Hydrogeomorphic processes emerge from interactions among fluid motion, sediment and granular materials, and evolving landforms. They span spatial and temporal scales from the entrainment and collective motion of individual grains to sediment-laden flows, reach-scale morphodynamics and landscape evolution. Although dynamic grain-scale mechanisms are increasingly resolved through high-resolution imaging, embedded sensing and particle-resolved simulations, translating this understanding into continuum representations and reliable field-scale forecasts remains a fundamental challenge in riverine geomorphology, hydrology, fluvial hydraulics and environmental fluid mechanics.

This session brings together field observations, physical experiments, theory, numerical modelling and data-driven approaches that advance process measurement, mechanistic understanding, scale bridging and prediction. We particularly welcome studies developing or integrating novel instrumentation and sensing, imaging and remote sensing, particle tracking, laboratory experiments, particle-resolved and discrete-element simulations, continuum modelling, data assimilation, uncertainty quantification, and model calibration, verification and validation.

Contributions may address particle entrainment and granular dynamics; grain–fluid and grain–grain interactions; stochastic sediment transport and size segregation; particle-laden, debris and granular flows; erosion, deposition and evolving boundaries; bedform development and morphodynamics; extreme or rapidly varying flows; and the representation of these processes across particle, reach and landscape scales. Applications may include rivers, hillslopes, infrastructure, environmental management, natural hazards and forecasting. Studies that connect observations to grain-scale mechanisms, upscale those mechanisms into reduced-order or continuum representations, and evaluate predictive capability across environments and scales are especially encouraged.