The Water Resources of the Nile Basin

Chapter 2

500 Soroti (1914–2003)

400

300

200

100 Average monthly rainfall

0 JFMAMJ JASOND

25 KEY MESSAGES

• The Nile Basin is characterized by high climatic • The headwater regions of the Nile are subject diversity and variability, a low percentage of rainfall to widespread soil erosion. Sediment yields are reaching the main river, and an uneven distribution particularly high in the Eastern Nile sub-basin, of its water resources. Potential evaporation rates which contributes 97 per cent of the total sediment in the Nile region are high, making the basin load. Most sediment is captured in reservoirs in The particularly vulnerable to drought. Sudan and Egypt, which leads to a rapid loss of • White Nile flows only contribute up to 15 per cent reservoir storage capacity. of the annual Nile discharge, but are fairly stable • The finite Nile flows are now fully utilized for throughout the year. The Eastern Nile region agricultural, domestic, industrial, and environmental supplies up to 90 per cent of annual Nile flows, but purposes, while water demand continues to rise its contribution is highly seasonal. steadily due to population growth and economic • Extensive regional aquifer systems holding development. substantial quantities of groundwater underlie the • Irrigated agriculture in Egypt and The Sudan Nile region. Some of the aquifers hold fossil water, represents the single most important consumer but others are recharged from precipitation over of the waters of the Nile, but the upper riparians the basin, or from irrigation areas and the baseflow are planning investments that will use the river’s of the Nile. Groundwater is the dominant source of renewable discharge and present challenges domestic water supply in rural communities across concerning the equitable appropriation of the the basin. Nile water resources amongst the Nile riparian • The quality of the Nile waters has generally countries. deteriorated because of population growth, • Recommended regional-level actions for intensification of agriculture, and industrial consideration by the Nile riparian countries include development. Across the basin, environmental the restoration of degraded water catchments sanitation is poor, resulting in bacteriological that are critical for sustaining the flow of the contamination and nutrient enrichment of the Nile major Nile tributaries, restoring badly degraded waters. While the quality of large parts of the Nile lands that export large quantities of sediments system – in particular in the sparsely populated and cause serious siltation in the Nile tributaries, areas – remains acceptable, localized high pollution and establishing a regional hydrometric and is experienced mainly around urban centres. environmental monitoring system. Groundwater in isolated locations also has naturally occurring high levels of dissolved minerals.

The River Nile, Egypt.

26 STATE OF THE RIVER NILE BASIN 2012 Water Resources

THE NILE BASIN Alexandria ! THE NILE BASIN The term ‘basin’ refers to the geographical 0 250 500 km ! ! Suez 2012 area drained by a river or lake. The Nile Basin, Cairo basin boundary in the context of this report, refers not only (Map prepared by the NBI) to the physical drainage area of the Nile with M a N in its associated biophysical and ecological N il elements, but also to the people living within e the basin and features of their social, cultural,

R and economic development. e d EGYPT ! Aswan S This chapter focuses on the hydrological e characteristics of the Nile river system, while a the other chapters of the report address the environmental, social, and economic ! Wadi Halfa aspects of the basin. The present chapter describes qualitatively and quantitatively the ! Port Sudan ile basin’s water resources – which comprise N n ai rivers, lakes, wetlands, groundwater, and M rainfall. It assesses the availability of the A tb a water resources in space and time, and their ra

(T e k e ERITREA ability, in terms of water quantity and quality, THE SUDAN z z e ! ) Asmara to sustainably support the consumptive Khartoum ! and non-consumptive demands for water R a h across the basin. It ends with a discussion on a d how benefits to the Nile riparians could be ! El Obeid

l D u in optimized through cooperative management e d e

N r e

i i le N and development of the common Nile water (A e b it a resources on a win–win basis. h y) Bahr el Arab W

Bahr el f So a ba Ghazal r t ! e ga Z a R l Baro Addis Ababa o e

p r Sudd o h S a A u B ko ur bo K Jur P ETHIOPIA The Nile, 6,695 kilometres in total length, is, by ib SOUTH B o a r h r most accounts, the longest river in the world. SUDAN e N l u J e m Its basin covers an area of 3.18 million square b a e t l i n S n u Juba ! kilometres – some 10 per cent of the African a o continent – and is shared by 11 countries.

e il A Below: The Victoria (White) Nile as it leaves s N w DR CONGO t a r e b Lake Victoria at Jinja. l A

KENYA UGANDA Kampala !

M Lake ig ori Victoria ! Nairobi ! R RWANDA uwan Kigali a M o Bujumbura am ! e Mombasa BURUNDI ! TANZANIA The NBI is not an authority on international boundaries.

27 The course of the Nile The most distant source of the Nile is the Ruvyironza River, which flows into Lake Victoria through the Ruvubu and Kagera rivers. Other rivers converging into Lake Victoria – the largest of the Nile Equatorial Lakes – include the Simiyu-Duma, Grumati- Rwana, Mara, Gucha-Migori, Sondu, Yala, Nzoia, Sio, Katonga and Ruizi. From Jinja in Uganda, the White Nile emerges from Lake Victoria as the Victoria Nile, and travels northwards, passing through two other Equatorial Lakes – Kyoga and Albert. Through these two lakes the Nile captures runoff from two mountainous and high-rainfall areas (Mts Rwenzori and Elgon) on the southwestern and southeastern A section of the White Nile, north of Lake Albert. peripheries of the basin. Nimule is at the point where the river narrows considerably and turns northwest, after which it The river re-emerges from Lake Albert as is known as the Bahr el Jebel. the Albert Nile and journeys northwards to Nimule near the South Sudan–Uganda border. From this point, the river, now known as the Bahr el Jebel (meaning river of the mountains), flows over the Fula rapids and The Blue Nile (Abay), flowing in from the bottom through the Sudd before meeting the Bahr el right of the photograph, and being joined by Ghazal (meaning river of the gazelles) at Lake the rivers Dinder and Rahad before meeting the No. The Bahr el Ghazal drains high rainfall White Nile at the top left of the photograph. areas of western South Sudan. From Lake No, the river turns eastwards to join with the Sobat River, which carries high, seasonally variable, flows originating in the Ethiopian Highlands. The combined Bahr el Jebel and Sobat rivers form the White Nile, which continues its northward descent and meets with the Blue Nile at Khartoum, The Sudan. The Blue Nile (also known as the Abbai or Abay) originates in Lake Tana in Ethiopia, and is the second principal stream of the Nile. Before meeting the White Nile, the Blue Nile is joined by a number of rivers, the main ones being the Rahad and Dinder, both originating in the Ethiopian Highlands.

28 STATE OF THE RIVER NILE BASIN 2012 Water Resources

The Nile as it flows through Egypt, providing valuable irrigation water to the agricultural land along its banks and in its delta.

The confluence of the White Nile and Blue Nile (Abay) bottom right, and the stretch of the river up to Lake Nasser/ Nubia and the Aswan Dam.

From Khartoum, the combined rivers of the Nile flow northwards, and are joined by the Atbara (Tekezze), also originating in the Ethiopian Highlands. The Main Nile continues travelling northwards and flows into Lake Nasser/Nubia, a major man-made reservoir on the border between The Sudan and Egypt that provides inter-annual regulation for Egypt. The Nile eventually discharges into the Mediterranean Sea via its delta.

29 RAINFALL ! Alexandria The NBI is not an authority on international boundaries. Annual rainfall distribution ! ! Suez 0 250 500 km Cairo Rainfall over the basin is characterized N by highly uneven seasonal and M spatial distribution. Most of the basin a in N experiences only one rainy season – ile typically in the summer months. Only the equatorial zone has two distinct rainy periods. R e The reliability and volume of precipitation d EGYPT ! generally declines moving northwards, with Aswan S e the arid regions in Egypt and the northern a region of The Sudan receiving insignificant ! annual rainfall. The spatial variability of Wadi Halfa rainfall is clearly illustrated by the pattern of vegetation and distribution of surface water ! ile bodies in the basin. N Bur Sudan n ai Large parts of the Nile watershed do not M

generate runoff. In fact, the main runoff- A tb a ra

producing areas are limited to the Ethiopian (T e k e z ERITREA z Highlands and the Equatorial Lakes Plateau, e THE SUDAN ! ) with some contribution from western South Khartoum ! Asmara Sudan. The relatively small size of the runoff- R a h a producing area is central to explaining the d ! D very low runoff coefficient of the Nile (3.9%). El Obeid B in l d u e e r

Total Nile discharge represents a depth of e

i i le N (A less than 30 mm if spread over the entire e b it a h y) watershed. Bahr el Arab W

So Bahr el f ba a t Ghazal r e ! ga Z a R l Baro o e Addis Ababa

p r

o h S SOUTH a A u B ko ur bo K Jur SUDAN P ETHIOPIA ib B o a r h r

e N l u J e m b a e t l i n S n u ! a o Juba

e il A s N w TOTAL RAINFALL t a r e b Average annual millimetres l A 1960–90 UGANDA DR CONGO under 300 Kampala KENYA 300 – 600 !

