The Fill sinks operation 'removes' local depressions (of single pixels and of multiple pixels) from a Digital Elevation Model (DEM).
- The height value of a single-pixel depression is raised to smallest value of the 8 neighbours of a single-pixel depression.
- The height values of a local depression consisting of multiple pixels are raised to the smallest value of a pixel that is both adjacent to the outlet for the depression, and that would discharge into the initial depression.
By using the Fill sinks operation,
- and a subsequent Flow direction operation on the output map of the Fill sinks operation,
- and a Flow accumulation operation on the output map of Flow direction operation,
it is ensured:
- that a flow direction will be found for every pixel in the map, and
- that water in any pixel will be discharged into outlets towards the edges of the map.