Drainage basin

A drainage basin's boundaries are determined by watershed delineation, a common task in environmental engineering and science.

[citation needed] In North America, surface water drains to the Atlantic via the Saint Lawrence River and Great Lakes basins, the Eastern Seaboard of the United States, the Canadian Maritimes, and most of Newfoundland and Labrador.

The Caribbean Sea and Gulf of Mexico basin includes most of the U.S. interior between the Appalachian and Rocky Mountains, a small part of the Canadian provinces of Alberta and Saskatchewan, eastern Central America, the islands of the Caribbean and the Gulf, and a small part of northern South America.

The Mediterranean Sea basin, with the Black Sea, includes much of North Africa, east-central Africa (through the Nile River), Southern, Central, and Eastern Europe, Turkey, and the coastal areas of Israel, Lebanon, and Syria.

The Arctic Ocean drains most of Western Canada and Northern Canada east of the Continental Divide, northern Alaska and parts of North Dakota, South Dakota, Minnesota, and Montana in the United States, the north shore of the Scandinavian peninsula in Europe, central and northern Russia, and parts of Kazakhstan and Mongolia in Asia, which totals to about 17% of the world's land.

[9] Its basin includes much of China, eastern and southeastern Russia, Japan, the Korean Peninsula, most of Indochina, Indonesia and Malaysia, the Philippines, all of the Pacific Islands, the northeast coast of Australia, and Canada and the United States west of the Continental Divide (including most of Alaska), as well as western Central America and South America west of the Andes.

If water evaporates or infiltrates into the ground at its terminus, the area can go by several names, such playa, salt flat, dry lake, or alkali sink.

Examples of such interstate compacts are the Great Lakes Commission and the Tahoe Regional Planning Agency.

This water will either remain underground, slowly making its way downhill and eventually reaching the basin, or it will permeate deeper into the soil and consolidate into groundwater aquifers.

In the unlikely event that the gauges are many and evenly distributed over an area of uniform precipitation, using the arithmetic mean method will give good results.

The isohyetal method involves contours of equal precipitation are drawn over the gauges on a map.

Isochrone maps can be used to show the time taken for runoff water within a drainage basin to reach a lake, reservoir or outlet, assuming constant and uniform effective rainfall.

As water flows over the ground and along rivers it can pick up nutrients, sediment, and pollutants.

Modern use of artificial fertilizers, containing nitrogen (as nitrates), phosphorus, and potassium, has affected the mouths of drainage basins.

Management of shared drainage basins is also seen as a way to build lasting peaceful relationships among countries.

Catchment factors are: topography, shape, size, soil type, and land use (paved or roofed areas).

Size will help determine the amount of water reaching the river, as the larger the catchment the greater the potential for flooding.

[5] Land use can contribute to the volume of water reaching the river, in a similar way to clay soils.

The Mississippi River drains the largest area of any U.S. river, much of it agricultural regions. Agricultural runoff and other water pollution that flows to the outlet is the cause of the hypoxic, or dead zone in the Gulf of Mexico .
Major continental divides , showing how terrestrial drainage basins drain into the oceans. Grey areas are endorheic basins that do not drain to the oceans
Endorheic basin in Central Asia
Drainage basin of the Ohio River , part of the Mississippi River drainage basin
Top-down illustration of a dendritic drainage basin. The dashed line is the main water divide of the hydrography basin.
Digital terrain map of the Latorița River 's drainage basin in Romania