The unprecedented socio-economic development of Ethiopia is becoming a vibrant pushing factor for the ever-increasing electric power demand. Since the demand for and the supply of electric energy is not growing in a corresponding manner, Ethiopian government has made extensive endeavors to alleviate the problem; and thereby has launched various hydroelectric power projects with some in their finishing phases like Tekeze (300MW), Gilgel Gibe II(420MW), Belese (460MW), Gibe III (1870MW),Fincha-Amerti-nesh (100MW) and some to start soon are Chemoga Yeda(280 MW), wind Project (120MW) and projects to start soon are Gibe IV (1472MW), Gibe V (560MW),and Halele-Werabesa(420 MW). Above all, utilization of the abundantly available water resource in generating electric power has given due emphasis. Being one of the monster hydropower projects with a generating capacity of 1,870MW, Gibe III Hydroelectric Project becomes a focus point for the government as well as the external donors.
GIBE III HYDROELECTRIC PROJECT
The objective of the project is to enhance the hydropower generation capacity of the country through developing a plant with a capacity of 1870 MW and with an annual energy production of 6,500 GWh, This in turn is expected to raise the present 800 MW installed capacity of the country by 234 percent.
Moreover, the project has the aim of ensuring exportation of power to the neighboring countries through regional Interconnection Transmission System so that Ethiopia will be in a place of gaining hard currency through sells of electricity.
Turnkey Contract Agreement adopted for the Gibe III Hydroelectric Project was issued by the Federation International Des Ingenieurs Conseils (FIDIC). The Agreement was signed between the Ethiopian Electric Power Corporation (EEPCo) and Salini Costruttori S.p.A of Italy (Contractor) on 19 th July 2006. Amendment was also made on the Contract Agreement on April 22, 2008 since changes happened to the scope of the work.
As far as the quality inspection is concerned, the quality control of the design and construction is carried out by a Joint Venture Consultant- ELC Electrocosult (Italy)& Coyne et Bellier(France) is hired by EEPCo as Employer representative.
Regarding the structure, the basic design of May 2006 foresaw a Rockfill Dam with a large spillway structure on the right bank and the power intakes, headrace tunnels, penstocks/manifolds, surge shafts, powerhouse, and switchyard on the left bank. However, due to difficulties with obtaining proper and sufficient insurance coverage for the Rockfill Dam, the dam has been changed to Roller Compacted Concrete (RCC).
The Gibe III hydroelectric Project which is anticipated to be completed on July 2013 has a construction cost of 1,470 Million Euro (20.7 Billion Ethiopian Birr).
The Gibe III Hydroelectric Project is located in the Southern Nations Nationalities & Peoples Regional State in Wolayta and Dawro Zones at about 470 km south west of Addis Ababa on the road via shashemene. It is situated along the lower course of the Omo River, some 155 km downstream of the Gilgel Gibe II Powerhouse.
GENERAL FEATURES OF THE PROJECT
The Gibe III Hydroelectric Project has the following major components:
Hydrology: The Gibe III catchment area is divided into two sections (monitored and unmonitored). The monitored section, approximately 66 percent of the total area, has 3 measurement stations and 40 years of flow records. The three stations are at;
a) The Gibe river near Abelti (the most important station)
b)Gojeb near Shebe, and
c) Wabi near Wolkitie. Run-off calculations made based on 40 years of reliable records.
For the section which is not monitored, approximately 33 percent of the total area, there are no direct measurements of flow available. Run-off is calculation made based on the rainfall data.
The catchment area for the project is 34,150 km2 with an average annual rainfall of 407mm. The average annual run-off estimated is 438 m3 /s and the total annual run-off is 13,876 million cubic meters .
Geology : The Gibe III Project site is located in the Jima volcanic formation, a thick succession of basalts and sialic rocks, divided into Jima Basalts and Jima Rhyolites. In the project area, the formation is constituted mainly by trachytes, basalts and pyroclastics.
Temporary and Permanent Facilities: Three temporary camps are provided on the right bank of the river, for the Employer/Employer's Representative staffs, the Contractor's expatriate staffs, and for the Workers. The Employer/Employer's Representative Camp includes accommodation, offices, canteen, laundry, and club. The Contractor's camp is similar but includes main clinic. The Contractor's offices are located elsewhere in a separate area on the right bank where other facilities such as the plant and equipment workshop, stores, and laboratory, are situated. The Workers' camp includes accommodation, canteens, clinic, and police station. Permanent camp will be constructeded on the left bank of the river.
