Relevancy and comparison of friction factor equations for gravel bed in bedload regime

Abstract

The friction coefficient f value is a dominant term in the open channel flow calculation. In this study, eight empirical flow resistance equations in a gravel bed are selected to calculate friction factor under bed load regime. To check the relevancy of these equations, 1,392 flume data are selected with measure values of friction factor in uniform and non-uniform bed materials. We used a friction evaluation approach based on the integration of velocity profiles with two types of equations under well-defined conditions. The first type based on relative depth R/D and the second type concern equations that depend on slope value S, Froude number Fr and Reynolds number Re. In this article, we have used each equation whatever conditions and fields of use. In the second step, friction coefficient f was calculated according to application conditions of each equation while maintaining same formula without change. We concluded that Ferro's (2018) equation is best one that estimates friction coefficient value with a mean normalised error of 12% for all dataset, in both cases.