# Computing volume of pits with a variable surface edge in a DEM? Multiple TINS per surface? [closed]

I have a DEM of the seafloor. The grid is highly variable, with scour pits throughout the lower right quadrant. I want to compute volume for these pits. It seems all the standard tools such as Cut/Fill using the DEM or Polygon Volume using a TIN (converted from DEM) use a set plane to represent the depth of the second surface. However, the edges of my scour pits have variable depths.

Is the best way to get a true volume to convert each individual scour polygon to a TIN, and then do a cut/fill or some TIN analysis/difference?

Is there a way to do this and have all polygons converted to TINs within a single layer? There are quite a few polygons, so separate layers and analyses would be very time intensive.

I have ArcGIS 10.5 on my Windows VM.

Looks like they opted to convert polygons to TINs, but unknown If they had to do each one separate or if they found another solution.

## closed as too broad by PolyGeo♦Dec 18 '18 at 1:34

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• Please decide which of ArcGIS Desktop and QGIS you wish to ask about in this particular question. – PolyGeo Dec 18 '18 at 1:35
• You may have to do it individually. Multigeometry may work though I never tried; Create a 3d surface of the variable edge (you can digitize a line then convert the line to 3D using the Interpolate Shape tool. Convert this to a TIN) Also convert your DEM to TIN and then run the Extrude Between tool to get the enclosed volume between the 2 surfaces. I believe the output is a multipatch feature from which you can obtain the volume. – Jakub Sisak GeoGraphics Dec 18 '18 at 14:03