Gravel-bed rivers: roughness surface identification and effect on flow characteristics

Riverbeds are often covered with gravels. The characterization of the gravel bed is very complex, depending on many factors such as the gravels’ shape, morphology and spatial distribution. The presence of gravels determines a significant impact on flow field (Ferraro et al., 2016). The evaluation of flow velocity and turbulence characteristics in natural rough beds is a complex subject, still poorly understood despite the effort of several researchers, requiring both theoretical and experimental analyses. On one hand the bed roughness exhibits a significant spatial variability, on the other hand the presence of gravels determines a significant effect on flow velocity distribution, especially affecting it in the near-bed flow zone and determining the formation of coherent turbulence structures. How to reasonably quantify gravel bed surface roughness is still an open question and different methods have been proposed in literature (among others Nikora et al., 1998; Aberle and Nikora, 2006). It is important to understand the turbulent flow characteristics by resolving the spatial heterogeneities.