Just south of Nimule, the White Nile enters South Sudan as the Bahr al Jabal (literally, “Mountain River”). The Achwa River’s confluence is just south of the town. With a length of 716 kilometers (445 miles), the Bahr al Ghazal joins the Bahr al Jabal at a small lagoon called Lake No.
From the white clay that is suspended in its waters, the Nile becomes known as the Bahr al Abyad, or the White Nile. The soil is fertilized by the rich silt that is left behind when the Nile floods. Since the Aswan Dam was completed in 1970, Egypt no longer experiences flooding along the Nile. The Bahr el Zeraf, an anabranch river, joins the White Nile from the Nile’s Bahr al Jabal section.
The Bahr al Jabal’s flow rate at Mongalla, which is approximately constant throughout the year, is 1,048 m3/s (37,000 cu ft/s). The Bahr Al Jabal enters the vast Sudd swamps following Mongalla. This swamp evaporates and transpires more than half of the water in the Nile. The typical stream pace of the White Nile at the tails of the bogs is around 510 m3/s (18,000 cu ft/s). At Malakal, it joins the Sobat River from here. Upstream of Malakal, the White Nile accounts for approximately 15% of the annual Nile outflow.
At Lake Kawaki Malakal, just below the Sobat River, the White Nile flows on average at 924 m3/s (32,600 cu ft/s); In October, the maximum flow is approximately 1,218 m3/s (43,000 cu ft/s), while in April, the minimum flow is approximately 609 m3/s (21,500 cu ft/s). The significant variation in the flow of the Sobat, which has a minimum flow of approximately 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, is the source of this variation. The White Nile accounts for between 70% and 90% of the total discharge from the Nile during the dry season (January to June).