Establishment of the stage-discharge relationship of the River Amazon at Obidos: "normaI difference in level" method using "variable geometry"

This paper describes the way in which the daily discharges of the River Ama zon were calculated at Obidos. The stage-discharge relationship is practica lly univocal in low and mean water. In high flow periods, the scatter of th e stream gaugings compared to the univocal rating curve effects the correct ion of the discharges according to the levels at Santarem then at Parintins . The "normal difference in level" method is not well adapted for Obidos: i t was replaced by a "normal difference in level with variable geometry" met hod, a function of the water levels at Obidos. While using only the Santare m station, the application of this new method reduced the scattering to 3.0 % on the entire rating curve.