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54-632: The river is 240 km long and its basin covers around 20,600 km. Thirty percent of the basin is located in the Andean range. It is born in Laguna del Maule in Talca Province , at an altitude of 2,200 mt in the vicinity of the border with Argentina . From that point the rivers flows westwardly and is soon joined on its left bank by one of its main tributaries , the Melado River , which

108-427: A hierarchical pattern . Other terms for a drainage basin are catchment area , catchment basin , drainage area , river basin , water basin , and impluvium . 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. A drainage basin's boundaries are determined by watershed delineation ,

162-426: A "raw" DEM, or analysts can download hydrologically-conditioned DEMs such as the near-global HydroSHEDS, MERIT-Hydro, or EDNA for the continental United States. The usual steps for hydrologic conditioning of a DEM are: Additionally, some methods allow for "fencing ridgelines" and burning in flow pathways through lakes. Some methods also enforce a small slope onto flat areas so that flow will continue to move toward

216-426: A DEM. The first method, introduced by Australian geographers O'Callaghan and Mark in 1984, is referred to as D8. Water flows from a pixel to one of 8 possible directions to a neighboring cell (including diagonally), based on the direction of steepest slope. There are disadvantages to this method as water flow is limited to 8 directions, separated by 45°, which may result in unrealistic flow patterns. Also, because all of

270-437: A common task in environmental engineering and science. In a closed drainage basin, or endorheic basin , rather than flowing to the ocean, water converges toward the interior of the basin, known as a sink , which may be a permanent lake, a dry lake , or a point where surface water is lost underground . Drainage basins are similar but not identical to hydrologic units , which are drainage areas delineated so as to nest into

324-454: 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 the arithmetic mean method will give good results. In the Thiessen polygon method, the drainage basin is divided into polygons with the rain gauge in the middle of each polygon assumed to be representative for

378-540: A drainage boundary is referred to as watershed 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 as precipitation falling on the basin. A portion of the water that enters the groundwater 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

432-403: A fundamental geographic unit in hydrology , the science concerned with the movement, distribution, and management of water on Earth. Delineating watersheds may be considered an application of hydrography , the branch of applied sciences which deals with the measurement and description of the physical features of oceans, seas, coastal areas, lakes and rivers. It is also related to geomorphometry ,

486-602: A multi-level hierarchical drainage 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. About 48.71% of the world's land drains to the Atlantic Ocean . In North America , surface water drains to the Atlantic via the Saint Lawrence River and Great Lakes basins,

540-769: A number of significant flora and fauna of Chile . Historically the Chilean Wine Palm , Jubaea chilensis , was present in the Maule River basin; however, due to expansion of the human population in this region, this endangered tree has a more restricted range that still includes some of the northern portion of the Maule Region. The Maule has been considered as Chile's literary river par excellence . The number of poets , writers, historians, orators , playwrights , journalists as well as composers and folk musicians that have been born or have settled in

594-495: A number of vector datasets representing watersheds as polygons that can be displayed and analyzed with GIS or other software. In these datasets, the entire land surface is divided into "subwatersheds" or "unit catchments." Individual unit watersheds can be combined or merged to find larger watersheds. The unit catchments have linked hydrological code data or similar metadata to create a flow network , so flow pathways and connections can be determined via network analysis. This list

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648-446: A topographic map, for example to identify ridges, valleys, and the direction of steepest slope. Even in the computer era, manual watershed delineation is still a useful skill, in order to check whether watersheds generated with software are correct. Instructions for manual watershed delineation can be found in some textbooks in geography or environmental management, in government pamphlets, or in online video tutorials. According to

702-493: A transparent overlay. The watershed area can then be estimated using a planimeter , by overlaying graph paper and counting grid cells, or the result can be digitized for use with mapping software. The same process can be done on a computer, sketching the watershed boundary (with a mouse or stylus) over a digital copy of a topographic map. This is referred to as "heads up digitizing" or "on-screen digitizing." For "manual" watershed delination, one must know how to read and interpret

756-475: 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. The activity of watershed delineation is typically performed by geographers, scientists, and engineers. Historically, watershed delineation was done by hand on paper topographic maps , sometimes supplemented with field research. In

810-405: Is a tradeoff, as a finer grid with more pixels increases computing time. Nevertheless, even high-resolution data may not adequately capture flow pathways in complex environments like cities and suburbs, where flow is directed by curbs, culverts, and storm drains. Finally, some errors can result from the algorithm or the choice of parameters. Because errors are common, some authorities insist that

864-418: Is an area of land in which 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 . A basin is separated from adjacent basins by a perimeter, the drainage divide , made up of a succession of elevated features, such as ridges and hills . A basin may consist of smaller basins that merge at river confluences , forming

918-700: Is born in Laguna Dial, in Linares Province . Further on, and still in its upper course, the Maule is joined, this time on its right bank by rivers Colorado, Claro, Puelche and Cipreses. Before arriving at the central valley , the Maule is dammed into the Colbún dam lake that feeds the hydroelectric power station of the same name. Further on, the Maule is joined by the Claro (another river named Claro) and