M 600 – 900 Lake ig ori Victoria ! Nairobi 900 – 1,200 Kigali R ! uwana RWANDA 1,200 – 1,500 M o am 1,500 – 1,800 Bujumbura e ! BURUNDI TANZANIA 1,800 – 2,100 over 2,100 (Map prepared by the NBI; source of data: Climatic Research Unit)

30 STATE OF THE RIVER NILE BASIN 2012 Water Resources

WEATHER PATTERNS IN THE NILE BASIN

The weather patterns over the Nile Basin are influenced by many factors, key among which are the movement of the Intertropical Convergence Zone (ITCZ) and the physiographic features of the basin. The ITCZ is a belt of low pressure caused by solar heating forcing air to rise through convection, which draws in air from the polar regions. The rising mass of converging air leads to cloud formation and heavy precipitation in the region of the ITCZ. Its location varies throughout the year as it follows the sun’s zenith point, producing wet and dry seasons in the tropics. Areas in the Nile Basin located on or near the equator experience two passages of the ITCZ in a year, and have a twin-peaked rainfall distribution pattern, while areas to the north and south, have a single-peaked pattern. Rainfall in Ethiopia, South Sudan, and The Sudan is concentrated in the summer months. A large part of the Nile Basin is January February March April traversed by northeasterly trade winds from the Eurasia landmass. These carry little moisture and generate little rainfall, explaining the low precipitation over much of the basin, and the Nile’s very low specific runoff. The physiographic features of the basin – in particular the mountain chain along the margins of the western arm of the Rift Valley, the May June July August broad Equatorial Plateau, the Mt Elgon area, and Ethiopian Highlands – have a marked effect on rainfall distribution. The windward side of the raised land masses receives high rainfall, while the leeward side is typically drier.

MONTHLY RAINFALL September October November December Average millimetres per month 1960–90

0 – 30 30 – 60 60 – 90 90 – 120 120 – 150 150 – 180

(Map prepared by the NBI; source of data: Climatic Research Unit)

31 900 Seasonal rainfall distribution 700 Nyala (1920–2000) Rashad (1916–2000) 700 El Renk (1906–2000) 800 600 600 The high temporal variability of rainfall in the basin is demonstrated 700 500 500 by the monthly rain records. Broadly speaking, there are three patterns 600 400 500 400

of seasonal rainfall variation: 300 400 300 300 200 200 A single rain peak June–October, with little or no rainfall in other 200 100 100 Average monthly rainfall Average monthly rainfall Average monthly rainfal l 100 months. Found in sub-basins of Eastern Nile and Main Nile. See MONITORING RAINFALL 0 0 0 histograms from Atbara to Wau. Average monthly rainfall in millimetres JFMAMJ JASOND JFMAMJ JASOND JFMAMJ JASOND Varying periods 1914–2003 A fairly evenly distributed rainfall, with a single peak from April– 800 Malakal (1940–2000) Wau (1904–2000) Juba (1949–2000) 700 700 October. Found in northern Uganda and South Sudan. See histograms range to one standard deviation 600 for Juba to Eldoret. 600 600 average monthly rainfall 500 500 400 A twin-peaked distribution, peaking in March–May and September– highest observation recorded 400 400 300 300 November, with considerable but lower rain in other months. Found in lowest observation recorded 200 200 200 ! Nile Equatorial Lakes Plateau. See histograms from Kijura to Mwanza. 100 Average monthly rainfall monitoring stations Average monthly rainfall 100 Average monthly rainfall

0 0 0 (Source data: FAO 2009; WRPM 2011) JFMAMJ JASOND JFMAMJ JASOND JFMAMJ JASOND

400 500 Wadi Halfa (1943–2000) Dongola (1945–2000) N Kotido (1947–2003) Gulu 500 Soroti (1914–2003) (1937–2003) 100 100 400 300 400

75 75 300 300 200 50 50 200 200

25 25 100 100 100 verage monthly rainfall verage monthly rainfall A A Average monthly rainfall Average monthly rainfall Average monthly rainfall 0 0 0 250 500 km 0 0 0 JFMAMJ JASOND JFMAMJ JASOND D JFMAMJ JASOND JFMAMJ JASOND JFMAMJ JASOND

Lake Nasser ! Wadi Halfa 400 400 Atbara (1908–2000) 350 Khartoum (1901–2000) Kijura (1943–2003) 500 Entebbe (1933–2003) Eldoret (1950–2000)

300 250 400 300 300 250 ! ile 200 Dongola N 300 i n 200 a M 200 200 150 Atbara 150 ! 200 100 100 100 100 100 50 50 Average monthly rainfall Average monthly rainfall Average monthly rainfall Average monthly rainfall Khartoum Average monthly rainfall ! ! 0 0 Kassala 0 0 0 JFMAMJ JASOND JFMAMJ JASON D JFMAMJ JASOND JFMAMJ JASOND JFMAMJ JASOND ! El Qaderif El Obeid ! ! Kosti 500 500

Kassala (1907–2000) El Qaderif (1904–2000) Rashad e 600 Bukoba (1950–2000) Keekorok (1950–2000)

300 Nyala l Kisumu (1950–2000) ! ! i !

N El Renk Lake Tana

e 300 250 400 i t 400 500 h W B lu 200 e N 400 300 Malakal ile (Abay) 300 ! 200 150 300 200 200 100 Wau 200 ! 100 100 100 50 100 Average monthly rainfall Average monthly rainfall Average monthly rainfall Average monthly rainfall Average monthly rainfall

0 0 0 0 0 JFMAMJ JASOND JFMAMJ JASON D Juba JFMAMJ JASOND JFMAMJ JASOND ! JFMAMJ JASOND

350 400 400 Kotido 400 350 El Obeid (1943–2000) Kosti (1931–2000) ! Mwanza (1950–2000) Giheta (1950–2000) ! Gulu Kigali (1962–2003) 350 300 300 ! 300 300 Lake Albert 300 250 Soroti ! Eldoret 250 Kijura ! Entebbe 200 200 Lake George ! 200 ! Kisumu 200 200 150 Lake 150 Bukoba ! Victoria 100 ! 100 100 Keekorok 100 100 ! Kigali ! Average monthly rainfall

50 Average monthly rainfall

Mwanza Average monthly rainfall Average monthly rainfall Average monthly rainfall 50 ! 0 0 Giheta 0 0 0 JFMAMJ JASOND JFMAMJ JASON JFMAMJ JASOND JFMAMJ JASOND JFMAMJ JASOND

32 STATE OF THE RIVER NILE BASIN 2012 Water Resources

900 700 Nyala (1920–2000) Rashad (1916–2000) 700 El Renk (1906–2000) 800 600 600 700 500 500 600 400 500 400

300 400 300 300 200 200 200 100 100 Average monthly rainfall Average monthly rainfall Average monthly rainfal l 100 MONITORING RAINFALL 0 0 0 Average monthly rainfall in millimetres JFMAMJ JASOND JFMAMJ JASOND JFMAMJ JASOND Varying periods 1914–2003 800 Malakal (1940–2000) Wau (1904–2000) Juba (1949–2000) 700 700 range to one standard deviation 600 600 600 average monthly rainfall 500 500 400 highest observation recorded 400 400 300 300 lowest observation recorded 200 200 200 ! 100 Average monthly rainfall monitoring stations Average monthly rainfall 100 Average monthly rainfall

0 0 0 (Source data: FAO 2009; WRPM 2011) JFMAMJ JASOND JFMAMJ JASOND JFMAMJ JASOND

400 500 Wadi Halfa (1943–2000) Dongola (1945–2000) N Kotido (1947–2003) Gulu 500 Soroti (1914–2003) (1937–2003) 100 100 400 300 400

75 75 300 300 200 50 50 200 200

Lake Nasser ! Wadi Halfa 400 400 Atbara (1908–2000) 350 Khartoum (1901–2000) Kijura (1943–2003) 500 Entebbe (1933–2003) Eldoret (1950–2000)

Kassala (1907–2000) El Qaderif (1904–2000) Rashad e 600 Bukoba (1950–2000) Keekorok (1950–2000)

300 Nyala l Kisumu (1950–2000) ! ! i !

N El Renk Lake Tana

0 0 0 0 0 JFMAMJ JASOND JFMAMJ JASON D Juba JFMAMJ JASOND JFMAMJ JASOND ! JFMAMJ JASOND

50 Average monthly rainfall

Mwanza Average monthly rainfall Average monthly rainfall Average monthly rainfall 50 ! 0 0 Giheta 0 0 0 JFMAMJ JASOND JFMAMJ JASON JFMAMJ JASOND JFMAMJ JASOND JFMAMJ JASOND

