# filling up a depression to create new surface

A collegue here has a problem I cannot help with. She has the surface (as raster) of a landslide release area (from AFTER the slide) and wants to calculate the calculate the theoretical/approximate volume of the release surface. Is there a funtion in ArcGIS or GRASS GIS 7 that fills the slide relesease area? The problem is that we do not have the pre-release surface, so cut/fill does not work here.

• Can you identify both the release area and the accumulation area, or do you have just the post-release elevations? (Showing us an image of the DEM would help.) Oct 24, 2013 at 21:32

You can perfectly use the stable GRASS GIS 6.4.x (7 is not necessary):

• depression areas can be filled with r.fill.dir (filters and generates a depressionless elevation map and a flow direction map from a given elevation layer)

• and resulting volume can be calculated by r.volume or r.lake

• This most likely is not a depression in the sense of areas that would fill with water. Even if it were to have such a shape, the amount of fill surely would grossly underestimate the landslide volume, because the fill would level out the depression but landslides never occur on level ground! Oct 24, 2013 at 21:29
• Thank you! She has not gotten back to me, but seems to have solved the issue with a tool in ArcGIS. For my part, I find the GRASS GIS solution offered more interesting and will use this for my work in the future. Dec 13, 2013 at 7:51

Do the cell values of the raster represent release volume or is the raster simply imagery (e.g. aerial/satellite)? Do you have a polygon (vector) representing the slide region?

If the raster does represent volume, and you have a polygon for the slide region, then you should be able to run zonal statistics tool from ArcGIS Spatial Analyst and get the descriptive statistics for the area.

http://resources.arcgis.com/en/help/main/10.2/index.html#//009z000000w7000000

• Could you explain how this would solve the problem? In particular, rasters rarely represent "volume": the relevant one in this case would be a DEM which, by construction, represents height. Regardless, descriptive statistics would only tell you what is currently there, not what was lost during the landslide! Oct 24, 2013 at 21:31