Abstract
The near-bed sediment concentration and vertical sediment flux are important in sediment transport mechanics, but they are known much less than the horizontal sediment flux, especially for fine sediment in unsteady flows. A developed two-phase model is applied to study the near-bed sediment concentration, vertical sediment flux, and the relevant total sediment amount for the velocity-skewed oscillatory sheet flow transport. With the sediment concentration hindered fall velocity, the classical reference concentration formulas conducted by Engelund and Fredsoe (1976) and Zyserman and Fredsoe (1994) are utilized for the comparison with the two-phase model and illustration of the phase-lag and sediment size effects in near-bed sediment concentration and vertical sediment flux. The concentration and vertical flux predicted by the two-phase model agree well with experimental data and are better than empirical formulas. Furthermore, the sediment size effect for pick-up flux function over starved bed is shown to be quite different from that containing sufficient sediment in oscillatory flows.
Highlights
The phenomenon of sediment entrainment and settlement is universal in river and coastal environment and extraordinarily important in the subaquatic geomorphology
In fully developed steady flows, the pick-up flux and settling flux are in balance and the total vertical flux is zero
The near-bed concentrations denoting vertical flux strength in steady flows [4,5,6] are applied and widely used in unsteady numerical models for sediment transport [7,8,9], and even their concentrations drop to zero near the flow reversal when the bottom shear stress is under a threshold
Summary
The phenomenon of sediment entrainment and settlement is universal in river and coastal environment and extraordinarily important in the subaquatic geomorphology. The near-bed concentrations denoting vertical flux strength in steady flows [4,5,6] are applied and widely used in unsteady numerical models for sediment transport [7,8,9], and even their concentrations drop to zero near the flow reversal when the bottom shear stress is under a threshold. Very little is known about the near-bed concentration and vertical flux for fine sediment and the phase-lag effects, which are important in the generation of net sediment transport, especially in velocity-skewed oscillatory flows with a sharp wave crest and gentle wave trough. Present study utilizes a two-phase model to study the near-bed sediment concentration and vertical fluxes in velocity-skewed oscillatory sheet flows containing sufficient amount of sediment. The results mainly exhibit and explain the phase-lag characteristics in concentration and vertical flux at the reference height, near-immobile bed, and very low concentration area for difference sediment sizes
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
