Misplaced Pages

#379620

53-451: The Chad Basin is the largest endorheic basin in Africa, centered approximately on Lake Chad . It has no outlet to the sea and contains large areas of semi-arid desert and savanna . The drainage basin is approximately coterminous with the sedimentary basin of the same name, but extends further to the northeast and east. The basin spans four modern nations, including most of Chad and

106-569: A "Tibesti-Cameroon Trough" running NE-SW. That is, the two deepest parts are an extension of the Benue Trough that runs northeast to the margin of the basin, and another extension running from below the present lake to below the Ténéré rift structure to the east of the Aïr massif. The southern part of the basin is underlain by another elongated depression. This runs in an ENE direction and extends from

159-598: A large part of Niger , Nigeria and Cameroon . A combination of dams, increased irrigation, climate change , and reduced rainfall are causing water shortages. Lake Chad continues to shrink. The geological basin, which is smaller than the drainage basin, is a Phanerozoic sedimentary basin formed during the plate divergence that opened the South Atlantic Ocean. The basin lies between the West African Craton and Congo Craton , and formed about

212-798: A large portion of Europe drains to the endorheic Caspian Sea, Europe's wet climate means it contains relatively few terminal lakes itself: any such basin is likely to continue to fill until it reaches an overflow level connecting it with an outlet or erodes the barrier blocking its exit. There are some seemingly endorheic lakes, but they are cryptorheic, being drained either through manmade canals , via karstic phenomena, or other subsurface seepage. A few minor true endorheic lakes exist in Spain (e.g. Laguna de Gallocanta , Estany de Banyoles ), Italy , Cyprus ( Larnaca and Akrotiri salt lakes) and Greece . Many small lakes and ponds in North Dakota and

265-709: A mountain range, cutting off water egress to the ocean. The inland water flows into dry watersheds where the water evaporates, leaving a high concentration of minerals and other inflow erosion products. Over time this input of erosion products can cause the endorheic lake to become relatively saline (a " salt lake "). Since the main outflow pathways of these lakes are chiefly through evaporation and seepage, endorheic lakes are usually more sensitive to environmental pollutant inputs than water bodies that have access to oceans, as pollution can be trapped in them and accumulate over time. Endorheic regions can occur in any climate but are most commonly found in desert locations. This reflects

318-470: A redistribution of water from these hydrologically landlocked basins such that endorheic water loss has contributed to sea level rise , and it is estimated that most of the terrestrial water lost ends up in the ocean. In regions such as Central Asia, where people depend on endorheic basins and other surface water sources to satisfy their water needs, human activity greatly impacts the availability of that water. Large endorheic regions in Africa are located in

371-535: A sequence of grey to bluish-grey clays from the Zanclean , is a second aquifer at a depth of 240 to 380 metres (790 to 1,250 ft). Due to intensive pumping, since the start of the 1980s the water levels in both aquifers has been lowered, and some wells no longer function. There is a third, much lower, aquifer in Bima Sandstones that lies at a depth of 2,700 to 4,600 metres (8,900 to 15,100 ft). Both

424-466: Is a drainage basin that normally retains water and allows no outflow to other external bodies of water (e.g. rivers and oceans ); instead, the water drainage flows into permanent and seasonal lakes and swamps that equilibrate through evaporation . Endorheic basins are also called closed basins , terminal basins , and internal drainage systems . Endorheic regions contrast with open lakes (exorheic regions), where surface waters eventually drain into

477-525: Is just 155 metres (509 ft) above sea level in its deepest portion, while the surface of Lake Chad is 275 metres (902 ft) above sea level. The basin spans parts of eight countries. These are: The northern half of the basin is desert, containing the Ténéré desert, Erg of Bilma and Djurab Desert . South of that is the Sahel zone, dry savanna and thorny shrub savanna. The main rivers include riparian forests, flooding savannas and wetland areas. In

530-403: Is one such case, with annual precipitation of 850 mm (33 in) and characterized by waterlogged soils that require draining. Endorheic regions tend to be far inland with their boundaries defined by mountains or other geological features that block their access to oceans. Since the inflowing water can evacuate only through seepage or evaporation, dried minerals or other products collect in