972-434: Is not always correct. Some errors stem from incorrectly placing the watershed outlet on the digital river network, or "snapping the pour point." Another class of errors stems from inaccuracies in the digital terrain data, or where its resolution is too coarse to capture flow pathways. In general, DEMs with higher spatial resolution can more realistically describe topography of the land surface and flow direction. However, there

1026-426: Is possible to use DEMs in different formats for watershed delineation, such as a Triangular Irregular Network (TIN), or Hexagonal tiling however most contemporary algorithms make use of a regular rectangular grid. In the 1980s and 1990s, digital elevation models were often obtained by scanning and digitizing the contours on paper topographic maps, which were then converted to a TIN or a gridded DEM. More recently,

1080-487: Is referred to as " watershed management ". In Brazil , 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 a transboundary river . Management of such basins becomes

1134-614: Is the Dead Sea . Drainage basins have been historically important for determining territorial boundaries, particularly in regions where trade by water has been important. For example, the English crown gave the Hudson's Bay Company a monopoly on the fur trade in the entire Hudson Bay basin, an area called Rupert's Land . Bioregional political organization today includes agreements of states (e.g., international treaties and, within

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1188-589: The 1980s, automated methods were developed for watershed delineation with computers and electronic data, and these are now in widespread use. Computerized methods for watershed delineation use digital elevation models (DEMs), datasets that represent the height of the Earth's land surface. Computerized watershed delineation may be done using specialized hydrologic modeling software such as WMS , geographic information system software like ArcGIS or QGIS , or with programming languages like Python or R . Watersheds are

1242-713: The African Great Lakes , the interiors of Australia and the Arabian Peninsula , and parts in Mexico and the Andes . Some of these, such as the Great Basin, are not single drainage basins but collections of separate, adjacent closed basins. In endorheic bodies 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

1296-607: The Eastern Seaboard of the United States, the Canadian Maritimes , and most of Newfoundland and Labrador . Nearly all of South America east of the Andes also drains to the Atlantic, as does most of Western and Central Europe and the greatest portion of western Sub-Saharan Africa , as well as Western Sahara and part of Morocco . The two major mediterranean seas of the world also flow to

1350-897: The Loncomilla . The latter flows from the south and receives several tributaries: the Putagán , the Achibueno - Ancoa system, the Perquilauquén , the Purapel and the Cauquenes . In its lower reaches, the river receives only one modest tributary , the Estero de los Puercos and, after flowing for nearly 250 kilometers, the Maule ends at the Pacific Ocean , north of the city of Constitución . The Maule River basin contains

1404-599: The Maule Region , to which "the river of the fogs" has given its name, is quite staggering. Many Latin American stories have had the river as the main background or protagonist. Several anthologies, author's dictionaries and essays have given vivid accounts of the vast cultural wealth of the region around river Maule. 35°19′00″S 72°24′30″W  /  35.31667°S 72.40833°W  / -35.31667; -72.40833 Drainage basin A drainage basin

1458-683: The Mississippi (3.22 million km ), and the Río de la Plata (3.17 million km ). 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 an Endorheic lake or Inland sea . Many of these lakes are ephemeral or vary dramatically in size depending on climate and inflow. If water evaporates or infiltrates into

1512-809: 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

1566-403: The groundwater . 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. Watershed delineation For watershed segmentation , a technique for image processing, see Watershed (image processing) . Watershed delineation is the process of identifying the boundary of

1620-433: The 1980s, and are now in widespread use in the science and engineering communities. Researchers have even used computer methods to delineate watersheds on Mars. Automated watershed delineation methods use digital data of the earth's elevation, a Digital Elevation Model , or DEM. Typically, algorithms use the method of "steepest slope" to calculate the flow direction from a grid cell (or pixel) to one of its neighbors. It

1674-789: The Andes. The Indian Ocean 's drainage basin also comprises about 13% of Earth's land. It drains the eastern coast of Africa, the coasts of the Red Sea and the Persian Gulf , the Indian subcontinent , Burma, and most parts of Australia . The five largest river basins (by area), from largest to smallest, are those of the Amazon (7 million km ), the Congo (4 million km ), the Nile (3.4 million km ),

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1728-726: The Atlantic. 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

1782-456: The DEM is obtained by aerial or satellite remote sensing , using stereophotogrammetry , lidar , or radar . To use a rectangular grid DEM for watershed delineation, it must first be processed or "conditioned" in order to return realistic results. The result is sometimes referred to as a "hydro-enforced" DEM or a "HydroDEM." Most of the software packages listed below can perform these functions on

1836-677: The US Geological Survey, there are 5 steps to manual watershed delineation: General Rules: One disadvantage to manual watershed delineation is that it is subject to errors and the individual judgment of the analyst. The Illinois Environmental Protection Agency wrote, "bear in mind that delineating a watershed is an inexact science. Any two people, even if both are experts, will come up with slightly different boundaries." Especially for smaller watersheds and when accurate results are important, field reconnaissance may be needed to find features that are not shown on maps. "Going out into

1890-623: 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 the Great Lakes Commission and the Tahoe Regional Planning Agency . In hydrology , the drainage basin is a logical unit of focus for studying the movement of water within the hydrological cycle . The process of finding

