NILE BASIN RESEARCH (N-AFRICA)
The Nile River, about 6,695 kilometers in total length, is the longest river in the world. Its basin covers an area of 3.18 million square kilometers – some 10 per cent of the African continent. The river basin straddles 35° of latitude (4° S to 31° N) encompassing a wide variety of climates, river regimes, biomes and terrains. The basin is shared by 11 countries (i.e., Rwanda, Burundi, Tanzania, Kenya, Democratic Republic of Congo, Uganda, South Sudan, Sudan, Ethiopia, Eritrea, and Egypt). It comprises two major tributaries, the White Nile and the Blue Nile (known as the Abay in Ethiopia).
The White Nile originates with most distant source of the Nile, the Ruvyironza River, which flows into Lake Victoria through the Ruvubu and Kagera rivers. Other rivers (e.g., the Simiyu-Duma, Grumati-Rwana, Mara, Gucha-Migori, Sondu, Yala, Nzoia, Sio, Katonga and Ruizi) also congregate into Lake Victoria – the largest of the Nile Equatorial Lakes.
The White Nile emerges from Lake Victoria in Uganda as the Victoria Nile, and travels northwards, passing through two other Equatorial Lakes – Kyoga and Albert. The river re-emerges from Lake Albert as the Albert Nile and journeys northwards to South Sudan and to Khartoum. The Blue Nile emerges at Lake Tana in Ethiopia, and flows into Sudan from the southeast. The two rivers meet at the Sudanese capital Khartoum and flow north through Sudan and Egypt to drain into the Mediterranean Sea.
The Nile consists of a fortuitous convergence of at least five distinct physiographical segments (Wolman and Giegengack, 2008).
The White Nile headwaters, the Equatorial lake plateau is characterized as densely forested, tropical catchments with perennial flow regimes. The Sudd region and central Sudan has low gradient floodplains with wide-ranging swamplands and broad channel belts and low suspended sediment concentrations. The Ethiopian Highlands, the headwaters of the Blue Nile and the Atbara, is typify as deep ravines, unstable slopes, entrenched steep gradient streams with highly seasonal flows and high sediment loads. Another physiographic segment is the great bends and cataracts of the Nile in the desert with ephemeral tributary wadi systems and alluvial fans in the arid lands of Sudan and Egypt. It is categorized as the cataracts and vast alluvial reaches of the main Nile with a strongly modified flow and sediment regime downstream of the Aswan High Dam. The last segment is the Egyptian region including the low gradient delta complex with its large distributaries, promontories and lagoons, heavily modified drainage and dense network of irrigation canals.
Geology: Blue Nile
The geology of Blue Nile is dominated with the base rocks, the basement complex, acidic and metamorphic rocks and the unconsolidated sediments of Vertisol nature.
The base rocks of basaltic origin dominate in the eastern highland plateaus of the Blue Nile in Ethiopia and along the boundaries of Sudan and Atbara-Tekeze sub-basin. The lowlands of Ethiopia close to the Sudanese border as well as portions in the lower course of the Rahad and Dindir watersheds are largely covered with basement complex, acidic and metamorphic rocks. In Sudan, the central part of the Gezira scheme, starting from Ethiopian border including considerable portion of the Khartoum state are predominantly covered with unconsolidated sediments of largely clay in nature (ENTRO).
Land cover: Blue Nile
There five major land use land cover units in the Blue Nile sub-basin which comprise sedentary rain-fed crop land (26%), grass land (25%), wood land (17%), shrub-land (12%), and semi-mechanized farm (10%). Irrigated crops (2.6%), rock surfaces (2.4%), high forest areas (1.4%). Water bodies (1.3%), shifting rain-fed crops (1.1%) and the minor land use land cover units all together (10.7%) (ENTRO, 2007).
Soil: Blue Nile
Areas near the border between Ethiopia and Sudan exhibit Along the international boundary a Vertisols and Nitisols. The Nitisols covering 24% of the Blue Nile mainly covers the western highlands of Ethiopia while the eastern highlands are covered by Leptosols (19%). The flood plains surrounding Lake Tana are covered with Luvisols. The Sudan lowland plain in Blue Nile consists of unconsolidated sediments and mainly covered by Vertisol (29%) of the sub-basin. The flat land slope of the Ethiopian highland plateau are also covered with Vertisols (ENTRO, 2007).
References and further reading:
Conway, D. (2000) The climate and hydrology of the Upper Blue Nile, Ethiopia, Geographical Journal, 166, 49–62.
Camberlin, P. (2009) Nile Basin Climates, The Nile: Origin, Environments, Limnology and Human Use.
NBI (2012) State of the River Nile Basin Report, Nile Basin Initiative (NBI) Publishing, Entebbe, Uganda.
Sutcliffe, J., Parks, Y. P. (1999) The Hydrology of the Nile, IAHS Special Publication no. 5, IAHS Press, Institute of Hydrology, Wallingford, Oxfordshire OX10 8BB, UK, p. 33, and 57–87, 1999.
Wolman, M. G., Giegengack, R. F. (2008) The Nile River: Geology, Hydrology, Hydraulic Society, Large Rivers. John Wiley & Sons, Ltd, 471–490.
UNEP (2013) Adaptation to Climate-change Induced Water Stress in the Nile Basin: A Vulnerability Assessment Report, Division of Early Warning and Assessment (DEWA), United Nations Environment Programme (UNEP), Nairobi, Kenya.