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Watershed delineation is the process of identifying the boundary of a watershed, also referred to as a catchment, drainage basin, or river basin. It is an important step in many areas of environmental science, engineering, and management, for example to study flooding, aquatic habitat, or water pollution.
Other terms for a drainage basin are catchment area, catchment basin, drainage area, river basin, water basin, [3] [4] and impluvium. [5] [6] [7] In North America, they are commonly called a watershed, though in other English-speaking places, "watershed" is used only in its original sense, that of the drainage divide line.
Grey areas are endorheic basins that do not drain to the ocean. The list of drainage basins by area identifies basins (also known as "catchments" or, in North American usage, "watersheds"), sorted by area, which drain to oceans , mediterranean seas , rivers, lakes and other water bodies.
Drainage areas are delineated in a hierarchical fashion, with "level 1" watersheds at continental scales, subdivided into smaller level 2 watersheds, which are divided into level 3 watersheds, and so on. Each watershed is assigned a unique number, called a Pfafsetter Code, based on its location within the overall drainage system. [1]
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 .
The surrounding topography of a catchment zone influences the flow vectors and direction that the water flows. [1] Water flows from areas of high potential energy to low potential energy under the influence of gravity. The geometry of the slope leading to the catchment area influences the amount of water the catchment will contain. [1]
Watersheds of North America are large drainage basins which drain to separate oceans, seas, gulfs, or endorheic basins. There are six generally recognized hydrological continental divides which divide the continent into seven principal drainage basins spanning three oceans ( Arctic , Atlantic and Pacific ) and one endorheic basin.
These can form in areas with extensive limestone deposits, where surface streams can disappear into the groundwater via caves and subterranean drainage routes. [5] They can also form in areas where there has been much geological disruption. A classic example is the Canadian Shield.