Watershed delineation used to mean a real desktop GIS workflow — fill the DEM, compute flow direction, compute flow accumulation, then trace upstream from a pour point by hand or with a plugin. Each step depends on the one before it, and getting the depression-filling step wrong quietly breaks everything downstream. Hydrology Tools runs that entire pipeline for you — you pick the output you want, and every prerequisite step happens automatically underneath.
What you need before you start
A single-band DEM as a GeoTIFF (.tif or .tiff) — SRTM, a LiDAR-derived DEM, or any elevation raster in a real coordinate system. That's it. No pre-processing required; the tool handles depression filling itself.
The steps
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Upload your DEM
Drag your GeoTIFF onto Hydrology Tools. The tool reads its real geographic bounds immediately and shows them on the map, so you can confirm you've got the right file before running anything.
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Choose "Watershed Delineation"
Of the 8 operations listed, pick Watershed Delineation. Depression filling and flow direction — the two steps a real watershed calculation depends on — run automatically; you never have to trigger them yourself.
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Click your pour point
Click anywhere on the map — the outlet of the catchment you care about, a stream gauge location, a proposed dam site. That click becomes the pour point.
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Get a real polygon, not just a picture
The result is an actual watershed polygon with its area computed in real square meters — exportable as GeoJSON, Shapefile, or KML for further use, not just a preview image.
Want the stream network too?
The same tool extracts a full stream network with Strahler stream order from the same DEM — pick "Stream to Feature" instead of (or alongside) watershed delineation. Raise or lower the stream threshold to get a sparser network of major channels or a denser one including small tributaries.
A note on accuracy
This is genuine D8 flow routing with Priority-Flood depression filling — the same class of algorithm used in desktop hydrology software, not an approximation. What it deliberately doesn't do: account for subsurface flow, karst drainage, or engineered drainage infrastructure (culverts, storm drains) that redirects flow away from what the DEM's surface alone would suggest.
Have a DEM you need a watershed or stream network from?
Open Hydrology Tools →