Environmental and Social Impact Assessment - Gibe III

Gibe III – Environmental and Social Impact Assessment 300 ENV R CS 002 C - A9003099
3.2 General layout
The Gibe III hydropower plant includes the following main structures:
• a Roller Compacted Concrete gravity dam with spillway and middle outlets
• three hydraulic tunnels and two cofferdams for the river diversion
• two hydraulic tunnels, penstocks and surge shafts for the power waterways
• an outdoor Power House, equipped with No. 10 Francis turbines, and a switchyard
• access roads
The table below summarizes the main characteristics of the project (ref. Level 1 Design, 2008) illustrated in
the following paragraphs.
HYDROLOGY
Catchment area (km 2 ) 34150
Average annual runoff (m 3 /sec) 438.2
(Mm 3 /year) 13820
10,000 years return peak flood (m 3 /sec) 10600
Probable maximum flood (m 3 /sec) 18660
Mean annual sediment yield (Mm 3 /year) 18.3
RESERVOIR
Extreme flood level (PMF level) (m a.s.l.) 892.5
Max/Normal O.L. (max. ret. level) (m a.s.l.) 892
Minimum O.L. (m a.s.l.) 800
Total storage (Mm 3 ) 14700
Live storage (max. regulated capacity) (Mm 3 ) 11750
Surface area at max o.l. (km 2 ) 211
RCC DAM
Crest el. (m a.s.l.) 896
Crest length (m) 610
Max. height above river bed (m) 223
Max. height above foundations (m) 243
Basic triangle opening 0.75
RIVER DIVERSION
Diversion tunnels (No, D) (#, m) 3, 7/13.5
Cofferdam crest el. (m a.s.l.) 720
Design flood (m 3 /sec) 5200
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