Glossary

Dissipation rate of TKE - Rate of dissipation of TKE per unit volume of water and per unit time. This energy is dissipated into heat by internal friction among fluid elements described by viscosity.

Nepheloid layer - Particle-rich layer above the sediment. This layer is sustained by a balance between gravitational settling and turbulent vertical diffusion counteracting it.

Pore water - Water that fills the interstitial space between sediment grains.

Reynolds number - The dimensionless Reynolds number Re is the ratio of inertial to viscous forces acting on a fluid element, obstacle in the flow, or submerged organism and describes the transition from laminar to turbulent flow regimes.

Shear stress - Force per unit area acting in parallel (tangential) to the surface of a fluid element or interface (e.g., bed shear stress).

Turbulent eddies - Turbulence is composed of eddies: patches of zigzagging, often swirling fluid, moving randomly around and about the overall direction of motion. Technically, the chaotic state of fluid motion arises when the speed of the fluid exceeds a specific threshold, below which viscous forces damp out the chaotic behaviour (see also Reynolds number).

Turbulent kinetic energy - Kinetic energy per unit volume of water, which is contained in the random fluctuations of turbulent motions. Turbulent velocity fluctuations u' can be separated from the mean current velocity u by Reynolds decomposition of the actual velocity u (u = u + u'). Turbulent kinetic energy (TKE) is then defined by, TKE = 1/2pU2, where p denotes density of water.

See also: Biological-Physical Interactions; Currents in Stratified Water Bodies 1: Density-Driven Flows; Currents in Stratified Water Bodies 2: Internal Waves; Currents in Stratified Water Bodies 3: Effects of Rotation; Currents in the Upper Mixed Layer and in Unstratified Water Bodies; Density Stratification and Stability; Small-Scale Turbulence and Mixing: Energy Fluxes in Stratified Lakes.

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