Advances in River Sediment Research – Fukuoka et al. (eds)© 2013 Taylor & Francis Group, London, ISBN 978-1-138-00062-9

Reservoir sedimentation and sediment management techniquesin the Nile River basin countries
S.A. Kantoush
Civil Engineering Department, German University in Cairo, New Cairo City, Egypt

T. SumiWater Resources Research Center, Disaster Prevention Research Institute, Kyoto University, Japan

ABSTRACT: Currently, there are thirteen large dams on the Nile and around thirteen future damsplanned. The Nile has been the major supplier of suspended sediment to the eastern Mediterranean
Sea until the construction of the Aswan High Dam (AHD). The objective of water and sediment incorporation is to manipulate the river-reservoir system to achieve sediment balance while maximizing thebeneficial storage and minimizing environmental impacts and socioeconomic costs. The paper aims at
reviewing the current state of Nile Basin reservoir sedimentation and sediment yield. It also summarizes the response of AHD to reservoir sedimentations of the newly constructed or planned dams in the
upstream regions. As the Ethiopian Highlands are the main source of sediment, the river systems draining
this region have witnessed severe sediment management problems since the construction of large dams.
Coordinated sediment management and dam operation are highly recommended for the cascade dams
along the Blue Nile.

1

INTRODUCTION

The Nile River is the main source of water for theeleven countries that make up the Nile basin asshown in Figure 1. The climate and hydrology of
the Nile Basin (NB) ranges from Equatorial in the
White Nile headwaters to arid in the desert regionof northern Sudan and Egypt. Thus, for much ofits course, the Nile is an exotic river (Woodward,
et al. 2007). Stretching over 35 degrees latitude of
the north-eastern African quadrant, the Nile Riverbasin represents one-third of the entire African
continent. With an area of almost 3,176,543 km2
extending over different geographical, topographical and climatological regions, the basin spans overten African countries: Burundi, Democratic Republic of Congo (DRC), Egypt, Eritrea, Ethiopia,
Kenya, Rwanda, Sudan, S. Sudan, Tanzania andUganda, (Fig. 1).
NB catchment suffer severe land degradationand soil erosion due to extended dry seasons insome parts of the Basin, torrential rain and geological nature, bringing large quantities of sedimentin the drainage systems (Abdelsalam, 2008). This
leads to land degradation in the watershed and theupper lands, e.g. in Ethiopia Highlands in the east,
and around upstream Lake Victoria in the south.
At the same time, the sediment deposition in thereservoirs and irrigation systems downstream leadto serious reduction in reservoirs storage capacities
and hence leading to hydropower generation problems, banks flooding and ultimately negatively
impact on the socio-economic lives of the users,
environment and ecosystem in general. The reduction of sediment supply in large alluvial systems
due to sediment trapping in upstream reservoirs
might lead to long-term impacts on the fluvial
process.
One such example is the river channel downstream of the Aswan High Dam (AHD) on the
Nile River, where river bed degradation and bankerosion occurred and serious shore erosion wasobserved at the river mouth area. In the case of
the AHD, the aggregate storage capacity of Lake
Nasser, which is twice as large as the annual runoff of the Nile River at the dam site, is sufficient
to change both the flow regime and sedimentsupply to the river channels downstream of the
AHD. Thus, the downstream section of the Nile istransformed into a system with a non-equilibrium
sediment transport process. As a result, the annual
peak discharge has been reduced to less than athird of its original value, which caused navigation
problems (Abdelbary 2004).
Dams and their reservoirs are constructed andoperated for multipurpose including power generation, flood protection, drinking water, agricultural water supply, recreation, fishing, and others.

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Figure 1. Map of the Nile Basin showing basin sources,
the Nile course and the drainage network (Nile Basin
Initiative, State of the River Nile Basin 2012).

Until now in the Nile Basin (NB) the common
engineering practice has been to design and operate reservoirs to fill with sediment. With such an
approach, the consequences of sedimentation andproject abandonment are left to be taken care of by
future generations. Therefore we need to develop
ingenious solutions for integrated sediment andwater management; unless we will lose the struggle
to enhance the available water resources. Regardlessof their purpose, all multipurpose dams trap sediment and inevitably lead to physical and ecologicalchanges downstream of the reservoir site, as wellas in the reservoir itself, and in some cases also

