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Simulating current and future water
resources development in the
Blue Nile River Basin
Matthew P. McCartney, Tadesse Alemayehu, Zachary M. Easton
and Seleshi B. Awulachew
Key messages
Both Ethiopia and Sudan have plans to unilaterally develop the water resources of the mue Nile for hydropower and irrigation. The extent to which these plam will actually be imple mented is unclear. However, if both countries totally fulfil their stated obJectives the following are estimated to occur: the total reservoir storage in Ethiopia will increase from the current 11.6 to more than 167 billion cubic metres (i.e. more than 3 times the mean annual flow at the Ethiopia·-Sudan border); large-scale irrigation withdrawals in Sudan will increase irom the current 8.5 to 13. billion m 1 yr'; large-scale irrigation withdrawals in Ethiopia will increase from the current 0.26 to 3. billion m' , and electricity generation in Ethiopia will increase from the current 1383 to 31,297 giga\vatt h0urS (GWh) yr". Increased 'Vater storage in dams and greater withdrawals will inevitably alter the now regime of the river and its main tributaries. If full development occurs, the total flow at the Ethiopia-Sudan border is predicted to decrease from the current (near natural) 45.1 to 42. billion m' yr' and at Khartoum from the current 40A to 31.8 billion m^1 yr". However, although there is a significant reduction in wet season flow at both locations, dry season flow will actually increase because of the greater upstream How regulation. By increasing water availability in the dry season and reducing t100ding in the wet season this increased regula tion promises significant benefits for Sudan. There is great potential for increased water resources development in the Blue Nile. However, if Ethiopia and Sudan continue to implement development unilaterally, the bene fits of water resources development are unlikely to be fully realized. It is tberefore essential that the countries eooperate closely to (i) identifY priority development options, (ii) improve irrigation efficiencies, (iii) mitigate any adverse impacts (e.g. to the environment)
The Nile River Basin
and (iv) manage water resources in a \vay that brings benetlts to all. To take full advantage of the water resources of the basin it is necessary that they are managed as a single system (i.e. without considering national borders) that, in turn, requires the establishment of much more effective institutional arrangements than those currently existing.
Introduction
The Blue Nile River is an important shared resource of Ethiopia and Sudan, and also because it is the major contributor of water to the main Nile River Egypt. However, tensions over the basin's water resources remain unresolved. Although the riparian countries have agreed to collaborate in principle, formal mechanisms to cooperatively develop the basin's water resources are limited. Currently, a Cooperative Framework Agreement (CFA) is being negoti ated, but this process has been under way for more than a decade and no final agreement has yet been achieved (Cascao, 2009). Recently, t1ve of the riparian countries, Ethiopia, Kenya, It,vanda, Tanzania and Uganda signed an agreement, but both Egypt and Sudan remain opposed to the current version. Under the auspices of the Nile Basin Initiative (NBI) twO primary programmes have been established: (i) the basin-wide Shared Vision Program, designed to build confIdence and capac ity across the basin, and (ii) the Subsidiary Action Program, which aims to initiate concrete investments and action at sub-basin level (Metawie, 2004). However, both programmes are developing slowly, and there are few tangible activities on the ground. As a result, all riparian countries continue to pursue unilateral plans for development. The potential benetlts of regional cooperation and integrated joint basin management are signiticant and well documented (Whittington et al., 2005;Jigerskog et aI., 2007; Cascao, 20(9). A prerequisite for such cooperation is the development of shared knowledge bases and appro priate analytical tools to support decision-making processes. Currently, knowledge of the basin is fragmented and inconsistent and there is limited sharing of data and information. There is also a lack of analytical tools to evaluate water resources and analyse the implications of differ ent development options. These are l1l~or impediments to building consensus on appropriate development strategies and cooperative investments in the basin. A number of computer models have been developed to assess various aspects of hydropower and irrigation potential within the Blue Nile and the wider Nile basins (Guariso and Whittington, 1987; Georgakakos, 2003; Block et al., 2007;E1ala, 2(08). However, these models have focused primarily