# Thread: Calculating Volume from Contour Lines

1. ## Calculating Volume from Contour Lines

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I'm having a lot of trouble trying to calculate the amount of dirt that is going to be dug up for a new pond. I have attached the file I have been working with.

The inner blue circle is the bottom of the pond: Elevation 30'
The outer blue circle is the outside of the pond: Elevation 35'

The green circle is where the ground starts to slope down to the edge (outer blue circle) of the pond: Elevation vary and depend on the surface.

Note: The elevations should be in decimal feet but are in decimal inches. This shouldn't be a problem. I believe if a multiply the final volume by 12 it should give me the correct volume of dirt.

I need help ASAP. Any help would be greatly appreciated!

Forgot to mention: I am using Autodesk Land Desktop 2007
Please let me know if I need to include any other files or if you need further clarification on what I'm trying to do.

The file is uploaded here: Hmm it's not letting me post a link to the file.

3. If you are using LDD why don't you make surface DTMs of existing and finish grades, a volume surface and calculate the volume?

the old fashioned way...
using average end area method
((top area+bottom area)/2) * difference in elevation=volume
((47809 sf+33117 sf)/2) * (35-30)= 202315 cf

BTW... if you have a volume in cubic inches, you need to divide it by 1728 to get cubic feet

4. Wow fast reply. Thanks you. That is the volume of the pond only right? There is still extra dirt on top of where the pond will be ranging from Elevation 38 to about 48 that I need to account for. Also the dirt that needs to be removed from between the green and outer blue line in order to make a 1.25 to 1 slope.

5. It's kinda tough to tell, the existing and final contours don't tie in to each other.

6. Ya, this is my first attempt at something like this. Never made contour lines before. Is there something I can do to fix it or help you in any way?

7. Actually the formula in post #3 will give you the volume of the pond, not the earthwork. If you want the earthwork, you'll need to draw the proposed contours and tie them into the existing contours ( or model them in LDD). If you do that I'll be willing to calc the earthworks.

8. Originally Posted by lpseifert
... you'll need to draw the proposed contours and tie them into the existing contours ...

How do you that? I'm not exactly too sure. I looked around the web for help but I keep getting unrelated info. Thanks again for your patience and help.

9. Don't you work for or with someone who is providing you some direction? This not an exercise to throw at someone with no training.

Here's a real quick description. If you can picture the final slopes then the contouring follows. You need some set elevations to begin with. Calulate where a certain elevation will fall starting at known points, using known slopes. After drawing a polyline through points, many other contours can be drawn by ofsetting this one, a distance based on the slope. Where slope changes, contour spacing will change. Where a "new "contour intercepts an existing of the same elevation, this is where you stop the contour, as it "ties in".

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Here is a stormwater pond from one of our projects. The inner slopes of the pond are 3:1 slopes; the contours are offset 6' (2' c.i.). The outer slopes are 2.5:1, offset 5'. Note how the outer slopes of the pond tie into existing contours.

I tried uploading a .dwg, too big. You'll need to settle for a jpeg.

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