Most of us can work our way through the 3D modeling of a detention pond in Civil 3D but when it comes to sizing that pond to hold specific amounts of water, or even figure out how much water we can hold in the initial design, we get lost. I still see engineers working with manual average-end-area section cuts and multiplying out the distances between to get the volumes at each contour level. That’s a ton of work and wasted time when, once you have a basin modeled, Civil 3D can generate a Stage Storage Report for you. It can even export a Stage Storage Table that you can import to tools like Storm & Sanitary Analysis to handle your watershed analysis.
Important Tip: When modeling your basin, take the top edge elevation to .1 above the elevation contour you need to calculate storage for. For example, in this basin I need to know the water storage up to elev. 969, so the top edge of my basin is modeled to 969.1.
Let me show you how easy this is. To begin, we start with a modeled detention pond (see below). Note that I’ve built this from a grading object and had C3D automatically build a surface for me.
3D Detention Pond
The surface is the key – you need a contoured surface to generate the SSC. We begin on the Analyze > Design ribbon tab and expand out the bottom drop down to select the Stage Storage option as shown below.
Analyze > Design > Stage Storage
This brings up the Stage Storage report generator dialog. Just fill in the information about your pond (see below) and set the volume calculation method to “Both”. Now, I know most engineers like the average end area method, because they can manually check it, but in truth the Conic Approximation method is far more accurate. I run “both” so I can see the results of each and look for any type of discrepancy that would denote a problem in my pond’s surface. Select the “Define Basin from Entity” option, then click the “Define Basin” button.
Stage Storage Report Dialog
This brings up the Basin Definition dialog (see below) where you choose “Define Basin from Surface Contours” then click the “Define” button. Civil 3D will prompt you to pick a surface on screen. Select any contour on your detention basin surface.
Define Basin Dialog
Civil 3D then generates the complete Stage Storage tables, with both methods of calculations, and the incremental and cumulative volumes for each contour level within your basin (see below).
Stage Storage Table
From here, just click the “Create Report” button to output to a text based report, or “Save Table” to output to a (.AeccSST) format that can be read directly into SSA or other hydrology calculation systems.
See? I told you it was easy!
– James Coppinger
