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76-688: The Quinault River's drainage basin is 188 square miles (487 km) in area. Its main tributaries include the North Fork Quinault River, Graves Creek, Fox Creek, and Cook Creek. A well maintained trail follows the East Fork of the Quinault from Graves Creek to the Enchanted Valley Ranger Station through old growth rain forest. In early summer snow melt creates many waterfalls in the valley, giving it

152-405: A derivative of Arabic . However, these areas are not generally considered part of North Africa, but rather Southern Europe, due to their proximity to mainland Europe and their European-based cultures and religion. The Maghreb or western North Africa on the whole is believed to have been inhabited by Berbers and their ancestors since at least 10,000 B.C., while the eastern part of North Africa or

228-540: 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 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

304-484: 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

380-414: 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

456-403: A continental scale rather than being confined to a particular corner of Africa. In September 2019, scientists reported the computerized determination, based on 260 CT scans , of a virtual skull shape of the last common human ancestor to modern humans / H. sapiens , representative of the earliest modern humans, and suggested that modern humans arose between 260,000 and 350,000 years ago through

532-613: A date of up to 1.8 million BCE. Recent finds in Jebel Irhoud in Morocco have been found to contain some of the oldest Homo sapiens remains; This suggests that, rather than arising only in East Africa around 200,000 years ago, early Homo sapiens may already have been present across the length of Africa 100,000 years earlier. According to study author Jean-Jacques Hublin, "The idea is that early Homo sapiens dispersed around

608-612: A distinctive Maghrebi ancestry formed from a mixture of Near Eastern and African ancestry, which is still found as a part of the genome of modern Northwest Africans. Later during the Neolithic , from around 7,500 years ago onwards, there was a migration into Northwest Africa of European Neolithic Farmers from the Iberian Peninsula (who had originated in Anatolia several thousand years prior), as well as pastoralists from

684-454: 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

760-540: 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

836-597: A merging of populations in East and Southern Africa . The cave paintings found at Tassili n'Ajjer , north of Tamanrasset, Algeria, and at other locations depict vibrant and vivid scenes of everyday life in central North Africa during the Neolithic Subpluvial period (about 8000 to 4000 BCE). Some parts of North Africa began to participate in the Neolithic revolution in the 6th millennium BCE, just before

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912-639: A narrow fertile thread that runs along the length of the country. Sheltered valleys in the Atlas Mountains, the Nile Valley and Delta , and the Mediterranean coast are the main sources of fertile farming land. A wide variety of valuable crops including cereals, rice and cotton, and woods such as cedar and cork , are grown. Typical Mediterranean crops, such as olives, figs, dates and citrus fruits, also thrive in these areas. The Nile Valley

988-575: A second official language after Arabic. French also serves as an administrative language in Algeria, Morocco and Tunisia. The most spoken dialects are Maghrebi Arabic , a form of ancient Arabic dating back from the 8th century AD, and Egyptian Arabic . The largest and most numerous ethnic group in North Africa are the Arabs . In Algeria and Morocco, Berbers are the second largest ethnic group after

1064-648: Is "no or scanty evidence" of human presence in the Egyptian Nile Valley during these periods, which may be due to problems in site preservation. Several scholars have argued that the African origins of the Egyptian civilisation derived from pastoral communities which emerged in both the Egyptian and Sudanese regions of the Nile Valley in the fifth millennium BCE. When Egypt entered the Bronze Age,

1140-662: Is a significant minority of Coptic Christians . The Copts are the largest Christian denomination in the Middle East and North Africa . The Maghreb formerly had a significant Jewish population, almost all of whom emigrated to France or Israel when the North African nations gained independence. Prior to the modern establishment of Israel, there were about 500,000 Jews in Northern Africa, including both Sephardi Jews (refugees from Spain, France and Portugal from

1216-642: Is particularly fertile and most of Egypt lives close to the river. Elsewhere, irrigation is essential to improve crop yields on the desert margins. The inhabitants of North Africa are roughly divided in a manner corresponding to the principal geographic regions of North Africa: the Maghreb , the Nile valley, and the Sahel . The countries making up North Africa all have Modern Standard Arabic as their official language. Additionally, Algeria and Morocco recognize Berber as

1292-487: 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

1368-586: Is sometimes defined as stretching from the Atlantic shores of the Western Sahara in the west, to Egypt and Sudan's Red Sea coast in the east. The most common definition for the region's boundaries includes Algeria , Egypt , Libya , Morocco , Tunisia , and Western Sahara , the territory disputed between Morocco and the partially recognized Sahrawi Arab Democratic Republic . The United Nations ' definition includes all these countries as well as

