An Experimental Study on Progressive and Reverse Fluxes of Sediments with Fine Fractions in Wave Motion

Abstract

The purpose of the study was to collect experimental data on the vertical structure of sediment fluxes during the wave crest and trough phase. The first stage of the experimental work included measurements of these fluxes using the particle image method, while in the second stage, measurements of sediment transport rates and granulometric distributions of sediments were collected in the traps on both sides of the initial area. The experimental data were compared with the results of a theoretical analysis based on a three-layer model of graded sediment transport. The comparison of the calculations with the measurements was conducted separately for fluxes of fine and very fine fractions in the diameter range di < 0.20 mm, coarse, and total fractions all outgoing in the crest and trough phase from the initial area and deposited in adjacent control areas. As this model did not take into account both the effects of vertical mixing and the phase-lag effects related to the presence of fine and very fine fractions, a modification of this model was proposed that was based on four coefficients that corrected for fluxes. The consistency of the sediment transport calculations according to the modified model with measurements was achieved within plus/minus a factor of 2 of the measurements.

An Experimental Study on Progressive and Reverse Fluxes of Sediments with Fine Fractions in the Wave Motion over Sloped Bed

“…Zou et al [42] in their studies noticed that the sloping bottom has a significant effect on vertical orbital velocities but not on horizontal velocities and shear stress. Moreover, the asymmetry of the considered velocities is much lower than the corresponding values recorded for flat bottom [31]. As a result of this procedure the curve f(t) was obtained and is denoted by red line in Figure 4.…”

“…The second layer-the contact layer-is also characterized by a high concentration but lower enough that vertical sorting of grains is possible. The third layer is an area of well-sorted suspended sediment, with very low concentration [31].…”

“…When considering the components of sediment transport involving fine and very fine fractions over a sloping bed, due to the varying nature of the physical processes occurring at different distances from the bed, several layers can be distinguished to facilitate the description of vertical structure of sediment transport flowing out of the control area. Figure 1 after [31] schematically depicts the vertical structure of sediment transport in wave motion over a sloping bed, divided into the crest and trough phases of the wave. The positive direction of sediment transport is described according to the wave direction (Figure 1).…”

“…fractions in the trap, as calculated using the model of Kaczmarek et al 2022, can be described as follows:…”

“…The main aim of the present study was to collect experimental data documenting the vertical structure of sediment fluxes outgoing in both directions from the computational area to adjacent control areas (and retained in traps), as well as the granulometric composition of these sediments on both sides of the output area under sloping bed conditions. Knowledge of these quantities allows to expand our knowledge of sediment transport in the crest and trough phase of the wave over the sloping bed, respectively, and allows to compare the obtained results with the measured results obtained over the flat bed [31]. The experimental results were then confronted with the results of theoretical analysis based on the three-layer model of heterogeneous sediment transport [32].…”