Threshold of motion of unconventional sediment under unidirectional flow

Abstract

The threshold of motion of commonly found sediments in streams and rivers, sand and gravel which are mainly siliceous in nature, has been studied thoroughly since the development of the field of sediment transport in fluvial hydraulics. There are other types of sediment, of more irregular shape, such as bioclastic, biogenic, and organic detritus which need a special focus vis-a-vis their transport. This study considers the incipient motion of such sediments and finding a better representation of their threshold of motion. This study considers the empirical curves of some previous researchers and the scatter of data from unconventional sediment to assess the threshold behaviour of such sediment under unidirectional flow. The consideration of the settling velocity in the sediment threshold studies is important in general and for the sediment studied here in particular. The Movability Number is found to be a better representation of the threshold than the Shields parameter or square of Movability Number as data show less scatter about empirical curves.