Splitting rivers at their seams: bifurcations and avulsion

River bifurcations are critical but poorly understood elements of many geomorphological systems. They are integralelements of alluvial fans, braided rivers, fluvial lowland plains, and deltas and control the partitioning of water and sediment throughthese systems. Bifurcations are commonly unstable but their lifespan varies greatly. In braided rivers bars and channels migrate, splitand merge at annual or shorter timescales, thereby creating and abandoning bifurcations. This behaviour has been studied mainly bygeomorphologists and fluid dynamicists. Bifurcations also exist during avulsion, the process of a river changing course on afloodplain or in a delta, which may take 102–103years and has been studied mainly by sedimentologists. This review synthesizesour current understanding of bifurcations and brings together insights from different research communities and different environmen-tal settings. We consider the causes and initiation of bifurcations and avulsion, the physical mechanisms controlling bifurcation andavulsion evolution, mathematical and numerical modelling of these processes, and the possibility of stable bifurcations. We end thereview with some open questions. Copyright © 2012 John Wiley & Sons, Ltd