on the upper Blue Nile in Ethiopia and the development of hydraulic infrastructure on the main stem of the river. Relatively little attention has been paid to water diversions and development on the tributaries or future development in Sudan. In this chapter we report the t1ndings of research conducted to determine the impact of current and possible future water demand throughout the whole of the Blue Nile Basin (BNE). The Water Evaluation And Planning (WEAP) model was used to evaluate the water resource implications of existing and proposed irrigation and hydropower development in both Ethiopia and Sudan. The current situation and two future development scenarios were simulated; one representing a relatively near future (the medirmHerm scenario) and the other a more distant future (the long-term scenario). Since year-to-year variation is important for water management, 33 years of monthly time step flow data wer'2 used to simulate the natural hydrological varia tion in all the major tributaries. The water demands of the scenarios, incorporating all existing and planned development on both the main stem and the tributaries were superimposed on these time series. However, because the planned large reservoirs require considerable time to fill, a 20-year warm-up period was used and comparison between the scenarios was made over
90'0"*
33"O'O"E
Legend RIvers IIIIIIIiIIlakes c::J Sub Basins Ethro_Sudan border
The Nile River Basin
3'"O'O"E 3!rO'O"E
N A
FiJi!!rl' 14.1 Map of the Blue Nile Basin showing the major tribntaries and sub-basins SoU/(e: Yilma and AWllIJchew. 2009
12'O'O"N
9'O'O"N
1\t Khartoum, annual tlovv varies from approximately 23 billion to 63 billion 111\ (Figure 14.2). Mean monthly flow also varies considerably at all locations along the river (Table 14.1; Figure 14.3). Typically, IUore than 80 per cent of the flow occurs during the flood season Ouly-October) while only 4 per cent of the flow occurs during the dry season (February-May) (Awlliachew ct <11., 20(8).
Current water resources development Currently, Ethiopia utilizes very little of the Blue Nile water, partly because of its inaccessibil ity, partly because the major centres of population lie Oll tside of the basin and partly because, to date, there has been only limited development of hydraulic infrastructure on the river. To date, only two relatively minor hydraulic structures (i.e. Chara Chara weir and Finchaa dam) have been constructed in the Ethiopian part of the catchment (Table 14.2). These two dams were built primarily to provide hydropower. They regulate tlow from Lake Tam and the Finchaa River, respectively. The combined capacity of the power stations they serve (218 MW) represented approximately 13 per cent of the total installed generating capacity of the country in 2009 (i.e. 1618 MW. of which 95'% was hydropower). In 2010, a new power station on the Ueles River came on line (see below) and the total illS taIled capacity increased to 1994 MW
Simulating current and future water resources development in the Blue Nile River Basin
a (^) 70,
60,
50,
l' 40, 6
u::: 20,
10,
a 1960 1963 1966 1969 1972 1975 1978 1981 1984 1987 1990
b 70,
60,
50,^ ..
E 40, 6 ?l: 0 30, u::: 20,
10,
a 1960 1963 1966 1969 1972 1975 1978 1981 1984 1987 1990
Fit?IJrC 14.2 Annual !low of the I3lue Nile measured at (a) Khartollm (1960-1 ()R2) and the EthIOpia-Sudan border (1 %0-] 9(2) Source: Data obt.lined from the C;]ob,,] Data Runoff Cemre and Ethiopian Ministry ofWat<:r Re,ourc,",
Agriculture, which is the main occupation of the inhabitants in the basin. is primarily raill-ted with almost no irrigation. Although there is some informal small-scale irrigation, currently the only formal irrigation scheme in the Ethiopian part of the catchment is the Finchaa sugar cane plantation (8145 hal, which utilizes WJ,er after it has passed through the Finchaa hydropower plant (1:1ble 14.2). In contrast to Ethiopia, Sudan utilizes signiticant volumes of Blue Nile water for both irri gation and hydropower production. T\vo dams Roseires and Sennar), constructed 011 the
Simulating current and future water resources development in the Blue Nile River Basin
16 14 12
i
10· 8· u:^ ~ 6
__ .•_ _i~
- Outflow from lake Tana Abay at Kessie • Blue Nile at EI diem b Blue Nile at Khartoum
Fif!,lIrc 14.3 Mean monthly flow (million tn') at gauging stations located on the main stem o[ the Blue Nile SOlmy': Data provIded by the Ministry ofWarer Remurces. Ethiopia and the UNESCO Chair in Warer Resources, Sudan
irrigated area in the Sudanese part of the Blue Nile is estimated to be 1,305,000 ha, consisting of a variety of crops including cotton, sugar cane and vegetables. The installed power capacity at the two dams is 295 MW, which represents 25 per cent of the country's total generating capacity (i.e. 1200 MW from both thermal and hydropower stations).
