Other terms for a drainage basin arecatchment area,catchment basin,drainage area,river basin,water basin,[3][4] andimpluvium.[5][6][7] In North America, they are commonly called awatershed, though in other English-speaking places, "watershed" is used only in its original sense, that of the drainage divide line.
A drainage basin's boundaries are determined bywatershed delineation, a common task in environmental engineering and science.
In a closed drainage basin, orendorheic basin, rather than flowing to the ocean, water converges toward the interior of the basin, known as asink, which may be a permanent lake, adry lake, or a point where surface water islost underground.[8]
Drainage basins are similar but not identical tohydrologic units, which are drainage areas delineated so as to nest into a multi-level hierarchicaldrainage system. Hydrologic units are defined to allow multiple inlets, outlets, or sinks. In a strict sense, all drainage basins are hydrologic units but not all hydrologic units are drainage basins.[8]
Majorcontinental divides, showing how terrestrial drainage basins drain into the oceans. Grey areas areendorheic basins that do not drain to the oceans
Just over 13% of the land in the world drains to thePacific Ocean.[9] Its basin includes much of China, eastern and southeastern Russia, Japan, theKorean Peninsula, most of Indochina, Indonesia and Malaysia, the Philippines, all of thePacific Islands, the northeast coast ofAustralia, 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.
The five largest river basins (by area), from largest to smallest, are those of theAmazon (7 million km2), theCongo (4 million km2), theNile (3.4 million km2), theMississippi (3.22 million km2), and theRío de la Plata (3.17 million km2). The three rivers that drain the most water, from most to least, are the Amazon,Ganges, and Congo rivers.
Endorheic basin are inland basins that do not drain to an ocean. Endorheic basins cover around 18% of the Earth's land. Some endorheic basins drain to anEndorheic lake orInland sea. Many of these lakes areephemeral or vary dramatically in size depending on climate and inflow. If water evaporates or infiltrates into the ground at its terminus, the area can go by several names, such playa, salt flat,dry lake, oralkali sink.
In endorheicbodies of water where evaporation is the primary means of water loss, the water is typically more saline than the oceans. An extreme example of this is theDead Sea.[citation needed]
Drainage basins have been historically important for determining territorial boundaries, particularly in regions where trade by water has been important. For example, theEnglish crown gave theHudson's Bay Company a monopoly on thefur trade in the entireHudson Bay basin, an area calledRupert's Land.Bioregional political organization today includes agreements of states (e.g., internationaltreaties and, within the US,interstate compacts) or other political entities in a particular drainage basin to manage the body or bodies of water into which it drains. Examples of such interstate compacts are theGreat Lakes Commission and theTahoe Regional Planning Agency.
Inhydrology, the drainage basin is a logical unit of focus[clarification needed] for studying the movement of water within thehydrological cycle. The process of finding a drainage boundary is referred to aswatershed delineation. Finding the area and extent of a drainage basin is an important step in many areas of science and engineering.
Most of the water that discharges from the basin outlet originated asprecipitation falling on the basin.[11] A portion of the water that enters thegroundwater system beneath the drainage basin may flow towards the outlet of another drainage basin because groundwater flow directions do not always match those of their overlying drainage network. Measurement of the discharge of water from a basin may be made by astream gauge located at the basin's outlet. Depending on the conditions of the drainage basin, as rainfall occurs some of it seeps directly into the ground. 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.[12]
As water flows through the basin, it can form tributaries that change the structure of the land. There are three different main types, which are affected by the rocks and ground underneath. Rock that is quick to erode formsdendritic patterns, and these are seen most often. The two other types of patterns that form are trellis patterns and rectangular patterns.[13]
Rain gauge data is used to measure total precipitation over a drainage basin, and there are different ways to interpret that data. In the unlikely event that the gauges are many and evenly distributed over an area of uniform precipitation, using thearithmetic mean method will give good results. In theThiessen polygon method, the drainage basin is divided into polygons with the rain gauge in the middle of each polygon assumed to be representative for the rainfall on the area of land included in its polygon. These polygons are made by drawing lines between gauges, then making perpendicular bisectors of those lines form the polygons. Theisohyetal method involves contours of equal precipitation are drawn over the gauges on a map. Calculating the area between these curves and adding up the volume of water is time-consuming.
Isochrone maps can be used to show the time taken forrunoff water within a drainage basin to reach a lake, reservoir or outlet, assuming constant and uniform effective rainfall.[14][15][16][17]
Drainage basins are the principal hydrologic unit considered influvialgeomorphology. A drainage basin is the source for water andsediment that moves from higher elevation through the river system to lower elevations as they reshape the channel forms.
