Search

This paper examines the on-shelf circulation of the eastern Australian continental shelf for a region off southeast Queensland. We identify a characteristic seasonally reoccurring wind-driven cyclonic flow. It influences the cross-shelf exchange with the East Australian Current (EAC), which is the western boundary current of the South Pacific Ocean. We refer to this cyclonic circulation as the Fraser Gyre. It is located south of Fraser Island between about 25 °S and 27 °S. The region is adjacent to the intensification zone of the EAC where the current accelerates and establishes a swift, albeit seasonally variable southward boundary flow. Through the analysis of several data sets including remotely sensed sea surface temperature and sea surface height anomaly, satellite tracked surface drifters, ocean and atmospheric reanalysis data as well as geostrophic currents from altimetry, we find that the on-shelf Fraser Gyre develops during the southern hemisphere autumn and winter months. The gyre is associated with a longshore near-coast northward flow. Maximum northward on-shelf depth averaged velocities are estimated with about 0.15–0.26 ms-1. The flow turns eastward just to the south of Fraser Island and joins the persistent southward EAC flow along the shelf break. The annual mean net cross-shelf outward and inward flow associated with the gyre is about -1.17 ± 0.23 Sv in the north and 0.23 ± 0.13 Sv (1 Sv = 106 m3s−1) in the south. Mean seasonal water renewal time scales of the continental shelf are longest during austral winter with an average of about 3.3 days due to the Fraser Gyre retaining water over the shelf, however, monthly estimates range from 2 to 8 days with the longer timescale during the austral autumn and winter. The southerly wind during austral autumn and winter is identified as controlling the on shelf circulation and is the principal driver of the seasonally appearing Fraser Gyre. The conceptual model of the Fraser Gyre is consistent with general p

Transport timescales (TTS), namely residence time and exposure time, were computed for adjacent shallow meso-tidal tropical estuarines system using the Lagrangian model D-Waq Part coupled with the hydrodynamic model Delft3D-Flow, and the Constituent-oriented Age and Residence time Theory, CART. The main results are threefold: (a) The TTS differs more between releases at high or low tide than between those at spring and neap tides. The exposure time was also calculated and found to be larger than the residence time by a few days. (b) The exposure and residence times were used to evaluate the return coefficient (r) for different scenarios. As with residence and exposure times, the return coefficient was found to differ more between releases at high or low tide than between those at spring and neap tides. (c) For the Caravelas Estuary, where the river inflow was low (~4 m3 s−1), the residence time was found to be much larger than for the Peruípe Estuary, where the river discharge was greater and nearly constant during the sampling period (~20 m3 s−1). These results shows the importance of advection in decreasing TTS in the Peruípe Estuary compared to the Caravelas Estuary. The influence of the advection and dispersion agrees with previous simple estimates obtained using the newly modified Land Ocean Interaction Coastal Zone (LOICZ) model by Andutta et al. (2014).

Transport timescales (TTS), namely residence time and exposure time, were computed for adjacent shallow meso-tidal tropical estuarines system using the Lagrangian model D-Waq Part coupled with the hydrodynamic model Delft3D-Flow, and the Constituent-oriented Age and Residence time Theory, CART. The main results are threefold: (a) The TTS differs more between releases at high or low tide than between those at spring and neap tides. The exposure time was also calculated and found to be larger than the residence time by a few days. (b) The exposure and residence times were used to evaluate the return coefficient (r) for different scenarios. As with residence and exposure times, the return coefficient was found to differ more between releases at high or low tide than between those at spring and neap tides. (c) For the Caravelas Estuary, where the river inflow was low (~4 m3 s-1), the residence time was found to be much larger than for the Peruípe Estuary, where the river discharge was greater and nearly constant during the sampling period (~20 m3 s-1). These results shows the importance of advection in decreasing TTS in the Peruípe Estuary compared to the Caravelas Estuary. The influence of the advection and dispersion agrees with previous simple estimates obtained using the newly modified Land Ocean Interaction Coastal Zone (LOICZ) model by Andutta et al. (2014)., Accepted author manuscript, Mathematical Physics

Full Text, Thesis (PhD Doctorate), Doctor of Philosophy (PhD), Griffith School of Engineering, Science, Environment, Engineering and Technology, Effective prediction of objects drifting on the water surface is essential to successful maritime search and rescue (SAR) services, since a more accurate prediction of the object’s likely location results in a greater probability for the success of a SAR operation. SAR drift models, based on Lagrangian stochastic particle trajectory models, are frequently utilised for this task. More recently, metocean (meteorological and oceanographic) forecast data has been used as input to these models to provide the environmental forcing (due to winds and ocean currents) that the object may be subject to. Further, the slip of a drifting object across the water surface due to the ambient wind and waves (irrespective of currents) is described by its leeway drift coefficients, which are also required by the SAR drift model to calculate the potential drift of the object. This study examined several ways to improve the prediction of an objects drift on the water surface, with the primary focus being the improvement of SAR forecasting. To achieve this, many simulations were undertaken, comparing the trajectories of actual drifters deployed in the ocean, and the corresponding model simulations of drift, using the commercially available SARMAP (Search and Rescue Mapping and Analysis Program) SAR drift model. Each drifter trajectory was simulated independently using a different ocean model to provide ocean current forcing. The ocean models tested included BLUElink, FOAM (Forecasting Ocean Assimilation Model), HYCOM (Hybrid Coordinate Ocean Model) and NCOM (Navy Coastal Ocean Model).

