Hydrology
The Hydrology toolbox answers where water goes. Starting from a digital elevation model, it works out which way each cell drains, how much water accumulates along the way, where the streams are, and which area feeds a given point.
Its 97 tools come from the Whitebox analysis suite and run entirely in your browser. Almost all of them take a raster elevation model as input, which you load through Add Data like any other layer.
The usual order of work
Section titled “The usual order of work”Hydrology tools are meant to be chained, and the order matters more here than anywhere else in the panel. Running flow accumulation on a raw elevation model gives a broken, unusable drainage network.
- Condition the elevation model. Real DEMs contain pits and closed hollows, some genuine, most of them artefacts. Water reaching them has nowhere to go, so the algorithms stop there. Fixing that is the job of Depressions & Storage.
- Route the flow. Compute a pointer raster saying where each cell drains, then a flow accumulation raster counting how many cells drain through each one. This is Flow Routing.
- Extract the streams. Threshold the accumulation raster to get the channels, then clean and vectorise them. See Streams: network extraction.
- Delineate the basins. Place your pour points, snap them onto the network, and get the area draining to each. See Watersheds & Basins.
Along the way, Hydrologic Indices and Streams: ordering metrics turn those intermediate rasters into readable measures, such as wetness indices and Strahler order.
The sub toolboxes
Section titled “The sub toolboxes”| Sub toolbox | What it is for | Tools |
|---|---|---|
| GeoLibre | Extract and delineate nested depressions and mounts, from the GeoLibre engine. | 3 |
| Depressions & Storage | Condition the DEM: fill or breach depressions, burn streams, measure storage. | 18 |
| Flow Routing | Flow pointers and accumulation, in D8, D infinity, FD8, Rho8 and others. | 23 |
| Hydrologic Indices | Wetness, stream power and related terrain indices. | 14 |
| Streams: longitudinal analysis | Profiles and distances along a channel. | 5 |
| Streams: network extraction | Extract, prune, repair and vectorise the channel network. | 8 |
| Streams: ordering metrics | Strahler, Shreve, Horton and other ordering schemes. | 14 |
| Watersheds & Basins | Watersheds, subbasins, hillslopes and pour point snapping. | 12 |
What you need to know before starting
Section titled “What you need to know before starting”Your DEM defines everything. Resolution sets the smallest channel you can detect, and vertical accuracy decides whether a hollow is a real pond or noise. A 30 metre global DEM will not give you a farm ditch network.
Keep the intermediate rasters. The pointer and accumulation rasters are inputs to most of the later tools. Each run adds its result as a new layer, so name them as you go and your workflow stays readable.
Size matters here. The whole computation happens in your browser’s memory. A national DEM will not fit. Clip to your catchment first, and if the input comes from a large file, load only the area you need.
Credits
Section titled “Credits”These tools come from WhiteboxTools by Prof. John Lindsay, University of Guelph, whose manual documents the algorithms and cites the research behind them.