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The kinematics of turbulent suspension currents (turbidity currents) on inclined boundaries

1985; Elsevier BV; Volume: 64; Issue: 1-2 Linguagem: Inglês

10.1016/0025-3227(85)90158-6

1872-6151

Christoph Siegenthaler, Johannes Bühler,

Hydrology and Sediment Transport Processes

Turbulent suspension currents are investigated theoretically and experimentally for a wide density range of suspended particles. It was found that suspension currents approach an equilibrium state (normal state) with a balance between gravity, entrainment of ambient water, bottom friction and the sedimentation of suspended particles. For given boundary conditions the equilibrium state can be described by only four characteristic and easily measurable parameters such as a velocity, a length or time scale, a scale for the buoyancy and one for the buoyancy loss due to sedimentation. An important dimensionless product is the sedimentation number which is proportional to the rate at which the buoyancy is lost and which remains approximately constant during an experiment. Other dimensionless products such as the Richardson number are therefore also spatially invariant. A large sedimentation number decreases the Richardson number, and the latter is always smaller for suspension currents which loose sediment than for density currents without buoyancy loss. In the case of the geologically important suspension clouds (currents fed by an instantaneous source, e.g. a slump), experimental and field data suggest an invariant number δ g′sedU2 which contains the thickness (δ) of the deposit, the densimetric gravitational acceleration acting on the bulk of the deposit (g′sed) and the front velocity of the current (U). The magnitude of the invariant number is about 0.3.