Forms and processes of two highly contrasting rivers in arid central Australia, and the implications for channel-pattern discrimination and prediction

Description and quantification of the diverse controls on alluvial-river styles have long been key themes in the fluvial literature, but many uncertainties and contentions remain. On the Northern Plains in arid central Australia, ephemeral rivers are commonly low sinuosity (P <1.15) but vary from single thread to anabranching, thus providing an opportunity to examine concepts of channel-pattern discrimination and prediction. Comparison of the closely adjacent middle reaches of the Plenty and Marshall Rivers demonstrates that although channel-bed gradient, discharge, and bank strength are essentially similar, bed-material caliber and the pattern of tributary drainage are markedly different. These differences result in strong contrasts in channel cross-sectional geometry and planform. The Plenty River, which transports medium to coarse sand and is joined by few tributaries, remains predominantly single thread but is variably wide (100–1200 m) and in places appears transitional to braiding. By contrast, the Marshall River, which transports coarse sand to granules and is joined by several minor tributaries, has numerous narrow (usually