Forms of Bed Roughness in Alluvial Channels

Abstract

Laboratory experiments in a large recirculating flume, in addition to field studies, have established that resistance to flow and sediment transport in alluvial channels are related to the form of bed roughness. The forms of bed roughness that have been observed in the laboratory flume and in natural alluvial channels can be divided into two regimes of flow, on the basis of their shape, resistance to flow, and sediment transport. These divisions are the lower flow regime and the upper flow regime. Between the two regimes there is a transition zone. The bed forms are ripples and dunes in the lower flow regime and plane bed, standing waves, and antidunes in the upper flow regime. The bed form in the transition zone is variable, ranging from that which is typical of the lower flow regime to that for the upper regime. Resistance to flow in the lower flow regime is relatively large and sediment transport is relatively small. Conversely, in the upper flow regime the resistance to flow is relatively small and sediment transport is large. In the transition zone both resistance to flow and sediment transport vary appreciably.