33 EVAPOTRANSPIRATION Water loss from the Earth’s surface Evapotranspiration (ET), which is the sum of evaporation and plant transpiration, is an important element of the water cycle. Evaporation accounts for the movement of water from sources such as soil, canopy interception, and open water bodies, to the air, while transpiration accounts for the movement of water within a plant, and its subsequent loss to the atmosphere through plant stomata. Evapotranspiration represents a significant loss of water from drainage basins. Another important term with regard to water loss from the earth’s surface is Potential Evapotranspiration (PET). This is a measure of the amount of water that would be evaporated and transpired if there were sufficient water available. PET is calculated indirectly from other climatic parameters and incorporates the energy available for evaporation as well as the ability of the lower atmosphere to transport evaporated moisture away from the land surface. Actual evapotranspiration (ET) is said to equal potential evapotranspiration (PET) when there is ample water. Actual evapotranspiration in the Nile Basin is generally high compared to other river/lake basins of The lush vegetation of the upper Blue Nile basin the world. leads to high evapotranspiration, although the Spatial and temporal evapotranspiration trends region’s potential evapotranspiration rate is lower than that of Egypt and The Sudan, where Potential evapotranspiration varies considerably across geographical temperatures are much higher. regions and over time. PET is higher in locations and during periods when there are higher levels of solar radiation and higher temperatures (and hence where there is greater energy for evaporation). Accordingly, PET is higher in hot deserts, low-lying lands, and areas near the equator. PET is also higher on less cloudy days and during the dry season (or summer). PET is higher on windy days because evaporated moisture can be quickly transported away from the ground or plant surface, allowing more evaporation to fill its place. Potential evapotranspiration further depends on relative humidity, the surface type (such as open water), percentage soil cover, the soil type (for bare land), and the vegetation type. Across the Nile region, actual and potential evapotranspiration vary markedly. The arid lands in The Sudan and Egypt have higher potential evapotranspiration rates than the humid headwater regions of the Nile. However, they have much lower actual evapotranspiration rates because there is little available water and vegetation to cause evapotranspiration. Total annual evapotranspiration is highest in the Lake Victoria sub-basin, estimated at about 307 BCM, followed by the Blue Nile sub-basin, estimated at 264 BCM, then by the Sudd sub- basin estimated at 260 BCM. The Main Nile sub-basin downstream of Khartoum has the lowest evapotranspiration rates, estimated at 7 BCM per year. (See page 35 for sub-basin map.) In terms of components of evapotranspiration, the Blue Nile (Abay) sub-basin has the highest ET losses over land; Lake Victoria sub-basin

34 STATE OF THE RIVER NILE BASIN 2012 Water Resources

has the highest evaporation losses over open ! Alexandria 0 250 500 km water; and the Sudd sub-basin has the highest ! ! Suez N ET losses over wetlands. Cairo Seasonal/monthly variability of evapotranspiration is a function of temperature, wind M a speed, relative humidity, solar radiation, and in N biomass production. No significant month-to- ile month or year-to-year variation is noted in the upper reaches of the Nile as the areas lie in the tropics that are characterized by all-year EGYPT !Aswan sunshine and humid conditions.

R A diverse and highly variable climate e d ! The within-year and between-years variability S Wadi Halfa e in rainfall over the Nile Basin is high, making a over-reliance on rainfed supply or production ! systems risky. The high potential evaporation ile Bur Sudan N n ai values in the Nile region – ranging from some M 3,000 mm/year in northern Sudan to 1,400 At ba ra mm/year in the Ethiopian Highlands, and (T e k e z around 1,100 mm/year in the hills in Rwanda z e ERITREA ) and Burundi – make the basin particularly ! THE SUDAN Khartoum ! vulnerable to drought events. Asmara Drought risks are further amplified by the high !

variability of the rainfall between seasons and El Obeid

B l years. This is manifested by uncertainty in the u

e e l i N N onset of rains, occasional cessation of rainfall il e e it ( h A ba during the growing season, and consecutive W y ) years of below-average rainfall. It has a marked adverse impact on the productivity of ! rainfed agriculture, and represents a serious Sudd Addis Ababa constraint to rural development. B ETHIOPIA a h r

The impact of the climatic variability on SOUTH e l J SUDAN e b agricultural production is further aggravated e l by widespread soil degradation that has led Juba ! to a reduction in the capacity of soils to hold moisture. Rain deficits, therefore, quickly DR CONGO translate into crop failure. UGANDA POTENTIAL EVAPOTRANSPIRATION Average annual millimetres per year Kampala KENYA Average values for 1960–90 ! Lake under 800 1,600 –1,800 2,600 –2,800 Victoria ! Nairobi 800 –1,000 1,800 –2,000 2,800 –3,000 RWANDA ! Kigali The NBI is not an 1,000 –1,200 2,000 –2,200 over 3,000 authority on international 1,200 –1,400 2,200 –2,400 Bujumbura BURUNDI ! TANZANIA boundaries. 1,400 –1,600 2,400 –2,600 (Map prepared by the NBI; source of data: FAO)

35 SUB-SYSTEMS AND SUB-BASINS The Nile sub-systems The Nile Basin comprises three broad sub-systems. The Eastern Nile sub-system: This covers the catchments of the Blue Nile (Abay), Atbara (Tekezze), and Baro, which encompass large parts of the Ethiopian Highlands and the plains of the eastern region of The Sudan. 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. Cattle grazing on flooded grasslands. The Equatorial Nile sub-system: This covers the entire watershed upstream of the Sobat–White Nile confluence. It includes the Equatorial Lakes region as well as most of South Sudan. The regulating effect of the lakes, combined with extensive wetlands in the White Nile Basin, attenuate river flow. The large swamps are also responsible for high evapotranspiration losses. White Nile flows, therefore, only contribute between 10 and 15 per cent to the annual Nile discharge, but are fairly stable throughout the year.

THE SUDD AND ITS INFLUENCE ON THE NILE HYDROLOGY

The confluence of the main tributaries of the White Nile surrounding lands, leading to extensive flooding and in South Sudan has vast expanses of tropical freshwater wetland formation. The Sudd wetlands have a permanent wetlands that exert a considerable influence on the and seasonal component, the extent of which varies from hydrologic regime of the Nile. The wetlands, now known year to year following local and regional climatic variation, collectively as the Sudd, include the Bahr el Jebel swamps, and the flow regime of the Bahr el Jebel and Sobat Rivers. the Bahr el Ghazal swamps, the wetlands at the Baro– Evaporation from the flooded lands greatly exceeds Pibor–Akobo confluence, and the Machar marshes. rainfall, and the wetlands therefore result in a net water loss Sudd is an Arabic word for ‘barrier’ or ‘blockage’. In its to the Nile system. While the complexity of the channels original usage, the Sudd referred to the islands and and the problems of measuring evaporation from swamp massive floating mats of vegetation found on the Bahr vegetation have meant that the flows in the wetland areas el Jebel between Malakal and Bor, which occasionally are not well understood, it is estimated that only about completely sealed off the Nile to navigation. half of the inflow to the Sudd emerges as outflow. The area at the confluence of the White Nile tributaries Sudd outflows show little seasonal variation, providing a is extremely flat, with an average slope of 10 cm per km. fairly constant contribution to the White Nile throughout Furthermore, river channels at the confluence are very the year. By buffering peak flows, the swamps have a shallow and annually spill large volumes of water into regulating effect on the downstream river regime.

The Sudd in flood.

36 STATE OF THE RIVER NILE BASIN 2012 Water Resources

The Main Nile Zone: This encompasses the downstream river reach, starting at the Blue–White Nile confluence at Khartoum. This large area generates virtually no runoff, and in-stream evaporation results in a net loss. River flow in the lower reaches is controlled by Lake Nasser, which is subject to significant evaporation losses. Most river flow is diverted to the irrigation schemes in the north of The Sudan and in Egypt, and only drainage and re-used water is discharged into the Mediterranean Sea.

Aswan dam 84.0 TOTAL FLOWS OF THE NILE –10.5 billion cubic metres per year N river ow 94.5 in ows evaporative losses 12.0 (Source of data: Blackmore and Whittington 2008) Main Nile

Atbara (T ekezze)

82.5 Rahad & Dinder –6.0 54.0 Blue Nile (Abay) 50.0 n/a L. Tana 13.0 28.5 –1.0 Sobat 3.8 15.0 Baro west inflow to 13.5 Pibo Bahr el Ghazal r –94.5

Sudd –30.9 11.3 rainfall west inflow to 100 Bahr el Jebel 4.8

3.3 26.5 3.0

–2.5 L. Albert L. Kyoga L. Victoria

6.5 22.5 23.5 18.0

–4.0

6,000 NILE FLOWS Average monthly ow, 5,000 cubic metres per second 4,000 White Nile at Mogren 1962–88 3,000 Blue Nile (Abay) at 2,000 Khartoum 1962–88 1,000 Main Nile at Tamaniat 1962–90 0 JJan FbFeb MMar AAprMMay JJunJJlul AAugSSep OtOctNNov DDec (Source of data: NBI WRPM Project 2012)

37 The Nile sub-basins Alexandria N ! Within the three broad sub-systems, nine distinct catchment areas or sub-basins can be found, namely Lake Victoria, Victoria–Albert Nile, ! ! Suez Cairo Sudd, Bahr el Ghazal, Baro–Pibor–Sobat, Blue Nile (Abay), Atbara (Tekezze), White Nile, and Main Nile sub-basins. Each one of these M a has unique hydrological characteristics as summarized below. in N il THE MAIN SUB-BASINS e AND THEIR CONTRIBUTION CHARACTERISTICS OF THE NILE SUB-BASINS TO THE NILE R 2 e Sub-basin Area (km ) Average Average Specific Runoff Specific Comments billion cubic metres per year EGYPT d ! Aswan annual annual runoff coefficient yield S e precipitation reference (mm/ (%) (MCM/ (Map prepared by the NBI; source of data: Blackmore a and Whittington 2008) (mm/yr) evapo- km2/yr) km2/yr) transpiration (mm/yr) ! Wadi Halfa