7,1hle 14.2 Existing dams in the BIne Nile catchment Dam Country River Storage Year darn Purposf (mil/iott In ') was built
Chara Chara Ethiopia Abay 9100' 2000 Regulation of Lake Tana outflows [or hydropower production at Tis Abay I and Tis Abay II power stations (installed capacity 84 MW) and, since 2010, for transfer o[ water to the Beles River hydropower station (installed capacity 460 MW) Finchaa" Ethiopia Finchaa 2395 1971 Regulation for hydropower production (installed capacity 1.34 M W) and also [or irrigating sugar cane plantations (8145 hal Roseires Sudan nIue Nile 3024 1964 Regulation tor hydropower production (installed capacity 280 MW) and [or sl1pply to irrigation schemes (1,305, hal Sen naT Sudan Blue Nile 930 1925 Regulation tor hydropower production (installed capacity 15 MW) and [or supply to irrigation schemes (1.093,502 hal Notes: "' This is the active storage of Lake TaIlJ that is controlled by the operation ot'the weir (i.e. jake levels between 1784 and 1787 masl). It represents 2.4 rimes the average annual ourtlow of the lake 'There is small dam located on the Amerty River (storage 40 million m'). which diverts water [rom the A111erty ftiver into the Finehaa reservoir
The Nile River Basin
Future water resources development
Both Ethiopia and Sudan contend that utilization of the Nile water resources is essential for socio-economic development and poverty alleviation. Consequently, both countries are plan ning significant development of the Blue Nile River water resources ill the future. In Ethiopia, current planning is focused primarily on the Lake Tana and the Bell'S River catchments which have been identified by the government as an economic 'growth corridor' (McCartney ct al., 2(10). However, additional projects are planned in nearly all the sub catchments as well as along tbe main river. Possible irrigation projects have been investigated over a number of years (e.g. Labmeyer. 1962; USBR. 1964; JICA, 1977; WAPCOS, 1990; BCEOM, 1(98) and tbe total potential irrigated area is estimated to be 815,581 ha. compris ing 45.856 ha of small-scale, 130,395 ha of medium-scale and 639,330 ha of large-scale schemes. Of this, 461 ,OOU ha are envisaged to be developed in tbe long term (BCEOM, 19(8). In the Ethiopian Blue Nile, more than 120 potential hydropower sites have been identified (WAPCOS, 1990). Of these, 26 were investigated in detail during the preparation of the Abay River Basin Master Plan (BCEOM, 1(98). The major hydropower projects currently being contemplated in Ethiopia have a combined installed capacity of between 3634 and 7629 MW (cf the Aswan High Dam, which has an installed capacity of 2100 MW). The exact value depends on the fmal design of the dams and the consequent head that is produced at each. The four largest schemes being considered are dams on the main stem of the Blue Nile River. Of these schemes the furthest advanced is the Karadobi project for which the pre-feasibility study was conducted in 2006 (NorcollSult,2006}. In addition to the single-purpose hydropower schemes, electricity generation is expected to be added to several of the proposed irrigation projects where dams are being built. This is esti mated to provide an ;ldditional 216 MW of capacity (BCEOM, 199R). The total energy produced by all the hydropower schemes being considered is in the range 16,000-33.000 GWh yr '. This represents 20 to 40 per cent of the technical potential in the Ethiopian Blue Nile 70,000 GWh yr- i^ ) estimated by the Ministry of Water Resources (Beyene and Abebe, 2(06).
