Solomon B. GebreProject Manger

Design of (four) dams in Lake Tana Sub-basin Project

Potential & Experience of Dams in Ethiopia

Outline of the Presentation• Country Background• Water Resources• Potential & Status of Development

– Irrigation– Hydropower– Water Supply

• Existing dams– Lessons To be Learnt (Two Case Studies)

• Dams under construction• Future for dams

– Local Context– Regional Context

Country Background

• One of the 10 Nile Riparian Countries• Population - 72.4 Million in 2004• Growth rate - 2.3 % per annum• Population by 2016 – 96 Million• Total Land Area - 1.104 x 10^6 Km2• Socio-economy

– Agriculture is the dominant sector– Largest Livestock population in Africa– Per Capita income 90 -100 USD– Water Supply coverage ca.35 %– Electricity coverage ca.

Water Resources

• 12 River Basins• Total Surface water

Potential of 122 BCM• Renewable ground water

Potential of 2.6 BCM• About 97% of the surface

water drains to neighbouring countries

• Water Tower• Contribution to Nile

Water ca. 86 %

ABBAY

AWASH

WABI SHEBELE

GENALE DAWA

TEKEZE

OGADEN

OMO GIBE

DENAKIL

BARO AKOBO

RIFT VALLY

AYSHA

MEREB GASH

SudanDjibouti

Eritrea

Somalia

Kenya

Sudan

Somalia

Primary x-ics of Water Resources

• Extreme interannual & Intra-annual variability– Droughts– 19 periods of widespread &

severe food shortages in the past 100 yrs alone

• Spatial variability of rain flow – Rainfall mainly in the

highlands– Lowlands are arid to semi-

arid

• International nature of its most significant water resources

Potential & Status of WR Development

• Hydropower– Pot. Economical - 160 GWh or

30,000 MW– Developed: ca. 800 MW– < 3 %

• Irrigation– Pot. Economical – 2.7 Million ha– Developed: ca. 290,000 ha– ~ 10.8 %

• Water Supply coverage (Recent estimate by the MoWR)

– Overall – 47 %– Urban – 80 %– Rural - 41 %

Justification for Dams• Low level of development

– Food security of its peoples– Access to Safe drinking water supply – Access to affordable electricity supplies

• Resources of the country (Land, Water, Labour)• Water resources are highly variable (spatially and

temporally)• Dams are required to safeguard its people against

the ill-effects of recurrent drought and bring about development

• Regional development – specially by tapping the country’s huge Hydropower Resources for the regional market

Existing dams

FAO - Aquastat Database 200610 Large dams

Author’s compilation from various sources> 50 Large dams ( According to ICOLD Classification (2003))

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OROMIA

Afar

Somali Region

AMHARA

TIGRAY

SOUTHERN REGION

BENISHANGUL-GUM

GAMBELLA

DIRE DAWA

HARARIADDIS ABEBA

Sudan Djibouti

Eritrea

Somalia

Kenya

Sudan

Somalia

400 0 400 800 Kilometers

#S Under construction dams%U Existing Dams

N

greater than 15 m in height from base to crest, or storage capacity exceeding 3 million cubic meters for heights between 5 and 15 m

N° Name of dam Major basinYr.

Completed Height

(m)

Initial Capacity (x10^3 CM)

Purpose

1 Abasamuel* Awash 1939 22.00 65 000 HP2 Alwero** Baro Akobo 1995 16.00 74 600 IRR

3 Angereb Tekeze 1991 34.00 5 300 WS

4 Dire Awash 1999 46.00 19 000 WS

5 Finchaa Blue Nile 1973 25.00 650 000 HP,IRR

6 Gafarsa Awash 1955 17.00 7 000 WS

7 Gilgel Gibe Omo-Gibe 2004 41.00 839 000 HP

8 Koka Awash 1960 42.00 1 860 000 HP,IRR,FP9 Legadadi (Main) Awash 1979 40.00 38 000 WS

10 Legadadi (Subsidiary) Awash 1979 22.00 4 000 WS

11 Melka Wakena Wabeshebele 1988 40.00 750 000 HP

12 Midimar Tekeze 1996 33.00 10 000 WS

Important Large Dams in Ethiopia

* Inoperative since 1970 ** Only the dam construction has been completed CM: Cubic Meters

HP-Hydropower, IRR-Irrigation

WS-Water Supply, FP-Flood Protection

13 Chara Chara Blue Nile 1996 9 9,100,000 Regulation

Microdams• Small dams (micro-dams)

constructed for irrigation supply are concentrated in the Northern Amhara and Tigray regional states.

