Velocity and concentration profiles of saline and turbidity currents flowing in a straight channel under quasi-uniform conditions

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.

The Structure and Entrainment Characteristics of Partially Confined Gravity Currents

“…Variations are to be expected with differences in basal materials, laboratory conditions and the difficulty in defining a current's height. A dependence of h max on both the flow's Richardson number (Sequeiros et al, ) and Reynolds number (Stagnaro & Pittaluga, ) has also been observed. For the partially confined flows analyzed here, h max remains nearly constant for all the laboratory‐scale flows at a height equal to half the channel depth, regardless of flow height or Richardson number.…”

“…However, this approach has limitations for erosional or bypassing flows as it does not take into account Reynolds‐dependent turbulent effects in the lower boundary (Imran et al, ). Also, high‐velocity maximum heights were not replicated in the simulations of Kneller et al (), despite the stably stratified layer, nor in further experiments of subcritical flows which found limited dependence on Richardson number (Stagnaro & Pittaluga, ).…”

Breaching Flow Slides and the Associated Turbidity Current

“…Stagnaro and Pittaluga [58] validated the empirical relation suggested by [56] using their experimental values of the entrainment coefficient and found that it provides a good estimate.…”

Coupling of Ultrasonic and Photometric Techniques for Synchronous Measurements of Unconfined Turbidity Currents

“…Lock-exchange generated turbidity currents have discontinuous flow properties; hence velocity measurements must be collected instantaneously to obtain a discrete, representative velocity profile. UVP is therefore gaining popularity as a method for measuring lock-exchange turbidity currents due to its ability to measure multiple velocity profiles [8,[26][27][28]. However, it remains under-utilized for experimental studies incorporating obstacles and substrates.…”