing was showing. I did my own guick and dirty end area method and figured out that I was using the design drawing for pond 2 which is a much larger pond! It was a rough day friday and today is really monday!! Thanks everyone for all of your suggestions and ideas letting me know I was on the right track with my surface and zero elevation issue. I appreciate it as always.
Kim