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About Eastern Nile

The Eastern Nile sub-system: This covers the catchments of the Blue Nile (Abay), Atbara (Tekezze), and Baro. The runoff from this region contributes between 85 and 90 per cent of the annual Nile flows, but the Blue Nile (Abay) can be seen to respond directly to the seasonal rain patterns, exhibiting clear dry and wet spells. The Eastern Nile supports an extraordinary range of ecosystems from high mountain moorlands, afromontane forests, savanna woodlands, extensive wetlands, intensively cultivated catchments, groundwater systems, and arid deserts.

The Eastern Nile Basin

A river basin is a land mass dissected by tributaries as they flow downstream and join each other to form larger and larger rivers. The Nile Basin looked at southward from the delta in Alexandria, Egypt, is one such large basin. The Nile Basin in turn is divided into several sub-basins, the Eastern Nile being one of them. The Eastern Nile basin covers some 2,695,300 km2, which in turn is sub divided into sub basins that include Main Nile (covering 44 %), the Baro-Akobo-Sobat and White Nile (26 %), the Abbay/Blue Nile (17 %), and the Tekeze-Atbara (13%).  It is estimated that more than 156 million people live in the four sub basins of Eastern Nile.  The Abbay/Blue Nile and Main Nile are the most heavily populated, accounting 79 % of the total population. Each of these sub-basins offers distinctive natural resources potentials and constraints that entail the need for context- specific short- and long-term development interventions.  

Abbay-Blue Nile Sub Basin

General/Geography: The Abbay-Blue Nile Sub-Basin covers 311,548 km2 (35 and 65 percent of which is in Sudan and Ethiopia respectively). Seventy and thirty percent of the population lives on the Ethiopian and Sudanese sides respectively.

The Abbay's source is Gish Abbay in West Gojam, Ethiopia, which flows northward as the Gilgel Abbay into Lake Tana. Three major rivers (Megech, Rib and Gumara) also flow into Lake Tana. The Abbay exits from the southeastern corner of the lake, cuts a deep gorge first south then westwards, later joined by a number of tributaries: Beshilo, Derame, Jema, Muger, Finchaa, Didessa and Dabus from the east and south; and the Suha, Chemoga, Keshem, Dera and Beles from the north. The Abbay exits Ethiopia near Bambudi and becomes the Blue Nile in Sudan.

Hydrology: The Dinder and Rahad (seasonal rivers) rise to the west of Lake Tana, flow westwards across the border joining the Blue Nile below Sennar in Sudan. The Blue Nile meets the White Nile at Khartoum.  Mean annual discharge of Abbay  (1920-2000) at the Sudanese border is approximately 50.0 km3, additional 4.0 km3 coming from Rahad and Dinder. In contrast to the more steady White Nile, considerable seasonal flow variations characterize  the Abbay/Blue Nile -  ranging from 302 million m3/month in February to a peak of 13,151 million m3/month in August (annual peak flow occurs July-October).

Abbay has a channel length of 922 km to the Sudan border. Abbay falls 1295 meters to the Sudan border (490 masl), beginning with the spectacular Tissat Falls in Lake Tana (1,785 masl). There is a 10-fold increase in discharge between Lake Tana and the Sudan border. Rainfall in Abbay-Blue Nile Sub-Basin ranges from nearly 2,000 mm/yr in the Ethiopian Highlands to less than 200 mm/yr at the junction with the White Nile.

Land use: Abbay-Blue Nile Sub-basin land use consists of: farming - small scale sedentary and semi-mechanize (36%); irrigated land (3%); grassland and woodland (42%); high forest (1.4%); swamp (0.5%); rock (2.4%); water body (1.3%); other (15%).

Main Nile Sub Basin

General/Geography: The Main Nile sub-basin covers 656,398 km2, from the confluence of the Blue and White Niles in Khartoum to the Delta in Egypt in the North, covering  over 14 degrees of latitude. Tekeze-Atbara River is the only tributary along the Main Nile. Except in years of exceptional rainfall there is no other inflow.  Meroe dam in Sudan is located between Khartoum and the Aswan High Dam at the Fourth Cataract.

Hydrology: The average annual flow of the Main Nile at Tamaniat is approximately 72.691 km3 (1911 – 1995). The river flows through a series of cataracts with a total drop of 192 m (from 375 masl at Khartoum to 183 masl at Lake Nubia/Nasser) over a length 1,490 kms.  Though there are year-on-year variation, the total annual flow at the border with Egypt has historically been taken (before any significant abstraction) as 84 km3 (1905-1959).  In Sudan the annual rainfall ranges from less than 25 mm in the north to 400 mm. In Egypt most rain falls along the coast but even the wettest area, around Alexandria, receives only about 200 mm of precipitation per year.

Land use:  Sixty five percent of the Main Nile Sub-Basin is categorized as bare land and bare soil, 14 percent is loose sand, 13 percent covered by grass and shrub, 4 percent is under irrigated land and 0.2 percent is woodland. The remaining portion of the sub basin land is used for other purposes.