Main Nile 958,639 198 2,206 0.0 0.0% – With no surface runoff MAIN NILE contribution, in-stream flow ! Port Sudan losses result in a net loss to the ile N n Nile System. ai M Atbara 232,370 733 1,778 50.4 7.3% 0.054 All runoff is concentrated in the (Tekezze) July to September period. A tb a ra

(T e ERITREA k Blue Nile 308,157 1,099 1,765 148.9 15.9% 0.175 Seasonal runoff in July to e THE SUDAN z z (Abay) November, with only base flow in e ! Khartoum ) the rest of the year. ! Asmara

R White Nile 237,391 754 1,983 0.0 0.0% – a TEKEZZE-ATBARA h a d 12.0 ! El Obeid

Baro-Pibor- 230,293 1,338 1,592 45.3 4.4% 0.059 Runoff is attenuated by the large LOWER B l D u in e d Sobat wetland areas in the basin. WHITE NILE e

N r BAHR EL GHAZAL e

i i le N 11.3 (A e b Bahr el 555,428 826 1,807 0.1 2.5% 0.020 Sub-basin has a low runoff due it a BLUE NILE h y) Ghazal to high evapotranspiration in the Bahr el Arab W 54.0 Bahr el Ghazal wetlands. So Bahr el f ba a t Ghazal r ! Sudd (Bahr 169,665 1,067 1,694 -12.6% -0.134 Because of evaporation in the e ga Z a R l Baro o e Addis Ababa

p el Jebel) large wetland areas, there is a r o h SOUTH S a A u B ko net loss of water in the Sudd sub- ur bo K Jur SUDAN basin. P ib B o a r SUDD h Victoria – 243,080 1,179 1,544 37.7 1.0% 0.012 The low runoff coefficient is r

e BARA-AKABO- N –22.8 l u J Albert-Nile caused by net losses due to high e PIBOR m b a e t l 13.5 i evapotranspiration rates in the n S n u Juba ! large lakes and wetland systems. a o ETHIOPIA

Lake 241,520 1,368 1,486 107.5 7.1% 0.097 Over the lake, rainfall and the le i A s N w DR CONGO t a Victoria lake evaporation are the largest r e b l VICTORIA NILE / components of the water A KENYA balance of Lake Victoria. The ALBERT NILE 3.0 large storage capacity of the lake attenuates seasonal flow UGANDA ! variations and leads to relatively Kampala stable Victoria Nile flows. M Lake ig ori Victoria ! Nairobi Combined 3,176,543 1,046 1,972 26.4 3.9% 0.030 ! LAKE VICTORIA R RWANDA uwan Nile System Kigali 23.4 a M o Bujumbura am Sources: NBI-GIS Unit GIS/CRU dataset GIS/CRU dataset Sutcliffe & Computed Computed ! e 1960–90 1960–90 Parks from JMP from JMP BURUNDI Scoping Scoping ! Mombasa Study figures Study The NBI is not an authority on 0 250 500 km figures international boundaries. TANZANIA

38 STATE OF THE RIVER NILE BASIN 2012 Water Resources

Alexandria N !

! ! Suez Cairo

M a in N il THE MAIN SUB-BASINS e AND THEIR CONTRIBUTION

TO THE NILE R e billion cubic metres per year d EGYPT ! Aswan S e (Map prepared by the NBI; source of data: Blackmore a and Whittington 2008)

! Wadi Halfa

MAIN NILE

! Port Sudan ile N n ai M

A tb a ra

(T e ERITREA k e THE SUDAN z z e ! Khartoum ) ! Asmara

R a TEKEZZE-ATBARA h a d 12.0 ! El Obeid

LOWER B l D u in e d WHITE NILE e

N r BAHR EL GHAZAL e

i i le N 11.3 (A e b it a BLUE NILE h y) Bahr el Arab W 54.0

So Bahr el f ba a t Ghazal r ! e ga Z a R l Baro o e Addis Ababa

p r o h SOUTH S a A u B ko ur bo K Jur SUDAN P ib B o a r SUDD h r

e BARA-AKABO- N –22.8 l u J e PIBOR m b a e t l 13.5 i n S n u Juba ! a o ETHIOPIA

e il A s N w DR CONGO t a r e b l VICTORIA NILE / A KENYA ALBERT NILE 3.0 UGANDA Kampala !

M Lake ig ori Victoria ! Nairobi ! LAKE VICTORIA R RWANDA uwan Kigali 23.4 a M o Bujumbura am ! e BURUNDI ! Mombasa The NBI is not an authority on 0 250 500 km international boundaries. TANZANIA

39 RECORDING RIVER FLOW

Since the early years of the last century, records have been kept of the N monthly discharge at key sections of the Nile and its main tributaries. Because these were calculated from flow data with different periods they cannot be compared directly, but they do provide a good picture of the seasonal variation, and of the relative contribution of the respective tributaries to the total Nile flow. 0 250 500 km Hydrometric activities have declined in recent years, and data gaps

now exist for important sections of the Nile system (see Chapter 8). Lake Nasser This prevents proper water resources planning and management, and makes it difficult to validate climate models.

ile 1 N 1: Nile at Dongola (1910–95) 2: Atbara at Mouth (1903–94) 3: Nile at Tamania (1911–95) i n a 20 20 20 M

2 At ba ra

(T 15 15 15 e k e z 3 z e 4 5 ) 10 10 10

S et 6 it 5 5 5

T D Rah e in ad k d e e z e z 0 0 0 l r i e JFMAMJ JASOND JFMAMJ JASOND JFMAMJ JASOND

e t Lake Tana i 7 4: Khartoum (Blue Nile) (1900–95) 5: Nile at Mogren (1911–95) 6: Dinder Mouth (1907–97) h W B ahr el A l B ra u 20 20 20 b e N hazal ile y) hr el G 10 (Aba Ba 9 So 13 8 ba 15 15 15 aga t R o p 12 o Baro S 11 u A ur B ko K 14 a b r i h o 10 10 10 u r J nj P e ib To l o N Je r u b e m l 5 a 5 5 t i n n S 15 a u (Source) o 0 0 0 JFMAMJ JASOND JFMAMJ JASOND JFMAMJ JASOND

t Nile A 7: Blue Nile at Diem (1912–97) 8: White Nile at Malakal (1905–95) 9: Sudd Outflow (1905–83) 10: Hillet Dolieb sw a 20 20 20 20 (Sobat Mouth) 1905–83 Alber16

Lake Albert 18 Lake Kyoga 15 15 15 15 17 Lake George 19

10 Lake Edward 10 10 10 Lake M igo 20 Victoria ri R 5 5 5 5 uwana M o am 0 0 0 0 e JFMAMJ JASOND JFMAMJ JASOND JFMAMJ JASOND JFMAMJ JASOND

11: Baro at Gambeia (1905–59) 12: Baro at Mouth (1929–63) 13: Nyamlel (1944–85) 14: Jur at Wau (1942–86) 20 20 20 20 MEASURING RIVER FLOW 15 15 15 15 Average monthly runo in

10 10 10 10 billion cubic metres Varying periods 1900–95 5 5 5 5 (Map prepared by the NBI; source of data: Sutclie & Parks)

0 0 0 0 JFMAMJ JASOND JFMAMJ JASOND JFMAMJ JASOND JFMAMJ JASOND

15: Mongalia (1940–77) 16: Lake Albert outflow (1940–77) 17: Semliki Mouth (1940–77) 18: Kyoga outflow (1940–77) 19: Lake Victoria outflow (1940–77) 20: Kagera (Kyaka Ferry) (1940–78) 20 20 20 20 20 20

15 15 15 15 15 15

10 10 10 10 10 10

5 5 5 5 5 5

0 0 0 0 0 0 JFMAMJ JASOND JFMAMJ JASOND JFMAMJ JASOND JFMAMJ JASOND JFMAMJ JASOND JFMAMJ JASOND

40 STATE OF THE RIVER NILE BASIN 2012 Water Resources

GROUNDWATER

N Where groundwater occurs As well as surface waters, the Nile Basin countries have considerable groundwater resources occurring in localized and regional basins. Groundwater is an important resource, supporting the social and economic development of the Nile riparian countries and making an important contribution to water and food security in the region. The 0 250 500 km degree to which it is relied upon varies from country to country, but commonly it is the most important source of drinking water for rural Lake Nasser communities in the basin. Groundwater in the Nile Basin mainly occurs in four rock systems ile or hydrogeological environments: Precambrian crystalline/ 1 N 1: Nile at Dongola (1910–95) 2: Atbara at Mouth (1903–94) 3: Nile at Tamania (1911–95) i n a 20 20 20 M metamorphic basement rocks, volcanic rocks, unconsolidated 2 At ba ra sediments, and consolidated sedimentary rocks. Water in these four (T 15 15 15 e k e z 3 z rock types occurs in confined and unconfined conditions. e 4 5 ) 10 10 10

