IAS Visiting Fellow Dr Jens Martin Turowski delivers a seminar on their research - The width of channel belts and fluvial valleys and its temporal evolution is important for the hydraulics, hydrology, and ecology of landscapes, and for human activities such as farming, protecting infrastructure, and natural hazard mitigation. The width of a fluvial valley is set by the river undercutting valley walls and evacuating the resulting sediment. We have recently developed a model for the temporal evolution and steady-state valley width on the assumption of a non-standard one-dimensional random walk of channel migration. The model connects valley evolution to reach-scale hydraulic parameters. Here, I introduce the model and summarize some key results and compare model predictions to observations of natural and experimental rivers. For more information about the IAS, please visit - https://www.lboro.ac.uk/research/ias