Abstract

Erosion generally reduces the resilience of replenished gravel in rivers. This is why 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 downstream of the replenishment slow down the flow above the replenishment, decreasing shear stress on the gravel. Stabilization efficiency is shown to depend on the positioning of the boulders and arrangement of the replenishment surface. In order to achieve sustainable spawning, prospective scenarios with the numerical model highlight the need to limit the width of the replenishment area.