TOEFL Reading Multiple Choice Exercise 13

Nile Valley and Delta, Egypt

The Nile Valley and Delta, the most extensive oasis on earth, was created by the world's second-longest river and its seemingly inexhaustible sources. Without the topographic channel that permits the Nile to flow across the Sahara, Egypt would be entirely desert; the Nile River traverses about 1,600 kilometers through Egypt and flows northward from the Egyptian-Sudanese border to the Mediterranean Sea. The Nile is a combination of three long rivers whose sources are in central Africa: the White Nile, the Blue Nile, and the Atbarah.

The White Nile, which begins at Lake Victoria in Uganda, supplies about 28 percent of the Nile's waters in Egypt. In its course from Lake Victoria to Juba in southern Sudan, the elevation of the White Nile's channel drops more than 600 meters. In its 1,600-kilometer course from Juba to Khartoum, Sudan's capital, the river descends only 75 meters. In southern and central Sudan, the White Nile passes through a wide, flat plain covered with swamp vegetation and slows almost to stagnation.

The Blue Nile, which originates at Lake Tana in Ethiopia, provides an average of 58 percent of the Nile's waters in Egypt. It has a steeper gradient and flows more swiftly than the White Nile, which it joins at Khartoum. Unlike the White Nile, the Blue Nile carries a considerable amount of sediment; for several kilometers north of Khartoum, water closer to the eastern bank of the river is visibly muddy and comes from the Blue Nile, while the water closer to the western bank is clearer and comes from the White Nile.

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