Dynamics of

Abstract

This paper describes the dynamics o f Concentrated Benthic Suspensions (CBS). CBS is defined as a suspension o f cohesive sediment with a notable interaction between the sediment and the turbulent flow field through buoyancy effects, but still displaying near-Newtonian behaviour. The mechanisms which distinguish CBS from low-concentrated suspensions are described, and the focus is on the (hindered) settling and mixing processes. Experiments were carried out in an oscillating grid tank and in an rotating annular flume, simulating entrainment and mixing associated with the turbulent CBS-layer, as occur in tide-driven flows. It is shown that CBS can be modelled as a viscous fluid, and that the entrainment rates quantitatively match relations described in the literature on salt-fresh water induced stratified systems. Numerical simulations with one-dimensional vertical models using k-E and Prandtl mixing length turbulence closures were carried out for hypothetical open channel flows to study the behaviour o f CBS through sensitivity analyses. It is shown that high-concentrated mud suspensions may become saturated, generating a CBS-layer prior to the formation o f fluid mud. KEY-WORDS Concentrated Benthic Suspensions, fluid mud, entrainment, mixing, buyoanc