Flow dynamics and mixing processes in hydraulic jump arrays: Implications for channel-lobe transition zones

R.M Dorrell,J Peakall,E.J Sumner,D.R Parsons,S.E Darby,R.B Wynn,E Özsoy,D Tezcan

doi:10.1016/j.margeo.2016.09.009

R.M Dorrell, J Peakall + Show 6 more

Open Access

https://doi.org/10.1016/j.margeo.2016.09.009

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Abstract

A detailed field investigation of a saline gravity current in the southwest Black Sea has enabled the first complete analysis of three-dimensional flow structure and dynamics of a series of linked hydraulic jumps in stratified, density-driven, flows. These field observations were collected using an acoustic Doppler current profiler mounted on an autonomous underwater vehicle, and reveal that internal mixing processes in hydraulic jumps, including flow expansion and recirculation, provide a previously unrecognised mechanism for grain-size sorting and segregation in stratified density-driven flows. Field observations suggest a newly identified type of hydraulic jump, that is a stratified low Froude number (<1.5–2) subaqueous hydraulic jump, with an enhanced ability to transport sediment downstream of the jump, in comparison to hydraulic jumps in other subaerial and submarine flows. These novel field data underpin a new process-based conceptual model of channel lobe transition zones (CLTZs) that explains the scattered offset nature of scours within such settings, the temporal variations in infill and erosion between adjacent scours, how bed shear stresses are maintained across the CLTZ, and why the locus of deposition is so far downstream of the scour zone.

Highlights

Hydraulic jumps are characterised by a sudden decrease in velocity and an increase in thickness of a flow
For the first time we examine the three-dimensional flow dynamics of an array of subaqueous hydraulic jumps that are formed by a flow traversing a series of scours, in a natural field example
We demonstrate that these hydraulic jumps have depth-averaged Froude numbers around unity, and that the resulting flow dynamics are very different to higher depth-averaged Froude number (N 1.5–2) flows such as those associated with chutes-and-pools and cyclic steps

Summary

Introduction

Hydraulic jumps are characterised by a sudden decrease in velocity and an increase in thickness of a flow. Hydraulic jumps are thought to occur within gravity-driven flows located on the continental slope (Fildani et al, 2006; Fildani et al, 2013; Kostic et al, 2010; Maier et al, 2011), within submarine canyons and channels (Sumner et al, 2013; Covault et al, 2014; Symons et al, 2016), and in channel-lobe transition zones (Wynn et al, 2002; Kostic and Parker, 2006; Macdonald et al, 2011; Shaw et al, 2013; Hofstra et al, 2015).

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