Environmental and Social Impact Assessment - Gibe III

Gibe III – Environmental and Social Impact Assessment 300 ENV R CS 002 C - A9003099
b) Shebe station on the Gojeb River
Particular interest lies in the Shebe station on the Gojeb River as it drains an area not covered by the Abelti
hydrometric station on the Gibe River. The data used in the elaborations were those obtained in the Gojeb
Medium Hydropower Project, Pre-Feasibility Study, Vol.1 - Executive Summary, Vol. 3 - Annex A,
Hydrology, Oct 1996. In that study this series was integrated and extended from the OGMP Shebe record
suitably adjusted, obtaining a 40 years long series (1955-1994). The series was finally completed with the
more recent observation (1995-2003) available.
The addition of the record from 1995 to 2003 has the effect of slightly increasing the mean runoff as some of
those years were particularly wet. Figure 9 shows the yearly runoff for the total record period. A 5 years
moving average reveals the increasing trend of runoff during for the 1994 upwards with the only exception
of 2002 and 2003.
Figure 5.7: Annual runoff for the Shebe station on the Gojeb River
Tab. 6 and Tab. 7 of [200 HYD R SP 001 A - Hydrological report, Vol 1] report the runoff series for the
Shebe station in m 3 /s and Mm 3 respectively. The mean runoff is 60.05 m 3 /s. The yearly runoff is almost 1894
Mm 3 . Even in this case the monthly runoff follows the typical variability of rainfall with a dry and a wet
season, even if the behaviour is smoother than the Abelti’s one for with the increasing and decreasing of
runoff is steeper. The highest runoff is reached in August with a mean monthly flow of 147.9 m 3 /s.
c) Dam site OM19 on the Gojeb River
To enlarge the area covered by the Shebe hydrometric station, which drains an extension equal to 10% of the
total project area, the runoff time series at the Dam Site OM19 was considered (15% of the total area).
To obtain this series the data reported in the Gojeb Medium Hydropower Project, Pre-Feasibility Study,
Vol.1 - Executive Summary, Vol. 3 - Annex A, Hydrology, Oct 1996 were considered. The data reported for
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