upstream. Kondolf (1997) has described that, bychanging flow regime and sediment load, dams
can produce adjustments in alluvial channels, thenature of which depends upon the characteristicsof the original and altered flow regimes and sediment loads.
Downstream impacts develop through discontinuity in downstream gradients, e.g., sediment supply, water quality, temperature, flow and sediment
regimes. Sediment deficit is not only an environmental issue but also a socio-economic problem,
for instance due to loss of reservoir capacity (e.g.,
Fan and Springer, 1993). In addition, dams alter
the downstream flow regime of rivers (Williams
and Wolman, 1984), which controls many physical and ecological aspects of river form and processes, including sediment transport and nutrient
exchange (Poff et al., 1997). Hydrological effects
caused by dams include changes in flood frequency
and magnitude, reduction in overall flows, changes
in seasonal flows, and altered timing of releases. Ifflows released from dams have sufficient capacity
to move coarse sediment, water becomes ‘hungry water’ (Kondolf, 1997), which may transport
sediment downstream without replacement fromupstream and the ecological effects on fluvial anddeltaic systems.
Necessary elements of sediment management
strategies for sustainable reservoirs are to collectenough data of deposited sediment for evaluationand select a suitable management technique forcase by case. Furthermore, it is important to establish techniques for redeveloping existing dams, byconstruction of sediment bypass, and to develop
environmental impact assessment approaches.
These techniques minimize the minus impacts suchas water quality change, and maximize the plus
impacts such as the recovery of sediment routing.
Considering a sediment movement zone fromJapanese alpine mountainous regions throughcoastal areas, a comprehensive approach has
already been started in Japan to recover a soundsediment circulation in the sediment transport system. Reservoir sedimentation problems are common in all countries, whether they are developedor developing countries. Therefore, it is necessary
to exchange knowledge and collaboratively work
for a solution with countries having the same problems. Schleiss et al., (2008) presented the reasons,problems of reservoir sedimentation, and possible
measures against sedimentation. Putting its experience to use, Japan intends to make great international contributions to the promotion of reservoir
sedimentation management in the field of technological development in future.
Current state of Nile Basin reservoir sedimentation and sediment yield is presented. Dam impacts
on flow and sediment discharges to Nasser Lake1136

life span should be clarified and discussed. As
the Ethiopian Highlands are the main source ofsuspended sediment in the basin, the river systems draining this region have witnessed some of
the most severe sediment management problems.
There are still key gaps in our understanding ofbasin-wide sediment dynamics in the Nile. This
paper is to review the reservoir sedimentation status in the Nile basin.
2

THE ENVIRONMENTS OF NILE BASIN

The Nile is a major north-flowing river in northeastern Africa, and the major rivers of the NB
are the Main Nile, the Blue Nile, the Atbara, theWhite Nile, the Rahad, the Dindir, the Sobat,
the Akobo and the Baro, which are shown in
Figure 2. Formed by the confluence of the threemain tributaries, White Nile, Blue Nile andAtbara River, the Nile River flows over 6’695 km
from the south glaciated highlands throughalluvial plains and desert sands into the eastern
Mediterranean (NBI, 2012). The most distantsource of the Nile is the Ruvyironza River, whichflows into Lake Victoria through the Ruvubu andKagera rivers. From Jinja in Uganda, the White
Nile emerges from Lake Victoria as the Victoria
Nile, and travels northwards, passing through twoother Equatorial Lakes—Kyoga and Albert. The
river re-emerges from Lake Albert as the Albert
Nile and journeys northwards to Nimule near theSouth 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 through the Sudd before meeting the
Bahr el Ghazal (meaning river of the gazelles) at
Lake No (Fig. 1). The Bahr el Ghazal drains highrainfall areas of western South Sudan. From LakeNo, the river turns eastwards to join with the
Sobat River, which carries high, seasonally variable, flows originating in the Ethiopian Highlands.

Figure 2.
the NB.

Longitudinal profiles of the major rivers in

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. From Khartoum, thecombined rivers of the Nile flow northwards, andare joined by the Atbara (Tekezze), also originating in the Ethiopian Highlands. The Main Nile
continues travelling northwards and flows into
Lake Nasser. The Nile eventually discharges into
the Mediterranean Sea via its delta.
The longitudinal profile of major rivers
in the ENB is shown in Figure 2. The Akobo andthe Baro are two rivers in the upper part of ENB.
The Baro Originates at an elevation of 2,200 m andthe Akobo at an elevation of 1,000 m. These tworivers meet the Sobat River which joins the White
Nile. The Blue Nile originates at Lake Tana at anelevation of 1,800 m which meets the White Nileat Khartoum at an elevation of about 350 m andcommonly regarded as Main Nile. Finally it falls in
the Mediterranean Sea. In the Main Nile the High
Aswan Dam is one of the major dams where riverelevation falls about 100 m.
2.1

