Discharge measurements in a small ungauged river: comparison between conventional current-meter and tracer dilution methods

The majority of small rivers and channels that flow across the Emilia-Romagna region (Northern Italy) are monitored by an extensive network of level meters. Unfortunately a stage-discharge relationship is available only for the main among them. The purpose of this study is to determine the reliability and accuracy of discharge measurements carried out by tracer dilution method. Experimental investigations have been carried out on a small river nearby Bologna (Italy), performing slug injections of a conservative tracer (NaCl) and recording electrical conductivity in a downstream section, while at the same time, conventional current meter measurements have been taken in a section placed between the injection point and the conductivity meters. Data obtained from both the methods have been compared each other, giving also main relevance to the uncertainty analysis. Monte Carlo Simulations were performed to integrate single uncertainties coming from different potential sources of error, either experimental or analytical.