This topic gets posted on about once a month, maybe 2008 will have it built in.
If you have a surface that models the basin there is a fairly simple, yet still unreasonable method considering the "power" of C3D. Add a boundary around the area of the surface that has the pond (this may be a surface that you've had to paste a proposed surface into to make it correct). Use the Copy command and make a duplicate surface. Change the contours to the intervals desired. The Explode your copied surface till you have the contours as polylines. List their area, and then use some method of obtaining the volume, like average end area, or some more complicated method depending on the size of pond, and your best engineering judgment.
A faster way would be to use a 3rd party software.
As for using the surface table... and you thought my method was long, at least it give correct results.
Mark