Hydrology of the NB

The spatial pattern of rainfall inputs across the
Nile Basin is highly variable. Local water resources
are minimal in the arid and semi-arid regions ofEgypt and Sudan, and evaporation and seepage
losses are high in this part of the basin (UNEP,
2000). Precipitation dynamics in the Blue Nileand Atbara headwaters are influenced by threemain mechanisms (Conway, 2000): (1) the summer monsoon; (2) tropical upper easterlies; (3)local convergence in the Red Sea coastal region.
About 70% of the annual rainfall in the Blue
Nile headwaters of Ethiopia falls between Juneand September declining from 2000 mm in thesouthwest to less than 1000 mm in the northeast(Conway, 2000). On average about 85% of annual
flow of the Blue Nile is concentrated into one thirdof the year between July and October. The 1900
to 1982 gauging station records for the Blue
Nile at Khartoum show a mean monthly range
in discharge from 9 to 8834 m3/s with a mean of1513 m3/s. The flow regime of the Atbara exhibitseven greater seasonality and the river is commonly
dry from December to May with very low flows inNovember and June.
The present average contributions from each of
the three main tributaries to the entire Nile River

1137

flow are schematically represented in Figure 3.
Runoff from the Ethiopian Plateau via the Blue
Nile and Atbara accounts for roughly 70% of theannual water discharge, whereas the White Nile
contributes about 30% (Roskar, 2000). Although
the contribution of the White Nile to the total
annual flow is rather small, the White Nile is mostimportant because of its continuous flow during
the dry season when its discharge is large compared to that of the Blue Nile.
Subject to seasonal variations, about 80% of
the total annual discharge of the River Nile occurs
during the summer rainy season (July to October)mainly with the Blue Nile and the Atbara River(Woodward et al., 2001). Atbara River runs dry attimes of the year while the White Nile maintains
the flow in the Nile over the entire year. Without thedischarge of the upper White Nile the Nile Riverwould probably run dry in May. More than 95% of
the mean annual suspended sediment load of the
Nile River upstream of the Aswan High Dam (120Million t/yr, Woodward et al. 2001) comes with
the Blue Nile (72%) and the Atbara River (25%)
whereas the White Nile contributes only 3% of
the total load. Apart from seasonal variations, thetotal annual discharge of the Nile River is subject
to intense annual variations with the highest annual
flows of 154 km3/yr recorded in 1878 (Abu Zeid,
1987) and 120 km3/yr measured in 1984 (Woodward
et al., 2001). The lowest annual flow on record wasobserved in 1913 with only 42 km3/yr (Abu Zeid,
1987). The mean annual flow of the Nile Riverand the three tributaries calculated over the period
1901–1995 (Mohamed et al., 2005).

This section examines the sediment production andsuspended sediment budget of the basin upstreamof the delta complex sedimentation in reservoirs.
The sedimentation problems in the ENB started
from the Ethiopia. Rainfall in the Ethiopia Highlands falls on bare lands at the beginning of therainy season in July and brings high sedimentationload before the maximum runoff occurs in the area.
The highest sediment concentrations occur in therising flood waters in late July to the first ten daysof August. The average specific sediment yield rateof the basin is 9000 ton/sq. km/yr (Shenkut, 2006).
The Hydraulics Research Station (HRS) under
the MWRI, the Sudan measures sediment concentration and discharge in several locations of theGezira Scheme canalization system. It has concluded that 5% of the sediment settles in the main
canals, 23% in the major canals, 33% in the minor
canals and 39% passes into the farm fields. The huge
reduction of the original capacity of the Sudan reservoir due to sedimentation is easily noticeable. The
Sennar lost 66%, the Girba 60% and the Roseires
30% (Ahmed, 2006). Suspended sediment concentrations and loads have been measured at several
stations on the Egyptian Nile-especially in the decades leading up to the planning and constructionof the Aswan High Dam—but continuous longterm records are not presently available in the scientific literature. The suspended sediment load of the
Nile is rather modest in comparison with its basin
area. Milliman and Syvitski (1992) quote a valueof 120 million tonnes year 1 for the average annual
pre-Aswan High Dam load and a mean annual sediment yield of 40 t km 2 year 1.
It is important to realize that sediment production and sediment delivery vary markedly in the
major tributary basins and marked spatial andtemporal (annual and seasonal) variability in suspended sediment flux. Suspended sediment concentrations and loads are subject to considerable
annual variation. According to Abu El-Ata (1978)
the annual sediment load of the Nile at Aswan hasvaried between 50 and 228 million tons. Due to theerodible upland terrains, high sediment supply andhigh runoff, much of the suspended sediment load
measured at Aswan derives from the highlandsof Ethiopia. In fact, together the Blue Nile andAtbara contribute on average about 97% of the
Nile’s annual suspended sediment load (with about
72% from the Blue Nile and 25% from the Atbara)
and the White Nile the remaining 3.0% (Fig. 4)

Figure 3.

