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Ethiopia - Irrigation and Drainage Project : environmental assessment (Vol. 4) : Environmental and social impact assessment of the Ribb Irrigation and Drainage Project : annexes (Inglês)

The Ethiopia Irrigation and Drainage Project (EIDP) will finance up to 20,000 ha of new irrigated agriculture land and complete detailed feasibility studies of up to 80,000 ha. The key environmental impacts related to the project include: (1) changes to the low flow regime may have significant negative impacts on downstream users, whether they abstract water (irrigation schemes, drinking supplies) or use the river for transportation or hydropower; (2) uncontrolled floods can cause tremendous damage and flood control is therefore often an added environmental benefit of reservoirs built to supply irrigation water; (3) a number of negative consequences of a falling water table are irreversible and difficult to compensate; (4) in the long-term, one of the most frequent problems of irrigation schemes is the rise in the local water-table (water logging) as a result of poor water distribution systems, poor main system management and archaic in-field irrigation practices; (5) the changing hydrological regime associated with irrigation schemes may alter the capacity of the environment to assimilate water soluble pollution; (6) use of both natural and chemical fertilizers may result in an excess of nutrients which can cause problems in water bodies and to health; (7) the increased use of agro-chemicals, needed to retain productivity under intensification, can introduce toxic elements that occur in fertilizers and pesticides; (8) areas with a flat topography or with water tables that have a low hydraulic gradient are at risk from salinization; (9) irrigation schemes can have ecological impacts, particularly in wetland areas affecting natural habitats; and (10) construction of dams can cause social, environmental, and economic problems by increasing the relocation of communities against their will and inducing watershed land degradation. The blockage of fish movements upstream can have a very significant and negative impact on fish biodiversity. Generally, the dam will have an impact on the migratory Labeobarbus species that spawn past the dam in upstream Ribb River and its tributaries and that will, in turn, have some impact on the fishery of Lake Tana. It could also have effect on the quantity of water that will be available for the migratory fishes as well as for inundating the wetlands. However, the impact will be insignificant and tolerable if the following major mitigation measures are taken: the time of the blocking of the dam should not coincide with the period of migration of the fishes (the main rainy season). The fish stock from Lake Tana is sharply declining even before the construction of the dam. It is, therefore, important to rehabilitate the stock using artificial propagation.

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