A Fundamental Study of Turbulence and Turbulent Mixing in a Small Subtropical Estuary

Trevethan, Mark (2008). A Fundamental Study of Turbulence and Turbulent Mixing in a Small Subtropical Estuary PhD Thesis, Civil Engineering, The University of Queensland.

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Author Trevethan, Mark
Thesis Title A Fundamental Study of Turbulence and Turbulent Mixing in a Small Subtropical Estuary
School, Centre or Institute Civil Engineering
Institution The University of Queensland
Publication date 2008
Thesis type PhD Thesis
Supervisor Hubert Chanson
Total pages 342
Collection year 2008
Language eng
Subjects 290000 Engineering and Technology
290800 Civil Engineering
290802 Water and Sanitary Engineering
291800 Interdisciplinary Engineering
291803 Turbulent Flows
260502 Surfacewater Hydrology
260403 Physical Oceanography
Abstract/Summary The flow of water in natural systems such as estuaries is a turbulent process, with Reynolds numbers greater than 1E+5. Understanding the turbulence properties of an estuary is important for the investigation of mixing, dispersion and sediment transport within an estuary. This study investigates the turbulence properties in a typical small subtropical estuary (Eprapah Creek, Australia). Small coastal plain type estuaries constitute approximately 60 % of all estuaries in Australia, yet no thorough study of the turbulence properties of this type of estuary has been conducted. To date only a limited number of turbulence studies in estuaries have been undertaken. One reason for this was the lack of appropriate instrumentation to collect turbulent velocity measurements with fine spatial and temporal resolutions. This is especially true of turbulence studies in small estuaries, with the majority of published turbulence studies being performed in relatively large systems. Previous studies of turbulence in estuaries were mostly conducted for relatively short periods (up to 6 hours) and by collecting data over long periods in bursts of several minutes. The present study showed that acoustic Doppler velocimetry (ADV) was well suited for the measurement of turbulence properties in small estuarine systems. A unique aspect of this study was the continuous collection of turbulence data at high frequency (fscane ≥ 25 Hz) for relatively long periods (Tstudy up to 50 hours). This approach characterised the estuarine turbulence properties for up to two complete tidal cycles. The data analysis showed that continuous collection of high frequency turbulence data was essential to accurately characterise the rapid fluctuations of turbulence in an estuary. The field data showed that the turbulence flow properties were highly fluctuating in a small estuary. All turbulence properties exhibited large and rapid fluctuations over the investigation period of each field study. The variations in time scales were related to both the instantaneous local flow properties and the tidal fluctuations. Some long period oscillations observed in the water level and velocity data also had a significant impact on the turbulence properties. These long period oscillations had periods similar to resonance periods generated both internally in and externally to the creek. Many turbulence properties showed an asymmetrical response to the tidal forcing, especially under spring tidal conditions. Large turbulent velocity fluctuations were, however, observed throughout all investigation periods, including during the slack tides. Substantial fluctuations in the normal and tangential Reynolds stresses were observed in the middle and upper estuarine zones. The turbulent velocity data showed some non-Gaussian behaviour and the Reynolds stresses were non-Gaussian throughout all investigation periods. Field data collected mid estuary under spring and neap tidal conditions showed two distinctly different turbulence responses for spring and neap tides. During spring tides, the magnitudes of all turbulence properties were up to an order of magnitude larger than for neap tides. The turbulence properties showed some increased tidal asymmetries under spring tidal conditions. Further two field studies were conducted under similar neap tidal conditions in the middle and upper estuarine zones. A comparison of these two data sets showed that the turbulence properties in the middle and upper estuaries differed substantially. Mid estuary, the magnitude of the turbulence properties were up to an order of magnitude larger than those observed in the upper estuary, thereby indicating that at least three distinct sets of turbulence properties existed in this small subtropical estuary. This study included some turbulence data collected in a large tidal lake with a restricted entrance (Hamana Lake, Japan). This turbulence data was compared with the data measured in Eprapah Creek. The comparison showed similar tidal patterns in some turbulence properties were observed close to the bed despite the distinct topography and hydrodynamics of the two estuaries. Some of these patterns in turbulence properties were also observed in previous studies of turbulence in estuaries. However, the spring tide data collected in the small estuary showed an increased magnitude of turbulence and a more asymmetrical response than other estuarine turbulence studies. The ratio of local tidal amplitude and local mean depth was used to characterise the local turbulence properties for a certain tidal range. A critical value of the ratio a1/h1 was 0.5, corresponding to the local tidal range being equal to the local mean depth. If the tidal range was greater than the local mean depth (i.e. a1/h1 > 0.5), a more asymmetrical tidal response and some increased turbulence property magnitudes were observed. A comparison of the turbulence properties in two distinct tidal systems (Eprapah Creek and Hamana Lake) showed similar tidal patterns for a1/h1 < 0.5.
