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.