Threshold constraints on the size, shape and stability of alluvial rivers

The geometry of alluvial river channels both controls and adjusts to the flow water sediment within them. This feedback between form modulates flood risk, impacts climate land-use change. Considering widely varying hydro-climates, supply, geology vegetation, it is surprising that rivers follow remarkably consistent hydraulic scaling relations. In this Perspective, we explore factors governing channel geometry, specifically how threshold motion constrains size shape channels. We highlight utility near-threshold model as a suitable framework explain average stability channels, show deviations relate complex higher-order behaviours. Further characterization transport adjustment timescales, coupled with probabilistic descriptions promise development future models capable capturing rivers’ natural complexity. control adjust sediment, consequences for flooding ecological habitat. Perspective examines entrainment size, dynamics rivers.