Drainage divide

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Drainage divides (red lines) separating drainage basins (grey regions)

A drainage divide, water divide, divide, ridgeline,[1] watershed, water parting, or (in Canada) height of land[citation needed], is the line that separates neighbouring drainage basins. In hilly country, the divide lies along topographical ridges, and may be in the form of a single range of hills or mountains, known as a dividing range. In flat country—especially where the ground is marshy—the divide may be harder to discern.

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

Since ridgelines are easy to see and agree about, drainage divides are often natural borders defining political boundaries, as with 18th century North America's Royal Proclamation of 1763 that preceded the American Revolution.


Drainage divides can be grouped in three types:

A divide in which waters on each side flow to different oceans (for example: the Congo-Nile Divide)
  • Major drainage divide
Waters on each side of the divide never meet, but do flow into the same ocean (for example: the divide between the Yellow River basin and the Yangtze, or a more subtle example the Schuylkill-Lehigh divide at Pisgah Mountain in Pennsylvania, where two minor creeks divide to flow and grow east and west respectively joining the Lehigh River and Delaware River or the Susquehanna River and Potomac River each tributary complex having separate outlets into the Atlantic.)
  • Minor drainage divide
Waters part, but eventually rejoin at a river confluence (for example: the Mississippi and Missouri divides)

Drainage divides hinder river navigation. In pre-industrial times, water divides were crossed at portages. Later, canals connected adjoining drainage basins; a key problem in such canals is ensuring a sufficient water supply. Important examples are the Chicago Portage, connecting the Great Lakes and Mississippi by the Chicago Sanitary and Ship Canal, and the Canal des Deux Mers in France, connecting the Atlantic and the Mediterranean.

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  1. ^ a b "ridgeline. Dictionary.com" (Dictionary.com Unabridged ed.). Random House Inc. Retrieved 7 September 2013. ridgeline ridge·line [rij-lahyn] noun 1. a line formed along the highest points of a mountain ridge. 2. an area of higher ground separating two adjacent streams or watersheds.