Author(s): Ivan Pascal; Patricio Bohorquez; Christophe Ancey
Keywords: Ntidune; Mountain stream; Non-uniform flow; Bedload transport; Gravel-bed river
Abstract: Upstream migrating antidunes develop in streams under supercritical flow conditions. These bedforms are often organised in trains (i.e. sequences of well-developed antidunes). In shallow flows over coarse sediments, the dynamics of a single antidune can be significantly influenced by the surrounding bedforms. The drivers and behaviour of these interactions remain unclear. We conducted an experimental study to investigate the morphodynamics of antidune trains in narrow streams with a particular focus on mechanisms that could systematically influence bedform geometry as antidunes migrate upstream. The incipient antidunes near the flume outlet (which is a bed discontinuity) often exhibited migration periods notably longer than the typical value observed further upstream. Far from the boundaries, antidune sequences were mostly affected by transient downstream travelling disturbances and we did not observe any systematic change of antidune shape and dynamics along their migration path. Such insights into potential sources of non-uniformity are helpful for interpreting the differences between the outcomes of experimental and numerical simulations.