Currently, it is anticipated that much of the electricity generated by these power stations will
be sold to Sudan and possibly to other countries in the Nile Basin. Sudan is also planning to increase the area irrigated in the BNB. Additional new projects OJld extension of existing schemes are anticipated to add an additional 889,340 ha by 2025. An additional 4()OO million Ill' of storage will be created by raising the height of the existing Roseries dam by 10 111 (Omer, 2(10). However, currently there are no plans for additional darns to be constructed on the Blue Nile. Technically feasible hydropower energy production in the Nile Basin of Sudan is estimated to be 24,137 GWb yr-r (Omer, 20(9), 1110St of which is on the main Nile downstream of the White and Blue Nile confluence. Currently, the Merowe dam, with an installed capacity of 2500 MW, is being commissioned 011 the Nile downstream of Khartonm. Several other major hydropower dams are being planned, nOlle of which are to be located on the Blue Nile River.
Application of the Water Evaluation And Planning model
Model description
Developed by the Stockholm Environment Institute (SEI), the WEAl' model is intended to be used to evaluate planning and management issues associated with water resources development. The WEAP model essentially calculates a llJass balance of flow sequentially down a river
The Nile River Basin
~--------"- I .. -~-
-
Jemma Jemma Il[^ • Lem,
Muger
Flow gHugmg stallOflS e(care/wen! ama :> 1.000 j.(nf) ~, Gude,^ /^ Reservoir a (^) Didessa Finchaa
- Khano"", SUDAN
Downstream ---. __~__Rahxad\ Roha<! 148,293 ha Irrigation upstream^ of Lake Tana 7,200 ha Senna, 167,200 na 'Di~;;~;-'--~
Gezira and Managii 882,195ha .. -- - -~~;i;.. ~~"nnar / / \ Ou(!el Lake Tana Upstream Sennar 71,717 na / \
Suki 29,827 ha
Dabus^ Finchaa V8,145ha
InigallOn V ReserVOIr Guder b (^) Finchaa^ Irrigation^ scheme
Simulating current and future water resources development in the Blue Nile River Basin
SuIO 32,767 ha North GOlam
I
Irfigaijon upstream of Lake Tan. 69,053ha
/ r___ Anger ':t)v--- (^) Finchaa
- Irrigahon^ o^ Diversions Anger 20, 14,45000 V^ Reservoir Guder c (^) FlOchaa - Khartoum . SUDAN^ Rahad^ If^ 210.046ha
Oownstrean 6)0^ Irriga_^ ups1ream^ of
Sennar 228.111 00 f"^ Lake^ Tana^ 69,053 ha
Gezlra and Managil .. (^) ,L~ .'.~_lake iTana^ ..PumpingNW Lake 6,720ha Tana 882.195 ha Upo!",.m Senna, 117,626 ha^ ,^2424 1 ~
./ , / ~^ t,^ ~,.---- Oultel Lake^ Tana^ ,...--_
Kanana I & II 420,0931>0 ~ (^) \ _. ., O-Cjf Beles ~''''~ Bosheilo (^0) !,.;10( d at Upper Dioder 10,000..... ' ,~.ha'!'-f.) '"lit) ~', Suki 36.128 ha (^) ^ r::::1---^ ,^ Welaka
,_.•~-·'--VD.ngu.rD.m Upper Bele. 53,7ooha .J---.--
f lower Beles North Gojam Jemma
ETHIOPIA \ 85,000 ha South GOlam •••. Lo.. or )\ !WOmber. I Mobrr !... /' Dab~ \ ..:t.. _" ~aya*--t> _t>dObl _, A" '.,.. _~ _____ ~~S!e(
UpperD,D,~US /' ~o:e~sa rv'.; Nekemte 11.220ha fNestle;i
Oabus 9,661ha.. .• _ (^) : • ~ T r-"". 7,217 ha ,!
