A hydraulic study on the applicability of flood rating curves

Several hydrological studies have shown that river discharge records are affected by significantuncertainty. This uncertainty is expected to be very high for river flow data referred to floodevents, when the stage–discharge rating curve is extrapolated far beyond the measurementrange. This study examines the standard methodologies for the construction and extrapolation ofrating curves to extreme flow depths and shows the need of proper approaches to reduce theuncertainty of flood discharge data. To this end, a comprehensive analysis is performed on a16 km reach of the River Po (Italy) where five hydraulic models (HEC-RAS) were built. The resultsof five topographical surveys conducted during the last 50 years are used as geometric input. Theapplication demonstrates that hydraulically built stage–discharge curves for the five cases differonly for ordinary flows, so that a common rating curve for flood discharges can be derived. Thisresult confirms the validity of statistical approaches to the estimation of the so-called ‘flood ratingcurve’, a unique stage–discharge curve based on data of contemporaneous annual maxima ofstage and discharge values, which appears insensitive to marginal changes in river geomet