RUHM: An open-source tool for rapid stage–discharge Rating curve Uncertainty estimation using Hydraulic Modelling and UAV data

We present RUHM (Rating curve Uncertainty estimation using Hydraulic Modelling), a new open-source tool for rapid estimation of stage–discharge rating curves and their uncertainty at river discharge monitoring stations. A rating curve models the relation between stage (water level) and discharge at a river location and is used to derive discharge time series from water level at most discharge monitoring stations worldwide. However, many stage-discharge field gaugings are needed to estimate rating curves and their uncertainty using traditional approaches. RUHM combines a 1D hydraulic model with Bayesian inference and uncertainty estimation techniques to more rapidly estimate a rating curve and its associated uncertainty with a minimum of three low to middle flow gaugings. The data needed to use RUHM can be effectively collected using drone/UAV (Unmanned Aerial Vehicle) surveys, reducing field efforts compared with traditional approaches. Our open-source implementation of RUHM is written in Python and features a graphical user interface, a user manual, two workflows for pre-processing UAV-derived and/or traditionally surveyed data to generate the RUHM input data files, and example datasets with UAV data. Applications of RUHM to Swedish stations show well-constrained and robust uncertainty estimates where the 1D-flow assumption holds, and wider uncertainty intervals where it does not.