Friction Factor Evaluation in Gravel‐Bed Rivers

Field data gathered from 43 river reaches of Calabria (southern Italy) were employed to develop a theoretically based equation for predicting the f‐friction factor that takes into account both the Froude number and the sediment mobility parameter. The river reaches investigated have: (1) Reasonably uniform and relatively low flow; (2) no appreciable vegetation in the channel bed and banks; (3) a fully developed turbulent flow; (4) a friction slope greater than 0.2%; (5) small and intermediate scale roughness; (6) a mobility parameter greater than the critical value in more than 50% of the cases; and (7) a Froude number between 0.20–1.30. Statistical techniques were used to derive an equation for estimating f that takes into account the physical processes controlling flow resistance beyond the range of the collected data.