Bed form characteristics in a live bed alluvial channel


Department of Civil and Environmental Engineering, Amirkabir University of Technology, No. 424, Hafez Ave., Tehran, P.O. Box 15914, Iran


Bed forms are generated in alluvial streams due to mutual interaction between flow and erodible bed material. Among the variety of possible bed forms, dunes are the most important feature and much attention has been paid to them in the literature. In the present study, an experimental approach was carried out to investigate the geometry of dunes and their celerity in an erodible sand bed. The tests were conducted under live bed conditions in an experimental flume capable of re-circulating both water and sediment. Present experiments showed that the Shields number had a considerable eff ect on dune height and celerity, while the e ect of this parameter on the dune length was not signi cant. Furthermore, dimensional analysis is used to present the relationships between dune height and length, as well as celerity. These relationships were also compared with previous empirical equations and experimental data, which showed their acceptable accuracy. Bed roughness related to bed forms was also analyzed based on all available experimental and eld data. Results demonstrated that by increasing the Shields number, the ratio of Manning coecient, related to bed forms, to total Manning coecient increased with a logarithmic trend.