Variable backwater and channel roughness: effects on Solimões River discharge

Historically, streamflow daily values are obtained indirectly by applying a rating curve on water level data. In several Amazon basin stations, a backwater effect impacts the flow, thereby invalidating the rating curve method. To account for this effect, we generated a daily discharge data series by applying the Manning equation to daily water level data from the Manacapuru station located on the Solimões River. Each Manning parameter had to be established based on its relationship to the water level. The roughness coefficient was obtained by inverting the Manning equation for each discharge measurement, and a “coefficient–stage” relationship was established. The slope of the energy line was estimated by the water-surface slope between two fluviometric stations. Discretizing the equations for each parameter enhanced the discharge estimation for the Manacapuru station, thereby generating an accurate discharge data series