Beyond Water: Mapping Sediment Bars to Enhance Satellite Monitoring of River Dynamics

Unvegetated sediment bars are central to river morphodynamics but are rarely used as indicators of channel dynamicity in satellite-based studies. Linking sediment dynamics and river lateral mobility requires monitoring sustained changes in both water and sediment—the active channel (AC)—to avoid stage-dependent noise. Yet, such monitoring remains rare. We introduce an automated, globally applicable approach that detects and quantifies activation (erosion) and deactivation (vegetation colonization) by tracking multi-year sustained AC directional shifts from Sentinel-2 imagery. Applied to the Po River (Italy), this approach captures trajectories across different morphologies, distinguishing lateral mobility, widening, and narrowing from changes caused by stage-dependent hydrological forcing. Results identify the exposed sediment-to-water ratio as a strong predictor of AC dynamicity, with sediment-rich reaches showing greater instability and responsiveness to hydrological variations. Our findings demonstrate that incorporating sediment areas alongside the water channel improves understanding of river dynamics, with implications for river restoration and risk mitigation.