Figure 4. Daily flow and suspended sediment concentration for summer floods at Wadi Halfa and Gaafra(Shahin, 1985).

2.2 Sediment yield and suspended sediment budget

Water balance at Eastern Nile Basin.

1138

(Foucault and Stanley, 1989). Suspended sediment
flux is dominated by the summer flood in the Blue
Nile and Atbara catchments.
For example, with a peak flow to low flow ratioof 40:1, and typical mean August and June sediment concentrations of 4000 and 100 mg/l, respectively, the Blue Nile can transport up to 1600 times
more sediment during the summer floods than at
the end of the dry season (Williams et al., 1982).
The White Nile drains the resistant rocks of theEquatorial plateau and these terrains have much
lower erosion and a more effective cover of protective vegetation in contrast to the deeply dissectedBlue Nile headwaters. Consequently, suspended
sediment concentrations are much lower in thefloodwaters of the White Nile and the lower gradient White Nile is a much less efficient suspended
sediment delivery system (Fig. 4). A significant
proportion of its suspended sediment load is also
trapped in the swamps and marshes of the Sudd
region in the middle White Nile reaches. In themain Nile at Aswan the sediment wave tends topeak in August before the main flood peak andseveral weeks may separate these two events. The
suspended sediment concentrations for the summer
flood of 1955 at Gaafra (near Aswan) peak at over
5500 mg/l in mid-August and then decline steadilyto 500 mg/l by the end of October (Fig. 4).
2.3

Figure 5. Map of the Nile Basin showing location oflarge dam on Nile.

Dams on the Nile River Basin

Summarized by El-Hinnawi (1980), the Nile River
control measures started in the early 19th century
when a series of barrages were built to transformthe old recession irrigation system to perennial
irrigation so that instead of growing one crop
per year, two or three corps could be grown on
the same land. The Delta Barrage was built justbelow Cairo to control the Rosetta and Damietta
branches of the Nile together with the Zift a Barrage on the Damietta branch. Constructed in 1902
and enlarged in 1938, a dam at Assiut was built
to provide perennial irrigation in central Egypt.
In 1908, the Esna Barrage followed by NagHammady in 1930 was constructed on the Nile
River to improve the water supply for irrigation
schemes in Upper Egypt. Figure 5 shows the large
dams on the Nile and the location of one of theplanned dams as well.
The new Aswan High Dam, designed to be
never drained, caused a revolution in the Egyptian
irrigation system. Practically, all the fertile sediment from the Ethiopian Plateau was depositedin the reservoir. Although the missing suspended
particles created certain disadvantages, the extra
stored water and the reduction of silting in theirrigation channels allowed the perennial irrigation
as well as a significant increase in irrigated area.

About 45 km south of Kharthoum, the Jebel Aulia
reservoir was constructed in 1937 to hold backpart of the White Nile flow during rich dischargeof the Blue Nile. Since the Nile valley upstreamof Jebel Aulia is very flat and open, a large quantity of water is being lost due to evaporation andseepage.
The Owen Falls Dam (Fig. 5) completed in 1954
was the first control work on the upper White
Nile. With a primary goal of producing hydroelectric power, the dam controls the outflow of Lake
Victoria and therefore created the largest reservoir
in the world. In 1999, after a year-long debate,
the Ugandan Parliament approved the construction of the Bujagali hydropower dam as a private
hydroelectric power plant project in Uganda.
The project is one of several hydropower plants
planned to be scattered along the upper reaches ofthe White Nile including Owen Falls, Busowoko,
Ralangala, Raruma, Ayago North, Ayago Southand Murchison Falls. Situated 1’100 m a.s.l. at
Bujagali Falls, about 8 km north of Lake Victoria,
construction of the Bujagali plant was due to begin
in January 2003, but was initially delayed after
vocal protests by environmentalists and residents

