Sedimentary Processes: Fluvial geomorphology

Fluvial geomorphology is concerned with the creation of landforms by river processes through the removal and transfer of materials on Earth’s surface. Process studies are rooted in a number of disciplines, the earliest identifying ‘processes’ as evolutionary time sequences in landforms. In later work, this has continued in such fields as the study of meander dynamics. Hydrology-based approaches have involved the identification of formative (generally high river flow) events and their frequency, together with empirical relationships between river channel dimensions and river flow parameters. Work in engineering hydraulics, including the need to design stable channels, has also been a source of process understanding. Such work has led on to detailed analysis of water flow structures in river channels and prediction of thresholds for, and amounts of, sediment entrainment, transport, and deposition. Physical modelling both of channel reaches and of the treelike networks of rivers in their drainage basins has also now been joined by numerical modelling at a number of scales: flow in meander bends and confluences, the development of channel patterns, the evolution of drainage networks, and simulation of alluvial stratigraphy and sediment transfers within catchments as a whole. All this is particularly helpful because landform development, responding perhaps to only a few formative events in a year or to a rare flood, is only fractionally observable. In effect, modelling allows both a ‘speeding up’ of processes and experimentation with presumed controlling factors such as gradient and sediment sizes and mixtures. Results may then be checked against field observations.