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

Trevethan, M., Chanson, H. and Brown, R. (2008) Turbulence characteristics of a small subtropical estuary during and after some moderate rainfall. Estuarine Coastal And Shelf Science, 79 4: 661-670. doi:10.1016/j.ecss.2008.06.006

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Author Trevethan, M.
Chanson, H.
Brown, R.
Title Turbulence characteristics of a small subtropical estuary during and after some moderate rainfall
Journal name Estuarine Coastal And Shelf Science   Check publisher's open access policy
ISSN 0272-7714
Publication date 2008
Year available 2008
Sub-type Article (original research)
DOI 10.1016/j.ecss.2008.06.006
Open Access Status File (Author Post-print)
Volume 79
Issue 4
Start page 661
End page 670
Total pages 10
Place of publication London
Publisher Academic Press
Collection year 2008
Language eng
Subject 290000 Engineering and Technology
290800 Civil Engineering
290802 Water and Sanitary Engineering
291800 Interdisciplinary Engineering
291803 Turbulent Flows
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 hours. 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 Ib'/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.
Formatted 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 hours. 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 Ib'/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.
Keyword Turbulence
Small subtropical estuary
Covariances
Triple correlations
Field measurements
Acoustic Doppler velocimetry
Rainfall runoff
Q-Index Code C1
Q-Index Status Provisional Code
Additional Notes The full bibliographic details are : TREVETHAN, M., CHANSON, H., and BROWN, R. (2008). "Turbulence Characteristics of a Small Subtropical Estuary during and after some Moderate Rainfall." Estuarine Coastal and Shelf Science, Vol. 79, No. 4, pp. 661-670 (DOI: 10.1016/j.ecss.2008.06.006) (ISSN 0272-7714).

Document type: Journal Article
Sub-type: Article (original research)
Collection: School of Civil Engineering Publications
 
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Citation counts: TR Web of Science Citation Count  Cited 6 times in Thomson Reuters Web of Science Article | Citations
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Created: Thu, 04 Sep 2008, 20:53:16 EST by Hubert Chanson on behalf of School of Civil Engineering