/'C r ' ~ Anger (t OOi .... erslons
Dabus" ~=ah:"gation ...-t-.. Flnchaa ~ ;,~:ha
~ Ange' ;:t, 20,145ha 1'
If 14.450 ha V ( Arjo 13,665h. I Fincha.' ......... ./'1 t 1 J inigalion scheme
--.c....J- 8 -+1 ct Guderdiversion4,1ooha
d Dldes^ sa^ Guder
F(\iliYe 14,4 Schematic of the model contlguration for different scenarios: (a) the natural situation, (b) the current (2008) situation, (e) the medium-term (2010-2025) future, and (d) the long-term (2025-2050) future
Simulating current and future water resources development in the Blue Nile River Basin
Table 14.4 Continned
Schaw' Stih-basin Dc.<criplioll rislilllated
date Rahad and Rahad Rahad and Galegu scheme: 15,029 ha Long term Average annual demand: 607 millioll Ill; Dinder Dinder (^) Dilldcc scheme: 49,555 hJ Long term Average annual demand: 556 million ll1; Guder Guder Guder diversion: 4100 ha Long term Guder: 4R96 ha Average annual demand: 54.4 million Ill;
Nekemte Anger Nekemte scheme: 11,220 ha Long term Averag<;, anllual demand: 71.5 million Ill; Dides-;a Didessa Didessa irrigation scheme: 54,05R ha Long term Average annual demand: 769.4 million 1lJ" Sudan Raising Blue Nile Roseries dam raised by 10 III to provide total (gross) Medium Roscries main stem storage of 7400 million m'. term Dam
Extension Rahad Additional irrigation area: 1 'J, 7 40 ha Medium of Rahad Rahad II irrigation scheme: 210,000 ha terlll irrigation 1btal average annual demand: 2433 million m; scheme
Extemion J:)\ue Nile Additional irrigation area: 2940 h3/3361 ha Mediulll/ ofSuki main stem Total average allnual demand: 201 million m'/221 million 111; tcrm irngation scheme Extension Blue Nile Additional irrigation area: 39,910 ha Medium of Upstrealll main stem Total average annual demand: 745 million m' term Sennar Extc:nsion Blue Nik Additional irrigation area: 44,110 h3/6R04 ha Mcdunn/ of 11lain StC'lll Total average annual demand: 1414 million Ill'/ long term Downstream 1526 million^ Ill' Sennar Kenana II Blue Nile^ Additional irrigation area: 420,093^ ha^ Medium and III l11alll stelll Average allnual demand: 2352 million m' tenn Soutb Dinder Additional irrigation area: ~-l,O 19 ha/48,318 hah^ Medium/ Dindt'r Average annual demand: 541 million^ m^ ;/~51^ million^111 II^ lung term l'.lotc:s: ' Schelllt's arc extended partially in the mediUlll-tcnn future Jnd partially in the long-term filturc I'The slash in the third C:01Ulll11 demarcates values lwtweell the llledilllll-tcrm future and the ]ong-ttnll future
For many potential schemes there is currently considerable uncertainty about the dates when they will be completed. In the current study it was assumed that, for Ethiopian schemes, if prefeasibility studies have been undertaken then the scheme will be completed in the mediulll term. For all other planned schemes it was assumed that they will be completed in the long term. For the Sudanese schemes, information on likely completion dates was obtained
The Nile River Basin
TiJhle 14. .') Proposed hydropower development in the Blue Nile River Basin Scheme Suh-basin^ Descriptioll Estimated wmpletioN date Ethiopia Tana-Beles TlIld and Beles Transfer of water from Lake Tana to Beles catchment for hydropower production and lrrigatioll Hydropower capacity: 460 MW Average anllual transfer: 2424 million 111;
Medium term
Anger Anger Linked to the Anger irrigation scheme Hydropower capacity: 1.8-9.6 MW
