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42-553: Little is known about the Selonians. There is little archaeological evidence and in historic sources the region is often described as a "scarcely populated land". In written sources they are mentioned only few times. Archeological data can trace the Selonians back to the beginning of 1st millennium AD when they lived on both sides of the Daugava River . But since the 6th and 7th centuries their settlements can be traced only on

84-484: 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 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

126-414: 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 , 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

168-454: 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

210-540: 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

252-410: 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 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

294-807: Is a large river rising in the Valdai Hills of Russia that flows through Belarus and Latvia into the Gulf of Riga of the Baltic Sea . The Daugava rises close to the source of the Volga . It is 1,020 km (630 mi) in length, of which 352 km (219 mi) are in Latvia and 325 km (202 mi) in Russia. It is a westward-flowing river, tracing out a great south-bending curve as it passes through northern Belarus. Latvia's capital, Riga , bridges

336-643: Is about 0.82 milligrams per liter, ionic phosphate is 0.038 milligrams per liter, and oxygen saturation is 80%. The high nitrate and phosphate load of the Daugava has contributed to the extensive buildup of phytoplankton biomass in the Baltic Sea; the Oder and Vistula rivers also contribute to the high nutrient loading of the Baltic. In Belarus, water pollution of the Daugava is considered moderately severe, with

378-487: 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

420-614: 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

462-713: 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

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504-828: 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. 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,

546-714: 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. The Indian Ocean 's drainage basin also comprises about 13% of Earth's land. It drains

588-633: The Baltic interior. In medieval times, the Daugava was part of the trade route from the Varangians to the Greeks , an important route for the transport of furs from the north and of Byzantine silver from the south. The Riga area, inhabited by the Finnic -speaking Livs , became a key location of settlement and defence of the mouth of the Daugava at least as early as the Middle Ages, as evidenced by

630-566: The Proto-Indo-European *dānu , meaning "large river". The Finno-Ugric names Vēna ( Livonian ), Väinajogi ( Estonian ), and Väinäjoki ( Finnish ) all stem from Proto-Finnic *väin , meaning "a large, peacefully rolling river". The total catchment area of the river is 87,900 km (33,900 sq mi), of which 33,150 km (12,800 sq mi) are in Belarus. The following rivers are tributaries to

672-563: The Soviet era due to collective agriculture (producing considerable adverse water pollution runoff) and hydroelectric power projects. This is the river that the Vula river flows into. Upstream of the Latvian town of Jekabpils , the river's pH has a characteristic value of about 7.8 (slight alkaline ). In this area, the concentration of ionic calcium is around 43 milligrams per liter, nitrate

714-623: 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

756-866: The attack were German claims that Sēlpils hillfort was used as main Lithuanian support base for their attacks in Livonia . After a long siege the Selonians agreed to baptism and German rule and the stone Sēlpils Castle (German: Selburg) was built in place of the hillfort. The Selonians were last mentioned in written sources in the 15th century. This article about ethnicity is a stub . You can help Misplaced Pages by expanding it . Daugava River The Daugava ( Latgalian : Daugova ; Polish : Dźwina ; German : Düna [ˈdyːna] ) or Western Dvina ( Russian : Западная Двина , romanized :  Zapadnaya Dvina ; Belarusian : Заходняя Дзвіна ; Estonian : Väina ; Finnish : Väinäjoki )

798-406: 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

840-432: The chief sources being treated wastewater, fish-farming, and agricultural chemical runoff (such as herbicides, pesticides, nitrates, and phosphates). Catchment area (hydrology) A drainage basin 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

882-534: The chronicle describes the Selonians as Lithuanian allies . Their lands were subjects of the principalities of Jersika and Koknese , which were vassals of the principality of Polotsk . The Southern lands however were ruled by Lithuanian lords. In 1207, the German Brothers of Sword together with their Livonian and Latgalian allies besieged the main Selonian centre at Sēlpils hillfort . Reason for

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924-430: 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

966-441: 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

1008-697: 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

1050-857: 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 ), the Mississippi (3.22 million km ), and the Río de la Plata (3.17 million km ). The three rivers that drain

1092-583: 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 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 ,

1134-435: 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

1176-781: 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

1218-639: 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

1260-480: The left bank of the river. Selonian culture had a very strong Latgalian influence. Selonian and Latgalian burial traditions show little difference. Some scholars speculate that during the late Iron Age the Selonians had already partly merged with the Latgalians. The Chronicle of Henry of Livonia mentions the Selonians at the beginning of the 13th century, when they were conquered and christened. The author of

1302-514: 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

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1344-621: The now destroyed fort at Torņakalns on the west bank of the Daugava in present-day Riga. From the end of the Livonian War great part of the Daugava formed the northeastern border of Duchy of Courland and Semigallia saparating it initially from the Kingdom of Livonia , later Swedish Livonia and Riga Governorate . After the incorporation later in the Russian Empire the river formed a border between governorates of Courland on

1386-418: 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

1428-631: 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

1470-474: The river Daugava (from source to mouth): Humans have settled at the mouth of the Daugava and along the shores of the Gulf of Riga for millennia, initially participating in a hunter-gatherer economy and utilizing the waters of the Daugava estuary for fishing and gathering. Beginning around the sixth century CE, Viking explorers crossed the Baltic Sea and entered the Daugava River, navigating upriver into

1512-461: 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

1554-443: The river's estuary four times. Built on both riverbanks, the city centre is 15 kilometres (9.3 mi) from the river's mouth and is a significant port. According to Max Vasmer 's Etymological Dictionary , the toponym Dvina cannot stem from a Uralic language ; instead, it possibly comes from an Indo-European word which used to mean river or stream . The name Dvina resembles strongly Danuvius which itself derived from

1596-418: 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

1638-415: 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

1680-477: 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

1722-477: The western bank and Livonia and Vitebsk on the eastern bank. From 1936 to 1939 Ķegums Hydroelectric Power Station was built on the Daugava river in Latvia. Pļaviņas Hydroelectric Power Station was put into operation in 1968 and Riga Hydroelectric Power Plant in 1974. The following are some of the cities and towns built along the Daugava: The river began experiencing environmental deterioration in

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1764-673: 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, 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

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