Drainage basins are important inecology. As water flows over the ground and along rivers it can pick upnutrients,sediment, andpollutants. With the water, they are transported towards the outlet of the basin, and can affect the ecological processes along the way as well as in the receivingwater body.
Modern use ofartificial fertilizers, containingnitrogen (asnitrates),phosphorus, andpotassium, has affected the mouths of drainage basins. The minerals are carried by the drainage basin to the mouth, and may accumulate there, disturbing the natural mineral balance. This can causeeutrophication where plant growth is accelerated by the additional material.
Because drainage basins are coherent entities in a hydrological sense, it has become common to manage water resources on the basis of individual basins. In theU.S. state of Minnesota, governmental entities that perform this function are called "watershed districts".[18] In New Zealand, they are called catchment boards. Comparable community groups based in Ontario, Canada, are calledconservation authorities. In North America, this function is referred to as "watershed management".InBrazil, the National Policy of Water Resources, regulated by Act n° 9.433 of 1997, establishes the drainage basin as the territorial division of Brazilian water management.
When a river basin crosses at least one political border, either a border within a nation or an international boundary, it is identified as atransboundary river. Management of such basins becomes the responsibility of the countries sharing it.Nile Basin Initiative,OMVS forSenegal River,Mekong River Commission are a few examples of arrangements involving management of shared river basins.
Management of shared drainage basins is also seen as a way to build lasting peaceful relationships among countries.[19]
The catchment is the most significant factor determining the amount or likelihood offlooding.
Catchment factors are:topography, shape, size,soil type, andland use (paved orroofed areas). Catchment topography and shape determine the time taken forrain to reach the river, while catchment size, soil type, and development determine the amount of water to reach the river.
Generally, topography plays a big part in how fast runoff will reach a river. Rain that falls in steepmountainous areas will reach the primary river in the drainage basin faster than flat or lightly sloping areas (e.g., > 1% gradient).
Size will help determine the amount of water reaching the river, as the larger the catchment the greater the potential for flooding. It is also determined on the basis of length and width of the drainage basin.
Soil type will help determine how much water reaches the river. The runoff from the drainage area is dependent on the soil type. Certain soil types such assandy soils are very free-draining, and rainfall on sandy soil is likely to be absorbed by the ground. However, soils containingclay can be almost impermeable and therefore rainfall on clay soils will run off and contribute to flood volumes. After prolonged rainfall even free-draining soils can becomesaturated, meaning that any further rainfall will reach the river rather than being absorbed by the ground. If the surface is impermeable the precipitation will create surface run-off which will lead to higher risk of flooding; if the ground is permeable, the precipitation will infiltrate the soil.[5]
Land use can contribute to the volume of water reaching the river, in a similar way to clay soils. For example, rainfall on roofs,pavements, androads will be collected by rivers with almost no absorption into thegroundwater.A drainage basin is an area of land where all flowing surface water converges to a single point, such as a river mouth, or flows into another body of water, such as a lake or ocean.
Tenaja – type of water basin or retention area, implying a natural or geologic cistern in rock which retains water; often created by erosional processes within intermittent streamsPages displaying wikidata descriptions as a fallback
^abHuneau, F.; Jaunat, J.; Kavouri, K.; Plagnes, V.; Rey, F.; Dörfliger, N. (2013-07-18). "Intrinsic vulnerability mapping for small mountainouskarst aquifers, implementation of the new PaPRIKa method to Western Pyrenees (France)".Engineering Geology.161. Elsevier:81–93.Bibcode:2013EngGe.161...81H.doi:10.1016/j.enggeo.2013.03.028.Efficient management is strongly correlated to the proper protection perimeter definition around springs and proactive regulation of land uses over the spring's catchment area ("impluvium").
^Lachassagne, Patrick (2019-02-07)."Natural mineral waters". Encyclopédie de l'environnement. Retrieved2019-06-10.In order to preserve the long-term stability and purity of natural mineral water, bottlers have put in place "protection policies" for the impluviums (or catchment areas) of their sources. The catchment area is the territory on which the part of precipitated rainwater and/orsnowmelt that infiltrates the subsoil feeds the mineral aquifer and thus contributes to the renewal of the resource. In other words, a precipitated drop on the impluvium territory may join the mineral aquifer; ...
^Labat, D.; Ababou, R.; Manginb, A. (2000-12-05). "Rainfall–runoff relations forkarstic springs. Part I: convolution and spectral analyses".Journal of Hydrology.238 (3–4):123–148.Bibcode:2000JHyd..238..123L.doi:10.1016/S0022-1694(00)00321-8.The non-karstic impluvium comprises all elements of the ground surface and soils that are poorly permeable, on a part of which water is running while also infiltrating on another minor part. This superficial impluvium, if it exists, constitutes the first level of organization of the drainage system of the karstic basin.
