Hydrology & watersheds
Where water goes on a DEM: conditioning, flow direction and accumulation, watersheds, stream networks and HAND.
Everything on Spatial Workflow about hydrology & watersheds, in the order that usually works: understand the idea, then run the task, then fix it when it goes wrong. 20 guides in total.
One learning path runs through this topic — follow it if you would rather work through a route than pick a single guide.
🧭 Start with the concepts
The ideas the how-to guides below assume you already have.
- DEM Hydrology Explained: From Elevation to Where Water Goes dem hydrology explained
- Flow Direction Explained: D8, D-Infinity and MFD Compared d8 flow direction explained
- Pour Points Explained: Why Watershed Delineation Needs a Snapped Outlet pour point snapping explained
- Stream Order Explained: Strahler, Shreve and What They Measure strahler stream order explained
- How DEM Resolution and Source Change a Drainage Network dem resolution stream network
- Height Above Nearest Drainage Explained: A Quick Flood Proxy hand height above nearest drainage
⚙️ Then do the task
Step-by-step walkthroughs with code you can copy and adapt.
- How to Condition a DEM for Hydrology: Breaching or Filling breach depressions dem python
- How to Calculate Flow Accumulation from a DEM in Python flow accumulation python
- How to Delineate a Watershed from a Pour Point in Python watershed delineation python
- How to Extract a Stream Network from a DEM extract streams from dem python
- How to Calculate Strahler Stream Order in Python strahler order python
- How to Split a Catchment into Sub-basins at Many Outlets delineate subbasins python
- How to Summarise Catchment Attributes: Area, Slope and Land Cover catchment characteristics python
- How to Calculate Height Above Nearest Drainage (HAND) in Python hand python dem
- How to Burn a Known River Network into a DEM stream burning dem python
🔧 When it breaks
The errors this topic produces, with the cause explained rather than just the command.
- Fixing a Watershed That Comes Out as a Few Pixels watershed delineation wrong small
- Fixing Streams That Run in Straight Parallel Lines Across Flat Ground flow direction flat areas parallel streams
- Fixing Flow Accumulation That Is All Zeros, NoData or Stops at the Edge flow accumulation nodata
- Fixing Streams That Stop at Roads, Bridges and Embankments dem roads block flow bridges
- Fixing Catchment Areas That Are Wrong on a Latitude–Longitude DEM watershed area geographic crs wrong
Learning paths through this topic
A curated route rather than a list — the guides in the order that builds on itself.
Related topics
Subjects that keep coming up alongside this one, most overlap first.