Keyword Turbulent mixing
Turbulence
Dispersion
Subtropical estuary
Small estuarine system
Eprapah Creek
South-East Queensland
Australia
Hamana Lake
Japan
Field works
Acoutic Doppler Velocimetry ADV
Signal processing
Additional Notes The full bibliographic details are : [1] TREVETHAN, M. (2008). "A Fundamental Study of Turbulence and Turbulent Mixing in a Small Subtropical Estuary." Ph.D. thesis, Dept of Civil Engineering, The University of Queensland, 342 pages. This UQeSpace record is the Ph.D. thesis of Dr Mark TREVETHAN, undertaken in the Division of Civil Engineering at the University of Queensland. The record includes 3 files : (1) M_Trevethan_PhD_Thesis_2008.pdf (Ph.D. thesis, print version), (2) PHD_FD_Digital_Appendix.7z (Digital appendices) and (3) ReadMe.txt (ASCII information text file). The Digital Appendix (Filename PHD_FD_Digital_Appendix.7z) is a series of compressed files. The format is .7z. The file was prepared with 7-zip (version 4.43). 7-zip is an open source software. Most of the source code is under the GNU LGPL license. The unRAR code is under a mixed license: GNU LGPL + unRAR restrictions. The software 7-zip that may be freely downloaded from : {www.7-zip.org}. Any use of the material and data available in the digital appendix must acknowledge and cite [1]. Further details on the Ph.D. thesis including the digital appendix may be obtained from : Dr Mark TREVETHAN {mark.trevethan@gmail.com}. Alternately, information may be obtained from Mark's Ph.D. supervisor : Professor Hubert CHANSON {h.chanson@uq.edu.au}, Division of Civil Engineering, The University of Queensland, Brisbane QLD 4072, Australia, Ph.: (61 7) 3365 3619 / Fax: (61 7) 3365 45 99. ------------- The results of Dr Mark TREVETHAN's research study were published in a series of peer-reviewed scientific publications available at the UQ institutional open access repository UQeSpace {http://espace.library.uq.edu.au/} : {http://espace.library.uq.edu.au/list/browse=author&author_id=8578}. The list of publications includes on 28 Feb. 2008 : CHANSON, H., TREVETHAN, M., and AOKI, S. (2005). "Acoustic Doppler Velocimetry (ADV) in a Small Estuarine System. Field Experience and "Despiking"." Proc. 31st Biennial IAHR Congress, Seoul, Korea, B.H. JUN, S.I. LEE, I.W. SEO and G.W. CHOI Editors, Theme E2, Paper 0161, pp. 3954-3966 (ISBN 89 87898 24 5). {http://espace.library.uq.edu.au/view/UQ:9188}; TREVETHAN, M., CHANSON, H., and BROWN, R.J. (2006). "Two Series of Detailed Turbulence Measurements in a Small Subtropical Estuarine System." Report No. CH58/06, Div. of Civil Engineering, The University of Queensland, Brisbane, Australia, March, 153 pages (ISBN 978-1-86499-852-8) (ISBN 1864998520 [10 digits]). {http://espace.library.uq.edu.au/view/UQ:8200}; CHANSON, H., TAKEUCHI, M., and TREVETHAN, M. (2006). "Using Turbidity and Acoustic Backscatter Intensity as Surrogate Measures of Suspended Sediment Concentration. Application to a Sub-Tropical