Medium term Arjo Didessa Linked to the Atjo irrigation scheme Hydropower capacity: 33 MW
Medium term Karadobi Blue Nile main stem
Height of dam: 250 m Total storage: 40,220 million m; Hydropower capacity: 1600 MW
Medium term
Mendaya Blue Nile main stem
Height of dam: 164 Total storage: 15.900 million 111; Hydropower capacity: 1620 MW
Medium term
Border Blue Nile main stem
Height of dam: 90 111 Total storage: 11,100 million 111' Hydropower capacity: 1400 MW
Long term
Mabil Blue Nile main stem
Height of dam: 170 J1l Total storage: 17,200 million III 1 Hydropower capacity: 1200 MW
Long term
Lower Didessa Didessa Height of dam: 110 Il 'final storage: 5510 million 111; Hydropower capacity: 1')0 MW
Long terlll
Dabus Dabl1s Linked to the Dabus irrigation ,cheme. Hydropower capacity: 152 MW
Long term
Danguar Beles Height of dam: 120 m Total storage: 4640 million m' Hydropower capacity: 33 MW
Long term
Lower Daills Dabus Height of dam: 50 1Il 10tal storage: 1290 million m' Hydropower capacity: 164 MW
Long term
from discussions with water resources experts within the country. However, clearly the two scenarios reflect only an approximate timeline tor water resources development in the basin. In reality, development is dependent on many external factors and so it is impossible to predict exactly when many planned schemes will actually be implemented, or indeed the exact sequencing of schemes. As they stand the medium-term and long-term future scenarios repre sent a plausible development trajectory, but it is unlikely that it will actually come to pass in exactly the way envisaged.
The Nile River Basin
3.6 times the mean annual flow at the border) in the long term. Hydropower generated in Ethiopia, from the Tis Abay and Finchaa power stations, is currently estimated to be 1383 GWh yr '. With the construction of the Tana Ueles transfer, the Karadobi dam and other smaller schemes, this is estimated to increase to 12,908 GWh yr (^) 'in the medium term. With Uorder, Mendaya and Mabil hydropower stations, as well as with additional smaller schemes, electricity production in the long terll1 could increase to 31,297 GWh yr. Hydropower generated on the U1ue Nile in Sudan is currently estimated to be just over 1000 GWh ye (^) ', but there arc no publicly available data to confirm this estimate. Because of the additional head and increased storage, the raising of the Roseries dam will result in a very small increase to 1134 GWh yr I in the medium term and to 1205 GWh yr I in the long term. The increase in the long term is due entirely to greater dry season resulting from increased regulation upstream in Ethiopb.
a 40000
35000 I 30000 •
25000
•• :
l' (^) f • I .,
I I ~ 20000 ~o (^) : : : .. u:: (^15000) ,f^. I,^ "^. " ". 10000 ,:,II.. :.,' ,^ • ,: III^ I • ~:.. .. ..... \ I III. III 5000^ ...^ rl/^ ......^ ~:^ .. II. (^) • II• t I II. 'I,' .' .' '. (^) Ie ..II o^ •^ ..^ ·I#.^ ,^ ..^ '^ •.^ ,^ ......^ ,^ .....^ , (^0) ~ 0'\ .". (^) '" 0 M^ .....VI 0:).....^ ;;; N^ co VI^ '"<Xl 00 0 q; '"c^ '"c^ "?^ '"'"C^ '" i9^ "C^ '"'"c^ "C^ c^ "C'"^ C "C'"^ C^ "?'S^ "C^ "?^ C "? t (^) 'S .:.:; ~^ .:.:; ~^ !!; ~^ !!;"^ ~^ .:.:; ~^ .:.:; ~^ .:.:; ~^ !!; ~ !!; ~^ !!; ~^ !!; ~
- Observed Flow at Khartoum ••••^ SimUlated Flow at Khartoum
18000 16000 14000 ~E e 12000
.g^ ~^10000
.c^ > (^8000) C 0 E (^6000) c '" (^4000) : 2000 0 Jan. Feb. Mar. Apr. May June July Aug. Sep. Oct. Nov. Dec.
