Applying hypothesis of self-similarity for flow-resistance law in Calabrian gravel-bed rivers

In this paper, the results of an investigation carried out to test the applicability of a flow-resistance law on gravel-bed rivers in southern Italy (fiumare) are reported. First, dimensional analysis and self-similarity theory are applied for deducing the flow-resistance law (i.e., relationship among friction factor, mean velocity, shear stress, and physical properties) for gravel-bed rivers with a high boulder concentration. The proposed approach is calibrated and tested using two independent data sets (104 reaches of some Calabrian fiumare). Then, the incomplete self-similarity hypothesis is also applied to theoretically deduce the flow-velocity profile, which was integrated for obtaining the flow-resistance law. The estimate performance of both approaches is verified by field measurements of flow velocity, water depth, river width, and bed slope carried out in previously used data sets. The analysis shows that the theoretical approach based on the power velocity distribution yields a flow-resistance law characterized, in the comparison between measured and calculated friction-factor values, by the lowest root-mean square error and the highest Nash-Sutcliffe index.