Abstract

This study proposes a new definition of plane bed regimes. The upper plane bed is defined as a flat bedform that appears under conditions of active suspended load, whereas the lower plane bed forms when sediment particles are moved only by bed-load. Previous studies have recognized that two types of plane bed could be distinguished by shear stress, particle size, or flow regime. However, the compilation of a large amount of existing open-channel flow data indicates that the plane bed regimes cannot be differentiated by existing definitions. Newly produced phase diagrams indicate that plane bed data plot in two separate regions, and the gap between the two regions corresponds to the threshold condition of suspension. Further investigation is needed to understand the physical mechanisms generating lower plane beds and characterizations of parallel laminae from lower and upper plane beds.