1139

of the area. In February 2005, the Ugandan
Government announced that the project will goahead. With a volume of up to 750’000 m3 and a vertical drop of 30 m, the reservoir water will feed four turbines with a total installed capacity of 250 MW.
On the Blue Nile, the Sennar Dam (Fig. 5)completed in 1925 serves the needs of Sudan byproviding the basis for the Sudan’s agriculture
economy. Its main function is to store water for
the Gezira irrigation scheme during the flood
season of the Blue Nile. Further upstream, near
the Sudan-Ethiopian border, the Roseires Dam
was completed in 1966 with the two primary purposes of increasing the storage capacity of theBlue Nile water and producing hydropower. Far
above Roseires, below the Blue Nile Gorge, Lake
Tanna (Ethiopia) was considered for many years
as a good place for a storage reservoir to holdback a large proportion of the Blue Nile flood.
The first one is the Chara Chara weir that regulates the Lake Tana outflows to the 5 Tis Abbay
power complex, located some 32 km downstream
the Lake. Then, the Tana-Beles scheme (started
operation in May 2010) consists of an artificial
link between the Lake Tana and the Beles riverto generate hydroelectricy and aims at irrigate
around 150 000 ha in the future. In the upper
Ethiopian part of the Atbara sub-basin (Tekeze
river in Ethiopia), the largest Ethiopian hydraulicinfrastructure. With an over-year storage capacity
and an installed capacity of 300 MW, the Tekeze
dam started to generate hydropower in 2009 andaims to produce around 30% of current total
national electric production.
A large hydropower and irrigation project isnewly constructed on the Tezeke River in the Tigray
Region of northern Ethiopia. The Tezeke Damwith a height of 185 m will be 10 meters higher
than the highly controversial Three Gorges Damin China. In his study Aforki (2006) reported that
40% of the reservoir storage capacity is provided
as a room for the sediment inflow throughout the
50 years design life time of the dam. Therefore
the dead storage is about 3.7 billion m3. Hence therate of sedimentation expected annually is about
75 million m3 i.e. less than 1%. The sediment datain the feasibility study report of the dam is limited; hence the rate of sedimentation of Tekeze
reservoir still remains unpredicted. No doubt the
sediment load in Tekeze River is large compared toother Nile basin systems, since it falls within a dry
area with torrential rainfall during short period(July–Sept).
Recently constructed, the Merowe Dam on
the Nile River, about 800 km north of the capital Khartoum (Sudan) is the largest contemporary hydropower project in Africa. Merowe dam
will submerge the Fourth Cataract of the Nileand form a 200 km long artificial lake. Monenco(1993) estimated the storage capacity of the reservoir at level 298 masl as 11.05 billion m3 equivalents to a pool reservoir surface area of 724 km2.
The low supply level (290 masl) corresponds to
476 km2 surface area and 6.17 billion m3 i.e. live
storage of 4.88 billion m3 would be available.
However recently it was decided to raise the full
supply level to 300 masl, which correspond to a
storage capacity of 12.4 billion m3. The dam is
67 m high with 1250 MW hydropower generation
capacity, which was completed on 2009. Estimatesof sediment from Monenco, (1993) study indicatedaverage suspended sediment load into Merowe
reservoir as 134 million t/yr for the period 1929 to
1964, 121 million t/yr in 1971 and 181 million t/yr
in 1990. Monenco (1993) added 25% to the estimated suspended load as bed load, which resulted
in 180 million t/yr total sediment load received
by Merowe reservoir. It was then concluded thatover 50 years after the project implementation the
total deposited sediment into the reservoir will be
4.24 billion m3.
2.4

Reservoir sedimentations in the NBC

On the Nile system there are several dam reservoirs: two in Uganda, four in Ethiopia, five in
Sudan, and two in Egypt. However, in the Nile
Basin several new dams are planned for different
purposes. Assessments of sediment informationin the Nile Basin show that suspended sedimentdominates the total sediment in transport andfew meaningful of bed load transport have been
undertaken for the Nile system. Available datasuggests that suspended sediment commonly
accounts for approximately 90% of the total sediment load. Reservoir surveys to determine the volume of deposited sediment and hence the loss incapacity by bathymetric survey and other meansseem to be made often for larger than smaller size
reservoirs. AHD in Egypt is the most frequently
surveyed reservoir followed by Roseires andSennar reservoirs and less so by Khashm ElGirba
reservoir in Sudan. Angereb and Koka reservoirs
in Ethiopia and Owen and Bujagali reservoirs in
Uganda have not been surveyed so far. Smaller
reservoirs (Angereb, Koka, Sennar and Khashm
El Girba) are impacted more adversely by reservoir sedimentation than the larger ones (Roseiresand Aswan) because the relative loss in capacity ismuch faster.
In Egypt the deposited material in Lake Nasser
has resulted in delta formation and affects theuseful life of the reservoir see Figure 6 for sediment process in Lake Nasser Reservoir. The total
deposited sediment in AHD reservoir ranges
between (3.014 r 109 m3 and 3.732 r 109 m3).

