Alluvial ridge morphology on avulsing rivers

Alluvial ridges are built by preferential channel‐belt deposition and control river avulsions, yet a systematic analysis of their morphology has been missing. To address this gap, we analyse a globally distributed dataset of 8970 alluvial ridge flanks on 14 different rivers. We establish that ridge height scales sub‐linearly with width ( H AR ∝ W AR 0.75 ), indicating that ridges widen faster than they increase in height. Ridge dimensions also scale with the channel. Ridge height inversely scales with depth ( H AR ∝ H M −0.25 ), implying that on deep channels ridges are proportionally smaller relative to channel size. Because H AR decreases with increasing H M , deeper channels are less prone to superelevation. This geometric constraint helps explain the downstream shift in avulsion potential where upstream reaches are controlled by superelevation, and downstream reaches are increasingly governed by gradient advantage. We also characterise ridge flank shapes and show that concave flanks are the most common form. However, the prevalence of convex and quasi‐linear shapes demonstrates that no single idealised profile can capture the near‐channel topography that guides overbank flow. These morphologic scaling laws provide a new systematic description of how alluvial ridge geometry varies across avulsing river systems and how that geometry connects to the downstream evolution of avulsion potential.