Watershed delineation is the process of identifying the boundary of a watershed, also referred to as a catchment, drainage basin, or river basin. It is an important step in many areas of environmental science, engineering, and management, for example to study flooding, aquatic habitat, or water pollution.
The activity of watershed delineation is typically performed by geographers, scientists, and engineers. Historically, watershed delineation was done by hand on paper topographic maps, sometimes supplemented with field research. In the 1980s, automated methods were developed for watershed delineation with computers and electronic data, and these are now in widespread use.
Computerized methods for watershed delineation use digital elevation models (DEMs), datasets that represent the height of the Earth's land surface. Computerized watershed delineation may be done using specialized hydrologic modeling software such as WMS, geographic information system software like ArcGIS or QGIS, or with programming languages like Python or R.
Watersheds are a fundamental geographic unit in hydrology, the science concerned with the movement, distribution, and management of water on Earth. Delineating watersheds may be considered an application of hydrography, the branch of applied sciences which deals with the measurement and description of the physical features of oceans, seas, coastal areas, lakes and rivers. It is also related to geomorphometry, the quantitative science of analyzing land surfaces. Watershed delineation continues to be an active area of research, with scientists and programmers developing new algorithms and methods, and making use of increasingly high-resolution data from aerial or satellite remote sensing.