Hydro-morphodynamic numerical modeling indicates risk zones for riverbed clogging.

Abstract

Riverbed clogging compromises the ecological functioning of gravel-bed rivers. Physical clogging affects aquatic habitats and occurs when fine sediments infiltrate coarser substrates, reducing permeability, porosity, and oxygenation. Clogging analyses mostly rely on methods or models that assess the clogging state from field data without predictive capacity. However, predictive tools are essential to optimize habitat restoration in mountain rivers. This study evaluates a two-dimensional numerical model for simulating fine sediment infiltration and mobilization around two large wood pieces in a fully controlled morphodynamic gravel-bed channel. Field data from the morphodynamic channel, collected before and after an artificial flood, were used to calibrate the model and compare its outputs with measured sediment parameters. The model reproduces fine sediment fractions in the surface and subsurface layers, especially in a shallow, high-velocity zone that underwent substantial declogging. In contrast, fine sediment fractions increased in a deeper, slower-flowing zone. Additionally, simulated suspended sediment concentration and fine sediment fraction maps highlight how a swale saturated with fine sediment on the floodplain contributed to increased fine sediment infiltration and clogging downstream. These findings demonstrate that a robust 2d model capturing fine sediment dynamics can effectively identify clogging-prone areas in gravel-bed rivers.