Thesis (Ph.D.)--Aberdeen University, 2009. / Title from web page (viewed on July 23, 2009). Includes bibliographical references.

One objective of this project is to set up a two-dimensional model for exploring the flushing process of trapped saltwater subject to upstream freshwater turbulent flow. The multiphase Eulerian model, a part of commercial code FLUENT6.2, has been applied for the first time to study this complex mixing interaction in estuary. The distinguishing characteristic of this model is to treat saltwater and freshwater as two single miscible phases instead of a mixture phase with density variation, and the advantage of using a multiphase approach over a single-phase model is that it can efficiently and accurately treat both the free water surface and relatively high density excess between two fluids simultaneously. The other objective of this project is to develop a three-dimensional model based on the FVCOM open source code, with the aim to better understand the estuarine hydrodynamics with or without the presence of typhoon. It is found that the original FVCOM code can not reproduce an accurate tidal hydrodynamics in estuary. An improved simulation of the bed friction has been incorporated into the existing code for estuarine tide. This model has also been developed by including air-pressure gradient term to study the hydrodynamic response to cyclonic typhoon. To include the effect of typhoon (wind stress and pressure deficit), a symmetrical cyclone model is adopted. However, the typhoon-induced wind field has been predicted poorly when the typhoon enters the near-shore region. This is because the typhoon quickly loses its symmetrical property in the near-shore region. To overcome this difficulty, an asymmetrical cyclone model is derived on the basis of characteristic isobar. The accuracy of open sea boundary for storm surge model has also been improved by using large scale model. Comparison results show a good agreement with numerical simulations and physical measurements.

Thesis (M. Phil.)--University of Hong Kong, 1987.

Understanding and resolving the water quality problems that Florida Bay has endured requires an understanding of its salinity drivers. Because salinity is the prime factor that drives estuarine ecosystem, Florida Bay’s ecosystem health depends on the correct salinity balance of the Bay. In this thesis, the Regional Oceanic Modeling System - a hydrodynamic prognostic model -was implemented on Florida Bay and it was tailored for shallow waters. Results show that the model captures most of the salinity spatial and temporal variability of Florida Bay. Furthermore, it establishes the role of the major drivers like evaporation, precipitation, and runoff on Florida Bay’s salinity. The model resolves region specific salinity drivers in all four areas of Florida Bay characterized by their own salinity regimes. The model was also able to reveal the impact of surface runoff on salinity in the later part of the year when evaporation increases. A new technique was developed to estimate the discharge and salinity of unmonitored small creeks north of Florida Bay. Those data were estimated from the relationship between net freshwater flux, runoff, and salinity. Model results revealed the importance of accounting for these small creeks to accurately simulate Florida Bay’s salinity. / Includes bibliography. / Thesis (M.S.)--Florida Atlantic University, 2018. / FAU Electronic Theses and Dissertations Collection

