O UTLINE OF THE T HESIS

The research questions are addressed in Chapters Two, Five, Eight and Nine. Overall conclusions are presented in Chapter Ten. A short description of the chapters has been outlined in the next paragraphs.

Chapter Two brings together the literature on modelling of coastal flow fields and the phenomena caused by salt intrusion and the corresponding stratification in estuarine harbours and barrages, discussing the requirements for a numerical model to accurately prediction of combined turbulent tidal and gravity currents, their mixing and nature of their stratification.

The chapter provides a review of hydrodynamic and turbulence numerical and physical modelling of tidal flows in estuarine waters, harbours and barrages. Numerical modelling has received more attention with focusing on the projection method. Mechanisms of salinity stratified estuaries, harbours and barrages and their three-dimensional numerical modelling have been discussed. Turbulence modelling of estuarine harbours and barrages has been investigated and a review of some k-ε turbulence models is presented. Non-isotropy of turbulence stresses along with turbulence-stratification interaction is discussed. A review on the relevant literature of data acquisition and signal processing of laboratory measured values also has been included in the survey.

Chapter Three introduces the governing hydrodynamic equations of motion and mixing and outlines some of turbulence models including the models utilised in this research project.

Chapter Four provides a comprehensive description of the three-dimensional non-hydrostatic free surface numerical model with density variation developed herein and presents the solution method in arbitrary Lagrangian-Eulerian (ALE) coordinate system.

Chapter Five examines the ability of the numerical model in simulating advection, diffusion and wave propagation in complex bathymetries and with various temporal and spatial boundary conditions. The test cases also include the simulation of gravity flows in a number of lock-release, buoyant jet and salinity intrusion hydrodynamics. Different turbulence closures have been implemented to examine the suitability of each of them for stratified environments of interest. The chapter also discusses the changes in the turbulence structure and the effects on vertical transport of momentum and buoyant mass of stratified flows with the consideration of either isotropic or non-isotropic turbulence closures.

Chapter Six introduces the governing equations for physical modelling and illustrates a comprehensive description of the laboratory tidal basin and the model harbour design and set-up.

Chapter Seven is dedicated to description of test arrangements, instrumentation, calibration, data acquisition and signal processing and digital filtering of the measured values. A linear method has been introduced for minimising the noise and spikes by the establishment of temporal correlations for the flow field.

For the salinity concentrations recorded in the model harbour, a moving average strategy has been utilised to eliminate the noise from the signals.

Chapter Eight presents the measurement results and investigates the mechanisms that govern the hydrodynamics and dominate the advection of salinity, salt exchange, stratification and evolution of the internal flow structure of the model harbour in the laboratory tidal basin. This has been covered by analysing the measured values of velocities, water elevations and salinity concentrations for different laboratory set-ups. The spatial extent of the measurements served to determine whether the stratification remained stable during the ebb and flood tidal excursions along the entrance and harbour axes. Moreover the effect of salinity on hydrodynamics has been discussed and the effect of different barrier heights on the hydrodynamics has been investigated.

Chapter Nine further addresses the concepts developed in the previous chapters by the simulated values of the three-dimensional model. The data and analyses in the previous chapters provide requisite information to assess the predictive capability of the model. The data sets have been used for the calibration and verification of the three-dimensional numerical model to examine the accurately prediction of the hydrodynamics and stratification pattern of the tidal flow regime at the entrance and inside the model harbour. A discussion is provided on the discrepancies between the numerical model results and measurements. A distortion study has been conducted to emphasise the scale effects of vertically distorted models on the interpretation of the measured laboratory values and their comparisons with the numerical model predictions. As a part of the numerical investigations, different salinity contents and barrier heights for a range of mean water levels are simulated and the predicted results are compared. This served to study the relation between the advection of the salt and the spatial and temporal variability of the vertical structure of the tidal currents along the entrance and centreline axes of the model harbour.

Chapter Ten discusses and integrates the main concluding remarks of all chapters, and offers some recommendations for further research in the area.

CHAPTER TWO

LITERATURE REVIEW

"Water is the principle, or the element, of things. All things are water." Thales of Miletus (Plutarch, Placita Philosophorum)

(O'Connor and Robertson, 1999)

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This chapter has been aimed to address the relevant literature corresponding to the research questions posed in Chapter One, and affords evidence to the pertinent subjects of fundamental importance in a limited framework.

As the central part of this research project is the numerical and physical modelling of tidal flows in estuarine harbours, these two, with the dominance of numerical modelling, have received most of the attention. Three-dimensional numerical models are the focal point followed by two-dimensional laterally-averaged models, as the latter is the core of the three-dimensional model developed herein. The projection method, which has been deployed in the solution algorithm of the numerical model, has been also discussed in some detail.

Although the two-dimensional horizontal models are not in the area of interest of this research project, they have been reviewed as they still are powerful tools for shallow-water simulations, and provide valuable insight about the effects of

impoundment geometry, harbour flushing and overall water quality processes. However they are not capable of accurately modelling mixing and stratification as the vertical density gradients and vertical turbulence play a significant role in the dynamics of estuarine water bodies.

Physical models, on the other hand, have been the focus of many research projects, as they provide very useful means for a better comprehension of physical phenomena and clarification of the hydrodynamics and mechanisms of interest. They also provide invaluable data for calibration and validation of numerical models. However, they appear in a smaller number of publications in recent literature.

The velocity data recorded by acoustic Doppler velocity meters (ADVs) and the conductivity data are noticeably noisy. Data acquisition and signal processing procedures of the studies in the similar fields have been reviewed to provide the basics for the corresponding studies carried out in this thesis.

Stratified flows are of prime importance in estuarine studies, as salt intrusion is almost always present in harbours and barrages located in these areas. Their attractive and complicated hydrodynamics has been the reason for many analytical, physical and numerical studies. Their principal vertical behaviour makes the two-dimensional vertical models of major utilisation for such physical structures. However, it has to be emphasised that the hydrodynamics of stratification in a tidally-influenced harbour is fully three-dimensional, and therefore the relevant 3D models have been covered even if they have not fulfilled the expectations according to simulated results reported in the literature.

Turbulence modelling in conjunction with dynamics of estuaries and harbours and in combination and interaction with buoyant stratified flows makes it the most challenging subject of the detailed studies of estuarine hydrodynamics. Its inclusion in the numerical model as an important part of the predictive means of hydrodynamics of estuarine hydro-environments, even in the absence of salinity and stratification, is of prime importance.

The complicated nature of salinity-stratified hydrodynamics and non-isotropic behaviour of turbulence and mixing associated with such conditions, leads to the review of the relevant turbulence closures in the field.

A conclusion of the chapter provides the necessary information of an outlook for the fields of the interest of this research project.

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