ASABE Technical Library - Abstract

Abstract. The determination of water availability in a reservoir to meet the multiple uses depends on a thorough knowledge of evaporative losses. Thereby, the purpose of this study was to estimate the evaporation rates and the evaporated discharges in Tucuruí and Lajeado hydropower plants reservoirs, located in the Tocantins river basin, Brazil, through the application of the mathematical methods of Penman (1948), Linacre (1993), Kohler et al. (1955), Morton (1983) and deBruin & Keijman (1979). The comparison between the different methods was performed using Penman as standard method, and through variance analysis and multiple comparisons procedures. From the evaporation rates, obtained through Penman method and the reservoirs areas, it was possible to obtain the evaporated discharge and the net evaporated discharge, discounting what would be lost by evapotranspiration in the areas previous to the construction of the reservoirs. The results demonstrated that the mean annual evaporations in Tucuruí and Lajeado reservoirs, estimated by the Penman method were similar, with values of 1.784 mm and 1.882 mm, respectively. None of the alternative methods analyzed can be used to estimate the mean annual evaporation in both reservoirs in substitution of the Penman method, except for Linacre and deBruin & Keijman methods, which can be used to estimate the monthly evaporation in the dry season in Tucuruí. The mean evaporated discharge and the mean net evaporated discharge in Tucuruí reservoir correspond to 120% and 50% of total water demand in the Tocantins-Araguaia region, while the mean evaporated discharge and the mean net evaporated discharge in Lajeado reservoir correspond to 120% and 50% of total water demand in the basin.