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Towards a rational interpretation of the notion of formative discharge in meandering rivers
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Velocity and concentration profiles of saline and turbidity currents flowing in a straight channel under quasi-uniform conditions
No full textWe present a series of detailed experimental observations of saline and turbidity currents flowing
in a straight channel. Experiments are performed by continuously feeding the channel with a dense mixture
until a quasi-steady configuration is obtained. The flume, 12 m long, is characterized by a concrete fixed bed
with a uniform slope of 0.005. Longitudinal velocity profiles are measured in ten cross sections, 1 m apart,
employing an ultrasound Doppler velocity profiler. We also measure the density of the mixture using a rake
of siphons sampling at different heights from the bottom in order to obtain the vertical density distributions in
a cross section where the flow already attained a quasi-uniform configuration. We performed 27 experiments
changing the flow discharge, the fractional excess density, the character of the current (saline or turbidity)
and the roughness of the bed in order to observe the consequences of these variations on the vertical velocity
profiles and on the overall characteristics of the flow. Dimensionless velocity profiles under quasi-uniform
flow conditions were obtained by scaling longitudinal velocity with its depth averaged value and the vertical
coordinate with the flow thickness. They turned out to be influenced by the Reynolds number of the flow, by the
relative bed roughness, and by the presence of sediment in suspension. Unexpectedly, the densimetric Froude
number of the current turned out to have no influence on the dimensionless velocity profiles
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