Introduction to The Nile River
The Nile River, in Africa, is the longest river in the world.Nile River, the chief river of Africa and the longest in the world. Measured from its remote source, the Nile River is some 4,100 miles (6,600 km) long. The river system drains parts of 10 countries, from Tanzania northward to Egypt. It is the only major river that rises in the equatorial tropics and flows through desert. For centuries, millions of North Africans have depended on the water of the Nile for their crops.
Course of the River
Two major river systems join to form the mainstream of the Nile, in central Sudan. The White Nile, longer of the two, drains the central lake region of Africa. The Blue Nile, supplying most of the floodwater and about half of the total river volume, begins in the highlands of western Ethiopia. Because these two systems originate in humid regions, they supply enough water to prevent the main stream from drying up in the desert. The volume of flow in the main Nile varies greatly, being 16 times as great during flood stage (August and September) as at the lowest stage in April.
The source of the White Nile is the Kagera River, which is formed by headstreams in Rwanda and Burundi. Flowing northward and then eastward, the Kagera is fed by rivers in Uganda and Tanzania before emptying into Lake Victoria. Leaving the lake as the Victoria Nile, in Uganda, the river flows generally northwestward, passing through Lake Kyoga, dropping 130 feet (40 m) at Kabalega (formerly Murchison) Falls, and flowing into the northern tip of Lake Albert. The river, now the Albert Nile, turns sharply northward to cross the Sudan border, where it becomes the White Nile. (It is known locally as Bahr el Jebel, "river of the mountains.")
The river drops sharply to the Sudan plateau, and soon enters the Sudd, a vast swamp of papyrus, elephant grass, and water hyacinth. Floating vegetation often clogged the river channel (sudd means "block" in Arabic) until it was cleared in the early 1900's. Here the river loses a great deal of water through evaporation and seepage, meandering through several shallow channels which rejoin outside of the Sudd. After joining the Sobat from Ethiopia, the river turns northward to meet the Blue Nile.
The Blue Nile system, much less complex, begins 5,856 feet (1,785 m) above sea level in Lake Tana, in western Ethiopia. Starting southeastward, the river swings in a wide are to cross the Sudan border, continuing northwestward. It has no large tributaries, and gets its great seasonal volume from heavy summer rains. Continuing northwestward, it drops gradually to the Sudan plateau and joins the White Nile.
Here, at Khartoum, the main stream of the Nile begins. About 75 miles (120 km) downstream it tumbles over the first in a series of cataracts, or rapids. After being joined by the Atbara, its last tributary, the Nile begins its journey through the desert. With no streams and little rainfall to supply it, the river grows narrower as it continues. Vegetation—thorny shrubs and, in places, grain in irrigated fields—is limited to its narrow valley.
The Nile proceeds northward into Egypt, described by the Greek historian Herodotus as the "Gift of the Nile." Here about 90 per cent of the people live in the narrow valley, which accounts for only about 3 per cent of Egypt's land. At Cairo the Nile splits into several distributaries that flow across the wide delta into the Mediterranean Sea.
Almost all of the Lower (northern) Nile flows through barren desert. Most of the Upper (southern) Nile flows through grasslands, with scattered trees appearing in the more humid highland areas. Crocodiles, hippopotamuses, and various fish inhabit the upper course. Few people live near the river in the Upper Nile regions, and it is little used except for local transportation.
Importance
People have depended on the Nile for irrigation and transportation for some 6,000 years. The ancient Egyptians learned to benefit from the annual flood, and found the river a route between the two kingdoms of Upper and Lower Egypt. The main stream of the Nile is navigable for most of its 1,900 miles (3,100 km), except through the cataracts. The Blue and White Niles are navigable for much of their lengths, though they are not as heavily used. The chief importance of the Nile system is, as it was for the early Egyptians, its water supply.
There are two chief systems of irrigation. The basin system was developed thousands of years ago; it is now used only in parts of southern Egypt and northern Sudan. The perennial system, less dependent on the Nile flood, is used more widely. Basin irrigation requires the building of earth banks paralleling the river, to trap part of the returning flood waters. Because the land receives water and rich silt only once each year, only one basic crop—usually wheat or barley—can be supported. In perennial irrigation, low barrages block the river and form small reservoirs, whose waters are used throughout the year to support the valuable crops of cotton, corn, and rice. But because the land is not flooded, silt is not deposited and fertilizers must be used.
Perennial irrigation on a large scale was begun in the 1890's, with the building of large dams in various parts of the Nile system. The largest was Aswan Dam in southern Egypt, completed in 1902. Vast areas of desert land have been opened to farming in Egypt and Sudan, and such development continues today. The New Aswan High Dam, designed to improve irrigation and provide hydrolectric power, is a short distance south of the old dam. Lake Nasser, its huge reservoir, extends some 300 miles (480 km) upstream.