1444-614: 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

1520-713: 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

1596-584: The Afroasiatic language family . The Tuareg Berber languages are notably more conservative than those of the coastal cities. Over the years, Berbers have been influenced by contact with other cultures: Egyptians , Greeks , Punic people , Romans , Vandals , Arabs , Europeans , and Africans . The cultures of the Maghreb and the Sahara therefore combines Arab, indigenous Berber and African elements. In

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1672-540: The Canary Islands , which are all closer or as close to the African continent than Europe. Northwest Africa has been inhabited by Berbers since the beginning of recorded history , while the eastern part of North Africa has been home to the Egyptians . In the seventh and eighth centuries, Arabs from the Arabian Peninsula swept across the region during the early Muslim conquests . The Arab migrations to

1748-828: 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,

1824-714: 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

1900-484: The Levant , both of whom also significantly contributed to the ancestry of modern Northwest Africans. The proto-Berber tribes evolved from these prehistoric communities during the late Bronze - and early Iron ages. The majority of the people of the Maghreb and the Sahara regions speak varieties of Arabic and almost exclusively follow Islam. The Arabic and Berber languages are distantly related, both being members of

1976-600: The Middle Ages much of the area was loosely under the control of the Ottoman Empire . The Barbary pirates operated from the largely independent Barbary states located on the coast of North Africa. The Spanish Empire conquered several coastal cities between the 16th and 18th centuries. After the 19th century, the imperial and colonial presence of France , the United Kingdom , Spain and Italy left

2052-572: The Middle East / West Asia , a process that began with the Neolithic Revolution c.  10,000 BC and pre Dynastic Egypt. The countries of North Africa are also a major part of the Arab world . The Islamic and Arab influence in North Africa has remained dominant ever since, with the region being major part of the Muslim world . North Africa is associated with the Middle East in

2128-649: The Nile Valley has mainly been home to the Egyptians and Nubians . Ancient Egyptians record extensive contact in their Western desert with people that appear to have been Berber or proto-Berber. As the Tassili n'Ajjer and other rock art findings in the Sahara have shown, the Sahara also hosted various populations before its rapid desertification in 3500 B.C and even today continues to host small populations of nomadic trans-Saharan peoples . Laboratory examination of

2204-523: The Strait of Gibraltar , whereupon they overcame the fickle Roman defense. The loss of North Africa is considered a pinnacle point in the fall of the Western Roman Empire as Africa had previously been an important grain province that maintained Roman prosperity despite the barbarian incursions, and the wealth required to create new armies. The issue of regaining North Africa became paramount to

2280-742: The Sudan . The African Union defines the region similarly, only differing from the UN in excluding the Sudan. The Sahel , south of the Sahara Desert , can be considered as the southern boundary of North Africa. North Africa includes the Spanish cities of Ceuta and Melilla , and the plazas de soberanía . It can also be considered to include Malta , as well as other Italian, Portuguese, and Spanish regions such as Lampedusa and Lampione , Madeira , and

2356-748: The Uan Muhuggiag child mummy and Tin Hanakaten child, suggested that the Central Saharan peoples from the Epipaleolithic , Mesolithic , and Pastoral periods possessed dark skin complexions. The archaeological evidence from the Holocene period has shown that Nilo-Saharan speaking groups had populated the central and southern Sahara before the influx of Berber and Arabic speakers, around 1500 years ago, who now largely populate

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2432-461: 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. North Africa North Africa (sometimes Northern Africa ) is a region encompassing the northern portion of the African continent. There is no singularly accepted scope for the region, and it

2508-488: The hammada , a level rocky plateau without soil or sand; and the reg , a desert pavement . The Sahara covers the southern part of Algeria, Morocco and Tunisia, and most of Libya. Only two regions of Libya are outside the desert: Tripolitania in the northwest and Cyrenaica in the northeast. Most of Egypt is also desert, with the exception of the Nile River and the irrigated land along its banks. The Nile Valley forms

2584-668: The Arab majority. Arabs constitute 70% to 80% of the population of Algeria, 92% 97% of Libya, 67% to 70% of Morocco and 98% of Tunisia's population. The Berbers comprise 20% of Algeria, 10% of Libya, 35% of Morocco and 1% of Tunisia's population. The region is predominantly Muslim with a Jewish minority in Morocco and Tunisia , and significant Christian minority—the Copts —in Egypt , Algeria , Morocco, Libya, and Tunisia. In 2001,

2660-399: The Maghreb began immediately after, which started a long process of Islamization and Arabization that has defined the cultural landscape of North Africa ever since. Many but not all Berbers and Egyptians gradually merged into Arab - Islamic culture . The countries and people of North Africa share a large amount of their genetic, ethnic, cultural and linguistic identity and influence with

