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Course and Navigability
The trunk stream of the the Nile is formed at Khartoum, Sudan, 1,857 mi (2,988 km) from the sea, by the junction of the Blue Nile (c.1,000 mi/1,610 km long) and the White Nile (c.2,300 mi/3,700 km long). The Blue Nile rises in the headwaters of Lake Tana, NW Ethiopia, a region of heavy summer rains, and is the source of floodwaters that reach Egypt in September; the Blue Nile contributes more than half of all Nile waters throughout the year. During floodtime it also carries great quantities of silt from the highlands of Ethiopia; these now collect in Lake Nasser behind the Aswan High Dam, but for centuries they were left on the floodplain after the floods and helped replenish the fertility of Egypt's soils. The Merowe Dam, under construction below the fourth cataract in Sudan, will also capture the silt, though the dam there is designed to facilitate the flushing of sediment. The White Nile (known in various sections as the Bahr el Abiad, Bahr el Jebel, Albert Nile, and Victoria Nile) rises in the headwaters of Lake Victoria in a region of heavy, year-round rainfall; unlike the Blue Nile, it has a constant flow, owing in part to its source area and in part to the regulating effects of its passage through lakes Victoria and Albert and the Sudd swamps. Other important tributaries of the Nile are the Atbara and Sobat rivers. The Gezira, or “island,” formed between the Blue Nile and the White Nile as they come together at Khartoum is Sudan's principal agricultural area and the only large tract of land outside Egypt irrigated with Nile waters.
From Khartoum to the Egyptian border at Wadi Halfa (now submerged) and on to Aswan in Egypt, the Nile occupies a narrow entrenched valley with little floodplain for cultivation; in this stretch it is interrupted by six cataracts (rapids). From Aswan the river flows north 550 mi (885 km) to Cairo, bordered by a floodplain that gradually widens to c.12 mi (20 km); irrigated by the river, this intensively cultivated valley contrasts with the barren desert on either side. North of Cairo is the great Nile delta (c.100 mi/160 km long and up to 115 mi/185 km wide), which contains 60% of Egypt's cultivated land and extensive areas of swamps and shallow lakes. Two distributaries, the Dumyat (Damietta) on the east and the Rashid (Rosetta) on the west, each c.150 mi (240 km) long, carry the river's remaining water (after irrigation) to the Mediterranean Sea. Regular steamship service is maintained on the Nile between Alexandria (reached by canal) and Aswan; the Blue Nile is navigable June through December from Suki (above Sennar Dam) to Roseires Dam; the White Nile is navigable all year between Khartoum, Sudan, and Juba, South Sudan, and between Nimule, South Sudan, on the White Nile, and Murchison Falls, Uganda, on the Victoria Nile.
Irrigation along the Nile
The use of the Nile for irrigation dates back to at least 4000 B.C. in Egypt. The traditional system of basin irrigation—in which Nile floods were trapped in shallow basins and a cool-season crop of wheat or barley was grown in soaked and silt-replenished soil—has been replaced since the mid-1800s by a system of perennial irrigation and the production of two or three crops a year, including cotton, sugarcane, and peanuts. The delta barrages, just below Cairo, channel water into a system of feeder canals for the delta, and other barrages at Isna, Asyut, and Nag Hammadi keep the level of the Nile high enough all year for perennial irrigation in the valley of Upper Egypt; the Idfina Barrage on the Rashid prevents infiltration by the sea at low water. Nile water is also used for irrigation in the Faiyum Basin.
The Aswan Dam (completed 1902 and raised twice since then) was the first dam built on the Nile to store part of the autumn flood for later use; it has a storage capacity of 5 billion cu m and is now supplemented by the Aswan High Dam (completed 1971), 5 mi (8 km) upstream, with a storage capacity of 48 billion cu m, sufficient (with existing dams) to hold back the entire flood for later use. Construction of the Aswan High Dam has added c.1,800,000 acres (728,500 hectares) of irrigated land to Egypt's cultivable area and converted c.730,000 acres (295,400 hectares) from basin to perennial irrigation. Lake Nasser, created by the Aswan High Dam, has experienced problems with silting. There has been a reduction of soil replenishment downstream and a reduction of nutrients that once fed the E Mediterranean Sea. Other important storage dams, all outside Egypt, but built with Egypt's help or cooperation, are the Nalubaale Dam (formerly Owen Falls Dam; 1954) and Jabal Awliya Dam (1937) on the White Nile; the Sennar (1927) and Roseires (1966) on the Blue Nile; and the Kashm-el-Girba Dam (1964) on the Atbara River.