583-627: The Bonneville flood . The Malheur / Harney lake system in Oregon is normally cut off from drainage to the ocean, but has an outflow channel to the Malheur River . This is presently dry, but may have flowed as recently as 1,000 years ago. Examples of relatively humid regions in endorheic basins often exist at high elevation. These regions tend to be marshy and are subject to substantial flooding in wet years. The area containing Mexico City

SECTION 10

#1732765955380

636-891: The Sahara Desert , the Sahel , the Kalahari Desert , and the East African Rift : Endorheic lakes exist in Antarctica's McMurdo Dry Valleys , Victoria Land , the largest ice-free area. Much of Western and Central Asia is a giant endorheic region made up of a number of contiguous closed basins. The region contains several basins and terminal lakes, including: Other endorheic lakes and basins in Asia include: Australia , being very dry and having exceedingly low runoff ratios due to its ancient soils, has many endorheic drainages. The most important are: Though

689-572: The climate changed , with a maximum about 2,300 years ago. The remains of fish and molluscs from this period are found in what are now desert regions. The Chad Basin covers almost 8% of the African continent, with an area of about 2,434,000 square kilometres (940,000 sq mi). It is surrounded by mountains. The Aïr Mountains and the Termit Massif in Niger form the western boundary. To

742-624: The 12th century. The Kanem empire went into decline, shrank, and during the 14th century was defeated by Bilala invaders from the Lake Fitri region. The Kanuri people commanded by the Sayfuwa migrated to the west and south of the lake, where they established the Bornu Empire . By the late 16th century the Bornu empire had expanded and recaptured the parts of Kanem that had been conquered by

795-819: The Arabs conquered North Africa during the 7th and 8th centuries, the Chad Basin became increasingly linked to the Muslim countries. Trade and improved agricultural techniques enabled more sophisticated societies, resulting in the early kingdoms of the Kanem Empire , the Wadai Empire , and the Sultanate of Bagirmi . Kanem developed during the 8th century in the region to the north and east of Lake Chad. The Sayfuwa dynasty that ruled this kingdom had adopted Islam by

848-573: The Bilala. Satellite states of Bornu included the Sultanate of Damagaram in the west and Baguirmi to the southeast of Lake Chad. The Tunjur people initiated the Wadai Empire to the east of Bornu during the 16th century. During the 17th century, the Maba people revolted and established a Muslim dynasty. At first, Wadai paid tribute to Bornu and Durfur, but by the 18th century Wadai was fully independent and had become an aggressor against its neighbors. To

901-567: The British sphere. Parfait-Louis Monteil was given charge of an expedition to discover where this line actually ran. On 9 April 1892 he reached Kukawa on the shore of the lake. During the next twenty years a large part of the Chad Basin was incorporated by treaty or by force into French West Africa . On 2 June 1909 the Wadai capital of Abéché was occupied by the French. The remainder of the basin

954-623: The Chad Basin. The population is growing rapidly. Ethnic groups include Kanuri , Maba , Buduma , Hausa , Kanembu , Kotoko , Bagger, Haddad , Kuri , Fulani and Manga . The largest cities are Kano and Maiduguri in Nigeria , Maroua in Cameroon , N'Djamena in Chad and Diffa in Niger . The main economic activities are farming, herding and fishing. At least 40% of the rural population of

1007-690: The Chad and Nile watersheds. These highland areas are part of the East Saharan montane xeric woodlands ecoregion . The Yellow Nile is a former tributary that connected the Ouaddaï highlands of eastern Chad to the Nile River Valley ca. 8000 to ca. 1000 BCE. Its remains are known as the Wadi Howar . The wadi passes through West Darfur near the northern border with Chad and meets up with

1060-400: The French word endoréisme , which combines endo- ( Ancient Greek : ἔνδον éndon 'within') and ῥεῖν rheîn 'flow'. Endorheic lakes (terminal lakes) are bodies of water that do not flow into an ocean or a sea. Most of the water that falls to Earth percolates into the oceans and the seas by way of a network of rivers, lakes, and wetlands . Analogous to endorheic lakes is

1113-477: The Northern Great Plains are endorheic, and some have salt encrustations along their shores. Some of Earth's ancient endorheic systems and lakes include: Ouadda%C3%AF highlands Batha River is an important ephemeral river that carries water west from these highlands during rainy seasons, usually during flash flooding . Ouaddaï highlands mark Chad's eastern border and also divide