2736-514: The Maghreb remained focused on small-scale subsistence in small, highly mobile groups. Some Phoenician and Greek colonies were established along the Mediterranean coast during the 7th century BCE. The most notable nations of antiquity in western North Africa are Carthage , Numidia and Mauretania . The Phoenicians colonized much of North Africa including Carthage and parts of present-day Morocco (including Chellah , Essaouira and Volubilis ). The Carthaginians were of Phoenician origin, with

2812-633: The Renaissance era) as well as indigenous Mizrahi Jews . Today, less than 3,000 remain in the region, almost all in Morocco and Tunisia, and are mostly part of a French-speaking urban elite. (See Jewish exodus from Arab and Muslim countries .) Due to the recent African origin of modern humans , the history of Prehistoric North Africa is important to the understanding of pre-hominid and early modern human history in Africa. Some researchers have postulated that North Africa rather than East Africa served as

2888-554: The Roman myth of their origin being that Dido , a Phoenician princess, was granted land by a local ruler based on how much land she could cover with a piece of cowhide. She ingeniously devised a method to extend the cowhide to a high proportion, thus gaining a large territory. She was also rejected by the Trojan prince Aeneas according to Virgil , thus creating a historical enmity between Carthage and Rome , as Aeneas would eventually lay

2964-633: The Romans, resulting in the Carthaginian North African territories becoming the Roman province of Africa in 146 B.C. This led to tension and eventually conflict between Numidia and Rome. The Numidian wars are notable for launching the careers of both Gaius Marius , and Sulla , and stretching the constitutional burden of the Roman republic as Marius required a professional army, something previously contrary to Roman values, to overcome

3040-420: The Sahara in the modern era. After migrating to North Africa in the 1st millennium BC, Semitic Phoenician settlers from the Levant established over 300 coastal colonies throughout the region and built a powerful empire that controlled most of the region from the 8th century BC until the middle of the 2nd century BC. Several waves of Arab migrations to the Maghreb began in the 7th century, including

3116-444: The Sahara, the distinction between sedentary oasis inhabitants and nomadic Bedouin Arabs and Tuaregs is particularly marked. Egyptians over the centuries have shifted their language from Egyptian (in its late form, varieties of Coptic ) to modern Egyptian Arabic while retaining a sense of national identity that has historically set them apart from other people in the region. Most Egyptians are Sunni Muslim , although there

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3192-623: 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

3268-696: The Western Empire, but was frustrated by Vandal victories. The focus of Roman energy had to be on the emerging threat of the Huns . In 468 AD, the Romans made one last serious attempt to invade North Africa but were repelled. This perhaps marks the point of terminal decline for the Western Roman Empire . The last Roman emperor was deposed in 476 by the Heruli general Odoacer . Trade routes between Europe and North Africa remained intact until

3344-406: 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

3420-525: The coming of Islam. Some Berbers were members of the Early African Church (but evolved their own Donatist doctrine ), some were Berber Jews , and some adhered to traditional Berber religion . African pope Victor I served during the reign of Roman emperor Septimius Severus . Furthermore, during the rule of the Romans, Byzantines, Vandals, Ottomans and Carthaginians the Kabyle people were

3496-438: The continent and elements of human modernity appeared in different places, and so different parts of Africa contributed to the emergence of what we call modern humans today." Early humans may have comprised a large, interbreeding population dispersed across Africa whose spread was facilitated by a wetter climate that created a "green Sahara", around 330,000 to 300,000 years ago. The rise of modern humans may thus have taken place on

3572-430: 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

3648-441: 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

3724-642: 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

3800-432: 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

3876-458: The eleventh century, a reformist movement made up of members that called themselves the Almoravid dynasty expanded south into Sub-Saharan Africa . North Africa's populous and flourishing civilization collapsed after exhausting its resources in internal fighting and suffering devastation from the invasion of the Banu Sulaym and Banu Hilal . Ibn Khaldun noted that the lands ravaged by Banu Hilal invaders had become completely arid desert. After

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3952-479: The entirety of the region under one form of European occupation. In World War II from 1940 to 1943 the area was the setting for the North African Campaign . During the 1950s and 1960s all of the North African states gained independence. There remains a dispute over Western Sahara between Morocco and the Algerian -backed Polisario Front . The wider protest movement known as the Arab Spring began with revolutions in Tunisia and Egypt which ultimately led to

