Drainage divide
A drainage divide, water divide, ridgeline,[1] watershed, water parting or height of land is elevated terrain that separates neighboring drainage basins. On rugged land, 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. On flat terrain, especially where the ground is marshy, the divide may be difficult to discern.
A triple divide is a point, often a summit, where three drainage basins meet. A valley floor divide is a low drainage divide that runs across a valley, sometimes created by deposition or stream capture. Major divides separating rivers that drain to different seas or oceans are continental divides.
The term height of land is used in Canada and the United States to refer to a drainage divide.
Types
Drainage divides can be divided into three types:[5]
- Congo-Nile Divide.[6]
- Major drainage divides in which waters on each side of the divide never meet but flow into the same ocean, such as the divide between the Yangtze. Another, more subtle example is the Schuylkill-Lehigh divide at Pisgah Mountain in Pennsylvania in which 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, with each tributary complex having separate outlets into the Atlantic.
- Minor drainage divides in which waters are originally separate but eventually join at a river confluence, such as the Mississippi River and the Missouri River drainage divides.
Valley-floor divides
A valley-floor divide occurs on the bottom of a valley and arises as a result of subsequent depositions, such as scree, in a valley through which a river originally flowed continuously.[7]
Examples include the
.Settlements are often built on valley-floor divides in the Alps. Examples are
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Political boundaries
Since ridgelines are sometimes easy to see and agree about, drainage divides may form natural borders defining political boundaries, as with the Royal Proclamation of 1763 in British North America which coincided with the ridgeline of the Appalachian Mountains forming the Eastern Continental Divide that separated settled colonial lands in the east from Indian Territory to the west.[8] Another instance of a border matching a watershed in modern times involves the western border between Labrador and Quebec, as arbitrated by the privy council in 1927.[9]
Portages and canals
Drainage divides hinder waterway 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. The name is enshrined at the Height of Land Portage on the route from the Great Lakes in the Atlantic drainage basin to the Hudson Bay drainage basin.[10]
See also
- List of watershed topics – Watershed terms and topics
- River source – Starting point of a river
References
- ^ a b "ridgeline. Dictionary.com" (Dictionary.com Unabridged ed.). Random House Inc. Retrieved 7 September 2013.
- ^ Colombo, John Robert (16 December 2013). "Height of land". The Canadian Encyclopedia. Archived from the original on 20 June 2014.
- ISBN 978-0-07-463578-0.
- ^ Decker, Jody F. (2011). "Portages". In Wishart, David J. (ed.). Encyclopedia of the Great Plains.
- ^ "Divide". Resource Library. National Geographic Society. Retrieved 3 April 2022.
- ^ "Congo-Nile Divide Landscape". Albertine Rift. Wildlife conservation Society. Retrieved 3 April 2022.
- ISBN 978-3-423-03422-7.
- JSTOR 4247979.
- JSTOR 208004.
- ISBN 978-1-61069-105-5.
Further reading
- DeBarry, Paul A. (2004). Watersheds : processes, assessment, and management. Hoboken, N.J.: Wiley. ISBN 978-0471264231.