Statistical characterization of unworked and water-worked gravel-bed roughness structures

Gravel-bed roughness structures for an unworked bed and a water-worked bed are analysed at different topographic scales measuring the bed surfaces by a 3D terrestrial laser scanner in a laboratory flume. The study represents a novel contribution in assessing the role of water-work on a uniform gravel-bed, demonstrating the development of small-scale bedforms (i.e. clusters). To support these observations, an in-depth statistical analysis of the bed topographies before and after water-working was applied at the grain scale and the mesoscale (i.e. a scale larger than the biggest individual particles), revealing that this is an essential prerequisite to properly interpret the roughness structures thus formed. In addition, the results show that the unworked bed is characterized by a multiscaling behavioural feature that represents multifractality of the bed roughness structure. For the water-worked bed, a simple scaling is prevalent, which implies that at small spatial lags, a statistically self-similar characteristic is preserved.