1944-406: 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 forms dendritic patterns, and these are seen most often. The two other types of patterns that form are trellis patterns and rectangular patterns. Rain gauge data is used to measure total precipitation over

1998-430: The discharge of water from a basin may be made by a stream 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. As water flows through

2052-441: The drainage area is dependent on the soil type. Certain soil types such as sandy soils are very free-draining, and rainfall on sandy soil is likely to be absorbed by the ground. However, soils containing clay 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 become saturated , meaning that any further rainfall will reach

2106-697: The drainage basin to the mouth, and may accumulate there, disturbing the natural mineral balance. This can cause eutrophication 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 the U.S. state of Minnesota , governmental entities that perform this function are called " watershed districts ". In New Zealand, they are called catchment boards. Comparable community groups based in Ontario, Canada, are called conservation authorities . In North America, this function

2160-416: The field allows you to identify human alterations, such as road ditches, storm sewers and culverts that could change the direction of waters flow and thus change the watershed boundaries." Using computer software to delineate watersheds can be much faster than manual methods. It may also be more consistent, as it removes analyst's subjectivity. Automatic methods of watershed delineation have been in use since

2214-958: The first watershed delineation software was written in FORTRAN, such as CATCH and DEDNM. Watershed delineation tools are a part of several Geographic Information System software packages such as ArcGIS , QGIS , and GRASS GIS . There are standalone programs for watershed delineation such as TauDEM. Watershed delineation tools are also incorporated into some hydrologic modeling software packages. Software developers have also published libraries or modules in several languages (see list below). Many of these packages are free and open source, which means they can be expanded or adapted by those willing and able to write or modify code. Finally, there are web applications for delineating watersheds. Some of these web apps have extra features for science and engineering like calculating flow statistics or watershed land cover types (e.g.: StreamStats, Model My Watershed). There are

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2268-521: The flow is routed in one direction, the D8 method is unable to model situations where the flow diverges, such as on convex hillsides, in a river delta , or in branched or braided rivers . Alternative algorithms have been proposed and implemented to overcome this limitation, such as D∞. Nevertheless, the D8 algorithm remains in widespread use, and has been used to create important datasets such as HydroBasins and MERIT-Basins. Computerized watershed delineation

2322-435: The ground and along rivers it can pick up nutrients , sediment , and pollutants . 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 receiving water body . Modern use of artificial fertilizers , containing nitrogen (as nitrates ), phosphorus , and potassium , has affected the mouths of drainage basins. The minerals are carried by

2376-781: The ground at its terminus, the area can go by several names, such playa, salt flat, dry lake , or alkali sink . The largest endorheic basins are in Central Asia , including the Caspian Sea , the Aral Sea , and numerous smaller lakes. Other endorheic regions include the Great Basin in the United States, much of the Sahara Desert , the drainage basin of the Okavango River ( Kalahari Basin ), highlands near

2430-610: The outlet. The step of "burning in" stream channels involves artificially deepening the channel, by subtracting a large elevation value from pixels that represent the channel. This ensures that once flow has entered the channel, it will stay there rather than jumping out and flowing overland or into another channel. Some algorithms infer the location of channels automatically from the DEM. Better results are usually obtained by burning in mapped stream channels, or channels derived from satellite or aerial imagery. There are several different algorithms available for calculating flow direction from

2484-400: The quantitative science of analyzing land surfaces. Watershed delineation continues to be an active area of research, with scientists and programmers developing new algorithms and methods, and making use of increasingly high-resolution data from aerial or satellite remote sensing . The conventional method of finding a watershed boundary is to draw it by hand on a paper topographic map , or on

2538-418: 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. The isohyetal 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

2592-631: The responsibility of the countries sharing it. Nile Basin Initiative , OMVS for Senegal 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. The catchment is the most significant factor determining the amount or likelihood of flooding . Catchment factors are: topography , shape, size, soil type, and land use (paved or roofed areas). Catchment topography and shape determine

2646-484: The results of automated delineation must be carefully checked. The US Geological Survey's standards for the US Watershed Boundary Dataset allow the use of software "to generate intermediate or “draft” boundary lines," which then must be verified by the analyst by overlaying them on a computer display over basemaps (scanned topographic maps, aerial photographs) to verify their accuracy. Some of

2700-461: 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. 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 , and roads will be collected by rivers with almost no absorption into

2754-418: The speed with which the runoff reaches a river. A long thin catchment will take longer to drain than a circular catchment. 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

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2808-415: The time taken for rain 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 steep mountainous areas will reach the primary river in the drainage basin faster than flat or lightly sloping areas (e.g., > 1% gradient). Shape will contribute to

2862-477: The time taken for runoff water within a drainage basin to reach a lake, reservoir or outlet, assuming constant and uniform effective rainfall. Drainage basins are the principal hydrologic unit considered in fluvial geomorphology . A drainage basin is the source for water and sediment that moves from higher elevation through the river system to lower elevations as they reshape the channel forms. Drainage basins are important in ecology . As water flows over

2916-727: The world's land. Just over 13% of the land in the world drains to the Pacific Ocean . 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

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