River meandering dynamics are here explored in light of unsteady water flows. While mathematical models have usually focused on constant discharges—a reasonable and widely adopted approach for long-term considerations—we show that varying flows strongly affect the short-term planimetric evolution of meanders, before the cutoff occurrence. In particular, flow variability slows down the meanders' dynamics while does not significantly influence the wavelength selection. We support our arguments with numerical simulations and theoretical (linear and nonlinear) analyses, showing that an interplay between out-of-phase river geometry and flow is responsible for the meander-dynamics slowdown. Our results suggest that accounting for flow variability is critical in assessing yearly to decadal meander dynamics with important implications for river engineering and management strategies.