Enhancement and comprehensive evaluation of the Rating Curve Model for different river sites

This study presents an enhancement of the Rating Curve Model (RCM) proposed by which was initially formulated to assess discharge at a downstream river site where only stage is monitored while the flow is recorded at an upstream section and significant lateral inflow can occur along the river branch. The original model formulation is here of fact extended for upstream discharge estimate by assuming the flow known at a downstream site and stages measured at both ends. In this new configuration, the model can be applied to river reaches with negligible lateral inflow or to river reaches with significant lateral contribution but where a kinematic flow regime holds. The new model formulation is tested by considering two case studies, both selected in the Upper-Middle Tiber River basin, in central Italy. For the first case study, the model is applied to 22 flood events observed along three branches of the Tiber River with accurate rating curves at ends and having the same upstream river site. RCM successfully simulates the discharge hydrographs observed at the upstream section closely capturing both the peak rate and the time to peak, with average absolute errors less than 5% and 0.36 h, respectively. The model accuracy is found independent of the intermediate basin area and, hence, of the lateral inflow contribution. The rating curve computed in this upstream section by using the shortest reach is slightly overestimated whereas the ones derived by applying the model to the other two reaches are almost coincident and slightly underestimated, but for all of them the errors are less than 5%.