- Observed flow at Khartoum •••• Simulated flow at Khartoum
b
Simulating current and jutllre water resources development in the Blue Nile River Basin
40000 (^35000) ·t I 30000 t I _ 25000 E 620000 :;: 0 u: (^15000) 10000 5000 0
18000 16000 ~ 14000 ~E 5 12000 g 10000 .J::^ » C^8000 0 E (^6000) c ." (J) (^4000) ::i: 2000
o
(^0) "- 0\ 0 N M (^) ,..... 0\ ,..... 0
'" ~^ '"~^ ~^ '""^ '9^ r-;-^ r-;-^ "-'"^ r-;-'""^ '"^ '" "P^ '""P^ "^ '"'f'^ <Xl^ 'f''"^ 'l' q;
i: (^) ~ c;^ ~ '"r: (^) ~ '""C (^) ~ '"i: (^) ~ C (^) ~ i: (^) ~ c (^) ~ '"C (^) ~ C (^) ~ c; ~ .!Ji .!Ji .!Ji .!Ji .!Ji .!Ji .!Ji .!Ji .!Ji .!Ji .!Ji Observed flow at the border (^) - - - • Simulated flow at the border
Measured MAF in Ethiopia 50.68 m' Measured MAF in Sudan = WEAP Simulated MAF = 46.2 8m'
455Bm'
Jan. Feb. Mar. Apr. May June July Aug. 5ep. Oct. Nov. Dec.
- Observed flow in Ethiopia - - - • Simulated flow at the border -- Observed flow in Sudan
F(qWf 14.5 Simulated and observed flow series and mean monthly flows (1960-1992) for the Blue Nile (current situation) at (a) Khartoum and (b) the Ethiopia-Sudan border
Comparison of the mean monthly flows at Khartoum tor the simulated natural condition, current situation and the mediulIl- and long-term scenarios, tor the 13 years 1980-1 SlSl2, indi cates how the mean annual flow is progressively reduced as a consequence of greater upstream abstractions (Table 14.7). Wet season flmvs are reduced significantly, but dry season flows are increased as a consequence offlow regulation (Figure 14.7;Table 14.7). Under natural condi tions, 84 per cent of the river flow occurs in the wet season months (July-October). In the medium-term and long-term scenarios this is reduced to 61 and 37 per cent, respectively.
Simulating current al1d future water resources developmel1t il1 the Blue Nile River Basin
a (^18000) Simulated natural MAF '" 48.2 Bm 3
16000 Simulated^ current^ MAF^ = 40A^ Bm^3
Simulated medium -term future MAF =33ABm 3
'f (^14000) Simulated long-term future MAF =31.9Bm 3 ~ 12000 ~ 10000
. -£ c 8000 0 E 6000 c: ~'"
(1l (^4000) 2000 0 Jan, Feb, Mar. Apr. May June July Aug. Sep. Oct, Nov, Dec.
-Natural flow -Current flow - - -Medium-term future _. Long-term future
18000 Simulated natural MAF = 45.2 Bm^3 16000
b
Simulated current MAF = 45.2 Bm) 'f 14000 Simulated^ medium ·term future^ MAF^ =^ 43.2^ Bm^3
~ 12000 Simulated^ long·term future^ MAF^ =42.7^ Bm'
3:
.g 10000
. £: c: 8000 (^0 ) E c ~'"
(1l (^4000) 2000 0 Jan. Feb. Mar. Apr. May June July Aug. Sep. Oct. Nov, Dec
- Natural flow - - • Medium-term future _. Long-term future
Fixure 14,7 Comparison of simulated mean monthly flow derived for natural, current, mecHum-term and long-term future scenarios at (a) Khartoum and (b) the Ethiopia·-Sudan border
irrigation demand in Ethiopia. The reason is partly that less water is diverted fi-om the Tana to the Beles catchmem ano more flow is routed down the main stem of Blue Nile. rurrently, shortfalls (i.e. failure in any given month to supply the full amount of water needed for irrigation withdrawals or hydropower needs) in Ethiopia are negligible. However, in the medium-term scenario shortfalls increase to 0.8 and 5.0 billion m l^ yr ' for irrigation and hydropower, respectively. In the long term, the increased storage means that shortfalls will aver age 0.4 billion m' for irrigation and 0.7 billion m l^ yr-' for hydropower. In comparison, under current conditions, there