Hydrology

Grass

https://grasswiki.osgeo.org/wiki/Hydrological_Sciences

https://grasswiki.osgeo.org/wiki/Creating_watersheds

https://baharmon.github.io/hydrology-in-grass

Automatically delineate a watershed in QGIS

ArcGeek

ArcGeek Calculator is a comprehensive QGIS plugin that provides various hydrological, geomorphological, and spatial analysis tools. https://github.com/franzpc/ArcGeekCalculator

Tuto video : https://www.youtube.com/watch?v=Cwudi26l4ow