This QGIS model is for hydrological modeling. I have created a model that can identify ditches (or streams, channels) in elevation raster data. The model makes use of neighborhood analysis in several steps. The purpose of the model is to make it easier to visually identify ditches at any scale or to classify ditches.
This model was presented in several steps on QGIS open day sept 24th, 2021:
Model description
This model identifies ditches in raster elevation data. The output is a raster and/or polylines.
Purpose
Runoff calculations normally require modifications to a laser based elevation raster. Highlighting ditches makes those modifications easier. In addition, even though ditches can be visible at small scales in a shadowed relief, having polylines makes it possible visualize ditches across all scales and without a shadowed relief in the background.
Notes
1. Different input values can be used to extract different ditch sizes. The smallest ditches that can be identified are in theory limited by the cell size.
2. It is recommended to try this algorithm first on a subset of a raster to fine tune parameters.
3. The opposite, elevated features, can also be extracted by changing one process in the model.
Contact
My model is available and well documented for anyone to be able to use it. If your are interested you can reach me through levallius@gmail.com.