Losses of water by evaporation in regulatory reservoirs are one of the problems that exist in water resources management, the reliable estimates of evaporation in the reservoirs becoming essential not only in the planning and administration of the water resources but also in studies of environmental impact. The objective of this paper was to estimate the net evaporation in the Sobradinho dam through the Class A tank methodology and the Linacre (1993), Kohler et al. (1955) and CRLE models, as well as to verify the impacts on the flow conditions due to the construction of the reservoir. The results showed that: the construction of the Sobradinho reservoir, associated to the other activities developed in the basin, caused a reduction of the average flow of 163 m³ s-1; the values obtained by the Kohler et al. (1955) model can be used as a reference base to estimate the annual average evaporation in the Sobradinho dam; the coefficient of Class A tank that represented better the seasonal variation of evaporation in the Sobradinho dam was 0.57 and the annual average flow corresponding to net evaporation of Sobradinho reservoir was 132 m³ s-1.
hydroelectric power; regulated flow; water resources