4028-438: The exit point for the modern humans who first trekked out of the continent in the Out of Africa migration. The earliest inhabitants of central North Africa have left behind significant remains: early remnants of hominid occupation in North Africa, for example, were found in Ain el Hanech, near Saïda ( c.  200,000 BCE ); in fact, more recent investigations have found signs of Oldowan technology there, and indicate

4104-411: The foundations for Rome. Ancient Carthage was a commercial power and had a strong navy, but relied on mercenaries for land soldiers. The Carthaginians developed an empire in the Iberian Peninsula , Malta , Sardinia , Corsica and northwest Sicily , the latter being the cause of First Punic War with the Romans . Over a hundred years and more, all Carthaginian territory was eventually conquered by

4180-412: 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 ,

4256-435: 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

4332-422: 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

4408-417: 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

4484-417: The migration of the Banu Hilal and the Banu Sulaym westward into the Maghreb in the eleventh century, which introduced Arab culture and language to the countryside. Historians mark their movement as a critical moment in the Arabization of North Africa. As Arab nomads spread, the territories of the local Berber tribes were moved and shrank. The Zenata were pushed to the west and the Kabyles were pushed to

4560-409: 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

4636-399: The name "Valley of a Thousand Waterfalls". The Quinault River has been reaching new recorded lows in recent years, as it was fed by the Anderson Glacier which had melted away by 2011. [REDACTED] Media related to Quinault River at Wikimedia Commons Drainage basin A drainage basin is an area of land in which all flowing surface water converges to a single point, such as

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4712-482: The north. The Berbers took refuge in the mountains whereas the plains were Arabized. This heavily shifted the demographics of the Maghreb. The trans-Saharan slave trade resulted in increased levels of sub-Saharan African ancestry in North Africa. The Haratin are commonly perceived as an endogamous group of former slaves or descendants of slaves. DNA studies of Iberomaurusian peoples at Taforalt , Morocco dating to around 15,000 years ago have found them to have

4788-417: The number of Christians in North Africa was estimated at 9 million, the majority of whom live in Egypt, with the remainder live in Maghreb countries. The inhabitants of the Spanish Canary Islands are of mixed Spanish and North African Berber ancestry, and the people of Malta are of primarily Southern Italian/Sicilian, as well as, to a lesser extent, North African and Middle Eastern ancestry and speak

4864-485: The only or one of the few in North Africa who remained independent. The Kabyle people were incredibly resistible so much so that even during the Arab conquest of North Africa they still had control and possession over their mountains. The early Muslim conquests included North Africa by 640. By 700, most of North Africa had come under Muslim rule. Indigenous Berbers subsequently started to form their own polities in response in places such as Fez and Sijilmasa . In

4940-418: 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

5016-412: The rapid desertification of the Sahara around 3500 B.C. largely due to a tilt in the Earth's orbit. It was during this period that domesticated plants and animals were introduced in the region, spreading from the north and east to the southwest. There has been an inferred connection between areas of rapid drying and the introduction of livestock in which the natural (orbital) aridification was amplified by

5092-448: The realm of geopolitics to form the Middle East-North Africa region. North Africa has three main geographic features: the Sahara desert in the south, the Atlas Mountains in the west, and the Nile River and delta in the east. The Atlas Mountains extend across much of northern Algeria , Morocco , and Tunisia . These mountains are part of the fold mountain system that also runs through much of Southern Europe . They recede to

5168-572: 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

5244-461: 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

5320-597: The south and east, becoming a steppe landscape before meeting the Sahara desert, which covers more than 75 percent of the region. The tallest peaks are in the High Atlas range in south-central Morocco, which has many snow-capped peaks. South of the Atlas Mountains is the dry and barren expanse of the Sahara desert, the largest sand desert in the world. In places the desert is cut by irregular watercourses called wadis —streams that flow only after rainfall but are usually dry. The Sahara's major landforms include ergs , large seas of sand that sometimes form into huge dunes ;

5396-418: 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

5472-616: The spread of shrubs and open land due to grazing. Nevertheless, changes in northern Africa's ecology after 3500 BCE provided the backdrop for the formation of dynastic civilizations and the construction of monumental architecture such as the Pyramids of Giza . Archaeological evidence has attested that population settlements occurred in Nubia as early as the Late Pleistocene era and from the 5th millennium BC onwards, whereas there

5548-576: The talented military leader Jugurtha . Kingdom of Mauretania remained independent until being annexed to the Roman Empire by Emperor Claudius in 42 AD. North Africa remained a part of the Roman Empire, producing notable citizens, including Augustine of Hippo , until incompetent leadership from Roman commanders in the early fifth century allowed the Germanic peoples , the Vandals , to cross

5624-415: 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

5700-477: 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

5776-673: 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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