Channel Instability in a Braided Sand Bed River

Citation data:

Water Resources Research, Vol: 17, Issue: 4, Page: 1087-1094

Publication Year:
1981
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article description
The Gila River of central Arizona is representative of braided, sand bed rivers in alluvial valleys that have inherent unstable behavior and destructive channel migration. The 112-year record of channel conditions along a portion of the Gila River provides data for the construction of locational probability maps for main flow channels. Zones of stability and hazardous instability alternate with each other at 3.2 km (2 mi) intervals. During the past century the overall sinuosity of the main flow channel has remained close to 1.18, despite numerous changes in actual location. Spatial and temporal variation of sinuosity have occurred in subreaches as a result of sedimentation behind a dam and fluctuations in the density of phreatophyte growth, which both affect the hydraulics of flood flows. Unstable zones of the channel correspond to the surface of the sediment wedge behind the dam and areas dense phreatophyte growth. Stable zones correspond to areas controlled by bedrock or man-made structures, as well as locations determined by these external factors plus the requirement to maintain a consistent sinuosity. Channels such as that of the Gila River do not meet most assumptions of equilibrium and are best understood through probabilistic approaches with an assumption of catastrophic adjustment.