Statistical analysis of the riverbed roughness structures

Bed roughness influences the hydrodynamic behaviour of the river, for example, elevating water levels for a constant flow discharge. In most hydrodynamic river models, the roughness is assumed as a function of the grain size. However, natural riverbeds are characterized by a wide variety of bedforms at different scales, from the small-to the largescale bedforms. Hence, bed roughness should be considered as a complex expression of topographical variability of a bed surface at multiple scales rather than being simply related to the grain size. Neglecting these important aspects may lead to high errors in the river water level results, inducing dramatic consequences on the flood risk and land use planning. To explore the bed roughness, an in-depth statistical analysis is applied, in this study, to three different surfaces simulated in an experimental laboratory flume. In fact, if the description of bed roughness structures is limited to second-order statistics, then some important information may remain unidentified. Higher-order structure functions are computed to provide information on the bed roughness structures and on their orientation and multifractal characteristics.