• Construction took place b/n 1995 – 2000

• 64 Dams in Tigrai Region– 28 are large dams according

to ICOLD classification

• 14 dams in Amhara Region– 12 are large dams according

to ICOLD

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OROMIA

Afar

Somali Region

AMHARA

TIGRAY

SOUTHERN REGION

BENISHANGUL-GUM

GAMBELLA

DIRE DAWA

HARARIADDIS ABEBA

Sudan Djibouti

Eritrea

Somalia

Kenya

Sudan

Somalia

400 0 400 800 Kilometers

#S Under construction dams%U Existing Dams

N

Performance of the Microdams

• According to a study in 2003 (VLIR), out of the 64 microdams in Tigrai– Only 18 dams had no

problems– 24 dams have seepage

problem– Nine dams have

sedimentation problems– 13 dams have both

sedimentation & seepage problems

• According to a study in 2006 (Tefera B.), out of the 14 microdams in Amhara – Only one of the 14 dams is

functioning according to the plan of implementation

– hydraulic problems (16.7%), – hydrological problems (41.7%), – sedimentation problems (33.3%), – seepage failures (58.3%), and – structural failures (8.3%).

• Damaged spillway (Hydraulic failure)

• Syphon used to offtake water b/c of clogging of the intake

Common Problems encountered in MicrodamsCommon problems identified include:• Overtopping due to inadequate spillway capacity – flood

estimation problem• Seepage through foundation, abutments and reservoir area –

site selection problem• Cracking or structural failure – geotechnical problem• Less inflow in the reservoir – hydrological analysis problem• Sedimentation- design problem and lack of watershed Mgt.• Lack of proper maintenance and rehabilitation work• The rush in implementation without adequate investigation in

all aspectsProblems identified should give a good lesson for future building

of similar dams.

Dams under construction

N° Name of dam River basin

Expected year of

completion

DamHt. (m) Purpose

1 Tendaho Awash 2008 40

 Irrigation of ca. 60,000ha 

2 Kesem Awash 2008 90

 Irrigation of ca. 20,000 ha 

3 Koga Abbay 2007 21Irrigation of ca. 7000 ha

4 Tekeze Tekeze 2011 185

Hydropower of 300 MW, irrigation d/s of 60,000 ha

           

5 Gilgel Gibe II Omo-Gibe 2008 21Hydropower of 420 MW

6 Gibe III*

 

2011 240

 

Omo-GibeHydropower of 1870 MW

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OROMIA

Afar

Somali Region

AMHARA

TIGRAY

SOUTHERN REGION

BENISHANGUL-GUM

GAMBELLA

DIRE DAWA

HARARIADDIS ABEBA

Sudan Djibouti

Eritrea

Somalia

Kenya

Sudan

Somalia

400 0 400 800 Kilometers

#S Under construction dams%U Existing Dams

N

* Construction to begin soon

Dams Under ConstructionKoga Dam

• Basin : Blue Nile• Purpose: Irrigation Ca. 7000ha• Project includes integrated WSM

on 22,000ha• Dam height 21m• Embankment Dam• Reservoir storage ~ • Reservoir area ~ 1400 ha• Financed by AfDB

Dams under construction cont’d

• Basin : Awash• Multipurpose dam• Dam ht. 90m• Embankment Dam• Irrigation 20 – 30,000 ha of

sugar cane• Hydropower – under study• Problems due to faults and

artesian hot spring at dam foundation

• Financed by ETH. Gov’t

Kesem Dam

Dams under construction Cont’d

• Basin : Awash• Irrigation dam• Dam ht. 40m• Embankment Dam• Reservoir storage 1.86 BCM• Irrigation 60,000 ha of sugar

cane• Financed by Eth. Gov’t• When Kesem & Tendaho

Projects start operation – sugar production will increase fivefold

Tendaho Dam

Dams versus the EnvironmentImpact of Environment on Dams

• Reservoir sedimentation due to land degradation

• Nutrient accumulation

Impact of dams on the Environment

• Physical, biological and socio-economic impacts of dams

Koka Dam – Reservoir Sedimentation & Its Impacts (Eyasu E. 2003)

• Sediment deposited in the reservoir (over the past 40 years) = 494 Mm3

• Average annual sedimentation rate = 12 Mm3 or 2115 t/km2 • Loss of storage volume from designed storage capacity:

a) Designed storage capacity = 1,667 Mm3b) Current storage volume = 1,186 Mm3c) Loss of storage volume = 481 Mm3

