New Zealand Journal of Marine and Freshwater Research abstracts
On stream periphyton-turbulence interactions
V. I. NIKORA
D. G. GORING
B. J. F. BIGGS
National Institute of Water and Atmospheric
Research Ltd
P. O. Box 8602
Christchurch, New Zealand
Abstract A set of experiments was carried out to determine
what effects periphyton communities could have on near-bed hydraulic fields. We
analysed velocity distribution, skewness and kurtosis coefficients, Reynolds
stresses, relative turbulence intensity, coefficient of eddy diffusivity,
velocity spectra, and turbulence scales at two flows with, and without,
diatom-dominated periphyton on the bed. We found that turbulence was affected
by the periphyton mat selectively. The largest influence occurred for the
velocity distribution, Reynolds stress, coefficient of eddy diffusivity, and
velocity cross-spectra. Changes as a result of the periphyton mat were revealed
in the large-scale turbulence structure. The periphyton affected not only the
region near the bottom but also the entire logarithmic layer. The periphyton
mat increased roughness length by a factor of ~5 whereas the integral
resistance to flow (reciprocal Chezy coefficient and Manning's roughness
coefficient) was increased by 20-25%. The microscale turbulence structure was
investigated using values of Kolmogorov's microscale [[eta]]K. These
appeared to be commensurate with the characteristic scales of periphyton
filaments. This allowed us to hypothesise that the mechanism of the
"periphyton-turbulence" interaction is connected, to a certain degree, with
viscous effects.
Keywords periphyton; open-channel flow; turbulence
New Zealand Journal of Marine and Freshwater Research, 1997, Vol. 31:
435-448
0028-8330/97/3104-0435 $7.00/0 (c) The Royal Society of New Zealand
1997
PDF file of entire paper: medium quality (1012K); (scanned from paper original: notes about this process)
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