Agreements signed in 1929 (between Egypt and Great Britain) and 1959 (between Egypt and Sudan) essentially apportioned nearly all of the Nile's flow to Egypt and Sudan, and gave Egypt the right to veto dams in the upstream nations. Those agreements as well as other colonial era agreements regarding the river have been disputed by the upper basin nations that are the sources of the Nile's waters; they regard the treaties as a vestige of colonialism and invalid. In 1999 the Nile Basin Initiative was established by the basin nations to develop the river in a cooperative manner. The upper basin nations (except Eritrea, which has not been active in the initiative) since have sought a treaty that would replace earlier agreements and apportion the waters in what they regarded as a more equitable manner. An agreement was signed by Ethiopia, Kenya, Rwanda, Tanzania, and Uganda in 2010 and by Burundi in 2011 that was intended to result in an reapportionment that would not have a significant affect on Egypt and Sudan; those two nations strongly objected. In 2011 Ethiopia began work on a massive hydroelectric dam on the Blue Nile not far from the border with Sudan. Egypt objected to its construction, but in 2015 Egypt, Ethiopia, and Sudan signed an agreement on principles concerning the dam. Further talks, however, have not resolved disagreements over the dam, and tensions over the issue have increased; the dam began to fill in 2020.
The Search for the Nile's Source
See B. Brander, The River Nile (2d ed. 1968); J. Waterbury, Hydropolitics of the Nile Valley (1979); A. Moorhead, The White Nile (rev. ed. 1983); T. Jeal, Explorers of the Nile (2011); R. Twigger, Red Nile (2015).
(present-day Egyptian name, “El Bahr”), a river in Africa. It is 6,671 km long and drains an area of 2.87 million sq km. It rises in the East African Highlands east of Lakes Kivu and Tanganyika and flows into the Mediterranean Sea, forming a delta. The largest tributaries in the upper half of its course are the Bahr el Ghazal (left) and the Aswa, Sobat, Blue Nile, and Atbara (right). Then the Nile receives no tributaries for 3,000 km as it flows through tropical and subtropical semideserts. The Nile basin encompasses part or all of Rwanda, Kenya, Tanzania, Uganda, Ethiopia, the Sudan, and Egypt.
The Nile has its source in one of the headstreams of the Kagera River, which flows into Lake Victoria. Issuing from the northern end of Lake Victoria as the Victoria Nile, the river cuts through rocky ridges, and, dropping 670 m, forms numerous rapids and waterfalls. After passing through the Lake Kyoga basin, the river drops 400 m over a comparatively short stretch (the Murchison and other falls) and flows into Lake Mobutu Sese Seko (Lake Albert). Leaving the lake, the river, now called the Albert Nile, receives the Aswa River from the right. It flows on a plateau and then breaks through a rocky barrier at the narrow Nimule Canyon to emerge on the Sudan Plains.
Below Juba the river crosses the swampy Sudd region for 900 km, as far as Malakal; here, throughout most of its course, it is called the Bahr el Jebel. The river channel in this region is clogged by masses of algae and papyrus, called sudd. The river winds sluggishly through the region, losing up to two-thirds of its water by evaporation, by transpiration from the vegetation of the Sudd, and by filling depressions. After receiving the Bahr el Ghazal, the river, now called the White Nile (or Bahr el Abyad), leaves the Sudd and is joined by the Sobat River from the right, which almost doubles its water volume. Below this junction the Nile flows placidly in a broad valley through a semidesert all the way to Khartoum. From the Nimule Canyon to Khartoum, a distance of about 1,800 km, the river drops about 80 m.
At Khartoum the Blue Nile, issuing from Lake Tana, pours its waters into the White Nile. From here to its mouth the river is called simply the Nile River. Between Khartoum and Aswan, a distance of about 1,850 km, the river drops about 290 m. Below the entrance of the Atbara River, the last major tributary, the Nile enters the Nubian Desert, where it crosses low mountain ranges, making a large bend. Outcrops of crystalline rock in one part of the river valley have created the six famous rapids, called cataracts, which hindered navigation before the construction of the Aswan High Dam.