S Main aquifers et 6 it 5 5 5 Victoria artesian aquifer: This occupies an area underlain by T D Rah e in ad k d e e z e z 0 0 0 l r

i Precambrian basement rocks and is distinguished by abundant e JFMAMJ JASOND JFMAMJ JASOND JFMAMJ JASOND

e t Lake Tana i 7 precipitation, a well-developed surface drainage system, and complex 4: Khartoum (Blue Nile) (1900–95) 5: Nile at Mogren (1911–95) 6: Dinder Mouth (1907–97) h W B ahr el A l B ra u 20 20 20 b e N geomorphology and structure produced by neotectonic movements. hazal ile y) hr el G 10 (Aba Ba 9 So 13 8 ba The aquifer is extremely abundant in surface water, which is present in 15 15 15 aga t R o p 12 o Baro S 11 u A ur B ko numerous swamps, rivers, and lakes. It also has many mineral springs, K 14 a b r i h o 10 10 10 u r J nj P e ib To l o some of which issue warm water. N Je r u b e m l 5 a 5 5 t i n Congo hydrogeological artesian aquifer: n S 15 This occupies an area a u (Source) o 0 0 0 JFMAMJ JASOND JFMAMJ JASOND JFMAMJ JASOND of more than 3.2 million square kilometres of Equatorial Africa. t Nile A 7: Blue Nile at Diem (1912–97) 8: White Nile at Malakal (1905–95) 9: Sudd Outflow (1905–83) 10: Hillet Dolieb sw The geologic section of the basin consists of Archean, Proterozoic, a (Sobat Mouth) 1905–83 Alber 20 20 20 20 16 Paleozoic, Mesozoic, and Cenozoic deposits. The characteristics of Lake Albert 18 Lake Kyoga 15 15 15 15 17 the aquifer have not been adequately studied due to the abundance Lake George 19 of surface water. 10 Lake Edward 10 10 10 Lake M igo 20 Victoria ri MAIN HYDROGEOLOGICAL ENVIRONMENTS IN THE NILE REGION R 5 5 5 5 uwana M o Crystalline igneous and metamorphic rocks: These Consolidated sedimentary rocks: This group has highly am 0 0 0 0 e JFMAMJ JASOND JFMAMJ JASOND JFMAMJ JASOND JFMAMJ JASOND rocks, dating from the Precambrian period, underlie variable rock types that vary from low-permeability 11: Baro at Gambeia (1905–59) 12: Baro at Mouth (1929–63) 13: Nyamlel (1944–85) 14: Jur at Wau (1942–86) large parts of the basin but are most extensive in the Nile mudstones and shale to more permeable sandstones and 20 20 20 20 Equatorial Lakes Plateau, the southern and southwestern limestones. They occur mostly in The Sudan and Egypt, MEASURING RIVER FLOW 15 15 15 15 Average monthly runo in parts of South Sudan, southern parts of The Sudan, and and form vast, regionally extensive, productive aquifers.

10 10 10 10 billion cubic metres parts of the Ethiopian Highlands. The parent rock is The Nubian sandstone aquifer system is the largest of the Varying periods 1900–95 essentially impermeable, and productive aquifers occur consolidated sedimentary rock aquifers, and one of the 5 5 5 5 (Map prepared by the NBI; source of data: Sutclie & Parks) in the weathered overburden (regolith) or where there is largest and most productive aquifers in the world.

0 0 0 0 extensive fracturing of the parent rock. Generally, the latter JFMAMJ JASOND JFMAMJ JASOND JFMAMJ JASOND JFMAMJ JASOND Unconsolidated sedimentary rocks: These are are the more productive crystalline basement aquifers. 15: Mongalia (1940–77) 16: Lake Albert outflow (1940–77) 17: Semliki Mouth (1940–77) 18: Kyoga outflow (1940–77) 19: Lake Victoria outflow (1940–77) 20: Kagera (Kyaka Ferry) (1940–78) distributed throughout the basin, occurring mainly along 20 20 20 20 20 20 Volcanic rocks: Volcanic rocks are mainly found in the the courses of the main rivers. In Ethiopia they occur in

15 15 15 15 15 15 highlands of Ethiopia, where they form variable but highly the Blue Nile (Abay), Atbara (Tekezze), and Baro sub- productive aquifers. Volcanic rock aquifers occur at deeper basins. In The Sudan, there are several unconsolidated 10 10 10 10 10 10 depth and typically have higher yields than the crystalline alluvium khors and wadis, the most notable being the El

5 5 5 5 5 5 basement aquifers. They are widely used for urban and Gash basin. In Egypt there are two main unconsolidated rural water supply in the Ethiopian Highlands. aquifers, namely the Nile Valley and Nile Delta aquifers. 0 0 0 0 0 0 JFMAMJ JASOND JFMAMJ JASOND JFMAMJ JASOND JFMAMJ JASOND JFMAMJ JASOND JFMAMJ JASOND

41 Upper Nile artesian aquifer: This lies in the extreme southern part of Bahr el Ghazal, White Nile, and Sobat plains. These plains constitute an internal recharge and accumulation area for the aquifer, while surrounding mountains (which are composed of metamorphic rocks, Precambrian granites, and Quaternary sediments), serve as an external recharge area. The northern parts of the basin are underlain by rocks of the Nubian series and have water occurring at depths of 25 to 100 metres, with sufficiently high artesian yields. In the Precambrian varieties, groundwater is encountered at depths varying from 3 to 60 metres. In spite of the limited reserves of water accumulating in the weathering crust; they are widely used for water supply. The alluvial deposits of the external recharge area of the basin contain fresh and brackish pheriatic waters occurring at depths of 6 to 10 metres. Water is the most precious resource in the drier Volcanic rock aquifers: These occur mainly in the Ethiopian regions. Goats, camels, and cattle all use this Highlands and cover large parts of the Gambela plains, the Lake Tana crowded water point in Southern Kordofan. area, the Shinile plain, the Rift Valley areas, and grabens filled with alluvial sediments at the foothill of the rift-bounding escarpments. The aquifer comprises of shallow to very shallow and loose sediments. Yields of the metamorphic rocks are variable, depending mainly on the degree of weathering. Nubian sandstone aquifer system: This covers an area of approximately 2 million square kilometres spanning parts of The Sudan, Egypt, Libya, and Chad. The aquifer holds fossil (non- renewable) water originating from the Pleistocene period when more humid conditions prevailed in the region. It varies in thickness from 200 to 600 metres, is highly porous and has high transmissivity (up to 4,000 m3/day). Other notable consolidated sedimentary aquifers in the region include the Umm Ruwaba, Gezira, and Al Atshan aquifers in The Sudan; the Moghra Aquifer found between the Nile Delta and the Qattara Depression in the Western Desert in Egypt; and fissured and karsified carbonate aquifers in the Wadi Araba areas in the Eastern Desert in Egypt. Nile Valley aquifer: This consists of fluvial and reworked sands, silts, and clays ranging in thickness from a few metres to over 300 metres. This high storage capacity combined with high transmissivity and active replenishment from the Nile River and irrigation canals makes the aquifer a highly valued resource. Nile Delta aquifer: Like the Nile Valley aquifer, this consists of sand and gravel with intercalated clay lenses. The aquifer, which is up to 1,000 metres thick in some areas and has high transmissivity (up to 25,000 m3/day) is an equally valuable resource. Groundwater recharge There is high variability in recharge in the groundwater systems in the Nile region, with rates ranging from a few millimetres to over 400 millimetres per year. This high variability is due to differences in the distribution and amount of rainfall across the basin, contrasting geomorphology, varying rock permeability, and uneven distribution

42 STATE OF THE RIVER NILE BASIN 2012 Water Resources

of large surface water bodies that recharge groundwater.

