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1 Department of Geography, University of Cambridge, Cambridge CB2 3EN, UK
2 Department of Earth Sciences, University of Cambridge, Cambridge CB2 3EN, UK
Fluvial processes in large subsiding sedimentary basins (e.g. tectonic foredeeps) must be adjusted in the long term to distribute sedimentation areally, although in the short term deposition is localized along the river courses. This means that the major long-term characteristic of the river pattern is that it is avulsion-dominated. Individual channels in an avulsive system display one of the conventional pattern types (e.g. meandering, braiding), but these patterns may reflect the behavioural relationships between the ‘dominant’ and ‘secondary’ channels in the system. These relationships change through time as aggradation along the dominant channel encourages avulsion into the course of former secondary channels, and the channels exchange roles. Thus, channel system behaviour is not explained by the variation of stream power used to analyse the behaviour of individual (meandering or braided) rivers, and palaeohydrological reconstructions for individual channels within such a system are of limited significance. Examples of avulsive systems are noted, including the northern Gangetic Plain.
