Title: Alluvial Ridge Morphology in Meandering Amazonian Rivers is Controlled by Discharge Variability and River Migration
Abstract: Alluvial ridges record continuous channel-floodplain sediment exchange during floods, preconditioning rivers for future avulsions. Despite their importance for predicting avulsion hazards, the fundamental controls on ridge growth remain poorly understood, particularly during active channel migration. Using hydrological data from 12 gage stations in meandering Amazonian rivers and numerical models, we examine how discharge variability and channel migration shape ridge morphology. Both field data and numerical model results confirm that ridge height and width increase with discharge variability. Higher discharge variability is associated with elevated flood stages and accelerated lateral migration, promoting vertical and lateral ridge accretion. In contrast, ridge slope does not correlate with discharge variability, whereas channel slope does, producing a greater gradient advantage (i.e., ridge-to-channel slope) in low-gradient channels. Our results provide a quantitative framework linking hydrology and river mobility to ridge morphology, forecasting how varying discharge regimes reconfigure channel-floodplain systems and influence future avulsion and flood risks.