SECTION 20

#1732765955380

1166-659: The Yola arm of the Benue trough. At times, parts of the basin were below the sea. In the northeastern part of the Benue Trough where it enters the Chad Basin there are marine sediments from the Late Cretaceous (100.5–66 Ma). These sediments seem to be considerably thicker towards the northeast. Boreholes under Maiduguri have found marine sediments 400 metres (1,300 ft) deep, lying over continental sediments 600 metres (2,000 ft) deep. The sea seems to have retreated from

1219-493: The balance between tectonic subsidence and rates of evaporation and sedimentation. Where the basin floor is dropping more rapidly than water and sediments can accumulate, any lake in the basin will remain below the sill level (the level at which water can find a path out of the basin). Low rainfall or rapid evaporation in the watershed favor this case. In areas where rainfall is higher, riparian erosion will generally carve drainage channels (particularly in times of flood), or cause

1272-426: The basin is impoverished and experiences chronic food shortages. Crop production based on rain is possible only in the southern belt. Flood recession agriculture is practiced around Lake Chad and in the riverine wetlands. Nomadic herders migrate with their animals into the grasslands of the northern part of the basin for a few weeks during each brief rainy season, where they intensively graze the nutritious grasses. When

1325-460: The basin, eventually making the water saline and also making the basin vulnerable to pollution. Continents vary in their concentration of endorheic regions due to conditions of geography and climate. Australia has the highest percentage of endorheic regions at 21 per cent while North America has the least at five per cent. Approximately 18 per cent of the Earth's land drains to endorheic lakes or seas,

1378-537: The class of bodies of water located in closed watersheds (endorheic watersheds) where the local topography prevents the drainage of water into the oceans and the seas. These endorheic watersheds (containing water in rivers or lakes that form a balance of surface inflows, evaporation and seepage) are often called sinks. Endorheic lakes are typically located in the interior of a landmass, far from an ocean, and in areas of relatively low rainfall. Their watersheds are often confined by natural geologic land formations such as

1431-653: The current and historical areas of the basin and the mega-basin contain concentrations of fossils. Fossil-fuels deposits in the area are estimated to exceed a trillion barrels of reserves. The Lake Chad Basin Commission was established in 1964 by Cameroon, Chad, Niger and Nigeria, the four countries that contain parts of Lake Chad. About 20% of the basin, lying in these countries, is termed the Conventional Basin. The Lake Chad Basin Commission manages use of water and other natural resources in this area. Although

1484-564: The degree that a lake no longer forms. Even most permanent endorheic lakes change size and shape dramatically over time, often becoming much smaller or breaking into several smaller parts during the dry season. As humans have expanded into previously uninhabitable desert areas, the river systems that feed many endorheic lakes have been altered by the construction of dams and aqueducts. As a result, many endorheic lakes in developed or developing countries have contracted dramatically, resulting in increased salinity, higher concentrations of pollutants, and

1537-440: The disruption of ecosystems. Even within exorheic basins, there can be "non-contributing", low-lying areas that trap runoff and prevent it from contributing to flows downstream during years of average or below-average runoff. In flat river basins, non-contributing areas can be a large fraction of the river basin, e.g. Lake Winnipeg 's basin. A lake may be endorheic during dry years and can overflow its basin during wet years, e.g.,

1590-473: The dry season starts they move back south, either to grazing lands around the lakes and floodplains, or to the savannas further to the south. During the period 2000-01, fisheries in the Lake Chad basin provided food and income to more than 10 million people, with a harvest of about 70,000 tons. Fisheries have been managed traditionally by a system where each village has recognized rights over a defined part of

1643-633: The end of this period the climate became drier. Around 20,000-40,000 years ago, eolianite sand dunes began to form in the north of the basin. During the Holocene , from 11,000 years ago until recently, a giant "Lake Mega-Chad" covered an area of more than 350,000 square kilometres (140,000 sq mi) in the basin. It would have drained to the Atlantic Ocean via the Benue River . Stratigraphic records show that "Mega-Chad" varied in size as

Chad Basin - Misplaced Pages Continue

1696-546: The far south there are dry forests. Rainfall varies widely from year to year. The amount of annual rainfall is very slight in the north of the basin, increasing to 1,200 millimetres (47 in) in the south. As late as 2000, the basin has remained home to large populations of wildlife. In the Sahel these include antelopes such as the addax and dama gazelle , and in the savanna there are korrigum and red-fronted gazelle . The black crowned crane and other waterbirds are found in