Recharge in the crystalline basement rock ! Alexandria aquifers ranges from 6 mm/yr close to the ! ! Suez shores of Lake Victoria to 200 mm/yr in Cairo the Kyoga sub-basin in central Uganda. In N the Ethiopian Highlands, where there is an 0 250 500 km M a in extremely complex hydrogeological setting, N ile and intricate interaction between recharge and discharge occurring at local, sub-regional, R and regional scales, recharge ranges from e d EGYPT ! below 50 mm/yr in Precambrian basement Aswan S e rock aquifers to well over 300 mm/yr in a the highly permeable volcanic sedimentary ! aquifers. Wadi Halfa The Nubian sandstone aquifer system has fossil water and very low modern-day ! ile N Bur Sudan n recharge rates, partly due to the long travel ai M time to reach the deep aquifer. The aquifer is

A tb recharged by Nile water seepage in a few areas, a ra

(T e by precipitation in some mountain regions, k e z ERITREA z e and by groundwater influx from the Blue THE SUDAN ! ) Asmara Khartoum ! Nile/Main Nile Rift system. Groundwater

R a infiltration by the above mechanisms is small h a d compared to the natural groundwater flow in ! D El Obeid B in l u d e the aquifer (estimated to be in the order of e r

N e

l i i 3 le N 109 m per year) that results from discharge (A e b it a h y) in depressions, evaporation in areas where W Bahr el Arab the groundwater table is close to the earth’s r el S ah f ob B a a r t surface, and leakage into confining beds. Ghazal e ! a Z g Ra l Baro o e Addis Ababa p r

o h The Moghra aquifer in Egypt has a mixture S a SOUTH A ru B ko u bo K Jur SUDAN of fossil and renewable water: recharge of B P ETHIOPIA a ib h o r r

e the aquifer occurs by upward leakage from l

J N e u b m e Sudd l the underlying Nubian sandstone aquifer a t i S n u n ! o and some rainfall input. The unconsolidated a Juba sedimentary aquifers in the proximity of the

e il A N s Nile River and Delta in Egypt receive high w t a r e b l recharge in excess of 400 mm/yr from the A DR CONGO UGANDA base of the river and irrigation seepage. The NBI is not an authority on international boundaries. Kampala KENYA ! REGIONAL GROUNDWATER AQUIFERS Lake Structure and recharge rate, millimetres per year Victoria ! Nairobi very high high medium lowvery low Kigali RWANDA in major aquifers ! in areas with complex Bujumbura hydrogeological structure ! BURUNDI TANZANIA in areas with local and shallow aquifers (Based on map by BGR / UNESCO.) areas of saline groundwater (>5,000 mg/l total dissolved solids) groundwater mining

43 Groundwater use Groundwater is widely used across the basin for domestic water supply (for drinking and other domestic uses) for both rural and urban communities. With the exception of Egypt, groundwater from dug wells, springs, and boreholes is the main source of drinking water for rural communities in the basin. In the Nile Equatorial Lakes Plateau and the Ethiopian Highlands, about 70 per cent of the rural population is dependent on groundwater. This proportion rises to about 80 per cent in The Sudan and close to 100 per cent in South Sudan. In Egypt, groundwater accounts for only about 13 per cent of total annual water requirements. The proportion of the population dependent on groundwater for domestic use in Egypt is not so high because most houses in urban areas and new settlements are connected to conventional piped water supplies based on surface water. The population in small rural settlements in Egypt largely uses water from small waterways to meet domestic water needs. In addition to domestic use, groundwater in the Nile region is also used for agricultural irrigation, livestock watering, and industrial processing. Groundwater use for agricultural irrigation is most widespread in the lower parts of the basin (The Sudan and Egypt), and low in the headwater regions of the basin due to sufficient rainfall and availability of large surface-water bodies. Conjunctive use of surface and groundwater is widely practised in the Nile Valley and Nile Delta, where farmers abstract water from shallow, unconsolidated aquifers during periods of peak irrigation demand and in lands located on the margins of the irrigation command areas. Groundwater use for industrial processing is most intensive in Egypt, particularly in Cairo and the Nile Delta.

GROUNDWATER POTENTIAL OF NILE BASIN COUNTRIES

Renewable Non-renewable Groundwater annual Groundwater Country groundwater groundwater extraction km3/year km3/year km3/year km3/year

Burundi 0.40 0.18 0.22 0.03

D R Congo 51.9 46.75 5.15 0.21

Egypt 4.00 0.09 3.91 0.90

Ethiopia 7.23 5.50 1.73 0.40

Kenya 2.34 1.01 1.33 0.42

Rwanda 0.40 0.32 0.09 0.04

Sudan 6.40 1.75 4.65 0.50

Tanzania 5.23 4.00 1.23 0.38

Uganda 2.12 1.95 0.17 0.18

(Source of data: Hassan, Attia & El-Attfy 2004)

44 STATE OF THE RIVER NILE BASIN 2012 Water Resources

Water quality Surface water The quality of surface waters in the Nile Basin is influenced by both natural and human factors, with human influences having far greater impact. Although the chemical quality of the water is good, its physical and bacteriological quality is generally poor. The headwater regions of the basin are densely populated and intensively used for rainfed agriculture. During the rainy season, the combination of hilly terrain, torrential rains, human-induced land-use change, and poor agricultural practices produce widespread soil erosion, leading to the problems of colour, turbidity, and suspended solids in the headwater rivers. Concentrations of suspended solids range from 1 to 1,500 mg/L in the Equatorial Lakes region, with the heaviest silt loads being carried by the Kagera river, and the rivers in western Kenya such The Winam Gulf, northeastern Lake Victoria, as the Yala and Nzoia. The Eastern Nile sub-basin rivers have much showing a greenish tinge indicative of the higher sediment loads, sometimes approaching 5,800 mg/L in the presence of algae. rainy season. The dry season in the headwater regions is associated with low-flow conditions and clearer waters. Colour ranges from 20 to 1,250 TCU in the Equatorial Lakes region and 0 to 350 TCU in the Eastern Nile headwater rivers. The Equatorial Lakes region has areas of dense forest and large tropical swamps that add a brown hue to the Nile waters from decomposing vegetable matter. However, the specific dissolved organic carbon output of the Nile, estimated at 0.089 t/km2/yr, is the lowest of all major world rivers. This is due, in part, to the low carbon content of soils in the basin and a large area of desert within the basin with little or no biomass production. Across the basin, environmental sanitation is poor, resulting in bacteriological contamination and nutrient enrichment of the Nile waters. Because of this poor bacteriological quality, most Nile waters are not fit for consumption in the raw form. Concentrations of faecal coliform bacteria are above 50 cfu/100 mL in nearly all surface waters in the basin. During the rainy season, this value may rise to above 1,000 cfu/100 mL. Total coliform concentrations are much higher, averaging 500 cfu/100 mL in most upstream rivers, and reaching levels of 150,000 cfu/100 mL in heavily polluted sections such as the Rosetta branch of the Nile Delta. The Equatorial Lakes are categorized as eutrophic to hypereutrophic systems, and experience frequent algal blooms and widespread water

45 hyacinth infestation. The presence of algae gives the headwater rivers and lakes their characteristic greenish tinge. Water hyacinth mats aggravate water quality problems and are a major nuisance to water transport as discussed in Chapter 3 and Chapter 7. Dissolved oxygen concentrations are high in most headwater rivers,

ranging from 6 to 9.5 mg O2/L. Concentrations below 5 mg O2 /L are encountered downstream of major cities and in the Nile Delta, and are attributed to pollution. Biochemical oxygen demand (BOD) does not show a clear distribution pattern in the basin but tends to be high

(above 100 mg O2/L) immediately downstream of major urban areas, pointing to pollution from domestic and industrial sources. The water chemistry of the Nile River is mainly determined by rock weathering. Bicarbonates strongly dominate the anion content of Nile waters and are strongly and positively correlated with electrical conductivity. The other major ions are chlorides and sulphates. Away from major pollution spots, surface waters in the upstream parts of the basin have good chemical quality and are generally fresh (low mineral levels). This is because much of the basin is underlain by very old and highly weathered rocks that contribute only small amounts of solute to the water. However, there are isolated areas, such as parts of the Atbara (Tekezze) sub-basin, where water is more mineralized, and may contain harmful concentrations of substances such as fluoride. Also, within Egypt, there are some enclosed water bodies derived from the Nile that are relatively more mineralized, such as the Khor Toshka, Lake Qarun, and Wadi Natrun. Upstream–downstream trends Changes in water quality, moving from upstream to downstream parts of the basin, do not occur in a linear fashion, owing to the influence of the Equatorial Lakes, the Sudd, and the reservoirs in The Sudan and An over-stretched sewerage capacity Egypt. The Equatorial Lakes play an important role in homogenizing resulting in raw sewage flowing into the contributions from various headwater sub- Nile, Khartoum 2007. basins, dampening seasonal variability in flow and water quality of the White Nile, and trapping sediments. The extensive wetlands of the Sudd impact water quality by bringing about a reduction in suspended solid load, decreasing dissolved oxygen concentrations, increasing acidity, increasing dissolved carbon dioxide concentrations, reducing sulphate concentrations, and increasing total dissolved solids concentrations. From high turbidity and silt loads in headwater areas, the White Nile just before Malakal has a relatively low suspended sediment concentration due to the sediment- retention property of the Equatorial Lakes, and the Sudd and Machar marshes.

