The Nile is a major north-flowing river in Africa, generally regarded as the longest river in the world.

 

The Nile has two major tributaries, the White Nile and Blue Nile, the latter being the source of most of the Nile's water and fertile soil, but the former being the longer of the two. The White Nile rises in the Great Lakes region of central Africa, with the most distant source in southern Rwanda and flows north from there through Tanzania, Lake Victoria, Uganda and southern Sudan, while the Blue Nile starts at Lake Tana in Ethiopia flowing into Sudan from the southeast. The two rivers meet near the Sudanese capital Khartoum.

 

The northern section of the river flows almost entirely through desert, from Sudan into Egypt, a country whose civilization has depended on the river since ancient times. Most of the population of Egypt and all of its cities, with the exception of those near the coast, lie along those parts of the Nile valley north of Aswan; and nearly all the cultural and historical sites of Ancient Egypt are found along the banks of the river. The Nile ends in a large delta that empties into the Mediterranean Sea.

 

 

There are two great tributaries of the Nile, joining at Khartoum: the White Nile, starting in equatorial East Africa, and the Blue Nile, beginning in Ethiopia. Both branches are on the western flanks of the East African Rift, the southern part of the Great Rift Valley. Below the Blue and White Nile confluence the only remaining major tributary is the Atbara River, which originates in Ethiopia north of Lake Tana, and is around 800 kilometres (500 mi) long. It flows only while there is rain in Ethiopia and dries very fast. It joins the Nile approximately 300 kilometres (200 mi) north of Khartoum.

 

The Nile is unusual in that its last tributary (the Atbara) joins it roughly halfway to the sea. From that point north, the Nile diminishes because of evaporation.

 

The course of the Nile in Sudan is distinctive. It flows over six groups of cataracts, from the first at Aswan to the sixth at Sabaloka (just north of Khartoum) and then turns to flow southward for a good portion of its course, before again returning to flow north to the sea. This is called the "Great Bend of the Nile".
 
East Africa, showing the course of the Nile River, with the "Blue" and "White" Niles marked in those coloursNorth of Cairo, the Nile splits into two branches (or distributaries) that feed the Mediterranean: the Rosetta Branch to the west and the Damietta to the east, forming the Nile Delta.

 

The source of the Nile is sometimes considered to be Lake Victoria, but the lake itself has feeder rivers of considerable size. The most distant stream—and thus the ultimate source of the Nile—emerges from Nyungwe Forest in Rwanda, via the Rukarara, Mwogo, Nyabarongo and Kagera rivers, before flowing into Lake Victoria in Tanzania near the town of Bukoba.

 

The Nile leaves Lake Victoria at Ripon Falls near Jinja, Uganda, as the Victoria Nile. It flows for approximately 500 kilometres (300 mi) farther, through Lake Kyoga, until it reaches Lake Albert. After leaving Lake Albert, the river is known as the Albert Nile. It then flows into Sudan, where it becomes known as the Bahr al Jabal ("River of the Mountain"). The Bahr al Ghazal, itself 716 kilometres (445 mi) long, joins the Bahr al Jabal at a small lagoon called Lake No, after which the Nile becomes known as the Bahr al Abyad, or the White Nile, from the whitish clay suspended in its waters. When the Nile flooded it left this rich material named silt. The Ancient Egyptians used this soil to farm. From Lake No, the river flows to Khartoum. An anabranch river called Bahr el Zeraf flows out of the Nile's Bahr al Jabal section and rejoins the White Nile.

 

The term "White Nile" is used in both a general sense, referring to the entire river above Khartoum, and a limited sense, the section between Lake No and Khartoum.

 

 

The Blue Nile springs from Lake Tana in the Ethiopian Highlands. The Blue Nile flows about 1,400 kilometres (870 mi) to Khartoum, where the Blue Nile and White Nile join to form the "Nile proper". 90% of the water and 96% of the transported sediment carried by the Nile originates in Ethiopia, with 59% of the water from the Blue Nile alone (the rest being from the Tekezé, Atbarah, Sobat, and small tributaries). The erosion and transportation of silt only occurs during the Ethiopian rainy season in the summer, however, when rainfall is especially high on the Ethiopian Plateau; the rest of the year, the great rivers draining Ethiopia into the Nile (Sobat, Blue Nile, Tekezé, and Atbarah) flow weakly.

 

 

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 Gharb Darfur near the northern border with Chad and meets up with the Nile and near the southern point of the Great Bend.

 

 

Hydrology
 
The flow rate of the Albert Nile at Mongalla is almost constant throughout the year and averages 1,048 m3/s (37,000 cu ft/s). After Mongalla, the Nile is known as the Bahr El Jebel which enters the enormous swamps of the Sudd region of Sudan. More than half of the Nile's water is lost in this swamp to evaporation and transpiration. The average flow rate in the Bahr El Jebel at the tails of the swamps is about 510 m3/s (18,000 cu ft/s). From here it soon meets with the Sobat River and forms the White Nile.

 

The Bahr al Ghazal and the Sobat River are the two most important tributaries of the White Nile in terms of drainage area and discharge. The Bahr al Ghazal's drainage basin is the largest of any of the Nile's sub-basins, measuring 520,000 square kilometres (200,000 sq mi) in size, but it contributes a relatively small amount of water, about 2 m3/s (71 cu ft/s) annually, due to tremendous volumes of water being lost in the Sudd wetlands. The Sobat River, which joins the Nile a short distance below Lake No, drains about half as much land, 225,000 km2 (86,900 sq mi), but contributes 412 cubic metres per second (14,500 cu ft/s) annually to the Nile. When in flood the Sobat carries a large amount of sediment, adding greatly to the White Nile's color.

