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Potential & Experience of Dams in Ethiopia

Potential & Experience of Dams in Ethiopia. Solomon B. Gebre Project Manger Design of (four) dams in Lake Tana Sub-basin Project. Outline of the Presentation. Country Background Water Resources Potential & Status of Development Irrigation Hydropower Water Supply Existing dams

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Potential & Experience of Dams in Ethiopia

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  1. Potential & Experience of Dams in Ethiopia Solomon B. Gebre Project Manger Design of (four) dams in Lake Tana Sub-basin Project

  2. 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

  3. 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.

  4. 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 %

  5. 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

  6. 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 %

  7. 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

  8. Existing dams 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 FAO - Aquastat Database 2006 10 Large dams Author’s compilation from various sources > 50 Large dams ( According to ICOLD Classification (2003))

  9. Important Large Dams in Ethiopia 13 Chara Chara Blue Nile 1996 9 9,100,000 Regulation * Inoperative since 1970 ** Only the dam construction has been completed CM: Cubic Meters HP-Hydropower, IRR-Irrigation WS-Water Supply, FP-Flood Protection

  10. 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

  11. 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%).

  12. Damaged spillway (Hydraulic failure) • Syphon used to offtake water b/c of clogging of the intake

  13. Common Problems encountered in Microdams Common 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 aspects Problems identified should give a good lesson for future building of similar dams.

  14. Dams under construction * Construction to begin soon

  15. Dams Under Construction Koga 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

  16. Dams under construction cont’d Kesem Dam • 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

  17. Dams under construction Cont’d Tendaho Dam • 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

  18. Dams versus the Environment Impact of Environment on Dams Impact of dams on the Environment Physical, biological and socio-economic impacts of dams • Reservoir sedimentation due to land degradation • Nutrient accumulation

  19. 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 Mm3 b) Current storage volume = 1,186 Mm3 c) 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

  20. • Loss of power generation capacity: c) Energy equivalent of per m3 of water = 0.266 KWh d) Energy equivalent of 481 Mm3 of lost volume = 128 Million KWh e) Price per KWh = 0.473 Eth. Birr f) 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.

  21. 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.

  22. 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

  23. 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

  24. Conclusions Drawn from The Post-Resettlement Assessment • 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.

  25. 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.

  26. Total 176,000 ha Total 2481 MW Involves 6 large dams Involves 7 large dams Regional projects under NBI • Projects accepted by the NBI Council of Ministers consist of 4 hydropower and 4 irrigation projects

  27. Dams in Lake Tana Sub-basin

  28. 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 Infrastructure where • Dams are at the heart of this investment However • Good governance of dams is a pre-requisite for sustainable development

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