Publication Date:
2018-03-07
Description:
It is widely recognized nowadays that there are at least two different phases of bed-load sediment transport in gravel-bed rivers. However, the transition between these phases is still poorly or subjectively defined, especially at bends in rivers, where cross-stream sediment transport can strongly influence changes in the texture of the transported sediment. In this paper, we use piecewise models to identify objectively, at two points in the cross-section of a river bend, the discharge at which the transition between bed-load transport phases occurs. Piecewise models were applied to a new bed-load data set collected during a wide range of discharges while analysing the associated changes in sediment texture. Results allowed the identification of two well-differentiated phases of sediment transport (phase I and phase II), with a breakpoint located around bankfull discharge. Associated with each phase there was a change in bed-load texture. In phase I there was non-dominance in the transport of fine or coarse fractions at a particular sampling point; but in phase II bed-load texture was strongly linked to the position of the sampling point across the channel. In this phase, fine particles tended to be transported to the inner bank, while coarse sizes were transferred throughout the middle parts of the channel. Moreover, bed-load texture at the inner sampling point became bimodal while the transport of pebble-sized particles was increasing in the central parts of the river channel. It is suggested that this general pattern may be related both to secondary currents, which transfer finer particles from the outer to the inner bank, and to the progressive dismantling of the riverbed surface layer.
Print ISSN:
0197-9337
Electronic ISSN:
1096-9837
Topics:
Geography
,
Geosciences
