Measurements of turbulence in the benthic boundary layer over a gravel bed

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ABSTRACT

It is now generally recognized that the mathematical description of sediment dynamics will be improved through an understanding of geophysical turbulence. In this study, therefore, the turbulence characteristics of the benthic boundary layer over coarse sediments are examined as a step towards the realization of such a description.

Examination of the turbulence has been conducted using spectral, correlation, quadrant and statistical analyses, and a number of features have been identified. Mean eddy length scales obtained using spectral and autocorrelation techniques were found to be similar. The interpretation of the duration and interval between the intermittent ‘bursting’ events, scaled using outer flow variables, was found to be dependent upon the sampling interval. Autocorrelation analysis revealed a high correlation between bedload transport and the instantaneous horizontal flow component rather than instantaneous kinematic stress. From the standpoint of developing prognostic transport models based on physically realistic benthic flow processes, it is considered that turbulence measurements will lead to such formulation.

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