Stage-discharge relation in non-uniform flow based on Strickler-Manning Equation on Amazon basin

Abstract. Hydrological modeling became an essential tool for planning and managing water resources. For that, an important issue is the availability of adequate hydrological databases to calibrate and validate the models. In this context, discharge data series play dominant role. Most often, these data are obtained by converting daily water levels records based on a stage-discharge relation. The relation usually applied is a simple rating curve, which is assumed to be valid at the cross-section in the reference hydraulic conditions. However, in non-uniform flow cases, the downstream boundary condition may also influence the stage-discharge relation and a simple monotonic function is not valid. This is the case of Solimões River, at Manacapuru Station. We suggest the stage-discharge relation to be based on Strickler-Manning Equation. Slope was calculated by the water level difference between the main station and a staff one, located a dozen of kilometers downstream. Geometric parameters were obtained as functions of water level, based on acoustic description of transversal section. Being all the others variables available, we estimated the roughness coefficient, or n, for each measurement data. Then, an n x stage relationship was established, for using in discharge data series estimates. Our results indicated that discretizing data used to this estimate by measurement method could improve the quality of generated data, mainly for maximum discharge. This finding was endorsed by statistical analyses which indicated that the measurement method can affect significantly the relationship between roughness coefficient and water level.