Nile (River)

The Nile is a large river in northeastern Africa. It is the world's longest stream of fresh water. It is 6,671 km long and drains an area of 2.87 million square 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 semi-deserts. 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.

The Nile, the longest river in the world, running through Egypt and Sudan.