## License Information

Use of this function requires a license for Whitebox Workflows for Python Professional (WbW-Pro). Please visit www.whiteboxgeo.com to purchase a license.

## Description

This tool locates low points, or passes, on the drainage divides between subbasins that are situated on headwater divides. A subbasin is the catchment draining to a link in a stream network. A headwater catchment is the portion of a subbasin that drains to the channel head. Only first-order streams contain channel heads and headwater catchments are sometimes referred to as zero-order basins. The lowest points along a zero-order catchment is likely to coincide with mountain passes in alpine environments.

The user must input a depressionless DEM (i.e. a DEM that has been pre-processed to remove all topographic depressions) and a raster stream network. The tool will work best if the raster stream network, generally derived by thresholding a flow-accumulation raster, is processed to remove shorter headwater streams. You can use the remove_short_streams tool remove shorter streams in the input raster. It is recommended to remove streams shorter than 2 or 3 grid cells in length. The algorithm proceeds by first deriving the D8 flow pointer from the input DEM. It then identifies all channel head cells in the input streams raster and the zero-order basins that drain to them. The stream network is then processed to assign a unique identifier to each segment, which is then used to extract subbasins. Lastly, zero-order basin edge cells are identified and the location of lowest grid cells for each pair of neighbouring basins is entered into the output vector file.

## See Also

remove_short_streams

## Project Links

WbW Homepage User Manual Support WbW