QGIS
The free, open-source GIS that has become the default spatial platform for water engineers worldwide.
Click anywhere on earth, get the upstream watershed in seconds — free delineation in the browser.
Global Watersheds (mghydro.com) delineates the upstream catchment and downstream flow path from any point on earth, in the browser, in about a second — built on the MERIT-Hydro global hydrography dataset. Results export as shapefile, GeoJSON or KML, and a free API serves programmatic requests.
Accuracy inherits MERIT-Hydro's ~90 m resolution, so it is a screening and communication tool, not a design deliverable — but for "how big is the catchment above this bridge" moments, teaching, and proposal figures, nothing is faster. A genuinely useful free service by Matthew Heberger.
Other geospatial & hydro-gis tools covering similar workflow stages.
The free, open-source GIS that has become the default spatial platform for water engineers worldwide.
500+ fast geospatial analysis tools with the best DEM hydrology toolkit in open source.
Esri's free hydrology framework for ArcGIS Pro — terrain preprocessing and the data model behind many agency workflows.
QGIS plugin for exploring mesh model results — animate TUFLOW, Telemac and HEC-RAS 2D outputs in the GIS.
Four decades of geospatial engineering — r.watershed and the most battle-tested hydrology modules in GIS.
Planetary-scale geospatial analysis in the cloud — the data catalogue and compute behind modern water remote sensing.