I'm looking for sinkholes in a karst area. I thought I would take the elevation raster created from a lidar file and run the Sink tool to find all the closed depressions. All I get with Sink are tiny sinks a few pixels in size, even though I can see large closed depressions on the contour map made from the same elevation file. When I run Fill, it fills all the closed depressions I see in the contours, so it seems like Fill is working fine. But Sink isn't identifying the sinks that Fill is filling. I can get at what I need if I create a second contour map from the Fill raster, and overlay the contour maps from the filled and unfilled rasters. With the filled contours on top, I can identify the sinkholes where the unfilled raster contours are visible. However, I would like to understand why the Sink routine isn't identifying these sinks.