Hydrodynamic Controls on the Particle Size of Resuspended Sediment from Sandy and Muddy Substrates in British Columbia, Canada

Abstract

A benthic annular flume, Sea Carousel, was deployed at both sand-dominated (Baynes Sound) and mud-dominated (Carrie Bay) stations in British Columbia, Canada, to examine the character of near-bed flow over these contrasting bottom types and its control on particle size of resuspended sediment. An assessment has also been made of the turbidityinduced drag reduction due to suspension of bottom sediments. The median sizes of suspended material from the sandy sites have been compared with the well-known Rouse theory, whereas the aggregates resuspended from muddy stations were scaled with the energy dissipation rate (e) determined from high-frequency three-dimensional flow measures in the flume. There was no evidence in the turbulence spectra in the Sea Carousel of energy inputs in the paddle and lid rotational frequencies, and a f-5/3 slope for f. 2 Hz in turbulent transitional flows was evident. The bed roughness length of sandy sites was Reynolds-number dependent but was asymptotic to a constant value of 2 mm at high flows. This equated to a dimensionless drag coefficient at 1 m above bed of a constant, 3 3 10-3 (also at high Reynolds numbers), which agrees well with values reported in the literature. The median size of suspended sand (from the sandy sites) and equivalent still water settling rate (w s) scaled with the friction velocity (u *) in the form w s /u * ¼ D * /8. The median size of resuspended aggregates (d f) scaled inversely with dissipation (e) in the form d f ¼ 5 3 10-6 e-0.24 m, which is close to the relationship found in the literature.

The Mass Settling Flux of Suspended Particulate Matter in Venice Lagoon, Italy

“…Smoothed three-dimensional plots of G, C t , and d f showed a positive relationship of d f with G. That is, the larger the applied stress, the larger is the sedimentation diameter. This is opposite to that expected from Kassem, Sutherland, andAmos (2021), Lick, Huang, andJepsen (1993), Mehta (2014), andWinterwerp (2011), who suggest d f ; 1 ffiffiffi G p . A positive relationship is typical of silica sand (van Rijn, 1994) or dense aggregates suspended from an eroding bed.…”

“…Strong evidence suggests that, under conditions of flow, this diameter is controlled by shear rate (G) (Kassem, Sutherland, and Amos, 2021), whereas in still water, particle concentration and differential settling are important. An examination of factors influencing d f is thus justified and is the focus of the next section.…”

“…The extent to which the sedimentation diameter, settling rate, and settling flux relate to the measured diameters (and settling rates) reported by Dyer (1989) and Dyer and Manning (1999) is examined. According to Baugh and Manning (2007), settling flux is dominated by the largest particles (macroflocs), which in turn are controlled by the shear rate within the flow (Kassem, Sutherland, and Amos, 2021). The Mini Flume data from Venice Lagoon for summer and winter deployments fit very well with the data from Sternberg, Berhane and Ogston (1999) (Figure 5), resulting in the relationship W s ¼ 0:145d f 1:58 (r 2 ¼ 0.78, n ¼ 151) (where d f has units of microns [lm] and W s has units of lm s -1 ).…”

Role of saltmarsh systems in estuarine trapping of microplastics

“…This increase in turbulent forces within the saltmarsh and mudflat tests at this low height may be attributed to irregularities and unevenness of their bed surfaces (Fig. 4) due to benthic activities and is an indication of the effect of bed roughness on turbulent flows 29,30. The calculated hydrodynamic roughnesses, z 0 = 10 -4 to 10 -6 m, were typical of muddy environments in the flatbed case 31 . A similar effect of bed roughness on the flow regimes can be observed from the mean velocities and bed shear stress (Table S2), with an increase in the downstream direction from P1 to P3.…”

Vegetation variety affected by local environments in a coral reef lagoon

“…Additionally, winter winds can enhance water exchange throughout the lagoon through mixing induced by wave and wind action. Such complex water motions often affect the size composition of the deposition particles (Kassem et al 2021). nMDS indicated that monthly means of flow velocity and diurnal flow velocity have both positive and negative correlations with the size fractions of deposited particles (Fig.…”