DISPONIBILIDADE HÍDRICA E BALANÇO HÍDRICO DA BACIA DO RIO CACHOEIRA NA REGIÃO DE ITABUNA/BA

The water balance calculation was carried out for the period from 1973 to 2005 in the Cachoeira River Basin, located in the south of Bahia state. Using the time series data of the Cachoeira River flow and the accumulated precipitation was calculated based on the data from five rainfall stations. For the calculation of the base and superficial flows the digital filter technique was applied, which allows to separate in an automated and systematic way the contribution of the components base flow and surface flow. The average annual cumulative evapotranspiration of the catchment area corresponds to about 85% of the precipitation, while 15% of it is drained by the rivers. The runoff represents the largest part of the water flowed by the rivers, with an annual average of 84.53% and a maximum of 92.2% in the rainy season and indicates the low water infiltration capacity in the subsoil. The estimated annual average recharge for the aquifer (27.35 mm/y) corresponds to 15% of the average flow of the Cachoeira river and 2.34% of the average annual rainfall.