Is steady sediment transport possible in graded sediments?

Roca, M. and Bettess, R. (2009) Is steady sediment transport possible in graded sediments? In: RCEM 2009 (6th IAHR Symposium on River, Coastal and Estuarine Morphodynamics), 21-25 September 2009, Santa Fe, Argentina.

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Abstract

Measurements of bed load sediment in rivers frequently show pulsing. Such pulses have also been frequently noticed in laboratory experiments. This paper presents a one-layer model where the Exner equation was written for each sediment size to represent continuity and assumptions were made about hiding functions and their impact on the predictions. Results were compared with experimental tests which simulated very well the general behavior of the transport rate at the downstream end of the flume. However, by its nature, it cannot reproduce the unsteady behavior of bed-load pulses. In this paper it is suggested that bed load pulses arise from non-linear effects generated by the interaction of the different sizes forming the graded bed. Practical implications of the non-linearity are related to the measurement of bed-load in channels in which the duration of the sampling has to exceed the time-scale of the non-linear pulses and the bed composition may vary in each pulse.

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