There is a growing interest in tidal energy, owing to its predictable nature in comparison to other renewable sources. In the case of the UK, its importance also lies on the availability of exploitable areas as well as their total capacity, which is estimated to cover more than 20% of the country demand. However, the level of development of this kind of technology is still far behind other types of renewable energy. However, several studies focused on a variety of individual devices, followed by more recent research on the deployment of large arrays or tidal farms. Potential sites for energy extraction can be found in narrows between islands and the coast or estuaries. The latter present some advantages for the installation and the connection to the grid but estuaries are often prone to flood risk from tides and surges. Therefore, the objective of this thesis is to evaluate the effect that very large groups of turbines could have on peak water levels during flooding events in the case of being deployed in estuarine areas. For that purpose, a new methodology has been developed, which implies the use of a numerical model (MIKE 21 by DHI), and it has been demonstrated against a real case study in the UK: the Solway Firth estuary. Another objective has consisted of integrating in this thesis the results from detailed CFD modelling and optimisation techniques involved in the project. A literature review has been carried out in order to identify the current state of the art for the different subjects considered in the thesis. Different aspects of the numerical model used for this study (MIKE 21) have been presented and the modelling of the turbines within the code has been validated against experimental and CFD data. The procedure to include large numbers of turbines in the code is also developed. An analysis has been done of the different estuaries existing in the UK suitable for tidal energy extraction, identifying their main geometrical features. Based on this, idealised models of estuaries have been used to assess the influence that the channel geometry could have on the impact of tidal farms under extreme water levels. The effect has been measured by comparing the results of the numerical model between the case with and without turbines under different flooding scenarios. Finally, the same methodology has been applied to a real case study selected from the previous group of estuaries namely the Solway Firth. An initial model has been created, according to the available data at the start of the research, which contained some errors related to the water depth at the intertidal areas in the upper estuary. Therefore, when a more realistic dataset became available, an improved model was created. The improved model has been used to assess the effects of tidal farms in the estuary under a coastal flooding event. It is concluded that there is significant influence of the channel geometry over the locations where the maximum changes in water levels due to the tidal farms will happen. Nevertheless, the effects seem to be more relevant in terms of the decrease rather than the increase of peak water levels for all geometries and the maximum changes seem to be in the order of dm. This is in agreement with the results of the Solway Firth models and can be summarised as a positive net effect over flood risk. On the other hand, a concern has been raised about the impact on intertidal areas, which could be the subject of future research.

