There is no accepted standard equation for predicting flow resistance in gravel rivers. This is mainly because of the lack of an effective approach for describing the roughness of the gravel surface. This paper aims at describing the roughness of gravel surfaces based on characteristics of the elevation field rather than conventionally used grain size distribution. A new parameter—the coarseness parameter—in addition to the steepness parameter and standard deviation of the elevation field is proposed for characterizing the roughness of gravel surfaces. Two groups of rough surfaces (A and B) were generated using unconditional Gaussian simulation to study the influence of the coarseness and steepness parameters on effective roughness. The effective roughness of groups A and B was calculated by a two-equation turbulence model, and a quantitative relationship between the effective roughness and proposed parameters was derived. The resulting relationship derived from groups A and B was validated using ...

This study investigates the roughness of water-worked gravel surfaces using stable gravel-beds armoured in flume and field experiments. As an alternative to traditional approaches, multifractal analysis is employed to investigate the roughness of these surfaces. Power spectra analysis is used to study scale-invariant regimes, defined by the ranges of scales where the spectra follow power laws. Then, multifractal spectra are calculated and analysed. The strength of multifractality reflecting heterogeneity of elevations is related to the development of a stable armour layer. The development of armouring processes of the gravel surfaces formed in the flume experiments is investigated using the effective grain size approach based on Gessler's model. For surfaces in the field, the two-dimensional second-order structure function is used to study the static armour surfaces due to the absence of historical hydrological data. The results of these analyses confirm the results of multifractal analyses.