1749-473: The floodplains are drying. The Yedseram - Ngadda sub-basin further south is fed by the Yedseram River and Ngadda River , which join to form an 80 square kilometres (31 sq mi) swamp to the southwest of the lake. There is not any significant water flow from the swamp to the lake. The Central African Republic (CAR) contains the sources of the rivers Chari and Logone , which flow north into

1802-783: The former Tulare Lake . Because the Earth's climate has recently been through a warming and drying phase with the end of the Ice Ages, many endorheic areas such as Death Valley that are now dry deserts were large lakes relatively recently. During the last ice age, the Sahara may have contained lakes larger than any now existing. Climate change coupled with the mismanagement of water in these endorheic regions has led to devastating losses in ecosystem services and toxic surges of pollutants. The desiccation of saline lakes produces fine dust particles that impair agriculture productivity and harm human health. Anthropogenic activity has also caused

1855-539: The lake by 1000 BC. Permanent villages were established to the south of the lake by 500 BC at the start of the Iron Age . The Chad Basin contained important trade routes to the east and to the north across the Sahara. By the 5th century AD camels were being used for trans-Saharan trade via the Fezzan , or to the east via Darfur , where slaves and ivory were exchanged for salt, horses, glass beads, and, later, firearms. After

1908-553: The lake fluctuates considerably in size from one year to another, the general trend has been for water levels to decrease. There has been a proposal to supply water from the Congo Basin via a canal 2,400 kilometres (1,500 mi) long, but major political, technical, and economic challenges would have to be overcome to make this practical. Humans have lived in the inner Chad Basin from at least eight thousand years ago, and were engaging in agriculture and livestock management around

1961-540: The lake. The volume of water entering Chad annually from the CAR has decreased from about 33 cubic kilometres (7.9 cu mi) before the 1970s to 17 cubic kilometres (4.1 cu mi) during the 1980s. A further 3 cubic kilometres (0.72 cu mi) to 7 cubic kilometres (1.7 cu mi) of water annually flows from Cameroon into Chad via the Logone River. The Chari-Logone system accounts for about 95% of

2014-422: The largest of these land areas being the interior of Asia. In deserts, water inflow is low and loss to solar evaporation high, drastically reducing the formation of complete drainage systems . In the extreme case, where there is no discernible drainage system, the basin is described as arheic . Closed water flow areas often lead to the concentration of salts and other minerals in the basin. Minerals leached from

2067-563: The north contains the Hadejia and Jama'are rivers, which supply the 6,000 square kilometres (2,300 sq mi) Hadejia-Nguru wetlands . They converge to form the Yobe , which defines the border between Niger and Nigeria for 300 kilometres (190 mi), flowing into Lake Chad. About .5 cubic kilometres (0.12 cu mi) of water reaches Lake Chad annually. Construction of upstream dams and growth in irrigation have reduced water flow, and

2120-793: The northwest, in Algeria, are the Tassili n'Ajjer mountains, including the 2,158 metres (7,080 ft) Jebel Azao . The Tibesti Mountains to the north of the basin include Emi Koussi , the highest mountain in the Sahara at 3,415 metres (11,204 ft). The Ennedi Plateau lies to the northeast, rising to 1,450 metres (4,760 ft). The Ouaddaï highlands lies the east. They include the Marrah Mountains in Darfur at up to 3,088 metres (10,131 ft) in height. The Adamawa Plateau , Jos Plateau , Biu Plateau , and Mandara Mountains lie to

2173-462: The ocean. In general, water basins with subsurface outflows that lead to the ocean are not considered endorheic; but cryptorheic . Endorheic basins constitute local base levels , defining a limit of the erosion and deposition processes of nearby areas. Endorheic water bodies include the Caspian Sea , which is the world's largest inland body of water. The term endorheic derives from

Chad Basin - Misplaced Pages Continue

2226-517: The river, wetland or lake, and fishers from elsewhere must seek permission and pay a fee to use this area. The governments only enforced rules and regulations to a limited extent. Fishery management practices vary. For example, on the Katagum river in Jigawa State , Nigeria, a village will have a water management council that collects a portion of each fisherman's catch and redistributes it among

