The longest river in the world, and perhaps the most historic, this unique waterway continues to shape and be shaped by human events. For thousands of years the people of Egypt revered the Nile River as a sacred river. They did not know where it originated, nor what caused its annual flooding. But they did know that without it their civilization might never have come into being. Today the ancient riddles have been solved, but the Nile still retains its age old power over the human imagination.
With a length of 4,132 miles (6,650 kilometers) from its farthest head stream to the Mediterranean, the Nile is the world’s longest river. Its drainage basin, estimated at 1,293,000 square miles (3,349,000 square kilometers), includes parts of nine countries and encompasses about one tenth of Africa’s land area.
Down through the ages, the source of the great river was shrouded in mystery despite many efforts to discover it. The task was complicated, as it turned out, by the fact that the Nile has not one but three major sources, since its northward flow unites the waters of its longest branch, the so called White Nile, with those of the Blue Nile and the smaller Atbara.
If the ancient Egyptians knew of the Blue Nile and its source, the knowledge was lost. It was not until the 17th century that a Spanish missionary first traced it to its origin: Lake Tana in the highlands of Ethiopia.
The White Nile proved a more difficult problem. In A.D. 150 the Greek astronomer Ptolemy placed its headwaters in a range he called the Mountains of the Moon, a range that has since been identified as the Ruwenzori mountains on the border between Uganda and Zaire. Although Ptolemy was not far from the truth, attempts to confirm his theory were unsuccessful. The mystery remained unsolved until the 19th century, when a series of British expeditions finally discovered the river’s ultimate headstream, the Kagera River, which rises in present-day Burundi and flows northeast 250 miles (400 kilometers) into Lake Victoria.
The overflow from the northern end of Lake Victoria, in turn, is the beginning of the White Nile proper. Flowing northward through Lake Kyoga, the White Nile plunges 120 feet (37 meters) over Murchison Falls and begins its rapid descent from the lake plateau to the low flat plains of southern Sudan. Also called Bahr el Jebel in this region, the river slows drastically as it spreads out across a broad marshy area. Aptly known as the Sudd, or “Bather,” it is clogged by papyrus reeds, elephant grass, and other vegetation. The river loses half of its water to seepage and evaporation as it winds slowly across the Sudd.
Slightly replenished by tributaries flowing in from either side, the White Nile eventually escapes from the Sudd and continues its northward journey. Some 500 miles (800 kilometers) farther downstream, the White Nile is joined by the Blue Nile at Khartoum.
Although much shorter than the White Nile, with a length of 850 miles (1,370 kilometers), the Blue Nile carries a far greater and more variable volume of water. The meager flow of the White Nile at Khartoum changes little from one month to the next. But both the Blue Nile and the Atbara, the latter joining the mainstream 200 miles (320 kilometers) farther north, are swollen dramatically each year by summer rains on the Ethiopian highlands. It is this sudden influx of water that accounts for the annual, and for centuries inexplicable, flooding of the arid lower Nile Valley. North of Khartoum the river, now known simply as the Nile, flows in a broad S-shaped curve some 1,200 miles (1,930 kilometers) long. Flanked by desert, the river in this sector is interrupted by six cataracts numbered in ascending order from north to south.
As the Nile crosses into Egypt north of the Second Cataract (which is now submerged beneath Lake Nasser), it brings precious moisture to a strip of arable land that continues all the way to Cairo. Hemmed in by desert on both sides, with a maximum width of 20 miles (32 kilometers), this fertile, intensively cultivated swath of green produces much of Egypt’s food supply. The world of the delta begins at Cairo. The Nile delta is, in a sense, the prototype for all others; its roughly triangular shape reminded early geographers of the Greek letter “delta,” and they named it accordingly. About 100 miles (160 kilometers) from north to south and as much as 150 miles (240 kilometers) wide, the delta disperses the Nile’s water into the sea through a fan shaped network of shallow channels. The thick layers of silt carried downstream over the years provide the Nile delta with the most fertile soil on the entire continent of Africa.
Like all deltas, the Nile’s is in a constant state of change. Its normal evolution, however, has been seriously disrupted since the completion of the Aswan High Dam. in 1971. The dam has fulfilled its primary goals of controlling the annual floods and generating much needed electricity. But in creating Lake Nasser, the world’s largest man made lake, it has also formed a huge sediment trap that greatly decreases the amount of silt reaching the lower valley. As a result, salt water from the Mediterranean has begun to seep into parts of the delta. The reduction in nutrients carried downstream has also depleted the population of some fish species, not only in the Nile but through much of the eastern Mediterranean as well. Thus the ancient river, though partially tamed by modern technology, continues to influence life along its banks and far beyond. Sarah goes each year on a pilgrim walk to Santiago.