Water dynamics and transport timescales of coastal waters and estuaries

Andutta, Fernando Pinheiro (2012) Water dynamics and transport timescales of coastal waters and estuaries. PhD thesis, James Cook University.

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Abstract

The transport time scales of water have been of considerable interest to marine biologists and biological oceanographers, as they are important parameters to determine aquatic ecosystem health and sensitivity to pollution threats (Lucas et al., 2009; McLusky and Elliott, 2004; Wolanski, 2007; Wolanski, et al., 2012). This thesis has two major components, (a) application of a numerical model to determine transport timescales of the GBR (Great Barrier Reef), and (b) the development and application of a new analytical model to determine timescales for river estuaries.

The SLIM model was used for the numerical simulations in the GBR (SLIM: Second-generation Louvain-la-Neuve Ice-ocean Model). The simulations were run with the Eulerian and Lagrangian schemes depending upon the application. This is the first model of the GBR that has been calibrated to accurately model mixing processes, which was done by comparison of model results with measurements of the hypersaline conditions of the dry season. The model properly simulated the rise of the salinity concentration, and the time to achieve steady state conditions in the dry season.

Model results of the hypersaline coastal waters in the central Great Barrier Reef have shown that the hypersaline waters formed near the coast and inside the bays are exported along the coast from bay to bay during the dry season. The bays supply hypersaline waters to coastal areas. The cross-shelf gradient of the hypersaline waters is mainly controlled by turbulent diffusion, whereas along the coast the salinity gradient is controlled by the residual currents due to the North Caledonia Jet inflow (NCJ) and the wind driven currents.

Results of the flushing time and the age of waters from the North Caledonia Jet inflow into the GBR were estimated under realistic boundary forces. The wind decreases the flushing time in the bays. In contrast, in coastal waters the wind may increase this timescale because the normal southerly flow due to the ocean inflow is opposed by the northward directed wind stress. A typical flushing time for the GBR under real wind conditions was about 70 days.

The sticky water effect in the Great Barrier Reef was estimated quantitatively using the SLIM model. It was demonstrated that some reef configurations result in high exposure time, which depends on the reef density (i.e. degree of aggregation by reefs). Two empirical formulations to estimate larvae retention within the reef matrix were provided. One formula required measurement of tidal and mean currents, and the other formula, that was less accurate, requires only information of the bathymetry and reef density.

The transport time scales, namely water renewal, residence time and exposure time were calculated using analytical solutions for a range of estuaries worldwide, and the results were compared with residence time results from numerical models where estimates were available. A new modified LOICZ model has been developed that quantifies the relative contribution of advection and diffusion to water renewal in estuaries using simple measurements of river discharge, salinity and the estuarine geometry. The modified LOICZ model resulted in the best fit against numerical results. A graphic conceptual model, the advection/diffusion timescale diagram, was also developed, which was used to visualize where different estuaries lie in the advective/diffusive timescale space diagram. Estuaries can now be divided into those which are dominated by diffusion, those which are dominated by advection and those where diffusion and advection are of similar magnitude.

Item ID: 27181
Item Type: Thesis (PhD)
Keywords: age, CART model, classification, Coral Sea inflow, diffusion, diffusion-advection balance, estuaries, evaporation, exposure times, flushing times, Great Barrier Reef, hypersalinity, larval dispersion, LOICZ model, mixing rates, North Caledonian Jet, patchiness, residence time, residual circulation, residual currents, return coefficient, salinity, salt balance, sediment dynamics, self-seeding, tidal currents, tidal flushing, transport timescales, trapping, water renewal
Additional Information:

Publications arising from this thesis are available from the Related URLs field. The publications are:

Chapter 2. Andutta, Fernando P., Ridd, Peter V., and Wolanski, Eric (2011) Dynamics of hypersaline coastal waters in the Great Barrier Reef. Estuarine, Coastal and Shelf Science, 94 (4). pp. 299-305.

Chapter 3. Andutta, Fernando P., Ridd, Peter V., and Wolanski, E. (2013) The age and the flushing time of the Great Barrier Reef Waters. Continental Shelf Research, 53 . pp. 11-19.

Chapter 4. Andutta, Fernando P., Kingsford, Michael J., and Wolanski, Eric (2012) 'Sticky water' enables the retention of larvae in a reef mosaic. Estuarine, Coastal and Shelf Science , 101 . pp. 54-63.

Chapter 5. Wolanski, Eric, Andutta, Fernando, and Delhez, Eric (2012) Estuarine hydrology. In: Encyclopedia of Lakes and Reservoirs. Encyclopedia of Earth Sciences Series . Springer-Verlag, pp. 238-249.

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Date Deposited: 27 May 2013 04:10
FoR Codes: 04 EARTH SCIENCES > 0405 Oceanography > 040503 Physical Oceanography @ 50%
04 EARTH SCIENCES > 0405 Oceanography > 040599 Oceanography not elsewhere classified @ 50%
SEO Codes: 96 ENVIRONMENT > 9609 Land and Water Management > 960903 Coastal and Estuarine Water Management @ 34%
96 ENVIRONMENT > 9609 Land and Water Management > 960999 Land and Water Management of Environments not elsewhere classified @ 33%
97 EXPANDING KNOWLEDGE > 970102 Expanding Knowledge in the Physical Sciences @ 33%
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