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Assessment of Water Availability from Superficial Reservoirs in Semi-Arid Northeast Brazil

Congress: 2008
Author(s): Pedro Henrique Augusto MEDEIROS; José Alexandre Moreira de FARIAS; Elano Lamartine Leão JOCA; Pedro Antônio MOLINAS


Keyword(s): water availability, reservoirs operation, semi-arid Brazil
AbstractThe climatic condition of Brazilian Semi-Arid Northeast, characterized by a much temporally variable rainfall regime and high evaporation rates, as well as the existence of shallow soils above crystalline bedrocks, results in the intermittency of most rivers. Therefore, the establishment of a water supply infrastructure was historically based on the construction of superficial reservoirs as a way to minimize the region’s water deficit problems. In fact, one of the current priorities of the Brazilian Federal Government consists of a water transboundary project, to diverge water from São Francisco River Basin to several strategic reservoirs in other watersheds in the semi-arid portion of the country. In this context, a detailed study of the current water offer from reservoirs in the Brazilian Northeast was carried out. In order to assess water yields associated to different reliability levels for each reservoir, for the macro-basins and for the entire system, a long-term hydrological simulation (1931-2004) was performed comprehending the operation of a system of reservoirs in a 250.000 km² area with a population of 18.850.000 habitants. The research comprehends 330 superficial reservoirs with a total storage capacity of 25.615 hm³, varying from <1 to 6.700 hm³ each reservoir. Simulations were carried out on a monthly basis, with inflows to the reservoirs obtained by hydrological simulation (rainfall-runoff models). The operation of the system was realized in an integrated way, i.e. outflow from one reservoir consists of inflow to the next reservoir downstream, and computational iteration was used to estimate maximum water withdrawal for a previously established reliability level. For the entire region, potential water yields from superficial reservoirs (including designed dams) was estimated in 240 m³/s and 153 m³/s with 90% and 99% reliability levels, respectively, which corresponds to per capita annual volumes of 401 m³/hab/year and 256 m³/hab/year. However, in some critical areas of Brazilian Northeast, per capita water availability can be as low as 44 m³/hab/year, as observed in the “Zona da Mata” and “Recife Metropolitan Region” basins for a 99% reliability level. The results of the study are extensively discussed and represent an important information tool for river basins management and water resources planning.
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