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 development on locations with sensitive habitat and wildlife resources. There will also be no effects on agricultural lands or to settlements. The following measures are recommended to be taken for the rehabilitation of the quarry areas: reestablishment of vegetation, restoration of natural water courses, avoidance of flooding of the excavated areas, achievement of stable slopes, and avoidance of features which would otherwise constitute a risk to health and safety or a source of environmental pollution. Quarry faces and excavations be made safe and buildings, plant, equipment and debris and stockpiles of material be removed from the areas. 7.6.2 Spoil and Waste Material Disposal Areas The construction of Gibe III hydropower scheme is expected to generate large quantities of spoil material and these spoils will need to be disposed off. The potential environmental concerns related to the spoil disposal include loss of productive land, grazing land and natural vegetation, interference with natural drainage, increase in erosion and sediment deposition, increase in slope instability and visual alternation of landscapes quality. There is a possibility of soil erosion and adverse aesthetic impact if spoils are not properly placed and rehabilitated Spoil disposal activities should be planned to be executed in a manner which minimizes these potential damage to environment and maintains stability during all stages of placement and when the site is in its final form. For disposal of waste soil and rock, both the placement of the materials and the rehabilitation methods are important. Therefore, to mitigate and minimize the impacts of spoil disposal on the local environment the following mitigation measures are recommended: • Locate spoil disposal sites as much as possible in unproductive land and outside flood conveyance areas with preference being given to backfilling quarry and borrow sites which have been developed by the contracted. However, spoil disposal sites to be located in flood storage areas only in those cases where the studies have determined that the impact is not significant; • Locate disposal sites in areas of land, which, prior to the commencement of the construction works, were not used for agricultural purposes or designated for agricultural purposes; • For each disposal site incorporate the most appropriate stabilization techniques; • Placement and rehabilitation of spoils and waste be executed with sensitivity to topographic and visual aspects and in such a way that the disposal areas enhance rather than detract visual quality of the route. After the completion of construction, most of the disturbed areas will require some recontouring to encourage natural drainage pattern, improve slope stability, and mimic the original shape of the slope. The amount of grading and re-contouring will depend heavily on the type of disturbance and the quantity of material deposited. Re-contouring will also consider drainage such that water neither pools on the site, nor flows through with sufficient velocity to erode soils and overburden; • Adopt restoration measures to reinstate the site for its previous use. For this, soil excavated during construction be stockpiled separately and used for landscaping and restoration of work areas. Topsoil stockpiles are deep ripped to provide for moisture retention and re-growth of local trees and bushes. However, it is also recommended to prepare a site environmental management plan for each proposed spoil disposal sites and this plan should include environmental studies and consultation to assess the potential impacts of each proposed spoil disposal sites and the recommend site specific management measures. The CESI SpA - Mid-Day International Consulting Engineers Page 235
Gibe III – Environmental and Social Impact Assessment 300 ENV R CS 002 C - A9003099 plan should detail the locations, designs and environmental safeguards, etc. The additional investigations include the following: • Contoured site plan showing the location, maximum area to be used for spoil disposal area; • Field inspection of sites and geomorphologic studies to determine if any proposed spoil disposal areas are located in floodway zones of the flood plain; • Land use impact assessment, with attention to those areas of land used and designated for agricultural purposes; and • Consultations with the communities, if any, living close to the proposed spoil disposal sites which may be affected. The findings and results of the above activities are used to prepare a Spoil Disposal and Management Plan as a sub-plan under the Contractor’s Site Environmental Management Plan. The Owner shall review the proposed plan and may require modifications to the proposals. Therefore, in accordance with the comments provided by the Owner, the Contractor shall finalize site selection or design. 7.7 Cumulative Impact Assessment 7.7.1 Background The Omo-Gibe basin is one of the significant surface water resources of Ethiopia. The Gibe cascade project is one of the most attractive potential hydroelectric developments in the country and it has been selected by EEPCO as one of its key hydroelectric development areas. In subsequent studies various several options were considered for the Gibe river development plan and as a result hydro-projects in series along the main Gibe river in a cascade style were proposed. The general layout of the Gibe cascade plan is shown in Figure 7.6. These four projects are shown in the longitudinal profile in Figure 7.7from upstream to downstream. The Gibe III hydroelectric project is a third stage of the Gibe hydroelectric cascade scheme on the Greater Gibe (Omo) River which includes three other schemes. The Gibe III scheme is designed to generate 6,400 GWh of electricity with an installed capacity of 1,870 MW. Table 7.6 shows the list of existing and planned hydropower projects. CESI SpA - Mid-Day International Consulting Engineers Page 236
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