The River Amazon at Obidos (Brazil): Statistical studies of the discharges and water balance

New discharge measurements carried out within the "Hidrologia e geoquimica na Bacia Amazonica" (HiBAm) Project at Obidos have improved the knowledge about the hydrological characteristics of the Amazon at this station, which controls the highest discharges in the world. A new correction method determines the daily discharge with an accuracy of +/-3.0%. The reconstruction of the missing data, using observations from Manaus, makes it possible to build a chronology for almost one century. With this sample starting in 1902, the interannual average discharge of the Amazon at Obidos is 163 000 m(3) s(-1), with an extremely weak irregularity coefficient (K3 = 1.28). The decennial low water (78 000 m(3) s(-1)) is similar to the centenary flood of the River Congo at Brazzaville. The decennial flood is estimated to be 260 000 m(3) s(-1). Water balance studies indicate an outflow deficit of 1193 mm, which can be identified with actual evapotranspiration. In conclusion, the Amazon is confirmed to be the most powerful and regular river of the planet.