Self-Formed Straight Channels in Sandy Beds

The hydraulic geometry and the local features of straight, relatively wide self-formed channels composed of sandy bed are studied in laboratory flumes. Introduction of one loose and the other rigid bank in experiments excludes the tendency toward meanders and provides good examples to test hydraulic regime relations. The experiments support a few regime relations derived rationally. The transverse bed shapes in equilibrium have a universal profile regardless of initially-molded cross section, discharge of flow, and sand diameter within the scope of the experiments. A theoretical analysis of secondary currents in straight channels provides reasonable interpretation of the local features of self-formed channels such as the longitudinal sand ridges, and this analysis suggests the insignificant effect of secondary currents on the size of self-formed channels.