Scouring process in river sinuosities: Insights from a large field dataset from south-east France

Scouring at the toe of riverbanks drives bank instability and is a leading cause of failure of streambank protection structures. It affects both civil engineering and soil and water bioengineering structures, and is particularly pronounced in meanders, where channel curvature generates helicoidal secondary flows. Despite numerous studies on scouring and filling processes, the combined influence of hydrodynamic, morphological and ecological controls remains incompletely understood. As a result, prediction of scour depths at riverbank toe is imprecise. This study presents a new independent field dataset of 116 meander scour holes across diverse geomorphological contexts. For each site and under field flow conditions, scour depths, ecological and physical measurements were collected. First, we analysed how scour depth was linked to dimensionless physical variables and the presence of vegetation to better understand the drivers of scour development in meandering rivers. Second, we evaluated the performance of empirical equations calculating meander scour depth by comparing predicted and observed values. We also assessed their robustness against our dataset and previously published data. The results revealed that hydraulic and geomorphological characteristics combine to influence scouring in meanders, and that the curvature-to-width ratio is a key parameter. Vegetation also exerts a measurable influence on scour depths. The comparison with predictions revealed the limitations of empirical field-based approaches, which generally reflect instantaneous rather than peak scour conditions. Nonetheless, two equations performed well as envelope predictors. Adjustments are suggested to refine their applicability under specific conditions and to help improve the design of riverbank stabilisation projects in meandering rivers.