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A modelling investigation into the water exchange timescales in estuarine waters

Ren, Yuheng 2014. A modelling investigation into the water exchange timescales in estuarine waters. PhD Thesis, Cardiff University.
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Abstract

Based on the concepts of water exchange timescales, a three-dimensional model has been refined to predict the age of water (AW). The model has been applied to two estuaries with very different characteristics. One estuary is a partially stratified micro-tidal estuary, i.e., the Pearl River Estuary (PRE), China and the other one is a well-mixed macro-tidal estuary, i.e., the Severn Estuary and Bristol Channel, UK (SEBC). The focus of this study is to investigate the influence of density-induced circulation on the estuarine water exchange process. A comparison between the predictions made using the barotropic mode and the baroclinic mode has been undertaken in the above two estuaries. The results indicate that due to the partially stratified phenomenon, in the PRE lower AW values are observed at the water surface, with higher AW values occurring near the bed. In the wet season, a more obvious AW stratification can be observed. The density-induced circulation causes an increase in the water mixing rate and a decrease in the timescales by a ratio greater than 50%. The stratification of the AW distribution is also enhanced. However, in the homogenous phenomenon of the SEBC, the baroclinic forcing’s impact on the water exchange process is very small. A model investigation is then carried out to predict the spatio-temporal variation of AW distribution in response to other dynamic factors. A regression analysis reveals that the age of freshwater exponentially decreases with the growth of discharge. Scenario analyses show that the tidal influence becomes more pronounced when the discharge is relatively small, and the varying tidal range mainly impacts on the fluctuation range of the AW, instead of its depth-averaged value. Moreover, the iv vertical variation in the AW is enhanced during neap tides due to less mixing. The age of seawater in the estuary is lowest near the estuary mouth and it increases further upstream. In the SEBC, the impacts of proposed tidal stream turbines with two different array arrangements on the water exchange process are analysed to investigate changes in the water level, current speed and AW distributions. A physical model investigation into the water exchange processes in a small scale model of the SEBC is then undertaken to estimate the travel time between different locations, and the water and tracer fluxes through two selected cross sections.

Item Type: Thesis (PhD)
Status: Unpublished
Schools: Engineering
Subjects: T Technology > TA Engineering (General). Civil engineering (General)
T Technology > TC Hydraulic engineering. Ocean engineering
Uncontrolled Keywords: Numerical modelling; Water exchange timescales; Estuarine water; Physical model; Water age; residence time.
Date of First Compliant Deposit: 30 March 2016
Last Modified: 19 Mar 2016 23:45
URI: http://orca-mwe.cf.ac.uk/id/eprint/64132

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