Drainage divide

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(Redirected from Water divide)

Main European drainage divides (red lines) separating catchments (gray regions).

A drainage divide, water divide, or simply divide is the separation between neighbouring drainage basins (catchments). In hilly country, the divide lies along topographical peaks and ridges, but in flat country or on a high plateau (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 country 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 the need for bridges.

A divide is also known as:

In British Isles usage, 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 is used instead for the drainage basin itself);
a water parting;
a height of land (in Canada).

[edit] Types of drainage divide

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 meet 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.