National Water Act Definition
Catchment in relation to watercourse or watercourses or part of a watercourse, means the area from which any rainfall will drain into the watercourses or part of a watercourse through surface flow to a common point or points.
[Source: National Water Act (Act No. 36 of 1998)]
The area from which water - which could include both surface and subsurface water - drains towards a common point. The surface and subsurface catchment areas may not coincide. The extent of catchment areas is defined by hydrological divides. This is a term essentially used by surface hydrologists.
Why are catchments important?