Direct measurement of river discharge is difficult, time consuming and costly. Therefore a rating curve is often used to estimate the river discharge. Limited measurements under extreme conditions result in extrapolation of the rating curve for high flow conditions. This induces uncertainties and errors in the stage-discharge relation. Recently there has been a gradual shift to more physically based rating curves, where the geometry of a river is included and no extrapolation is needed. This seems to be a promising shift to improve traditional river rating. However, the challenge now is to accurately determine the parameters bed roughness and hydraulic slope. The aim of this research is to develop and evaluate a method to better estimate the hydraulic parameters bed roughness and hydraulic slope. To do so a case study has been carried out in the Luangwa river catchment in Zambia.