Present address: Centre for Catchment to Coast Research, School of Ocean Sciences, University of Wales Bangor, Menai Bridge, Anglesey LL59 5AB, UK.
The dynamics of turbulent, transitional and laminar clay-laden flow over a fixed current ripple
Article first published online: 21 NOV 2007
© 2007 The Authors. Journal compilation © 2007 International Association of Sedimentologists
Volume 55, Issue 3, pages 635–666, June 2008
How to Cite
BAAS, J. H. and BEST, J. L. (2008), The dynamics of turbulent, transitional and laminar clay-laden flow over a fixed current ripple. Sedimentology, 55: 635–666. doi: 10.1111/j.1365-3091.2007.00916.x
- Issue published online: 21 NOV 2007
- Article first published online: 21 NOV 2007
- Manuscript received 9 December 2006; revision accepted 14 September 2007
- Clay suspensions;
- current ripples;
- turbulence modulation;
- ultrasonic Doppler velocity profiling
Most aqueous sedimentary environments contain varying concentrations of fine-grained, often clay-rich, sediment that is transported in suspension and may modify the properties of the flow and underlying mobile bed. This paper presents results from a series of laboratory experiments examining the mean and turbulent properties of clay-laden (kaolinite) flows, of various volumetric sediment concentrations between 0·046% and 12·7%, moving over a fixed, idealized current ripple.
As the kaolinite concentration was raised, with flow velocity and depth constant, four flow types were observed to occur: (i) turbulent flow, in which flow separation is dominant in the leeside of the ripple; (ii) turbulence-enhanced transitional flow, in which turbulence in the leeside separation zone region is enhanced; (iii) turbulence-attenuated transitional flow, in which turbulence along the separation zone shear layer and in the free flow above it becomes damped, eventually leading to a reduction in the size of the separation zone wake region; and (iv) laminar plug flow, in which turbulence is damped and flow is almost stagnant in the lee of the ripple. Such modulation of turbulence by increasing clay concentrations suggests that many paradigms of flow and bedform dynamics, which have been based on extensive past work in clear water flows, require revision. The present results highlight a need to fully characterize the boundary conditions for turbulence modulation as a function of clay type and applied flow conditions, and the effects of such flows on fully mobile cohesionless beds.