Dryland Rivers: Processes and Forms

Dryland alluvial rivers vary considerably in character. In terms of processes, high energy, sediment-laden flash floods in upland rivers contrast dramatically with the low sediment loads and languid flows of their lowland counterparts while from a form perspective, the unstable wide, shallow and sandy braid plains of piedmont rivers are quite different from the relatively stable, narrow, deep and muddy channels of anastomosing systems (Nanson et al. 2002). It is also apparent that few, if any, morphological features are unique to dryland rivers. The variety of dryland river forms and the absence of a set of defining dryland river characteristics makes it difficult to generalise about dryland rivers and raises questions about whether it is necessary (or even desirable) to consider dryland river systems separately from those in other climatic zones. Indeed, as noted in the introduction to this volume, the recent shift away from the study of morphogenesis within specific climatic regimes (e.g. Tricart and Cailleux 1972) towards the study of geomorphological processes per se (e.g. Bates et al. 2005) has largely undermined the distinctiveness of desert geomorphology. This is not to say rivers draining different climatic regions do not differ in aspects of their behaviour. They clearly do, as exemplified in several reviews of tropical (Gupta 1995), periglacial (McEwen and Matthews 1998) and dryland (Graf 1988; Knighton and Nanson 1997; Reid and Frostick 1997; Tooth 2000a) fluvial geomorphology. However, given the diversity of dryland river mor-