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 turbidity-induced 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 (ε) 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 × 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 (ws) scaled with the friction velocity (u*) in the form ws/u* = D*/8. The median size of resuspended aggregates (df) scaled inversely with dissipation (ε) in the form df = 5 × 10–6ε–0.24m, which is close to the relationship found in the literature.

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