1140

3

Figure 6. Sediment distribution in Nasser Lake andnewly formed Delta in the reservoir.

The percentage of losses from the dead storage
zone (under level 147 m) ranges between (3.3%
and 3.348%). The percentage of losses from thelife storage zone (between level 147 m and 175 m)
ranges between (2.9% and 2.97%). The percentage of losses from the total reservoir capacity(162 r 109 m3 at level 182 m) ranges between (2.3%
and 2.304%). Suitable methods to control sedimentation and water quality deterioration necessitate
the importance of using coupling model in orderto perceive a better understanding to the problem.
This is to minimize the expected impacts and propose mitigation measures. Mitigation measures
may include revising and improve the operation
system, using river regulation works such as dredging or flushing and pollution control.
The Roseires Dam (1966) on the Blue Nileand the Khashm el Girba Dam (1964) on the
Atbara River (Fig. 5) both encountered major
problems with sedimentation within a decadeof their construction (Elsheikh et al., 1991). The
Roseires Dam was built close to the Ethiopian
border to store Blue Nile water for irrigation use
in central Sudan. According to these authors,
the storage capacity of the Roseires reservoir(3.02 r 109 m3) had fallen by 18% after 10 years
and 21% after 15 years—while the capacity of
the Khasm el Girba reservoir fell by 25.4% after
7 years of operation and by 42.3% after 12 years.
Bathymetric survey showed that 540 million m3
of sediment had been deposited in the Roseires
reservoir between 1966 and the 1975/1976 hydrological year—giving a mean annual value forsediment deposition of about 54 million m3 forthis period. The total volume of deposited sediment had increased to 640 million m3 by 1980/81(Elsheikh et al., 1991).

SEDIMENT MANAGEMENTTECHNIQUE IN THE NBC

Although there are several large dams on the Nile
Basin that are subjected to high suspended sediment budget and sediment deposition, there is noeffective sediment management techniques implemented in integrated way. Most of Nile Basin reservoirs have traditionally been planned, designed,and operated on the assumption that they have afinite (life), frequently as short as 100 years, which
will eventually be terminated by sediment accumulation. However, the sustainability criterion
was recently introduced by United Nation (UN)towards the end of the last century to suggest aminimum of 1000 years of operation for new
designed reservoir projects.
Downstream, water released from the dam possesses the energy to erode the channel bed andbanks, but has little or no sediment load. The
rapid reservoir sedimentation not only decreases
the storage capacity, but also increases the probability of flood inundation in the upstream reaches
due to heightening of the bed elevations at the
upstream end of the reservoir and the confluencesof the tributaries. In order to remove and reduce
reservoir sedimentation, many approaches such as
flushing, sluicing, dredging and water and soil conservation are developed (ICOLD, 1989).
Among these approaches, flushing is considered the only economic approach to swiftly restore
the storage capacity of the reservoir with severe
deposition. Basically, there are two types of flushing operations with, and without drawdown, andoptional techniques can be used with the complete
drawn flushing as shown in Figure 7. Drawdown
is the lowering the water levels in a reservoir.
Hydraulic flushing involves reservoir drawdown by
opening the bottom outlet to generate and accelerate unsteady flow towards the outlet (Morris andFan, 1998). This accelerated flow possesses anincreased stream power and consequently eroding a channel through the deposits and flushing
the fine and coarse sediments through the outlet.
During this process a progressive and a retrogressive erosion patterns can occurs in the tail andFigure 7. Classification of sediment flushing techniques.

