15. Fluvial Processes in Braided Rivers

Braided rivers are characterized by an unstable network of multiple channels and very active channel processes. They can be found in different climate regions (e.g. from glacial areas to arid regions) and physiographic settings (e.g. from steep mountain areas to low coastal plains). This chapter aims to summarize the present knowledge about braided rivers and to point out some gaps that still require further research. The first part of the chapter focuses on channel processes while the second part deals with channel changes through time. As for the first part, the following processes are illustrated: bar formation and development; processes at bifurcations and confluences; lateral mobility; bedload transport; role of vegetation on river morphodynamics. The second part deals with the evolution of braided rivers, mainly in response to human alteration of fluvial systems, over some decades up to some centuries. The historical perspective is crucial to understand present morphology and processes, as well as to assess future channel evolution. Understanding about braided river morphology and processes has significantly increased over the last three decades or so, through physical modeling, field observations, and, to a lesser extent, numerical modeling. On the other hand, several open questions still remain and future research should address aspects such as metrics used to characterized braided rivers, measurements of flow and sediment transport, and prediction of future channel evolution.