<P> A drainage basin or catchment area is any area of land where precipitation collects and drains off into a common outlet, such as into a river, bay, or other body of water . The drainage basin includes all the surface water from rain runoff, snowmelt, and nearby streams that run downslope towards the shared outlet, as well as the groundwater underneath the earth's surface . Drainage basins connect into other drainage basins at lower elevations in a hierarchical pattern, with smaller sub-drainage basins, which in turn drain into another common outlet . </P> <P> Other terms used to describe drainage basins are catchment, catchment basin, drainage area, river basin and water basin . In North America, the term watershed is commonly used to mean a drainage basin, though in other English - speaking countries, it is used only in its original sense, to mean a drainage divide, a ridge that separates adjacent drainage basins . </P>

Area of land drained by a single river