Fluvial geomorphology has witnessed a continuing reduction in the time-
and space-scales of research, with increasing emphasis on the dynamics
of small site-specific river reaches. This shift can be regarded as
part of a trend towards the understanding and explanation rather than
description of how rivers change, which raises important questions
regarding the relevance of such short time-scale and small space-scale
research to understanding longer-term aspects of landform behaviour.
The methodological challenges that arise from such intensive case study
research are illustrated here using a detailed investigation of a river
reach. Morphological changes within this reach are shown to be driven
by: (i) catchment-scale processes associated with the interaction of
discharge and sediment supply waves; and (ii) modification of these
processes through morphological controls on erosion and deposition
patterns and hence net channel change. The `morphological conditioning'
of channel response reflects the configurational aspects of channel
change, and the importance of local characteristics in the
understanding of system behaviour. Sensitivity to local conditions
implies that short time-scale and small space-scale processes may be
critical to channel behaviour, particularly if the system is
interpreted in non-linear terms. Although it may be possible to
identify statistically averaged stable states, non-linear system
behaviour implies that system trajectories are sensitively dependent
upon instantaneous system states. Thus, changes between average states
can only be understood through an understanding of the sequence of
configurational states through which the system evolves.