As a result of interactions between streamflow andsediment, riverbeds are seldom smooth, but depending onhydraulic and sediment transport conditions, they exhibitbedforms, which grow and migrate over time (upstreamor downstream). Morphology migration may explainbedload transport pulses observed in field surveys andlaboratory experiments, even under steady supplyconditions (Gomez et al., 1989; Dhont and Ancey, 2018).Experimental investigations into the coupling betweenstream and bedform commonly focus on downstreammigrating forms (dunes or bars). Guala et al. (2014)documented the importance of considering the scale-dependent relationship between wave geometry andmigration celerity for estimating the sediment fluxes dueto downstream migrating dunes. Taking inspiration from their work, we investigated thecase of upstream migrating bedforms, called antidunes,on steep slopes. Antidunes of variable wavelengths havebeen observed in gravel-bed streams (see Video Clip S2in Froude et al., 2017). Well-controlled flumeexperiments are useful for assessing how bedformgeometry and celerity are interrelated.