ABSTRACTErosion generally reduces the resilience of replenished gravel in rivers. As a result, structures are sometimes added to modify the upstream flow and stabilize artificial spawning grounds. In particular, rows of boulders can be placed around the replenishment area to limit the transport of replenished gravel during flood events. This study aims to optimize the arrangement of these rows, based on field experiments as well as physical and numerical models. A combined hydro‐sedimentary numerical model is calibrated and validated by comparing simulated and measured morphological evolutions in nine laboratory experiments. The results show that boulders positioned downstream of the replenishment slow down the flow above the replenishment, decreasing shear stress over the gravel. The stabilization efficiency depends on both the positioning of the boulders and the arrangement of the replenished surface. To achieve sustainable spawning, prospective scenarios using the numerical model highlight the need to limit the width of the replenishment area. Experiments demonstrated that when the replenishment area spans the entire width flume, the erosion rate is significantly higher compared to a narrower replenishment area placed close to the edges. This effect is attributed to increased flow velocities in the center of the channel, leading to increased shear stress and gravel erosion.