Fill Sinks

Draft: written, not yet checked by a person Operation · fill-sinks

Raises cells in closed depressions of an elevation raster so every cell can drain to the edge.

Pitfall. Filling also flattens real depressions (quarries, sinkholes); breaching is the alternative that cuts through barriers.

Pitfall. Some engines add a tiny gradient across filled flats so water still flows; others leave them flat.

About this operation
Also called	Fill, fill depressions, pit filling, hydrologically conditioned DEM
Group	`raster/hydrology`
Checks	`raster.nodata`
Pitfalls	2 listed above
Columbus tool	Not stated
Notes	Not stated
Status	active
Broader	Not stated
Narrower	Not stated
Related	`flow-accumulation`

Parameters

Not stated

Direction	Name	Type	Geometry	Note
Input	`raster`	raster	Not stated	Not stated
Output	`output`	raster	Not stated	Not stated

Engine	Tool	Parameters	Differences
`grass`	`r.fill.dir`	`raster` → `input` `output` → `output`	Also writes a flow direction map (direction is required); one pass may leave some depressions, so it is often run more than once. Preset: `{"direction":"fill_direction"}`
`qgis`	`native:fillsinkswangliu`	`raster` → `INPUT` `output` → `OUTPUT_FILLED_DEM`	MIN_SLOPE (default 0.1 degrees) keeps a small gradient across filled areas; also writes flow directions and watershed basins.
`whiteboxtools`	`FillDepressions`	`raster` → `dem` `output` → `output`	fix_flats (default true) adds a small gradient across flats; max_depth limits how deep a depression is filled. WhiteboxTools 2.4.0: in the equivalence tests this tool panicked ('Error unwrapping output') in about a third of runs on a 20 by 20 raster, at random; FillDepressionsWangAndLiu and FillDepressionsPlanchonAndDarboux did not.
`whiteboxtools`	`FillDepressionsPlanchonAndDarboux`	`raster` → `dem` `output` → `output`	Planchon and Darboux's method (slower than Wang and Liu); fix_flats adds a small gradient across flats.
`whiteboxtools`	`FillDepressionsWangAndLiu`	`raster` → `dem` `output` → `output`	Wang and Liu's priority-flood method; fix_flats adds a small gradient across flats.
`xarray-spatial`	`xrspatial.hydro.fill_d8`	`raster` → `dem`	z_limit limits how much a cell may be raised.