Estuary (Eprapah Creek)." Report No. CH60/06, Div. of Civil Engineering, The University of Queensland, Brisbane, Australia, Aug, 44 pages (ISBN 978-1-86499-862-7) (ISBN 1864998628 [10 digits]). {http://espace.library.uq.edu.au/view/UQ:7975}; CHANSON, H., and TREVETHAN, M. (2006). "Turbulence in Small Sub-tropical Estuary with Semi-Diurnal Tides." Proceedings of 2nd International Conference on Estuaries and Coasts (ICEC-2006), Guangzhou, Guangdong Province, China, November 28-30, Invited paper, Guangdong Economy Publ., Vol. I, pp. 140-151 (ISBN 978-7-80728-422-2) (ISBN 7-80728-422-6 [10 digits]). {http://espace.library.uq.edu.au/view/UQ:7718}; CHANSON, H., and TREVETHAN, M. (2007). "Turbulence in Small Sub-Tropical Estuary with Semi-Diurnal Tides." Pearl River, Renmin Zhujiang, No. 1, Feb., pp. 16-22 (ISSN 1001- 9235) (in Chinese). {http://espace.library.uq.edu.au/view/UQ:13648}; TREVETHAN, M., CHANSON, H., and TAKEUCHI, M. (2007). "Continuous High-Frequency Turbulence and Sediment Concentration Measurements in an Upper Estuary." Estuarine Coastal and Shelf Science, Vol. 73, No. 1-2, pp. 341-350 (DOI:10.1016/j.ecss.2007.01.014) (ISSN 0272-7714). {http://espace.library.uq.edu.au/view.php?pid=UQ:13781}; TREVETHAN, M., and CHANSON, H. (2007). "Detailed Measurements during a Transient Front in a Small Subtropical Estuary." Estuarine Coastal and Shelf Science, Vol. 73, No. 3-4, pp. 735-742 (DOI 10.1016/j.ecss.2007.03.014) (ISSN 0272-7714). {http://espace.library.uq.edu.au/view/UQ:23601}; CHANSON, H., TREVETHAN, M., and TAKEUCHI, M. (2007). "High-Frequency Turbulence and Sediment Flux Measurements in an Upper Estuarine Zone." Proc. 32nd IAHR Biennial Congress, Venice, Italy, G. DI SILVIO and S. LANZONI Editors, Topic D1.b, 10 pages (CD-ROM). {http://espace.library.uq.edu.au/view/UQ:23905}; CHANSON, H., TAKEUCHI, M., and TREVETHAN, M. (2007). "High-Frequency Suspended Sediment Flux Measurements in a Small Estuary." Proc. 6th International Conference on Multiphase Flow ICMF 2007, Leipzig, Germany, July 9-13, M. SOMMERFIELD Editor, Session 7, Paper No. S7_Mon_C_S7_Mon_C_5, 12 pages (CD-ROM). {http://espace.library.uq.edu.au/view/UQ:23909}; CHANSON, H., TREVETHAN, M., and KOCH, C. (2007). "Turbulence Measurements with Acoustic Doppler Velocimeters. Discussion." Journal of Hydraulic Engineering, ASCE, Vol. 133, No. 11, pp. 1283-1286 (DOI: 10.1061/(ASCE)0733-9429(2005)131:12(1062)) (ISSN 0733-9429). {http://espace.library.uq.edu.au/view/UQ:120467}; In addition the following publication was derived from a related research project : TREVETHAN, M., CHANSON, H., and BROWN, R.J. (2007). "Turbulence and Turbulent Flux Events in a Small Subtropical Estuary." Report No. CH65/07, Hydraulic Model Report series, Div. of Civil Engineering, The University of Queensland, Brisbane, Australia, November, 67 pages (ISBN 9781864998993). {http://espace.library.uq.edu.au/view/UQ:121014}.

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