Author(s): Mamy Rija Andriamboavonjy; Adriano Coutinho Lima; Norihiro Izumi
Linked Author(s):
Keywords: Sandbar; Erosion; Uniformly curved channels; Mixed alluvial bedrock
Abstract: Difficult to be monitored from the surface, the riverbed erosion may affect the stability and durability of structures placed in the river channel. The knowledge of the erosion process on riverbed would help to prevent such adversity. This study focused on erosion in mixed alluvial-bedrock uniformly curved channels, here relating the formation of sandbars and the evolution of the erosion. An experimental study was carried out within an annular flume, made of Plexiglas, to simulate the erosion in such channels; using gypsum as the bedrock and sand as the abrasive material. The rotation of the top lid, put on the water surface, induces the water to flow. The relative bed elevation was surveyed using laser beam, both for the bed configuration and for the erosion, after 10 min, 3h, 6h, 12h, 24h, and 48 h of cumulative duration of the experiment. At the early stage of the experiment, the sand formed along the inner wall a uniform transverse slope of 22°. Then gradually, it turned into migrating sandbars. The bars morphology progressively changed - smooth to rectangular-like shape. Furthermore, the number of bars increased - from 5 to 9. Simultaneously, bed erosion occurred and grew at the base of the transverse slope. The sandbar morphology is related with the bed erosion growth: the more developed the erosion is, the more sandbars is generated, and the faster is the erosion rate.
Year: 2020