Abstract
Abstract. We 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.
Highlights
Turbidity currents flowing in submarine canyons are recognized as preferential conduits for sediment transfer from shallow to deep water
We were interested in quantifying how these parameters affect the dynamics of the current flowing in a straight channel, and if it was possible to identify some dimensionless parameter responsible for the vertical shape of the dimensionless longitudinal velocity
We focused our attention on the development of the currents in the first straight reach of our flume, where we observed the achievement of a quasiuniform state of the current characterized by self-similar dimensionless velocity profiles
Summary
Turbidity currents flowing in submarine canyons are recognized as preferential conduits for sediment transfer from shallow to deep water They have a tremendous impact on the deep-sea environment since they affect the ecosystem in various ways, including burial by sediment deposition, exposure by sediment removal, and food supply. A notable exception is the recent field observation performed by Xu et al (2004), who successfully measured vertical profiles of downstream velocity for four flow events over the space of 1 year, at three locations down Monterey Canyon, California Due to these difficulties, the majority of the investigations aimed at understanding the dynamic of turbidity currents has been either through theoretical investigations or through experimental observations
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