46 STATE OF THE RIVER NILE BASIN 2012 Water Resources

The series of dams constructed on the Blue and Main Nile act as sediment traps in a similar manner to that of the Equatorial Lakes, and have a combined trap efficiency close to 100 per cent. Suspended sediment concentrations downstream of Aswan are in the low range of 20 to 50 mg/L all year. Chloride concentrations are very low in the Equatorial Lakes headwater areas, and only Rosetta increase in the White Nile downstream of ! end of Rosetta branch of N Nile Delta: 415 Lake Albert. Downstream of the Sudd, ! Cairo the contributions of the Sobat and Delta lakes: salt content Blue Nile (Abay) help to bring down sometimes increased by chloride concentrations. Sulphate is M sea-water intrusion, a in evaporation, or local N present in low concentrations in all il pollution. e headwater areas. In the White Nile, sulphate concentrations increase from the contributions of the western rift Aswan: 171 system, but drop again after passage of the

White Nile through the Sudd. With respect ! Lake Nubia to cations, calcium (Ca2+), and magnesium (Mg2+) are dominant in the Ethiopian and Eritrean headwater areas, while sodium Dongola ! ile + + N (Na ) and potassium (K ) are dominant in a Khartoum to Dongola: M in the Equatorial Lakes headwater areas. !Atbara 60–120

! White Nile at Khartoum

!Wad Medani

l t

i u

h e

W N ile (A ! Jelhac ba y ELECTRICAL CONDUCTIVITY ) Abay Malakal: ! Variation in average annual electrical ! Malakal <20 S conductivity which re ects the total amount oba Sudd t of solids dissolved in water and is a good

indicator of salinity B a h r 2005 e l Je b μS/cm e l

more than 420 361 – 420 301 – 360 Panyango ! !Pakwach below Lake Albert: Wansek! 241 – 300 1,000 !Lake Albert !River Semuliki 181 – 240 ! ! Jinja River Malaba Lake Victoria 121 – 180 ! 60 – 120 ! River Kagera less than 60 Lake Victoria basin: ! water quality sampling point 10 to 100 0 250 500 km average total dissolved solid concentrations, mg/L (Map prepared by the NBI; source of data: NTEAP Regional Water Quality Monitoring Baseline Report, 2005)

47 EROSION, SEDIMENT TRANSPORT, AND RESERVOIR SEDIMENTATION From analysis of sediment accumulation in Sudanese reservoirs, the total load of sediment in the Nile is estimated to be about 230 million t/yr. Only about 2 SLOPES IN THE NILE BASIN per cent of this is bedload, while the rest is suspended Degrees load. The contribution from the different parts of the 0° – 0.5° 9° – 12° basin to the total load is not even, but is strongly focused 0.5° – 1° 12° – 15° towards the Ethiopian Highlands. The largest sediment contribution (61%) comes from the Blue Nile (Abay) 1° – 3° 15° – 21° catchment, followed by a considerable contribution (36%) 3° – 6° 21° – 38° from the Atbara (Tekezze), and an insignificant (3.5%) 6° – 9°

input from the rest of the Nile catchment – mainly the (Map prepared by the NBI; source of data: SRTM DEM) Equatorial Lakes plateau, the Sudd area and hyper-arid

Red Sea Hills region. N

The bulk (98%) of the annual suspended sediment load 0 500 km !Cairo is transported during the summer floods in the Blue Nile

(Abay) and Atbara (Tekezze) catchments. Owing to the M a in relatively small area actively contributing to sediment N ile production and export, the suspended solid load of the R e d

Nile is modest, when compared with its basin area and S e EGYPT a with other large rivers of the world. ! Aswan The disproportionately large contribution of sediments from the Ethiopian Highlands is due to a multiplicity of factors which include the deeply incised topography of the region, unstable and easily erodible slopes, high ile N n ai runoff concentrated in a single July–August peak, sparse M At vegetation cover, and intensive land use. The exceptionally ba ra ( Te THE SUDAN k high sediment yields from the Ethiopian Highlands e z z e ERITREA ! ) Khartoum ! The Blue Nile (Tis Issat) Falls, Ethiopia, Asmara

orange with sediment. B

e u l

i e

e i t le i ( h Ab W a y )

! Sudd Addis Ababa

B SOUTH a ETHIOPIA h r

SUDAN e l

J e

b e Juba ! l

UGANDA

DR CONGO Kampala KENYA ! Lake Victoria ! Nairobi Kigali ! RWANDA Bujumbura ! The NBI is not BURUNDI an authority on TANZANIA international boundaries.

48 STATE OF THE RIVER NILE BASIN 2012 Water Resources

partly reflect accelerated soil erosion caused by land-use the Egyptian Nile. Fluvial erosion of the river channel and changes over several centuries. direct inputs of aeolian dust are today the main sources of Erosion and land degradation are also occurring in the suspended sediments downstream of Aswan. Rather than Equatorial Lakes Plateau, but the specific yield of the accumulating within the Nile Delta and fan, huge volumes sub-basin is low because it is underlain by resistant, less- of sediment now accumulate in reservoirs, resulting in erodible rocks. The Equatorial Lakes region also has a more rapid loss of storage capacity on one side, and ravaging effective cover of protective vegetation, flatter (plateau) erosion of the deltaic cusps on the other. topography, more evenly distributed rainfall over the The dams constructed in the basin to deal with the year (twin peaks in March–May and September–October), problem of seasonal and interannual flow variability in and stronger chemical weathering. Furthermore, a major the Nile include the Aswan High Dam and Merowe Dam proportion of the sediment produced in the White Nile on the Main Nile, the Jebel Aulia on the White Nile, the headwaters is trapped in the Equatorial Lakes, retained Roseires Dam on the Blue Nile (Abay), and the Khasm in the Sudd marshes, or deposited along the river course el Girba on the Atbara (Tekezze). These dams provided downstream of the Sudd, where the Nile flows sluggishly essential storage to serve the ever-growing and year- over a low-gradient course. round irrigation demands in Egypt and The Sudan. For thousands of years, and until the closure of the Aswan However, the rapid sedimentation in the reservoirs has High Dam in 1964, the fertile volcanic muds carried by affected their effectiveness and shortened their lifespan. the summer floods of the Nile were a critical feature of The storage capacity of the Roseires and Khasm el Girba the farming system in Egypt, and brought prosperity reservoirs, for example, are estimated to have fallen by 60 to ancient Egyptian dynasties. Sands and mud of Nile per cent and 40 per cent respectively over the first 30 years provenance have been identified in the Nile cone and of operation. Desilting of these dams is not economically along the margins of Israel, while finer-grained clays have viable, although raising their height may be a short-term been traced as far north as Turkey. Over the last 100 years, option. dams have been built in Egypt and The Sudan for flood The lasting solution to reservoir sedimentation will have regulation, water supply, and hydropower generation. to come from introducing watershed management These dams have virtually halted the transport of measures in the upland parts of the basin to reduce sediment to the sea, and caused a dramatic shift in sediment production. This is already being done, as sediment dynamics and geomorphological processes in discussed under Chapter 3.

Raising the height of the Roseires Dam.

49 Groundwater quality AGRICULTURAL WATER The quality of groundwater in the Nile region is highly variable, WITHDRAWALS and depends on numerous factors such as the type of rock, type of As percentage of total water withdrawal water source, the residence time of water, and level of anthropogenic latest data 2000–10

influence. There are a number of features common to all the aquifer (Source of data: AQUASTAT 2012) DR Congo systems, but also differences between them. 18% In general, the groundwaters across the region are fresh and fit for human consumption with respect to physico-chemical quality. There are some localized cases of high salinity and naturally elevated levels of iron and manganese in the groundwater. There are also isolated 38% Uganda cases where the physico-chemical quality is potentially harmful to human health. With respect to bacteriological quality, the picture is mixed, with some sources being contaminated with bacteria of faecal origin and 68% Rwanda others being totally free of contamination. Bacterial contamination does not occur naturally but as a result of anthropogenic influence. Across the basin, elevated levels of nitrates occasionally occur from poor domestic waste disposal and agriculture (farm animals and fertilizers). This is most severe near large urban areas located close

to shallow aquifers and is most common in the downstream parts of Burundi 77% the basin. In the Precambrian basement rock systems in the Nile Equatorial Lakes region, groundwater is mainly of calcium-magnesium sulphate and calcium-magnesium bicarbonate type. It is mostly fresh and suitable Kenya for human consumption except for areas where there are high levels 79% of iron and manganese. Water in the Ethiopian Highlands is also fresh and naturally good for human consumption. There are some localized exceptions where there are high levels of mineralization (from more reactive rock types), high salinity, and high levels of sulphides, arsenic, Egypt 86% fluoride, and iodine. The waters are calcium-magnesium bicarbonates, calcium-magnesium sulphates, and calcium chlorides types. Water in the Nubian sandstone aquifer system is mainly of sodium bicarbonate type, with calcium and magnesium bicarbonate types near recharge zones. The waters are largely fit for human consumption Tanzania 89% except where water is highly mineralized. The Umm Ruwaba is the second most important groundwater aquifer in The Sudan following the Nubian sandstone aquifer. The aquifer is mostly fit for consumption but there are areas where salinity may exceed 5,000 mg/L. In Egypt, Ethiopia 94% as in the other parts of the basin, groundwater is mostly fit for human consumption: total dissolved solids are mostly below 1,500 mg/L. However, there are areas where salinity tends to be much higher, such as at the eastern and western margins of the Nile Valley and Nile Eritrea 95% Delta aquifers. Groundwater in the northern peripheries of the Nile Delta has elevated salinity levels due to an additional factor: salt-water intrusion from the sea.