Thesis (MEng)--Stellenbosch University, 2013. / ENGLISH ABSTRACT: The Touw River estuary and Wilderness coastal lakes is a sensitive system from a flooding and ecological viewpoint and, therefore, careful consideration is placed on the hydrodynamics and salinity levels within the system. The estuary consists of a “temporary open/closed” estuary, where during closed mouth conditions, the sand bar at the estuary mouth is artificially managed in an attempt to reduce flood water levels in the system. The reason behind this management strategy is the construction of residential property along the flood plains of the estuary and coastal lakes, which in the past, had been exposed to regular cycles of inundation during flood events. In an attempt to reduce flood water levels in all water bodies and hence reduce the risk of inundation, a management policy was formulated. The past and present management plan is to maintain the sand bar at Touw estuary mouth, during closed mouth conditions, at an elevation of between +2.1m to +2.4m MSL, based on proposals made by the CSIR in 1981. Recent flood events, after the implementation of the management policy, still occasionally result in significant inundation of residential property, which has raised concern for some interested parties over the effectiveness of the management strategy. Furthermore, a growing concern was also evident over the long term wellbeing of the system from an ecological viewpoint. Historical data shows significant changes in salinity levels since the implementation of the management strategy which could impose negative long term effects on the system. In this study, numerical models were consequently constructed and applied in order to analyse the effectiveness of the current management policy and recalculate flood water levels under a number of proposed scenarios. Long term salinity changes were also analysed in an attempt to better understand salinity propagation throughout the system, using extreme hypothetical cases. Through the analysis of the simulation results, it was concluded that flood water levels in the Touw estuary were almost completely dependent on the size of the Touw River flood and the initial height of the sand bar at the estuary mouth. Whereas, water levels in the coastal lakes are almost entirely dependent on the quantity of runoff into the lakes and their initial water levels. The current management plan, involving only artificial manipulation of the sand bar at the estuary mouth, therefore has a fairly insignificant effect on flood water levels achieved in the coastal lakes. Furthermore, it was concluded that the construction of the preparatory channel is a vitally important aspect of the current management plan and that skimming of the sand bar alone is ineffective to completely mitigate the risk of residential inundation along the banks of the Touw River. The salinity modelling study provided a first indication of the salinity characteristics within the system. It was found that the penetration of seawater into the system was less prominent as the water bodies became further removed from the ocean and that a direct relationship was evident between the volume of direct freshwater inflow to a water body and the degree of salinity variation in that specific water body. In water bodies with high volumes of direct freshwater inflow such as the Touw estuary, a large degree of salinity variation is evident. However, in water bodies with no freshwater inflow, such as Rondevlei, salinity levels remain more stable and are less likely to fluctuate. / AFRIKAANSE OPSOMMING: Uit ‘n vloed- en ekologiese oogpunt is die Touwsriviermonding en Wilderniskusmere ‘n uiters sensitiewe stelsel en daar is dus deeglike oorweging gegee aan die hidrodinamika en soutvlakke in die stelsel. Die monding bestaan uit 'n "tydelike oop / geslote" monding, en tydens geslote mondtoestande word die sandbank by die riviermond kunsmatig beheer in 'n poging om vloedwatervlakke binne die stelsel te verminder. Die rede vir hierdie strategie is omdat baie residensiële eiendomme langs die vloedvlaktes van die monding en kusmere gebou is, wat in die verlede aan 'n gereelde siklus van oorstromings blootgestel is tydens vloede. In 'n poging om vloedwatervlakke in al die watermassas te verminder, en sodoende die risiko van oorstroming te verminder, is 'n bestuursbeleid geformuleer. In beide die vorige en die huidige bestuursplanne is die sandbank in die Touwsriviermond tydens geslote mondtoestande in stand gehou op 'n hoogte van tussen 2,1 m en 2,4 m MSL, gebaseer op die voorstelle wat deur die WNNR in 1981 gemaak is. Onlangse vloede wat plaasgevind het na die implementering van die beleid, het steeds van tyd tot tyd gelei tot noemenswaardige oorstromings van residensiële eiendomme, en kommer is uitgespreek deur 'n paar belanghebbende partye oor die doeltreffendheid van die strategie vir die bestuur. Daar is verder kommer uitgespreek oor die langtermyn welstand van die stelsel uit 'n ekologiese oogpunt. Historiese data toon 'n beduidende verandering in soutvlakke sedert die implementering van die bestuurstrategie met ‘n negatiewe langtermyn uitwerking op die stelsel. In hierdie studie is daar derhalwe numeriese modelle opgestel en toegepas ten einde die doeltreffendheid van die huidige bestuur van die beleid te bepaal, asook om die vloedvlakke te herbereken en te analiseer na aanleiding van 'n aantal voorgestelde scenario's. Langtermyn soutgehalte veranderinge is ook ontleed in 'n poging om die soutgehalte verspreiding deur die hele stelsel beter te verstaan, deur gebruik te maak van uiterste hipotetiese gevalle. Deur die ontleding van die simulasie resultate, is daar tot die gevolgtrekking gekom dat vloedwatervlakke in die Touwsrivier-monding byna heeltemal afhanklik was van die grootte van die Touwsrivier vloed en die aanvanklike hoogte van die sandbank by die riviermond. Watervlakke in die kusmere is egter byna heeltemal afhanklik van die hoeveelheid afloop na die mere en die aanvanklike watervlakke. Die huidige bestuursplan, wat slegs ‘n kunsmatige manipulasie van die sandbank by die riviermond behels, het dus 'n redelik onbeduidend invloed op die vloedwatervlakke wat in die kusmere bereik is. Daar is verder tot die gevolgtrekking gekom dat die konstruksie van die voorbereidende kanaal 'n uiters belangrike aspek van die huidige bestuursplan is, en dat die afskraping van die sandbank alleen oneffektief sou wees om die risiko van residensiële oorstroming langs die oewer van die Touwsrivier uit te skakel. Die soutgehalte modelleringstudie verskaf 'n eerste aanduiding van die soutgehalte eienskappe binne die stelsel. Daar is gevind dat die penetrasie van seewater in die stelsel minder prominent was as in die watermassas verder van die see af, en dat daar 'n duidelike direkte verband is tussen die volume van die varswater wat direk invloei na 'n watermassa en die mate van soutgehalte variasie in daardie spesifieke watermassa. In watermassas waar hoë volumes varswater direk invloei soos die Touwsrivier-monding, is 'n groot mate van soutgehalte variasie sigbaar. In die watermassas waar geen varswater invloei nie, soos die Rondevlei, bly soutvlakke meer stabiel en is minder geneig om te wissel.