 

The average flow of the White Nile at Malakal, just below the Sobat River, is 924 m3/s (32,600 cu ft/s), the peak flow is approximately 1,218 m3/s (43,000 cu ft/s) in early March and minimum flow is about 609 m3/s (21,500 cu ft/s) in late August. The fluctuation there is due the substantial variation in the flow of the Sobat which has a minimum flow of about 99 m3/s (3,500 cu ft/s) in August and a peak flow of over 680 m3/s (24,000 cu ft/s) in early March.

 

From here the White Nile flows to Khartoum where it merges with the Blue Nile to form the Nile River. Further downstream the Atbara River, the last significant Nile tributary, merges with the Nile. During the dry season (January to June) the White Nile contributes between 70% and 90% of the total discharge from the Nile. During this period of time the natural discharge of the Blue Nile can be as low as 113 m3/s (4,000 cu ft/s), although upstream dams regulate the flow of the river. During the dry period, there will typically be no flow from the Atbara River.

 

The Blue Nile contributes approximately 80-90% of the Nile River discharge. The flow of the Blue Nile varies considerably over its yearly cycle and is the main contribution to the large natural variation of the Nile flow. During the wet season the peak flow of the Blue Nile will often exceed 5,663 m3/s (200,000 cu ft/s) in latter August (variation by a factor of 50).

 

Before the placement of dams on the river the yearly discharge varied by a factor of 15 at Aswan. Peak flows of over 8,212 m3/s (290,000 cu ft/s) would occur during the later portions of August and early September and minimum flows of about 552 m3/s (19,500 cu ft/s) would occur during later April and early May. The Nile basin is complex, and because of this, the discharge at any given point along the mainstem depends on many factors including weather, diversions, evaporation/evapotranspiration, and groundwater flow.

Role in the founding of Egyptian civilization
 
Reconstruction of the Oikoumene (inhabited world) ancient map based on Herodotus' description of the world, circa 450 BCE.The Nile, an unending source of sustenance, provided a crucial role in the development of Egyptian civilization. The Nile made the land surrounding it extremely fertile when it flooded or was inundated annually. The Egyptians were able to cultivate wheat and crops around the Nile, providing food for the general population. Also, the Nile’s water attracted game such as water buffalo; and after the Persians introduced them in the 7th century BC, camels. These animals could be killed for meat, or could be captured, tamed and used for ploughing — or in the camels' case, travelling. Water was vital to both people and livestock. The Nile was also a convenient and efficient way of transportation for people and goods.
 
The structure of Egypt’s society made it one of the most stable in history. In fact, it might easily have surpassed many modern societies. This stability was an immediate result of the Nile’s fertility. The Nile also provided flax for trade. Wheat was also traded, a crucial crop in the Middle East where famine was very common. This trading system secured the diplomatic relationship Egypt had with other countries, and often contributed to Egypt's economic stability. Also, the Nile provided the resources such as food or money, to quickly and efficiently raise an army for offensive or defensive roles.

 

The Nile played a major role in politics and social life. The pharaoh would supposedly flood the Nile, and in return for the life-giving water and crops, the peasants would cultivate the fertile soil and send a portion of the resources they had reaped to the Pharaoh. He or she would in turn use it for the well-being of Egyptian society.

 

The Nile was a source of spiritual dimension. The Nile was so significant to the lifestyle of the Egyptians, that they created a god dedicated to the welfare of the Nile’s annual inundation. The god’s name was Hapy, and both he and the pharaoh were thought to control the flooding of the Nile. Also, the Nile was considered as a causeway from life to death and afterlife. The east was thought of as a place of birth and growth, and the west was considered the place of death, as the god Ra, the Sun, underwent birth, death, and resurrection each time he crossed the sky. Thus, all tombs were located west of the Nile, because the Egyptians believed that in order to enter the afterlife, they must be buried on the side that symbolized death.

 

The Greek historian, Herodotus, wrote that ‘Egypt was the gift of the Nile’, and in a sense that is correct. Without the waters of the Nile River for irrigation, Egyptian civilization would probably have been short-lived. The Nile provided the elements that make a vigorous civilization, and contributed much to its lasting three thousand years.

That far-reaching trade has been carried on along the Nile since ancient times can be seen from the Ishango bone, possibly the earliest known indication of Ancient Egyptian multiplication, which was discovered along the headwaters of the Nile River (near Lake Edward, in northeastern Congo) and was carbon-dated to 20,000 BC.

 

^ River Encarta (Accessed 3 October 2006)
^ What did the ancient Egyptians call the Nile river? Open Egyptology. (Accessed 17 October 2006 - Login required or enter as Guest)
^ EarthTrends: The Environmental Information Portal
^ Marshall et al., Late Pleistocene and Holocene environmental and climatic change from Lake Tana, source of the Blue NilePDF (247 KiB), 2006
^ Keding, B (2000). "New data on the Holocene occupation of the Wadi Howar region (Eastern Sahara/Sudan)." Studies in African Archaeology 7, 89–104.
^ The Nile Basin Initiative
^ Shahin, Mamdouh (2002). Hydrology and Water Resources of Africa. Springer. pp. 286–287. ISBN 140200866X. ; online at Google Books
^ Shahin, Mamdouh (2002). Hydrology and Water Resources of Africa. Springer. pp. 276, 287–288. ISBN 140200866X. ; online at Google Books
^ "Sobat River". Encyclopædia Britannica Online Library Edition. Encyclopædia Britannica. http://www.library.eb.com/eb/article-9068426. Retrieved 2008-01-21.