 

Tekeze-Setit-Atbara Sub-basin

General/Geography: The Tekeze-Atbara sub-basin covers an area of 227,128 km2, including the Mereb-Gash basin.  Sixty percent of the Sub-Basin falls in Sudan and 40 % in Ethiopia. Seventy five percent of the population lives in Ethiopia.  The Tekeze River travels more than 750 km from its source near Lake Ashange in Ethiopia to the border with Sudan. In Sudan the river extends another 575 km in a north-westerly direction.

The Sudanese portion of the Tekeze-Atbara watershed is characterized by very low density of watercourses except in the south-west along the Blue Nile watershed where there are numerous intermittent khor channels.

Hydrology: The Atbara River contributes 12.7 % of the total discharge of the Main Nile. The average discharge at Kashm el Girba station (1986-2000) was 11.45 km3.   The total runoff is 52,834 m3 water per km2 per annum, compared with 169,612 m3/km2/yr for the Blue Nile, 28 833 m3/km2/yr for Baro-Akobo-Sobat.

Most of the Tekeze-Atbara water comes from Ethiopia, even though 50 % of the Sub-Basin is located in Sudan.  Rainfall in the sub-basin ranges from about 2 120 mm/yr in the highlands of Ethiopia to less than 50 mm/yr at the junction with the Main Nile at Atbara.

Land use: Sixty two percent of  the Sub- Basin  covered under grass land and shrub land, 12 % is categorized as bare land with  loose sand’ 10 % under small scale rain fed sedentary agriculture, 4 5 is woodland, 3 % rock, 1.2 % under irrigated crops, forest land accounts 0.1 Other land uses cover the remaining portion.

 

The Baro-Akobo-Sobat- White Nile Sub-basin

General/Geography: The Baro-Akobo-Sobat-White Nile Sub-basin covers 468,215 km2 (84% is in Republic of South Sudan and 16 % in Ethiopia). Nearly 80% of the population lives in Republic of South Sudan.   The main tributaries of the Sobat are the Baro, Gilo and Akobo that rise on the Ethiopian Plateau at some 3,300 masl. The Highlands are covered in dense Montane High Forest, although this is rapidly being converted to agriculture. The plains below are covered with a Lowland Baphia Forest that gives way to savanna woodland and then swamp grassland plains.

Hydrology: The Baro-Sobat-White Nile Sub-basin within Ethiopia is well-watered. However, spatial variation of the mean annual rainfall is considerable due to the great range in elevation across the basin. Average annual precipitation ranges between 600 mm in the lowlands (less than 500 masl), and 3,000 mm in the highlands (over 2,000 masl). Average rainfall greater than 100 mm occurs from May to October. Highest rainfall occurs June-September.

Within Republic of South Sudan the highest rainfall (greater than 1000 mm/year) is found in the southwest and southeast of the Sub-basin. Over much of the Pibor-Sobat Sub-basin it varies between 750 and 1,000 mm/yr. In the White Nile Sub-basin rainfall decreases northwards from 750 to 250 mm near the junction of the White and Blue Niles. However, everywhere rainfall exhibits both seasonal and year-on-year variability. Variability increases form south to north.

Land use: Grass and open shrub land is the dominant land cover constituting 52 % of the total land in the Sub-Basin. Open wood land covers 17 %, 7% is under permanent and seasonal swamp, 4 % sedentary crop land, 2% irrigated crop, and 18 % under other uses.

The Eastern Nile Countries

The Eastern Nile riparian countries include Ethiopia, Sudan and South Sudan, Egypt, and a small portion of Eritrea (about 3,500 km2):

Egypt

The most downstream country, with more than 96% of its freshwater inflow originating from outside its national boundaries, is also the most economically developed. Its population was estimated at 82.5 million and GDP per capita at USD 2781 (World Bank, 2012). About 96% of the population lives within the Nile basin. Egypt is one of the founding members of the NBI (ENTRO, 2013).

 Ethiopia

Ethiopia is the most upstream country with a population of 84.7 million and a GDP per capita of USD 374 (World Bank, 2012). The highlands of Ethiopia generate over 86% of the  Nile waters. The Nile basin covers 32% of the national land area and 40% of the population resides with in the basin. Ethiopia is one of the founding members of the NBI (ENTRO, 2013).

Republic of South Sudan

South Sudan is the youngest state encompassing portions of the White Nile and the Nile above the confluence of the Sobat and White Nile Rivers. The population of South Sudan is 10.3 million (World Bank, 2012). This area includes the extraordinary wetland, the Sudd, which controls the flow from the Equatorial Lakes region into the White Nile. About 97% of the country and 99% of the population falls within the Nile Basin. South Sudan joined NBI in 2012 (ENTRO, 2013).

Sudan

Sudan is the mid-stream country. Sudan has a population of 34.3 million and GDP per capita of USD 1234 (World Bank, 2012). It receives the flows of White Nile, Abbay/Blue Nile, Baro- Akobo-Sobat and Tekeze-Setit-Atabra tributaries. Khartoum is where the two Niles meet to form the Main Nile. About 74.9% of the country and 87% of the population resides with in the Nile Basin. Sudan is one of the founding members of the NBI(ENTRO, 2013).