Drainage divide

Main European drainage divides (red lines) separating drainage basins (gray regions)

A drainage divide, water divide, divide or (outside North America) watershed is the line separating neighbouring drainage basins (catchments). In hilly country, the divide lies along topographical peaks and ridges, and may be in the form of a single range of hills or mountains (known as a Dividing range), but in flat country (especially where the ground is marshy) the divide may be invisible – just a more or less notional line on the ground on either side of which falling raindrops will start a journey to different rivers, and even to different sides of a region or continent.

Drainage divides are important geographical, and often also political boundaries. Roads (such as ridgeways) and rail tracks often follow divides to minimise grades (gradients), and to avoid marshes and rivers.

A divide is also known as:

• A watershed, the line between drainage basins – shedding is an old term for splitting or dividing, so it is the line which divides the water (however in North America "watershed" has come to mean the drainage basin itself);
• a water parting;
• a height of land (in Canada).

A valley floor divide is a low drainage divide running across a valley, sometimes created by deposition or stream capture.

Types

Drainage divides can be grouped in three types:

• Continental divide

A divide in which the waters on each side flow to different oceans (example: the Nile and Congo divide, Lunghin Pass triple divide)

• Major drainage divide

The waters on each side of the divide never meet again, but do flow into the same ocean (example: the divide between the Yellow River basin and the Yangtze)

• Minor drainage divide

The waters part but eventually join again at a river confluence (example: the Mississippi and Missouri divide)

Drainage divides are a hindrance to river navigation. In pre-industrial times water divides were crossed at portages. Later, canals were built to connect the adjoining drainage basins.

See also

• Watersheds
• List of watershed topics
• European Watershed
• Scottish watershed
• Drainage basin
• Source (river or stream) (headwater)
• Mountain pass