97% The Sudan+ South Sudan

50 STATE OF THE RIVER NILE BASIN 2012 Water Resources

TOWARDS INCREASING WATER STRESS

The renewable Nile waters are now almost fully used for various productive purposes, although water utilization differs greatly among countries and sectors. Currently, the dominant use of Nile runoff is by the downstream riparians, with little of the river flows in the upstream reaches used. Irrigated agriculture in Egypt and The Sudan represents the single most important water consumer. Extensive irrigation systems with a combined acreage well exceeding 4.5 million hectares exist in the Nile Delta, along the Nile Valley in Egypt and northern Sudan, and around the confluence of the Blue and White Nile near Khartoum. Formal irrigation in the other riparians is very limited and is estimated at less than 50,000 hectares. A number of hydropower facilities have been established, although total installed capacity is still well below its potential. Hydropower is considered a non-consumptive water user; although it alters the downstream flow regime, it does not reduce flow volume. However, the loss of water through evaporation from the various reservoirs in the Nile system (such as lakes Nasser, Merowe, Jebel Aulia, Kashm el Girba, and Roseires) is very significant. Water use for domestic and industrial purposes is relatively small. In spite of an estimated 232 million people living within the Nile catchment, water for domestic and industrial use is estimated at some 2.0 billion cubic metres (BCM) per year. A number of concurrent developments point to increasing water stress in the Nile Basin. First, the demand curve is continuing its steady rise due to ongoing population growth and economic development. Secondly, the upper riparians – up to now barely using Nile waters –

68.3

37.1

5.6 5.2 2.7 0.6 0.6 0.3174 0.3 0.2 The Sudan & Egypt South Sudan Ethiopia Tanzania Kenya DR Congo Eritrea Uganda Burundi Rwanda

1.8 2.8 10.19.5 20.7 30.0 39.1 WATER WITHDRAWALS AND RESOURCES 84.0 Billion cubic metres per year total water withdrawals latest data 2000–10 122.0 internal renewable (Source of data: AQUASTART 2012) water resources 2009

900.0 51 are planning investments in the water sector, which will involve using some of the river’s renewable discharge, thereby reducing downstream flows. Lastly, while some potential exists to increase renewable water resources by draining wetlands, increasing abstractions upstream of the White Nile floodplains, or by reducing reservoir evaporation, the scope and feasibility of such projects is limited by the serious environmental and socio-political consequences associated with their implementation. Hence, for all practical purposes, the Nile water supply will remain more or less constant. In view of the finite nature of the water resources in the basin, reconciling the diverging interests among the various riparian countries and stakeholders is a critical task for Nile managers.

WATER-RELATED NATURAL DISASTERS AND CONFLICTS IN SOUTH SUDAN Competition for grazing lands and water, especially Apart from the problem of frequent droughts, the during the dry season is a regular source of conflict in floodplains experience occasional flooding that results in South Sudan. widespread crop failure, livestock deaths, loss of cropland, The extensive floodplains (toic) of South Sudan are subject and loss of pasture. Thus, even in the absence of conflicts, to periodic water logging and intensive drying. In drought communities in the floodplain are periodically displaced years, most water-holding features in the floodplains and forced to migrate beyond their territories, including dry up. Given the small number of boreholes and lack into neighbouring countries, by natural disasters. of water-storage facilities in the area, a large number of Water infrastructure is urgently needed in the floodplains people, livestock, and wildlife are left to depend on a few area for harnessing the water resources and facilitating perennial rivers, lakes, pools, and marshes. their use for socio-economic activities. The needed Fierce tribal fights frequently erupt over the limited water infrastructure includes boreholes, valley tanks, small dams, resources and the rights to fishing grounds, essential to river training works, and a variety of water-harvesting the livelihoods of the floodplains communities. These structures such as haffirs and dykes. conflicts lead occasionally to loss of life and internal displacement of people.

Source of information: Ministry of Water Resources and Irrigation, Republic of South Sudan.

52 STATE OF THE RIVER NILE BASIN 2012 Water Resources

TOWARDS IMPROVED WATER USE The NBI has EFFICIENCY Challenges related to surface water management initiated projects There are several challenges related to surface water management in the Nile Basin, the main ones being inadequate water infrastructure, to strengthen management weak surface-water monitoring networks, weak human capacity, and weak control of pollution activities. Egypt is an exception to the general and improve efficient use picture painted above. Egypt has a diversity of water infrastructure, small and large, a dense and fully functional network of surface- of water resources. water monitoring stations, a large force of water professionals, and a strong regulatory service. Institutional mechanisms for cooperative management of the common Nile water resources by riparian countries are still under development under the NBI. Challenges related to groundwater management The cross-cutting challenge in the region with respect to groundwater management is weak institutional and human capacity. With the exception of Egypt, and to a lesser extent The Sudan, information on groundwater is scanty, and monitoring networks are hardly in place. Groundwater abstraction is not properly controlled, which in some cases leads to unsustainable exploitation of groundwater. The most serious case of unsustainable use relates to the heavy mining of the Nubian sandstone aquifer by the countries that share the resource. Much remains to be done with respect to improving the understanding of the occurrence and distribution of groundwater, including surface water–groundwater interactions. The major aquifers of the Nile region do not follow national boundaries but there is as yet no clear mechanism for co-riparian states to cooperate in joint monitoring, development, and management of the shared aquifers. What NBI is doing The NBI has initiated a number of projects to strengthen regional water resources planning and management, and to increase the efficient use of the water resources in the basin. The Water Resources Planning and Management (WRPM) project has developed the Nile Decision Support System (Nile DSS), which is a computer-based platform for planning and information management. The tool enables the riparian states to assess the trade-offs and consequences of alternative basin-wide water-resources development options. The Nile DSS further provides a framework for data and knowledge sharing amongst the Nile riparians. The Eastern Nile Technical Regional Office (ENTRO) located in Addis Ababa is implementing the Eastern Nile Flood Preparedness and Early Warning Project. This project aims to improve the regional and national capacity in Ethiopia, South Sudan, and The Sudan to forecast floods in the Eastern Nile basin and mitigate possible flood damage. The project also serves to strengthen flood-risk management

53 and emergency preparedness. Under the project, flood-warning advisories are regularly issued to the communities in flood-risk zones of the Eastern Nile. Monographs have been prepared for the rivers Kagera, Mara, Sio- Malaba-Malakisi, and lakes Edward and Albert. These documents have compiled and organized all existing information on the water- resource-related sectors in the basins, and thus provide a factual basis for integrated water resources management, and the formulation of investment plans – currently in progress. Other notable interventions by the NBI include broad support to institutional- and human-capacity building in the Nile riparian countries, and promoting Integrated Water Resources Management (IWRM) approaches in the region. What broader cooperation could achieve The Nile Basin contains untapped potential for hydropower generation, irrigation, and navigation. A number of possible multi- lateral projects have been identified where – if sufficient inter-basin cooperation can be achieved – the total benefits to the Nile system will amply exceed losses to individual stakeholders. Examples of these so called win–win projects include: • Construction of dams to increase over-year water storage for hydropower production, irrigation, and flood protection. Location of the dams in high-altitude upstream areas could result in substantial reductions in evaporation losses. Cooperation will be needed to minimize downstream impacts during construction and operation. • Construction of a dam on the Baro could reduce overbank spillage into the Machar marshes and wetlands around the Baro–Akobo confluence. The wetlands are of unique environmental value, and such a development needs to be accompanied by a sound environmental impact assessment. • Coordinated reservoir operation would maximize the benefits from the whole system, but require high levels of cooperation and clear mechanisms for benefit sharing. • Regulation of outflows from Lake Victoria or Lake Albert, possibly in conjunction with increased abstractions upstream of the Sudd to minimize water losses from the Nile system. Chapters 5, 6, and 8 of this report examine the above options in greater detail. The bottom line for all of them is greater levels of cooperation, and pursuing sustainable development approaches.

54 STATE OF THE RIVER NILE BASIN 2012 Water Resources

SUMMARY AND CONCLUSIONS

The Nile has a total length of 6,695 km, making it the world’s longest river. Its drainage area, at 3.1 million square kilometres, is one of the largest on the African continent. The Nile hydrology is characterized by uneven distribution of water resources and high climatic variability in space and time. Despite the long length of the river and its expansive basin area, the flow in the Nile is a small fraction of the flow in other large rivers of the world, such as the Congo, Amazon, and Yangtze. This is partially explained by the low runoff coefficient of the Nile (below 5%) and the fact that about two-fifths of the basin area contributes little or no runoff as it is comprised of arid and hyper-arid drylands. The Nile countries have substantial groundwater resources that occur in extensive regional aquifer systems. The aquifers have varying properties, with some, such as the Nubian sandstone aquifer system and Nile Valley sedimentary aquifer, having high yields. The surface resources of the Nile are now almost all used up. Withdrawal of water from surface and groundwater resources is variable, with upstream riparian countries having lower withdrawals than downstream riparians. A high proportion of annual water withdrawals go to support agricultural use in the region. Rising population, increasing demand for food, and expanding urban areas, among other factors, are expected to escalate the strain on the Nile water resources. There is need to increase capacity building interventions across the region that target the strengthening of the human resource base and institutional framework for integrated water resources management. Increased cooperation is needed amongst Nile riparian countries to, inter alia, jointly operate water-resource monitoring networks and decision-support tools that facilitate rational management and development of the common Nile surface and groundwater resources. The Nile riparian countries also need to consider a number of possible multi-purpose projects through which they could collaboratively increase efficiency of water use, and optimize and equitably share the benefits of the cooperative development of the Nile water resources.

55 56 STATE OF THE RIVER NILE BASIN 2012