Environmental and Social Impact Assessment - Gibe III

Gibe III – Environmental and Social Impact Assessment 300 ENV R CS 002 C - A9003099
This scheme (stage 1) will be operating during the dry season while the diversion works are completed.
At the beginning of the wet season the complete river diversion will be achieved by means of the main
cofferdams on the Omo river and the three diversion tunnels.
The water levels on the diversion tunnels and at the cofferdam are illustrated in the following graph.
3.6.2 Diversion tunnels
Figure 3.4: Tunnels rating curve
The three quite parallel diversion tunnels are located on the right abutment of the dam.
The inlets are located in the Tsida valley, about 350 m from the Omo river junction. The Omo river flows
will be therefore detoured on the inlet canal along the Tsida river bed.
The inlet canal basically includes the natural Tsida estuary for about 300 m and an excavated canal,
broadening the natural valley, about 200 m long.
The excavation carried out, varying the width in the range of 20-30 m, improves the feeding conditions of
the three tunnels.
The tunnel inlets are envisaged with a bell-mouth entrance in order to guide the flow until it is contracted to
the dimensions of the tunnel.
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