Coexistent mud braids and anastomosing channels in an arid-zone river: Cooper Creek, central Australia

Abstract

With few exceptions, braided rivers transport sand- and gravel-sized bedload over relatively steep gradients. However, Cooper Creek, a major river of the Lake Eyre Basin, central Australia, transports clay-rich mud through a low-gradient network of braided channels. We attribute this unusual behavior to transport of mud as sand-sized pedogenic aggregates and to aggregate densities that are lower than those of single-mineral grains. A third factor may be appreciable bed shear associated with the steep energy gradient at the front of each flood wave. Although the braids were previously regarded as relict, we interpret those in the Cooper as contemporaneous with deeper, narrower anastomosing channels, both in equilibrium with present hydrologic conditions. The mud braids are active during flood, whereas the anastomosing channels operate at moderate flows and transport both sand and mud.