Environmental and Social Impact Assessment - Gibe III

Gibe III – Environmental and Social Impact Assessment 300 ENV R CS 002 C - A9003099
Runoff data
Another fundamental hydrological parameter was considered in the elaborations reported in the following
paragraphs: runoff. Unfortunately not as many gauging stations as rainfall ones are present in the basin under
investigation, but few of them at located at key sites, thus assuming particular importance. Gauging stations
are mainly maintained by the Hydrology Department of the Ethiopian Water Resources Authority which
processes and archives data. The longest record is that of the Abelti station on the Gibe River, starting in
1963.
The following table reports the available hydrometric data:
Station
Table 5.11: Runoff stations of the EWRA and periods of observation
Region Basin Longitude Latitude
Location Catchment Observation
Elevation
masl
CESI SpA - Mid-Day International Consulting Engineers Page 102
Area
km 2
Mean
elevation m asl
Max
elevation
m asl
1 GIBE nr LIMU
GENET
GIBE 36°56' 08°06' - 533 - - 14 84-04
SEKA GIBE 36°45 07°36' - 280 - - 24 80-03
3 GIBE river nr.
ABELTI
KEFA GIBE 37°35' 08°14' 1100 15746 2030 3386 40 63-04
4 BIDRU AWANA
nr. SEKORU
KEFA GIBE 37°24' 07°55' 1500 41 2262 2536 20 81-03
5 BULBULE nr.
SERBO
KEFA GIBE 37°02' 07°34' 1700 301 1977 2837 8 86-93
6 MEGECHA nr.
GUBRIE
KEFA GIBE 37°28' 08°11' 1500 286 1750 2000 32 67-04
7 GILGEL GIBE nr.
ASENDABO
KEFA GIBE 37°11' 07°45' 1650 2966 2200 3359 27 67-93
8 REBU river nr.
WOLKITIE
SHEWA GIBE 37°47' 08°21' 1500 480 2067 2882 23 67-89
9 WABI nr.
WOLKITIE
SHEWA GIBE 37°46' 08°15' 1700 1866 2487 3719 38 67-04
10 GOGHEB river nr.
ENDIBIR
SHEWA GIBE 37°54' 08°06' - 190 - - 32 67-99
11 GOJEB nr.
SHEBE
GOJEB 36°23' 07°25' 1080 3356 1976 3358 36 70-05
12 GECHA nr.
BONGA
36°13' 07°17' - 175 - - 23 82-04
13 SHETA nr.
BONGA
36°14' 07°17' - 191 - - 25 80-04
It should be noted that for the station of Asendabo the runoff time series was derived from the Gilgel Gibe
Hydroelectric Project, Hydrological Report, and November 1995. Most of the stations show a sufficiently
long period of record. In some cases of particular importance (Abelti and Wabi), as will be shown in the
following paragraphs, the infilling of missing data was necessary to obtain 40 years long time series. The
Serbo station, with an 6 years long period of record, was excluded from the elaborations. As it can be seen
the Abelti station on the Gibe River has particular importance as it represents alone a considerable
percentage of the entire area under investigation (almost 46%). Most of the gauging stations listed in Tab. 3
are located upstream Abelti. Also the Wolkite station on the Wabi River is of great importance, as it covers
an area, downstream Abelti, of 5% of the total area. The same consideration can be made for the Shebe
gauging station on the Gojeb River (10% of the total area), but to enlarge the area covered by this station the
runoff time series at the Gojeb Dam Site OM19 location was considered (15% of the total area), as reported
in the Gojeb Medium Hydropower Project, Pre-Feasibility Study, Vol.1 - Executive Summary, Vol. 3 -
Annex A, Hydrology, Oct 1996. The data reported for OM19 were suitably infilled for the years following
1996 according to the Shebe runoff, following the deterministic correlation existing between these two sites.
n.
year
Period