Between Aswan and Cairo (900 km) the drop is slight, and the river flows in a broad valley up to 20–25 km wide. The Nile delta begins 20 km from Cairo. It has an area of 22,000 to 24,000 sq km (according to different sources), with numerous arms and lakes stretching along the coast from Alexandria to Port Said for about 260 km. In the delta the main channel of the Nile divides into nine large branches and many small ones. The principal branches for navigation are the Dumyat (Damietta, eastern) and the Rashid (Rosetta, western), each of which is about 200 km long. Some of the Nile’s waters pass through the Ibrahimiya Canal and the Yusuf branch into Lake Birka Qarun and are to irrigate the Fayyum Oasis. Fresh Nile water is supplied to the Suez Canal region through the Ismailia Canal and to Alexandria and its environs through the Mahmudiya Canal. The lagoons of Lakes Manzilah, Burullus, and Maryut are in the northern part of the delta.
The Nile has a complex regime. In the equatorial part of the river basin there are two periods of maximum precipitation, one in the spring (March to May) and the other in the fall (September to November), causing an increase in the water volume below the Nimule Canyon in the summer and winter. In the Sudan and the Blue Nile basin, the Nile’s second main source of water, rain falls in the summer (June to September). In the Sudan the Nile overflows during the summer as a result of the monsoon rains, but it loses a great deal of water through evaporation so that the Blue Nile is the chief source of water for the Nile, contributing 60–70 percent of its water during the summer. As a result the waters of the Nile rise during the summer and fall in the central and northern Sudan and in Egypt. High water occurs in Lower Egypt between July and October. The average water discharge at Aswan is 2,600 cu m per sec, with a maximum of 15,000 cu m per sec and a minimum of about 500 cu m per sec. During average high water the river rises 6 to 7 m in Egypt. Severe flooding occurred before regulatory structures were built in the Nile Valley. The annual discharge of solid matter at Aswan is 62 million cu m, much of which is deposited as silt on fields, in irrigation canals, and in reservoirs.
The Nile Valley and particularly its delta were one of the centers of ancient civilization. Since ancient times the water resources of the Nile have been used for irrigation, the natural fertilization of fields, fishing, water supply, and navigation. The river is especially important for Egypt, where about 97 percent of the population lives in the 15 to 20 km wide Nile Valley. Construction of the Aswan hydroengineering complex has helped regulate the flow of the Nile and eliminate disastrous floods and has increased the area of irrigated land. In the Sudan the waters of the Nile are important for the cotton-growing Gezira region. To regulate the river’s flow and supply water to the canals, many dams have been built on the Nile and its tributaries: the old Aswan Dam (volume of the reservoir, 5.5 cu km), the Nasser Dam (164 cu km), and the Jebel Aulia Dam on the White Nile (2.5 cu km), as well as the water-raising dams (barrages) of Isna, Nag Hammadi, Asyut, Mohammed Ali, Zifta, and Idfina in Egypt and Sennar on the Blue Nile in the Sudan.
The Nile has potential energy resources of about 50 gigawatts (GW). Hydroelectric power stations include the Aswan (capacity, 2.1 GW), Nag Hammadi, el-Fayyum on the Yusuf Canal, and Owen Falls on the Victoria Nile in Uganda (capacity, 150 megawatts). The Nile is navigable for more than 3,000 km. There is also navigation on the Yusuf, Ibrahimiya, Mansura, and Ismailia canals and on Lakes Victoria, Kyoga, Mobutu Sese Seko (Albert), and Tana. The longest navigable stretches are from Khartoum to Juba and then from Nimule to Lake Mobutu Sese Seko. Beyond this area navigation is possible only in certain sectors. The waters of the Nile basin are rich in fish. Among commercially important fish are the Nile perch, bichir, tiger fish, catfish, killifish, and carp. The largest cities along the Nile are Cairo, Khartoum, and Aswan, and, in the delta, Alexandria.
REFERENCESPopov, I. V. Reka Nil. Leningrad, 1958.
Dmitrevskii, Iu. D. Vnutrennie vody Afriki i ikh ispol’zovanie. Leningrad, 1967.
Ob”edinennaia Arabskaia Respublika. Moscow, 1968.
A. P. MURANOV