1141

delta reaches of the reservoir, respectively (Batuca
and Jordaan, 2000).
For instance in Roseires and Khashm ElGirba
Dams the most effective sediment strategy is to
apply regulation rules to operate the reservoir taking into consideration how to get rid of the maximum possible quantity of sediment and pass it
downstream. Drawdown, sediment sluicing during
the rainy season and impounding only after thepassage of the peak of the flood are the preferred
methods to control sediment deposition in the
Sudanese reservoirs. Both reservoirs are provided
with low-level sluicing gates with discharge capacity comparable to river annual flood flows. In thecase of hydropower generation in Roseires reservoir, low level sluices are intended to pass the bulkof the larger sediment particles which are presence
during the flood season to minimize abrasion of
the runner blades of the turbines. Removal of thealready deposited sediment is rather very limited
for most of the reservoirs in the Nile. Occasional
flushing is made in Khashm ElGirba reservoir.
Sediment removal by dredging is regularly madein Roseires reservoir in front of the power house
intakes before the following flood. Excavation
or dredging of the deposited sediment is rather
very limited for most of the reservoirs in the Nile.
Occasional flushing is made in Khashm ElGirba
reservoir. Sediment removal by dredging is regularly made in Roseires reservoir in front of thepower house intakes before the flood.
Even for the newly constructed dams on theBlue Nile as Tekeze reservoir, almost the same
strategy of sediment management has been implemented, where 40% of the reservoir storage capacity is dead storage throughout the 50 years design
life time of the dam. Therefore the dead storageis about 3.7 billion m3. Aforki (2006) concluded
his study with three different scenarios for the
reduction of the sedimentation in Tekeze reservoir
through flushing (i) Empty drawdown; (ii) Partial
drawdown and empty drawdown but after the deadstorage is filled; (iii) Four hydro-suction pipes
options with different diameter (300 mm; 600 mm;
900 mm and 1200 mm). Therefore, further study
based on reliable and consistent time series sediment monitoring techniques is required in orderto reach a technically sound estimate of sedimentboth in terms of quantity. Lessons should belearned from the Roseires reservoir design which
was based on very limited sediment strategy.
To evaluate the influence of sediment flushing for three of reservoirs (Roseires, Merowe, andShereik dams) in Sudan, 1D numerical model
MIKE11 was used by Eizel-Din et al. (2010), toestimate the long-term water and bed level changes
due to reservoir impounding and to optimize theflushing activities during flood times. Roseires

dam was constructed in 1966 on, Merowe dam wascompleted on 2009, and Shereik dam is under planning. Based on Brune’s curves the estimated valueof the trap efficiency of the Roseires reservoir was
estimated to be about 79%. However, after 10 yearsof operation the sediment deposited in the reservoir revealed that the trap efficiency was 45.5%
and then decreased dramatically to 26.2% after 30
years. Based on the numerical simulation Eizel-Din
has concluded that the trap efficiency will decrease
from 39% after 10 years to 30.3% after 100 years
for the case without flushing. Applying flushing
schemes, the trap efficiency will decrease from
25.5% after 10 years to 23% after 100 years.
The question is how these newly constructed
dams will influence on the AHD operation andDelta formation. Merowe reservoir is going to faceserious sedimentation problems by receiving sediment load for both rivers (Blue Nile and Atbara
River). The upstream dams in the upstream countries will reduce the sediment yield to AHD and thewater quality in Nasser Lake will be questionable.
Moreover, the inflow discharge to AHD reservoir
is questionable and important issue for Egypt.
3.1 Sedimentation and expected life of AHD
A number of estimates of the expected life span of
Lake Nasser located in Egypt and Sudan has been
made in the past several years. Published estimates
range from as little as 20 years (Sterling 1970) toover 1500 years (Makary 1982). The wide rangeof differing values is a function of many variables,
including computation method, input data, andtheoretical assumptions underlying the mathematical approach taken. Such a broad range of values
is typical of sedimentation studies performed forareas that lack an adequate historic data base. The
trap efficiency of Lake Nasser/Nubia is close to100% and this has created a dramatic shift in sediment dynamics and geomorphological processes in
the reaches downstream of the Aswan High Dam.
The sluices of the dam are opened periodicallyto maintain main channel flows for navigation,
irrigation and for hydroelectric power. Between
1965 and 1973 the mean flux of suspended sediment passing through the Aswan High Dam wasestimated to be about 2.5 million tons (Shahin,1985). Stanley and Wingerath (1996) state thatabout 98% of the sediment load (mainly silt andfine sand) that had previously been transported
to the delta and the Mediterranean Sea is deposited in Lake Nasser/Nubia and clay-sized material(2 Mm) is now the major particulate fraction transported from the reservoir behind the Aswan HighDam to the downstream reaches of the Egyptian
Nile. The Ministry of Water Resources andIrrigation (MWRI) of Egypt carries out sediment1142

investigations three times a year, before, during andafter the flood period. It can be noticed from thehistorical records that the sediment concentration
decreases from 3000 ppm to just around 40 ppm,
before and after AHD respectively see Figure 8.
It has been noticed that almost all the sedimentdeposition occurs in the Nile reach between 345 km
and 430 km south of the dam site. In this region,
sediment has already deposited in the live storage
zone. However, several studies showed that until
1973, 99.98% of sediment was deposited in Lake
Nubia. Available data suggests that suspended sediment dominates the total sediment in transport,
which account to approximately 90% of the total
sediment load. This means less than 10% is left forthe bed load. If we assumed all the suspended sediment is deposited in the reservoir plus 10% for the
bed load (10 million tons), hence the expected life
span of the AHD is over 1000 years. However, thedead storage requires about 200 years to be filled,
but unfortunately most of the sediment if not all isdeposited in the live storage, which slightly reduces
the function of the dam.

