Preliminary experiments on the evolution of river dunes

Dunes are common large-scale bedforms in sand-bed rivers that can affect significantly hydraulic roughness and water levels. This paper is a part of ongoing investigations by the authors on the evolution of river dunes. Here the spatial and temporal development of solitary sand dunes is investigated experimentally. Experiments were carried out at University of Basilicata, Italy, in a 1 m wide and 20 m long rectangular channel. A nearly-uniform sand with median grain size d50=1.7 mm was used as mobile bed. The working section was 16 m long. Each run was performed in two phases. Phase 1 aimed to generate the typical shape of the dune starting from an arc-shaped sand bar, of the same material as the mobile bed, set in a cross section perpendicular to the longitudinal channel axis. Phase 2 aimed to promote the downstream propagation of dunes generated in Phase 1 by either lowering the tailwater level or increasing the discharge. Based on the experimental data new insights are provided on the equilibrium morphology and the rate of migration of solitary sand dunes.