White Nile

The source of the Nile is sometimes considered to be Lake Victoria, but the lake has feeder rivers of considerable size. The Kagera River, which flows into Lake Victoria near the Tanzanian town of Bukoba, is the longest feeder, although sources do not agree on which is the longest tributary of the Kagera and hence the most distant source of the Nile itself. It is either the Ruvyironza, which emerges in Bururi Province, Burundi, or the Nyabarongo, which flows from Nyungwe Forest in Rwanda. The two feeder rivers meet near Rusumo Falls on the Rwanda-Tanzania border.

The Nile leaves Lake Victoria at Ripon Falls near Jinja, Uganda, as the Victoria Nile. It flows for approximately 500 kilometres (300 mi) farther, through Lake Kyoga, until it reaches Lake Albert. After leaving Lake Albert, the river is known as the Albert Nile. It then flows into Sudan, where it is known as the Bahr al Jabal ("River of the Mountain"). The Bahr al Ghazal, itself 716 kilometres (445 mi) long, joins the Bahr al Jabal at a small lagoon called Lake No, after which the Nile becomes known as the Bahr al Abyad, or the White Nile, from the whitish clay suspended in its waters. When the Nile flooded it left a rich silty deposit which fertilized the soil. The Nile no longer floods annually since the completion of the Aswan Dam in 1970. From Lake No, the river flows to Khartoum. An anabranch river, the Bahr el Zeraf, flows out of the Nile's Bahr al Jabal section and rejoins the White Nile.

The term "White Nile" is used in both a general sense, referring to the entire river above Khartoum, and in a limited sense, describing the section between Lake No and Khartoum.

The flow rate of the Bahr al Jebal at Mongalla, Sudan is almost constant throughout the year and averages 1,048 m³/s (37,000 cu ft/s). After Mongalla, the Bahr Al Jabal enters the enormous swamps of the Sudd region of Sudan. More than half of the Nile's water is lost in this swamp to evaporation and transpiration. The average flow rate of the White Nile at the tails of the swamps is about 510 m³/s (18,000 cu ft/s). From here it soon meets with the Sobat River at Malakal. On an annual basis the White Nile upstream of Malakal contributes about 15% of the total outflow of the Nile River.

The Bahr al Jebal and the Sobat River are the two most important tributaries of the White Nile in terms of discharge. The Bahr al Ghazal's drainage basin is the largest of any of the Nile's sub-basins, measuring 520,000 square kilometres (200,000 sq mi) in size, but it contributes a relatively small amount of water, about 2 m³/s (71 cu ft/s) annually, due to tremendous volumes of water being lost in the Sudd wetlands. The Sobat River, which joins the Nile a short distance below Lake No, drains about half as much land, 225,000 km² (86,900 sq mi), but contributes 412 cubic metres per second (14,500 cu ft/s) annually to the Nile. When in flood the Sobat carries a large amount of sediment, adding greatly to the White Nile's color.

The average flow of the White Nile at Malakal, just below the Sobat River, is 924 m³/s (32,600 cu ft/s); the peak flow is approximately 1,218 m³/s (43,000 cu ft/s) in October and minimum flow is about 609 m³/s (21,500 cu ft/s) in April. This fluctuation is due the substantial variation in the flow of the Sobat, which has a minimum flow of about 99 m³/s (3,500 cu ft/s) in March and a peak flow of over 680 m³/s (24,000 cu ft/s) in October. During the dry season (January to June) the White Nile contributes between 70% and 90% of the total discharge from the Nile.

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