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.