# tools for calculating volume

I have been experimenting with certain tools to calculate the volume of water in potential dam sites. I have been using the 'pile volume' tool which gives an array of feature information including varied data on volume. when I calculate the volumes using mathematical formula I get a very different answer than that given by the pile volume data.
Is this tool accurate and reliable for this type of calculation? Is anyone using this tool for the same purpose? Can anyone shed some light on why there is so much variation in calculation methods?

Many Thanks
Bruce Kirk

• Global Mapper User
I would create a flat surface by drawing an area and setting its elevation to represent your dam water level, and then use the analysis tab - "measure volume between surfaces" to calculate the void between - always seems to work for me.  Ive never used the pile calc method.  If you reckon your units are doing something odd, you can control their behaviour in the unit display box here....

• coelodonta , but automatically interpolates the second surface using the area feature.
In this case the top of the dam surface would be an interpolated surface using the selected dam boundary area feature as the surface edge, and adding an additional 200 sample points along that border in addition to the existing feature vertices.
This is a convenient way to estimate what the surface was like before the pile or hole existed.
You may also want to look at the volume measurement tool itself, as just setting an explicit defined base height as the water level.
• Global Mapper User
curves said:
I have been experimenting with certain tools to calculate the volume of water in potential dam sites. I have been using the 'pile volume' tool which gives an array of feature information including varied data on volume. when I calculate the volumes using mathematical formula I get a very different answer than that given by the pile volume data.
Is this tool accurate and reliable for this type of calculation? Is anyone using this tool for the same purpose? Can anyone shed some light on why there is so much variation in calculation methods?

Many Thanks
Bruce Kirk
I'm not sure what "mathematical formula" you used for confirmation but before I started using GIS extensively, the normal method was to use your contour map to compute the area and the elevation of the contours within the reservoir area, then apply the conic or end-area method to compute the volume between the contours and cumulate for the entire reservoir. Usually we ended up with a plot of the Height-Area-Capacity curve to show the characteristics of each potential site.

My current work flow using Global Mapper involves:

1: Generating the contour map using the DEM and creating an area feature of the reservoir at the desired contour elevation.

2: Select the area feature and initiate the volume command

3: Choose the "Perform multiple calculations over a range of base heights" and enter the lowest and highest elevations within the area (425 to 440 as shown), then press "OK".

4: The results are shown below with the highest "fill volume" highlighted as 13,285,150m3.

5: You can copy to clipboard and paste to MS Excel to generate graphs live below.

6: If you want to have a more direct volume computation, just do step 1 - 2 and choose "Use same base height value for all vertices", enter the desired elevation (440 here) and ensure the value is selected as "above sea level".

7: Voila, the fill volume is same.

I have verified this with the manual method and the volumes are not significantly off.
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• Our company would find a dedicated tool for this very useful in our offices across the world. For instance, placing a point and getting global mapper to fill within the 'basin' to a specific elevation. We perform a lot of analysis for Tailings Facilities so having the ability to model a dam and then compute the capacity behind it would be awesome.

On that subject, having the ability to create a dam from a Line Feature would also be amazing too. We would need to enter the crest width, crest elevation and upstream and downstream slope parameters.
• Great, Thanks Coelodonta, Katrina, allienyouth, and Sphillips, really appreciate the feedback. Lots of methods to investigate.
• Greate.
i have a pre Solutions problem, do you have any sugestion?
i have a dem and point cloud with a dam, but i only have the water surface, (survey done with drone) what will be the best workflow to try to simulate the natural terrain under the water level and try to calculate the volume  approximate stored water.  trying to use the average slope of the main waterline and slopes of the surrounding land.
Tks
Pedro Reia
@Portugal.