It can be noticed that sediment deposition
started at the tail zone of the reservoir and steadily
progresses northward along the river bed. Several
research studies suggest that the dead storage
capacity was estimated to be sufficient to accommodate sediment load (130 million m3/ year) for
300 to 500 years. It has been proved that the characteristics of rocky-narrow channel of the southern part of Lake Nubia work as a place for a newdelta formation on the sides of the lake. A numberof estimates of the potential life span of Lake
Nasser located in Egypt and Sudan was published,ranging from 20 years to over 1500 years, Makary(1982). The time forecasted for filling the reservoir
by sediment deposition is estimated by MWRI to
be 362 years, which is less than the original design
life span of 500 years.
Stanley (1996) has described the sediment deposition in Lake Nasser as ‘the New Nile delta’, andby the mid-1990s this rapidly growing feature wasabout 200 km long, 12 km wide and about 40 m
thick—extending northwards to Abu Simbel. Whenthe annual flood reaches Lake Nubia, the flow velocity falls from 1.0 m s 1 to about 0.02 m s 1 (Shahin,1985). Thus, the trap efficiency in the Aswan HighDam is close to 100% and under normal conditions only the finest fractions of the suspended
load are transported to the downstream portion of
the reservoir. The total volume of deposited sediment between 1964 and 1998 has been estimatedto be 3.5 km3 and 90% of this sediment is within
the Sudanese side of the reservoir (El-Manadely
et al., 2002). This estimate is based on a series of resurveys of the original Nile river channel bed levels
and valley floor cross-sections that were conducted
before the construction of the dam.
In Figure 9, dams in the worldwide are plottedby the parameter of the turnover rate of water(CAP/MAR  Total capacity/Mean annual runoff)

Figure 8. Mean monthly discharges and suspended
sediment concentrations before and after the construction of AHD (El-Manadely et al., 2002).

Figure 9. Reservoir operation and classification of
sediment management techniques in the worldwide andin the Nile River Basin.

1143

and sediment (CAP/MAS  Total capacity/Meanannual inflow sediment) (Sumi, 2003). The selected
sediment management measures are changed bythese two parameters. It is understood that measures actually selected have changed in the order ofthe sediment flushing, the sediment bypass, sediment check dam and excavating, and dredging as
CAP/MAR increases. This is because of greatly
depending on the volume of water to be able touse the sediment management measure that can beselected for the sediment transport (Sumi, 2000).
Several research studies suggest that the deadstorage capacity was estimated to be sufficient toaccommodate sediment load (130 million m3/ year)
for 300 to 500 years. However, almost all the sediment load reaching the AHD reservoir depositedin the live storage. A number of estimates of thepotential life span of Lake Nasser located in Egypt
and Sudan was published, ranging from 20 years
to over 1500 years, Abdelsalam, (2008). The time
forecasted for filling the reservoir by sedimentdeposition is estimated by MWRI to be 362 years,
which is less than the original design life span of
500 years. AHD as the second largest artificial Lakein the world has its positive and negative impacts
on the region and the socio-economic developmentof Egypt in particular.
4

CONCLUSIONS

It is clear from this review that any discussion of thesediment production and reservoir sediment management techniques of the Nile Basin must be set
within an integrated sediment management. Assessing issues, depending on each case, of dam security,
sustainable management of water resources andsediment management in a sediment transport system, we have to draw up an effective sediment management plan with a limited budget and take specificaction. Needless to say, of course, our best endeavors should be exerted to minimize negative environmental impacts involved in sediment management.
A successful sediment management proceeds from apermanent change in river management: Sedimentmanagement is a relatively new issue which is neither well understood nor accepted.
Monitoring techniques are useful to evaluate
sediment transport during flushing, and should be
intensively studied and developed to support sediment management strategies.
Reservoir sedimentation management in Japanis entering a new era. Although there are still technical problems to be solved, it is believed that theimportance of sediment management will increasingly grow. Assessing issues of dam security, sustainable management of water and sediment in
a sediment routing system, an effective sedimentmanagement plan should be studied. The completion of the new dams at the upstream of AHD will
result in a marked reduction in flow and suspended
sediment budget to Lake Nasser; stakeholders
need to recognize that the river transports sediment addressed in the management equation. It is
a complex undertaking. Exact answers to all questions will not be known in advance.

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