Roads: The project includes construction of new permanent and temporary roads and rehabilitation of existing ones. The road from Welaita Sodo town to Bele via Chida town is a federal highway road which needs periodical rehabilitation .
Roller Compacted Concrete (RCC) Dam & Reservoir: The Roller Compacted Concrete Dam has a maximum height of 243 m and 610m of crest length. The dam will create a reservoir with total storage capacity of 14,700 million m3 (with live storage of 11,750 million m3 and dead storage of 2,950 million m3 ). The reservoir area covered by water is about 210 km 2 .
The dam has the following general features:
- crest level 896m
- total crest length 610m
- maximum flood level (PMF) 893m
- maximum/normal operating level 892m
- minimum operating level 800m
- overflow spillway level 873m
- overflow spillway length 108m
- maximum height above river bed 223m
- maximum height above foundation 243m
- basic triangle opening 0.75m
Diversion Tunnels: Two diversion tunnels of 13 m diameter and a smaller 7 m diameter diversion tunnel, located on the right bank of the river. The river diversion will be effected by a conventional layout of tunnels and cofferdams and is designed to pass a flood of 5,200m 3 /s, which is approximately a 30 years return period flood event.
Cofferdams: An upstream pre-cofferdam, upstream main cofferdam and a downstream cofferdam are envisaged. It will be useful to create a water head adequate to the large flow required to divert the water for the entire period of dam construction.
Power Tunnels: There are two power waterways comprising intakes, power tunnels, surge shafts, penstocks and manifolds, each branching into 5 turbine inlets are envisaged.
Powerhouse: A Powerhouse that is located at the toe of the dam on the left abutment, housing 10 Francis turbines with a power of 187 MW each for a total installed capacity of 1,870MW, 5 transformers are also installed at the back of the plant, converting the voltage from 15 kV to 400 kV.
Switch Yard: The switch yard is located on the left side of the river, on a plateau above the powerhouse at elevation of 1,010m above sea level equipped with a double bus bar scheme from where the five three-phase 400kV transmission lines start.
Spillway: A gated spillway is designed to pass:
o The design flood = 10,600 m 3 /s(10,000 years return period)
o The exceptional flood = 18,000m 3 /s(Probable Maximum Flood)
Electro- Mechanical: is one of the major undertaking activities subcontracted via International Competitive Bidding. The scope of work mainly comprises the design, supply, erection, site testing and commissioning and test running of 10 vertical type Francis type hydraulic turbines with their digital frequency governors and inlet valves, 10 vertical axis synchronous generators with a rating of 220MVA( rated power factor of 0.85 and 187MW) with their excitation systems. It also includes intake, powerhouse and switchyard protection, control and monitoring; telephone and communication, lifting, cooling, drainage, emergency diesel generators, ventilation and air conditioning, fire protection and compressed air supply systems, 15 mono-phase, 15kV/400kV step up transformers each one with 147MVA rating (441MVA, three phase rating to accommodate the outputs from two generating units) transformers.
Hydro Mechanical: is the other subcontracted activity that through International Competitive Bidding. The scope of work includes intake steel structures and gates, draft tube, middle level, diversion tunnel, spill way and ecological discharge gates with all their electro mechanical accessories. Steel linings for the penstocks and draft tubes and part of the surge shafts will also be undertaken. Spare parts and special tools will also be supplied by the subcontractor.
Transmission Lines: The power generated at Gibe III will be transmitted with two double circuit tower transmission lines. Line 1 has a length of 50.3km and it carries double three phase circuits at 400kV from Gibe III switchyard to Wolyta Sodo substation. Line 2 has a length of 51km and it carries single three phase circuit at 400kV from Gibe III switchyard to Wolyta Sodo substation. The Contractor who undertakes the design and construction of the transmission lines is a private company called TBEA from China. The Contract price is 34,007, 472.41USD, of which 85 percent is to be paid in foreign currency. The financing is facilitated by the Contractor using supplier's credit scheme from the EXIM Bank of China. The local component of the transmission line's project cost will be covered by the Ethiopian Electric Power Corporation (EEPCo)
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