complexity of river behavior

1. Complexity, self-organisation
and variation in behaviour in
meandering rivers

2. Abstract
River meanders are natural features on the surface of Earth that present some degree of regularity of form. They range from
being highly dynamic to being stable under present conditions. Conventional theory is that meanders develop to an
equilibrium
form which is related to discharge and sediment load. Other research has demonstrated that many highly active meanders
exhibit a
continuous evolution over time and a non-linearity in rate of development. Ideas of autogenesis and of self-organised
criticality as
being an explanation of some meander changes have been proposed. In this paper data from rivers around the world are
examined
for further evidence of autogenic, self-organised or non-linear behaviour through analysis of change in sinuosity over time for
reaches and change in individual bend form, particularly bend curvature and bend elongation. Some examples do exhibit
trends of
increasing sinuosity over time and a few show limits from which large decreases occur. Several case studies show non-linearity
of
behaviour and increasing complexity of form. Other case studies, however, do not exhibit such trends. Phase space plots are
used to
help uncover emergent behaviour but show a variety of patterns. The example of a reach in which multiple cut-offs occurred
is
analysed for mechanisms of self-organisation of the planform and in the pool-riffle pattern. Riffles are more closely spaced
and also
more transient in the more rapidly changing and higher sinuosity parts of the channel. Hypothetical trajectories of different
meander
behaviour, including for bedrock meanders, are plotted but the challenge remains to uncover the conditions for occurrence
and for
divergence of tendencies to stability and instability. Identification of attractors and phase space of behaviour of different
meandering systems offer the potential for application to sustainable channel management.
© 2007 Elsevier B.V. All rights reserved

3. The central issue to be addressed in this paper is the nature of changes in meander morphology, particularly
the extent to which these are autogenic, the range of behaviour of river meanders and the controls upon that
behaviour. It does not seek to address the question of why and how meanders are initiated. Various types of
explanation are currently invoked to explain changes in river meanders, with sometimes a lack of
communication between the proponents of the different theories and approaches. Questions arise as to
whether these frameworks and types of explanation are mutually exclusive or whether they are compatible,
or whether different explanations apply in different times and places.