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Calculating the fill volume for a dam shell can be done in a couple of ways. The first is to calculate the volume between a grid (the base topography grid) and a surface (the dam shell), using the command Grid >> Volumes >> Volume between a grid and a surface.

This command lets you calculate either the cut volume (volume below the base grid and above the surface), the fill volume (volume above the base grid and below the surface) or the total volume (net volume above/below the surface, to the grid).

For a dam you’ll want to calculate the fill volume. When prompted, select the base grid and the surface by clicking on each.  The resulting volume will be written to the Output Window.

This volume is the total volume enclosed above the base grid and the below the dam shell, i.e., the dam fill volume.

Volumes can be impacted by grid spacing and structure size.  Please refer to Selecting grid spacing for a discussion on volumes & grid spacing.

If you wanted to create a fill-volume vs elevation curve for the dam shell filling, you can calculate the horizontal slice volume vs elevation for the shell above the base grid using the command Grid >> Volumes >> Create peels between grid and surface.

Again, you’re interested in the fill volume (created above the base grid and below the dam shell).  When prompted select the base grid and the dam shell by clicking on each. 

This command will then calculate the slice volumes and a CSV file will be written to the current Working Directory.  If a file with the same name already exists in this directory it will be overwritten.

Another way to calculate the dam fill volume is to simply merge the dam shell into the base grid. This can be done using Grid >> Merge >> Merge dam into grid.

This command will take the selected base grid and dam shell, and change the elevations for the grid to reflect the elevation of the dam shell at each grid point, where the dam shell is above the base grid. Where the dam shell exists below the elevation of the base grid, the base grid will remain unmodified.

When prompted, select the base grid and the dam shell (by clicking).  The resulting fill volume will be automatically calculated and written to the Output Window.

If you hide all layers except for the base grid (by toggling the visible flag in the Scene Manager) you will see that the dam shell is now part of the grid. 

When structures are merged into a grid, the grid is modified to reflect the structure elevation.  The previous surface elevation has been ‘forgotten’ by the grid.  Grids always reflect the upper/lower-most elevations of what is being modelled.

Save the grid with the dam merged into it.  When you save the layer, make sure that you don’t overwrite the base grid layer.  You always have the chance to rename layers when you save them, so give this a unique name such as "grid+dam".

You’ll also notice that another layer was created called "footprint".  This is the outline of the dam shell on the base grid.  You can use this to calculate the plan or membrane area of the dam footprint, and it has some other uses as we’ll see in the next stage of the tutorial.  Save this file for later use.

Once you’ve saved the layers you need, unload all files.  Instead of removing them individually, you can use the command View >> Clear graphics.

You’ll be prompted to save any layers which have not been saved (or modified since it was loaded), or you can discard all unsaved layers.

Basic volume calculations

Determine the dam's fill volume by comparing the topography and dam shell. Create elevation curves to observe fill progression. Finally, integrate the dam design into the base grid, ensuring to save modifications and associated outlines.

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