is an average shortfall of 0.8 billion m' in water for the Sudanese irrigation schemes. However, because of the improved flow regulation there are no shortfalls in irrigation or hydropower in Sudan in either the medium- or the long-term scenar ios. These results reflect the fact that, in each scenario, the Sudanese schemes were given the same priority as those in Ethiopia. Hence, although in the medium term and long term more water is stored in Ethiopia, in these scenarios, no preference was given to the schemes in Ethiopia,
The Nile River Basin
lablr 14.7 Simulated mean monthly flow (million m') at the Ethiopia-Sudan border and Khartoum for natural, current, medium- and long-term tiJture scenarios (1980-1992) Atom" Naruml^ Currcrlt^ Aledium-term filturr^ Long-term^ future Border Khartollm Border Khartoum Border Khartoutll Border Khartoum .-.-~--.-~-~.---.-----~--------- January 835 835 955 B55 1565 3220 2710 4405 February 470 470 380 740 1180 2220 2110 3175 March 350 350 400 475 845 1615 19BO 2770 April 310 310 520 620 710 1315 1635 2250 May 390 390 645 710 680 1235 14B5 2055 June 980 990 1230 640 1390 2273 2203 3125 July 5930 6235 6105 5365 3870 2560 4820 3420 August 15,770 16.830 15,430 15,950 8400 8615 4H20 4245 September 10,590 11,6HO 10,130 10,165 H020 7490 4665 3760 October 53()O^ SH25 4970 3865 5315 1740 4105 420 November 2750 2795 2()^15 3JO 8870 2<>0 9095 250 December 1510 1510 1575 740 2305 H50 3055 1990 10ta1 45,245 48,220 45,155 40,435 43,150 33,395 42,6H5 3LB
Net evaporation (i.e. the difference between evaporation trom a reservoir and the rainfall directly onto its surface) from the Ethiopian reservoirs currently averages 0.8 billion m' yr-'. However, by f3r the bulk of this is from Lake Tana which is a natural geographic feature and would be evaporating even without regulation. By comparison, net evaporation from the Sudanese reservoirs is 0.4 billion 111' yr-'. In the medium term this increases to 1.2 billion 111' yr' in Ethiopia (0.3 billion m' yr' excluding Lake Tam) and to 1.4 billion m' yr' in Sudan. The increase in Sudan is due to the increased area of the Roseries reservoir arising from rais ing the Roseries Dam and the fact that water levels in both Roseries and Sennar reservoirs are maintained at higher levels because of the higher dry season inflows. In the long term, total net reservoir evaporation increases to 1.7 billion m' yr ' in Ethiopia (0.8 billion 111' yr • excluding Lake Tam) and remains at 1.4 billion m l yr- in Sudan. However, evaporation losses per cubic metre of water stored are considerably lower in Ethiopia than in Sudan in all the scenarios. In fact, as a result of the locations of the planned reservoirs, as storage increases in Ethiopia, losses per cubic metre of water stored decrease significantly over time (Table 14.H).
lab/e 14.8 Simulated average annual net evaporation trom reservoirs in Ethiopia and Sudan for each of the scenarios Sccnario Ethiopi,r' SHdml Tiltal 'lillal E!JaptJratiou Iblal Iotal E/lapomrioll storage evaporation from stOl'a.lZe st()ra,~e (,U(1poration^ fn)Jn^ _.;f{)ra~~l' (millioll m'l (millivlI^ /II')^ Im'm') (millioll m')^ (millioll tn') (m^ i^ 111-') Current 11,57il (^) H46 0.07 3370 443 0. Medium term 70,244 (^) l1SB (l.02 10,770 1363 0. Long term 167,079 1732 Cl.01 10,770 (^) 13H7 0. N(lres: 'Including from Lake 1,ma, which is a natural lake. though regulated by the Char" Chara weir
