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 consequences of the flooded biomass (and of water quality in general) is the ratio of the surface area flooded (indicating the volume of biomass) and the annual flow discharged (indicating the dilution potential). Regarding the GIBE III HPP, on the basis of the land cover assessment carried out as part of this study, it is estimated that the Gibe III reservoir will submerge an estimated 17,158 ha of deciduous woodland and 1,839 ha of riparian vegetation. Although the vegetation is more of woodland, a conservative estimate of the biomass indicates that 211,043 m 3 is woodland biomass and 194,015 m 3 of forest biomass would be inundated by the water at full supply level, with a really low ratio of less then 10t/ha. The annual volume of water used and released downstream is about 11,750 Mm 3 that is in the range of the average annual runoffs, about 13,800 Mm 3 : so, the annual recharge of the reservoir is important. Consequently the impact of the submerged biomass, due to the low biomass/area ratio and to the rapid turnover time of the water in the reservoir, on the water quality of the reservoir, can be considered non significant. 7.2.6.3 Water Pollution Construction activities may impact water quality and the major sources of construction-related impacts on water quality will be from erosion of disturbed areas required for the construction activities (construction sites, concrete batch plants, material storage areas, vehicle maintenance areas, spoil disposal areas), from wastewater discharge at the construction camps, and from contaminated water (oil, grease, petrochemicals, cement, chemicals). All cement-contaminated wastewater from cleaning or mixing is considered toxic, and should be prevented from entering any watercourse without proper treatment. All construction related activates should not pollute water ways, in accordance with applicable standards. Therefore, the contractor is required to carryout construction activities as much as possible by methods that will prevent entrance or accidental spillage of pollutants and wastes into flowing and dry water courses and groundwater resources. 7.2.7 Landscape The impact on landscape due to the project will be significant: a total modification of the middle Omo valley characteristics is expected. The main potential adverse impacts on landscape will be related to the construction works: • the dam (231 m high and 580 m long); • the 40 km long temporary access roads. Both roads R1 and L1 will be constructed in steep slopes areas, therefore the main potential adverse impact associated with the construction of the access roads will be slope stability, landscape and soil erosion; • the 80 km long permanent relocation road; • the quarry sites and the borrow areas; • the camps; • the excavated disposal areas; • the Power House; • the substation. CESI SpA - Mid-Day International Consulting Engineers Page 201
Gibe III – Environmental and Social Impact Assessment 300 ENV R CS 002 C - A9003099 Some attention must be paid to reduce the visibility of the project works. The impacts will be reduced, minimized and/or mitigated by properly managing construction activities (roads, camps, etc..) and recovering abandoned construction areas such as quarry sites or controlling (during waste disposal activities) and recuperating (at the end of dumping the excavated material) the waste disposal areas. The excavated materials must be properly disposed in order to prevent their instability, and should be vegetated for reducing on one side the erosion by wind and rain and on the other side to reduce the visibility of the disposal area. The construction roads no more necessary and not useful to local population and will be dismantled at the end of the works. The visual impact of the dam and of the reservoir, it is not negligible. The dam represents a big barrier along the present river course and the existing valley landscape. However its visual impact can be considered slightly negative, considering that its visibility upstream it is of minor magnitude. The construction of the BF rockfill dam would determine the excavation of a large amount of material (about 22 millions of m 3 ) and the opening of numerous quarries and also some disposal areas, while the selected RCC dam will involve much less material (about 6 million m 3 ) and less excavation areas, producing a minor impact on landscape setting. The reservoir will have a big landscape impact. The presence of a basin along the Omo valley will completely change its visual characteristics. This impact can be considered on one hand negative because it will create a man-made scenery in a presently natural landscape; on the other hand something positive, because a lake can be considered a new beautiful panorama, that can be seen from the surrounding highlands, increasing landscape attractiveness. 7.3 Impacts on Biological Environment 7.3.1 Forest and Natural Vegetation There will be impacts on the natural vegetation during the construction phase of the Gibe III scheme and these impacts will be either direct impacts related to the physical clearance, or disturbance and/or indirect impacts resulting from increased population and improved access. The major unavoidable direct impacts which results from implementation of this scheme is the flooding and clearing of natural vegetation for the operation of quarry and borrow areas, construction of access roads, construction of temporary campsites, operators dwelling, etc. On the basis of the land cover assessment carried out as part of this study, it is estimated that the Gibe III reservoir will submerge an estimated 17,158 ha of deciduous woodland and 1,839 ha of riparian vegetation. The vegetation that will be impacted as compared to the available resources in the affected Weredas is indicated in Table 7.1. This loss would not bring about marked differences in the carrying capacity as it represents only 5.0% and 1.0% of the available woodland and riparian vegetation in the affected weredas respectively. CESI SpA - Mid-Day International Consulting Engineers Page 202
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