Environmental and Social Impact Assessment - Gibe III

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Gibe III – Environmental and Social Impact Assessment 300 ENV R CS 002 C - A9003099 Similar ecological changes are anticipated at all sites of the Omo river - excessive growth of algae and macrophytes, establishment of vectors such as mosquitoes and snails and altered food webs in the standing reservoir. Previous ESIA studies done at the Gilgel Gibe I and II and other tributaries upstream document the presence of benthic communities such as Ephemeroptera (Mayflies such as Afronurus sp., Baetis sp., Centroptilium sp., Hydropsyche sp.), chironomid (phantom midges) nymphs and Tipulidae (horseflies). 5.2.3.2 Habitat Integrity Rating Rapid habitat assessment was used at the site and the score for each component was assessed out of 10 points. Category and interpretation was done according to EPA classification (1999). Table 5.33 and Table 5.34 give the criteria and the score of the habitat components considered for the ecological integrity assessment at the dam site and at Omo Bridge respectively. Dam site: The dam site is a largely natural system with very few modifications (mostly due to initiated project activities at the site). The ecosystem functions are unimpaired at the moment. The damming and operation facilities will definitely change this situation in the future. Table 5.33: Habitat integrity rating for the Omo dam site downstream Substrate quality and quantity Sediment deposition Channel alteration (modification) Bank stability (vegetation protection) Riparian vegetation zone width Frequency of riffles/bends Manure/dung wastes Nutrient enrichment Water quality (appearance) Exotic plants and animals introduction Habitat component (instream and riparian) Score (out of 10) Category and Interpretation Largely natural, few modifications, unchanged ecosystem functions 9 5 9 10 10 10 8 6 4 10 Total habitat score 81% Omo Bridge: This site appears more impacted than the other upstream and downstream sites on the Omo River. Both these sites are not conducive to human encroachment and still, the habitat category indicates that although some changes of the natural habitats and biota may have occurred, the basic ecosystem functions are still predominantly unchanged. Habitat integrity rating at the Omo bridge site is about 80% (Table 5.34) and this indicates that both sites (Dam site and Omo bridge) are relatively un-impacted by human activities at the moment. CESI SpA - Mid-Day International Consulting Engineers Page 131 B
Gibe III – Environmental and Social Impact Assessment 300 ENV R CS 002 C - A9003099 Table 5.34: Habitat integrity rating for the Omo bridge site Habitat component (instream and riparian) score (out of 10) Substrate quality and quantity Sediment deposition Channel alteration (modification) Bank stability (vegetation protection) Riparian vegetation zone width Frequency of riffles/bends Manure/dung wastes Nutrient enrichment Water quality (appearance and nutrients) Exotic plants and animals introduction Category and Interpretation Largely natural, few modifications, unchanged ecosystem functions 5.2.4 Fishery Resources 7 5 9 9 10 10 9 6 5 10 Total habitat score 80 % The fishery resources assessment was carried out with the following objectives: • Assess and document the current situation with regard to the diversity of the fish fauna in the Omo River system. • Evaluate the positive/negative impacts of Gibe III Hydropower project dam construction across the River Omo on the fish species diversity and fish stocks and recommend possible mitigation measures that may be required. • Assess and recommend the sustainable use, development and management of the reservoir fishery that would be created as a result of the dam construction. Published papers and unpublished reports of fish taxonomy studies in the Rivers Gibe, Gojeb and Omo were covered in the literature review. The project area was visited for primary data collection and direct observation. Fish samples were collected by experimental fishing using different mesh size gill nets, where possible, along the accessible parts of the river in the upper reaches of the proposed dam site. The study sites were at the bridge close to Bele town, Kindo Koyisha Wereda, at site near Modula town, Timbaro wereda (upstream from Bele) and at the Dam site. Information regarding fishing activities and fish types encountered were collected from government development offices and local communities in the visited areas. Traditional fishermen were interviewed on the variety and abundance of the fish stocks in the river. 5.2.4.1 Description of the Riverine Environment/Fish Habitat The River Omo is one of Ethiopia’s major perennial rivers in the south–west of the country. The river has several large tributaries like the Gojeb and Gibe Rivers in the north. In fact these are the two rivers that converge and form the River Omo at the confluence in the south-western highlands. The Gojeb River drains the western highlands and the Gibe River the highlands of the mid-west before they join to form the River Omo, that carries the huge amount of water southwards, draining into the lake Turkana and contributing over 90% of the river water inflow into the lake with all the allocthonous nutrient supply (Lake Turkana study, 1975). It also provides the breeding ground for many migratory fish species from the lake. CESI SpA - Mid-Day International Consulting Engineers Page 132 B
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