The dominance of dispersion in the evolution of bed material waves in gravel-bed rivers



Bed material waves are temporary zones of sediment accumulation created by large sediment inputs. Recent theoretical, experimental and field studies examine factors influencing dispersion and translation of bed material waves in quasi-uniform, gravel-bed channels. Exchanges of sediment between a channel and its floodplain are neglected. Within these constraints, two factors influence relative rates of dispersion and translation: (1) interactions between wave topography, flow and bed load transport; and (2) particle-size differences between wave material and original bed material. Our results indicate that dispersion dominates the evolution of bed material waves in gravel-bed channels. Significant translation requires a low Froude number, which is uncharacteristic of gravel-bed channels, and low wave amplitude which, for a large wave, can be achieved only after substantial dispersion. Wave material of small particle size can promote translation, but it primarily increases bed load transport rate and thereby accelerates wave evolution. Copyright © 2001 John Wiley & Sons, Ltd.