Hydrology of the White Nile
The White Nile is characterized by its gentle slope (1.5 cm/km). The average annual water flow reaching the White Nile at Malakal is 29.2 billion cubic meters, which consists of the inflow from the Sobat River in addition to that from the Bahr al-Jabal and the Ghazal. In the stretch between Malakal and Jebel Awliya, the river receives 2.5 billion cubic meters through the main tributaries (including the Khors: Adar, Wol, and the Renk, as well as others), bringing its total inflow to 31.7 billion cubic meters. The amount reaching Khartoum is 28.4 billion cubic meters. The White Nile is noted for its moderate and stable flow throughout the year (567 - 1270 cubic meters per second) and the presence of the hyacinth plant, as well as being free from silt, unlike the Blue Nile and Atbara rivers (Sayeif Al-Din Hamad,c2007؛Seifeldin
Abdalla, 2017
).
Hydrology of the Blue Nile
The source is a small river at an elevation of 2900 meters, located 100 km south of Lake Tana, and it feeds into the small Abay River, which flows into Lake Tana. Lake Tana is situated at an elevation of 1890 meters above sea level, with a surface area of 3000 square kilometers and a maximum depth of about 15 meters, making it the largest lake in Ethiopia. The area of the Lake Tana basin is 17,000 square kilometers, and it includes permanent springs such as Majish, Rib, and Jomira, in addition to other springs (Figure 4). Lake Tana contributes approximately 7-8% of the Blue Nile's flow..