Mark Squire, age 9, of E1 Paso, Texas, for his question:
WHICH IS THE WORLD'S LONGEST RIVER?
The Nile River of Africa is the longest river in the world. From Lake Victoria in east central Africa, it flows generally north through Uganda, Sudan and Egypt to the Mediterranean Sea, for a distance of 3,470 miles. From its remotest headstream, the Luvironza river in Burundi, the river is 4,145 miles long.
The Nile River basin has an area of more than 1 million square miles.
The source of the Nile is one of the upper branches of the Kagera River in Tanzania. The Kagera follows the boundary of Rwanda northward, turns along the boundary of Uganda and drains into Lake Victoria.
On leaving Lake Victoria at the site of the now submerged Ripon Falls, the Nile rushes for 300 miles between high rocky walls over rapids and cataracts, at first northwest and then west, until it enters Lake Albert. The section between the two lakes is called the Victoria Nile.
The river leaves the north end of Lake Albert as the Albert Nile, flows through north Uganda and at the Sudan border becomes the Bahr al Jabal. At its junction with the Bahr al Ghazal, the river becomes the Bahr al Abyad, or the White Nile.
Various tributaries flow through the Bahr al Ghazal district. At Khartoum, the White Nile is joined by the Blue Nile, or Bahr al Azraq. These are so named because of the color of the water.
The Blue Nile, which is 950 miles long, gathers its volume principally from Lake Tana in the Ethiopian Highlands. It is know here as the Abbi.
From Khartoum, the Nile flows northeast 200 miles below that city and is joined by the Atbara River. The black sediment brought down by this river settles in the Nile delta.
The Nile enters the Mediterranean Sea by a delta that separates into two main channels.
The Makwar Dam was built across the Blue Nile south of Khartoum shortly after World War I, providing storage water for cotton plantations in the Sudan. Today it is called the Sennar Dam, for the nearby town.
The Aswan Dam was heightened for a second time in 1936 and its storage capacity increased. In 1971 the Aswan High Dam was dedicated. Its large reservoir is called Lake Nasser.
At Jabal Awliya, on the White Nile south of Khartoum, another storage reservoir was provided in a dam built in 1937.
The Nile valley and Nile delta make up a total of about three percent of Egypt's area. However, almost all Egyptian farms lie in this densely populated region. Water from the Nile lets farmers in the valley and delta raise various crops the year around.
Chief winter crops include clover, wheat, beans and other vegetables. The main summer crops are cotton, corn, rice and millet. Cotton is Egypt's most important crop.