Formerly, the term watershed was used for the divide of a drainage basin. Since the UN conference on water at Mar del Plata, Argentina in 1977, however, the term watershed has come to mean also the drainage basin itself .
Accordingly, “watershed is defined as any surface area from which runoff resulting from rainfall is collected and drained through a common point. It is synonymous with a drainage basin or catchment area. A watershed may be only a few hectares as in small ponds or hundreds of square kilometres as in rivers. All watersheds can be divided into smaller sub-watersheds” .
A watershed embraces physical-biological features as well as socio-economic and political features which have to be integrated into the planning and management process.