• • • Remedial measures to reduce reservoir siltation• • Sediment removal options• Flushing: Unacceptable downstream impacts• Dredging Cost: Very expensive US $ 8 – 9 per m3 This means US$3.9 Billion for Koka dam• Disposal • Other Engineering solutions• Raising the dam• Interbasin transfer of the river flow• This will have serious social & environmental problems• Catchment protection• Structural and Vegetative measures• Most practical and cost effective solution• • Economic incentives to farmers• To encourage conservation-based farming

• Loss of power generation capacity:c) Energy equivalent of per m3 of water = 0.266 KWhd) Energy equivalent of 481 Mm3 of lost volume = 128 Million KWhe) Price per KWh = 0.473 Eth. Birrf) Total money value of lost power generation capacity:128 X 106 KWh X 0.473 Eth. Birr/KWh = 60.5 Million Birr or 7.5 Million USD

Other secondary but important impacts are:• loss of Reservoir capacity to regulate water supply for irrigation

and flood control services downstream.

• which in turn resulted in breakage of dikes and flooding of sugar plants and down stream towns.

• Severe flood hazards have become a common phenomenon in the downstream of Awash basin.

Experience from Gilgel Gibe Dam• found on the Gibe River in the Omo-

Gibe River basin• built for the purpose of hydropower.• Rock fill dam with bituminous

upstream facing• Maximum height of 41m with a total

storage capacity of 91 MCM• The generation capacity of the plant

is 184 MW (three 61.3MW units); • Firm capacity 640GWH• started in 1997• commissioned in 2004. • financed by the World Bank & the

Government of Ethiopia.

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OROMIA

Afar

Somali Region

AMHARA

TIGRAY

SOUTHERN REGION

BENISHANGUL-GUM

GAMBELLA

DIRE DAWA

HARARIADDIS ABEBA

Sudan Djibouti

Eritrea

Somalia

Kenya

Sudan

Somalia

400 0 400 800 Kilometers

#S Under construction dams%U Existing Dams

N

• Category "A" Environmental Impact Classification due to some major environmental and social issues

• the involuntary resettlement of 706 households (ca. 5,000 people);

• loss of 300 ha of riparian forest for wildlife• altered downstream flow of 16 km of the Gilgel Gibe river, • and increased habitat for water-borne disease vectors• resettlement was completed two years ahead of

impounding, 4 years ahead of completion of civil works.• resettlement cost was estimated at US$4,600 per

household

post-resettlement assessments carried out in Dec. 2005• the resettlement program was indeed carried out according to

the RAP in line with World Bank Guidelines• Positive Indicators:

– the quality of the new houses is superior to the old houses– walking distance to health centers as well as schools has

been considerably reduced• Underperformance indicators:

– the average yield level for all types of crops has been reduced by 54%,

– the number of livestock owned by the resettled household has been reduce by 72%

– social infrastructure such as schools, health clinics, and water points are in poor condition and in need of immediate maintenance

• In spite of some underperformance, all indications point to the fact that the PAPs are better off now than prior to the resettlement effort

• This has shown that with proper planning and implementation, it is possible to develop strong resettlement efforts

• In resettlement matters, this project was the first one in the history of Ethiopia to carry a constitutional resettlement under the New Constitution

• The Bank has also acknowledged (June 2001) the project as good practice.

Conclusions Drawn from The Post-Resettlement Assessment

Planned dams• At present, the feasibility study and detail design of at least

12 large dams for irrigation development in four river basins is underway

• When implemented, these dams will have a potential to irrigate well over 150,000 ha

• MoWR has planned at least 20 power projects involving large dams with an aggregated power generation capacity of over 10000 MW which are at various levels of study

• Four of these projects involve the construction of large dams on the main Blue Nile River.

• When implemented, these projects will enable Ethiopia to export environmentally friendly power to its neighbors and Nile Basin riparian countries.

Regional projects under NBI• Projects accepted by the NBI Council of

Ministers consist of 4 hydropower and 4 irrigation projects

Total 176,000 ha Total 2481 MW

Involves 6 large dams Involves 7 large dams

Dams in Lake Tana Sub-basin

IN CONCLUSION• Ethiopia’s Path to Survival & Development

Depends to a large extent on• Developing available resources (Land, Water &

Labour)Which requires

• Investing in Water Infrastructurewhere

• Dams are at the heart of this investmentHowever

• Good governance of dams is a pre-requisite for sustainable development