Nile

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 at 2°16'55.92S 29°19'52.32E / 2.2822°S 29.3312°E / -2.2822; 29.3312, and flows north from there through Tanzania, Lake Victoria, Uganda and southern Sudan.

While the Blue Nile starts at Lake Tana in Ethiopia at 12°2'8.8?N 37°15'53.11E / 12.035778°N 37.2647528°E / 12.035778; 37.2647528, flowing into Sudan from the southeast.

The two rivers meet near the Sudanese capital of KhartoumThe 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 and cities of Egypt 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.

Etymology Of The Word Nile

The word "Nile" comes from Greek Neilos, of unknown derivation. In the ancient Egyptian language, the Nile is called 'pi or iteru, meaning "great river", represented by the hieroglyphs shown on the right (literally itrw, and 'waters' determinative). In Coptic, the words piaro (Sahidic) or phiaro (Bohairic) meaning "the river" (lit. p(h).iar-o "the.canal-great") come from the same ancient name.

Tributaries And Distributaries

The drainage basin of the Nile covers 3,254,555 square kilometres (1,256,591 sq mi), about 10% of the area of Africa.

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. During the dry period of January to June, there is typically no flow from the Atbara River. It flows only while there is rain in Ethiopia and dries very rapidly. 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".

North 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 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 and evapotranspiration, and groundwater flow.

Lost Headwaters

Formerly Lake Tanganyika drained northwards along the African Rift Valley into the Albert Nile, making the Nile about 900 miles (1,400 km) longer, until blocked in Miocene times by the bulk of the Virunga Volcanoes.

History

The Nile (iteru in Ancient Egyptian) has been the lifeline of civilization in Egypt since the Stone Age, with most of the population and all of the cities of Egypt resting along those parts of the Nile valley lying north of Aswan. Climate change at the end of the most recent ice age led to the formation the Sahara desert, possibly as long ago as 3400 BC.

The Eonile
The present Nile is at least the fifth river that has flowed north from the Ethiopian Highlands. Satellite imagery was used to identify dry watercourses in the desert to the west of the Nile. An Eonile canyon, now filled by surface drift, represents an ancestral Nile called the Eonile that flowed during the later Miocene (23–5.3 million years before present). The Eonile transported clastic sediments to the Mediterranean; several natural gas fields have been discovered within these sediments.

During the late-Miocene Messinian salinity crisis, when the Mediterranean Sea was a closed basin and evaporated to the point of being empty or nearly so, the Nile cut its course down to the new base level until it was several hundred feet below world ocean level at Aswan and 8,000 feet (2,400 m) below Cairo. This created a very long and deep canyon which was filled with sediment when the Mediterranean was recreated, and is now underwater.

Lake Tanganyika drained northwards into the Nile until the Virunga Volcanoes blocked its course in Rwanda. The Nile was much longer at that time, with its furthest headwaters in northern Zambia.

The Integrated Nile

There are two theories in relation to the age of the integrated Nile. The first one is that the integrated drainage of the Nile is of young age, and that the Nile basin was formerly broken into series of separate basins, only the most northerly of which fed a river following the present course of the Nile in Egypt and Sudan. Said (1981) postulates that Egypt itself supplied most of the waters of the Nile during the early part of its history.

The other theory is that the drainage from Ethiopia via rivers equivalent to the Blue Nile and the Atbara and Takazze flowed to the Mediterranean via the Egyptian Nile since well back into Tertiary times.

Salama (1987) suggested that during the Tertiary (65 million to 2.588 million years ago) there were a series of separate closed continental basins, with each basin occupying one of the major parts of the Sudanese Rift System: Mellut Rift, White Nile Rift, Blue Nile Rift, Atbara Rift and Sag El Naam Rift. The Mellut Rift Basin is nearly 12 km deep at its central part. This rift is possibly still active, with reported tectonic activity in its northern and southern boundaries. The Sudd swamps which form the central part of the basin may still be subsiding. The White Nile Rift System, although shallower than Bahr al-Arab, is about 9 km deep. Geophysical exploration of the Blue Nile Rift System estimated the depth of the sediments to be 5–9 km. These basins were not interconnected until their subsidence ceased, and the rate of sediment deposition was enough to fill up the basins to such a level that the basins became connected. The Egyptian Nile became connected to the Sudanese Nile, which captures the Ethiopian and Equatorial head waters during the current stages of tectonic activity in the Eastern, Central and Sudanese Rift Systems. The connection of the different Niles occurred during cyclic wet periods. The River Atbara overflowed its closed basin during the wet periods which occurred about 100,000 to 120,000 years ago. The Blue Nile was connected to the main Nile during the 70,000–80,000 years B.P. wet period. The White Nile system in Bahr El Arab and White Nile Rifts remained a closed lake until the connection of the Victoria Nile to the main system some 12,500 years ago.