2279-686: The same time as the Benue Trough . It covers an area of about 2,335,000 square kilometres (902,000 sq mi). It merges into the Iullemmeden Basin to the west at the Damergou gap between the Aïr and Zinder massifs. The floor of the basin is made of Precambrian bedrock covered by more than 3,600 metres (11,800 ft) of sedimentary deposits. The basin may have resulted from the intersection of an "Aïr-Chad Trough" running NW-SE and

2332-546: The south. To the west the basin is separated by a watershed from the Niger River , and to the south it is separated by a basement dome from the Benue River . Further east, watersheds separate it from the Congo Basin and the river Nile . The lowest part of the basin is not Lake Chad, but the Bodélé Depression , at a distance of 480 kilometres (300 mi) to the northeast of the lake. The Bodélé Depression

2385-599: The surrounding rocks are deposited in the basin, and left behind when the water evaporates. Thus endorheic basins often contain extensive salt pans (also called salt flats, salt lakes, alkali flats , dry lake beds, or playas). These areas tend to be large, flat hardened surfaces and are sometimes used for aviation runways , or land speed record attempts, because of their extensive areas of perfectly level terrain. Both permanent and seasonal endorheic lakes can form in endorheic basins. Some endorheic basins are essentially stable because climate change has reduced precipitation to

2438-467: The villagers, or sells it and used the proceeds for communal projects. Local governments and traditional authorities are increasingly engaged in rent-seeking , collecting license fees with the help of the police or army. Notes Citations Sources Endorheic basin An endorheic basin ( / ˌ ɛ n d oʊ ˈ r iː . ɪ k / EN -doh- REE -ik ; also endoreic basin and endorreic basin )

2491-625: The water entering Lake Chad. The basin in the Nigerian section contains an upper aquifer of Early Pleistocene alluvial deposits that are often covered by recent sand dunes, varying in thickness from 15 to 100 metres (49 to 328 ft). It consists of interbedded sands, clays and silts, with discontinuous clay lenses. The aquifer recharges from run-off and rainfall. The local people access the water with hand-dug wells and shallow boreholes, and use it for domestic use, growing vegetables and watering their livestock. Below this aquifer, separated from it by

2544-495: The water level in the terminal lake to rise until it finds an outlet, breaking the enclosed endorheic hydrological system's geographical barrier and opening it to the surrounding terrain. The Black Sea was likely such a lake, having once been an independent hydrological system before the Mediterranean Sea broke through the terrain separating the two. Lake Bonneville was another such lake, overflowing its basin in

2597-722: The west of Bornu, by the 15th century the Kingdom of Kano had become the most powerful of the Hausa Kingdoms , with an unstable truce with the Kingdom of Katsina to the north. Both of these states adopted Islam during the 15th and 16th centuries. Both were absorbed into the Sokoto Caliphate during the Fulani War of 1805, which threatened Bornu itself. During the Berlin Conference in 1884-85 Africa

2650-684: The western part of the basin in the Turonian (93.5–89.3 Ma). In the Maastrichtian (72.1–66 Ma) the west was non-marine, but the southeast probably was still marine. No marine sediments have been found from the Paleocene (66–56 Ma). For most of the Quaternary , from 2.6 million years ago to the present, the basin seems to have been a huge, well-watered plain, with many rivers and water bodies, probably rich in plant and animal life. Towards

2703-472: The wetlands. There are populations of elephants , giraffes , and lions . The western black rhinoceros was once common but is now extinct. Elephants almost became extinct by the end of the nineteenth century due to European and American demand for ivory, but stocks have since recovered. The seasonal Korama River in the south of Niger does not reach Lake Chad. Nigeria includes two sub-basins that drain into Lake Chad. The Hadejia - Jama'are - Yobe sub-basin in

SECTION 50

#1732765955380

2756-531: Was divided between the European colonial powers, defining boundaries that are largely intact with the present post-colonial states. On 5 August 1890 the British and French concluded an agreement to define the boundary between French West Africa and what would become Nigeria . A boundary was agreed along a line from Say on the river Niger to Barruwa on Lake Chad, but leaving the Sokoto Caliphate in

2809-634: Was divided by the British in Nigeria who captured Kano in 1903, and the Germans in Kameroun. The countries of the basin regained their independence between 1956 and 1962, retaining the colonial administrative boundaries. The area is badly affected by the Boko Haram insurgency , which began in 2009 and is centred on Borno State in northeastern Nigeria. As of 2011, more than 30 million people lived in

#379620