Environmental and Social Impact Assessment - Gibe III

Gibe III – Environmental and Social Impact Assessment 300 ENV R CS 002 C - A9003099
5.2.3 Aquatic Ecology
The consultant has carried out an aquatic ecology assessment and the activities include the following:
• Inventoried the composition of the riverine and riparian fauna (invertebrates, plankton, benthos, etc)
of the Omo river at three critical points along the future reservoir area - Omo bridge, dam site and
confluence of Gojeb-Gibe rivers;
• Made a comprehensive habitat integrity assessment of the Omo river at two sites;
• Assessed the potential impact of the creation of a reservoir on the riparian and riverine fauna, disease
vectors, rare biota, etc.
Available literature was reviewed for previous studies done on aquatic communities of invertebrates in the
Omo basin. The major references consulted were studies conducted at the Gojeb, Gibe and Omo rivers by
Golubstov and Mina (2003) which summarizes the scientific results of the Joint Ethiopian-Russian
Biological Expedition (JERBE) and ESIA reports of Gilgel Gibe I, and Gojeb Hydropower Projects.
Rapid habitat integrity assessment was made at the Omo bridge and confluence sites using the criteria
developed for South African rivers by Kleynhams (1996) and the Rapid Bioassessment Protocol (RBP) of
EPA (1999). A few criteria were modified to suit the local conditions, such as pollution by dung and human
wastes. Weights are assigned to different in-stream and riparian characters of the river reach such as flow
modification, exotic macrophytes, bank erosion and vegetation cover. The ten most important habitat
components are considered for analysis with each component having a score of 10 points, adding up to a
total of 100 percent. A range of score points describe the habitat integrity status of the river. High scores
describe unimpaired conditions and low percentages apply to impacted rivers.
5.2.3.1 Riparian fauna - Omo bridge site
Table 5.32 lists some of the dominant riparian macro-invertebrates identified at the Omo Bridge.
Grasshoppers and crickets (Order Orthoptera) made up the most abundant group, in terms of biomass, and
butterflies in terms of diversity. Butterfly species such as Colotis and Odonata such as dragonflies were
noted on the bank. Observations of the riparian fauna indicate the predominance of grasshoppers (Acrididae
and Oxydae), damselflies, beetles and Hemipteran bugs.
Table 5.32: Riparian macro-invertebrates at the Omo bridge
Common name Scientific names Relative abundance
Meadow grasshoppers
Field crickets
Butterflies
Preying mantis
Forest damselflies
Blue damselfly
Beetles
Unidentified bugs
Acrida sp.
Oxya sp.
Gryllus sp.
Colotis sp.
Pieris sp.
Delais sp.
Belenois sp.
Pareronia sp.
Order Dictoptera
Fam. Platycnemidae
Enallagma sp.
Several species
Several species
Note: + indicates common, ++ very common and +++ highly abundant
CESI SpA - Mid-Day International Consulting Engineers Page 130
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