River and estuarine processes intersect hydrology, oceanography, geology and ecology. Climate change, relative sea-level rise, and human activities, such as dam construction and channel diversions, force rivers and estuaries into transitory states by affecting sediment supply and transport, channel stability, groundwater-surface water exchange, and ecological and biogeochemical functions. Floodplains and tidal flats are strongly impacted by these regime changes, which exacerbate conditions of river flooding and saline intrusion. Ongoing research efforts are motivated by a need to stabilize and restore ecosystem services provided by these dynamic environments, while sustaining societal interactions and reliance on them. This session brings together scientists studying estuarine and fluvial settings to discuss monodisciplinary as well as cross-disciplinary research examining surficial and subsurface processes in rivers, floodplains, estuaries, and tidal flats. We welcome submissions presenting new insights across a broad range of scales, highlighting novel approaches to field monitoring, remote sensing, numerical simulations, and physical experiments.