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Turbulence characteristics of a small subtropical estuary during and after some moderate rainfall

Trevethan , Mark, Chanson , Hubert, & Brown, Richard J. (2008) Turbulence characteristics of a small subtropical estuary during and after some moderate rainfall. Estuarine, Coastal and Shelf Science, 79(4), pp. 661-670.

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Abstract

In natural estuaries, scalar diffusion and dispersion are driven by turbulence. In the present study, detailed turbulence measurements were conducted in a small subtropical estuary with semi-diurnal tides under neap tide conditions. Three acoustic Doppler velocimeters were installed mid-estuary at fixed locations close together. The units were sampled simultaneously and continuously at relatively high frequency for 50 h. The results illustrated the influence of tidal forcing in the small estuary, although low frequency longitudinal velocity oscillations were observed and believed to be induced by external resonance. The boundary shear stress data implied that the turbulent shear in the lower flow region was one order of magnitude larger than the boundary shear itself. The observation differed from turbulence data in a laboratory channel, but a key feature of natural estuary flow was the significant three dimensional effects associated with strong secondary currents including transverse shear events. The velocity covariances and triple correlations, as well as the backscatter intensity and covariances, were calculated for the entire field study. The covariances of the longitudinal velocity component showed some tidal trend, while the covariances of the transverse horizontal velocity component exhibited trends that reflected changes in secondary current patterns between ebb and flood tides. The triple correlation data tended to show some differences between ebb and flood tides. The acoustic backscatter intensity data were characterised by large fluctuations during the entire study, with dimensionless fluctuation intensity I0b =Ib between 0.46 and 0.54. An unusual feature of the field study was some moderate rainfall prior to and during the first part of the sampling period. Visual observations showed some surface scars and marked channels, while some mini transient fronts were observed.

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ID Code: 46943
Item Type: Journal Article
Keywords: turbulence, small subtropical estuary, covariances, triple correlations, field measurements, acoustic Doppler velocimetry, rainfall runoff
DOI: 10.1016/j.ecss.2008.06.006
ISSN: 0272-7714
Subjects: Australian and New Zealand Standard Research Classification > ENGINEERING (090000) > ENVIRONMENTAL ENGINEERING (090700) > Environmental Engineering Modelling (090702)
Divisions: Past > QUT Faculties & Divisions > Faculty of Built Environment and Engineering
Past > Schools > School of Engineering Systems
Copyright Owner: Copyright 2008 Elsevier
Copyright Statement: This is the author’s version of a work that was accepted for publication in <Estuarine, Coastal and Shelf Science>. Changes resulting from the publishing process, such as peer review, editing, corrections, structural formatting, and other quality control mechanisms may not be reflected in this document. Changes may have been made to this work since it was submitted for publication. A definitive version was subsequently published in Estuarine, Coastal and Shelf Science, [VOL 79, ISSUE 4, (2008)] DOI: 10.1016/j.ecss.2008.06.006
Deposited On: 10 Nov 2011 08:23
Last Modified: 01 Mar 2012 11:30

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