Full Text, Thesis (PhD Doctorate), Doctor of Philosophy (PhD), Griffith School of Engineering, It is estimated that open water reservoirs in Australia lose around 40% of their total water storage capacity per year to evaporation. This can be attributed to the country’s dry climate, with high temperatures and strong winds. To further exacerbate this issue, temperature increases have been recorded during the past decades, and this is predicted to continue over the coming years in Australia. This has been directing even greater concern to how much water will be lost from Australian reservoirs in the future through the evaporation process. For several decades, Australia has been investigating mechanisms to minimize evaporation from reservoirs. These include the use of physical and chemical covers, windbreaks and even modifying the reservoir shape in order to reduce its surface area. Most of these techniques however, have been shown to be ineffective, as in the example of windbreaks; to be excessively expensive, as in the example of physical covers and modifying the reservoir shape; or to impose potential risks to the water quality, as in the use of chemical covers. Destratification by air-bubble plumes, which involves pumping compressed air into the interior of a reservoir, thereby allowing the resultant bubbles to rise and carry cold bottom water to the surface, is one technique that deserves further investigation. Air-bubble plumes have been suggested in literature as a potential mechanism for reducing evaporation from reservoirs due to their potential effects on water temperature change. The primary aim of destratification by air-bubble plumes is to maintain or improve the quality of the reservoir water, specifically by increasing dissolved oxygen in the water. The potential of these systems to reduce evaporative losses is related to the change in water temperature attributable to mixing. The intuitive principle is that cold hypolimnetic water is lifted by the air bubbles, and once at the surface, this water mixes with the lighter epilimnetic water, reducing i

Full Text, Thesis (Masters), Master of Philosophy (MPhil), Griffith School of Environment, Science, Environment, Engineering and Technology, One central challenge in the study of seagrass meadows is explaining the abundance and diversity of nekton associated with these productive habitats. While many models have been proposed to explain fish use of seagrass habitats, mainly focusing on their nursery and predator-avoidance values based on the complex habitat structure, most empirical studies were conducted on relatively large patches using catch data collected from invasive capture methods. Seagrass meadows on peri-urban coasts, however, continually being threatened and fragmented, while invasive surveying techniques could bias fish abundance data. This thesis aims to determine if small remnant Zostera capricorni patches in a peri-urban estuary provide small mobile fish with a flow-refuge within a strong tidal flow environment, using non-invasive video surveying techniques to monitor fish abundance and behaviour. The hydrodynamic characteristics of three small patches of Z. capricorni were measured using in situ deployment of Acoustic Doppler Current Profilers (ADCP) at the front and rear of the patches during tidal current flow between 20 and 30 cm/s. Seagrass canopies of densities and morphologies covered by these patches significantly baffled the free-stream flow (X), creating a near-zero, turbulent free, within-canopy hydraulic environment 0.25m from the canopy’s leading edge. Flows were deflected over the canopy surface causing the leaves to bend, compressing the canopy and thereby reducing the vertical flux under high flows. While lower flows were still significantly reduced, a small vertical flux occurred, with large turbulent eddies generating from the canopy friction. The hydraulic environment behind the patch was significantly different to that at the patch’s front – characterised by near zero flows and turbulent fluctuations (at 0m), and flow velocities increasing with downstream distance. This effect was noticeable due to the velocity above the canopy being significantly reduced from flows abo

Full Text, Thesis (Masters), Master of Philosophy (MPhil), Griffith School of Engineering, Science, Environment, Engineering and Technology, A new technique for measuring Depth of Disturbance in the Swash Zone. Depth of disturbance (DoD), also known as the sediment mixing depth, is a measure of the depth to which the beach face sediment is moved by wave action in the swash zone. By improving our understanding of DoD we can better predict important beach processes - such as natural beach evolution; sediment movement around engineering structures; the design and planning of beach renourishment schemes and sedimentassociated pollution transport patterns (Jackson and Malvarez 2002). Three main ways of measuring DoD have commonly been used in the past, The techniques are: - Coloured sediment filled channels and holes (Williams 1971, Sherman et al 1994, Ferreria et al 1998), - Depth of Disturbance rods and washers (Greenwood and Hale 1980), and - Tracers to mark sediment deposited in a section of the beach face (Sunamura and Kraus 1985).

Full Text, Thesis (Masters), Master of Philosophy (MPhil), Griffith School of Engineering, Science, Environment, Engineering and Technology, Coastal rivers that discharge freshwater, with sediment and nutrients, into the ocean often generate a buoyant river plume in the vicinity of the river mouth. The river plume, driven by river floods, has become a significant environmental issue, which may be increasing in occurrence and severity as a consequence of climate change. The excess runoff created by floods has the capacity to carry a large amount of sediment and contaminants from land-based human activities into the coastal and shelf waters. The purpose of this research was to examine the dynamic and transport characteristics of the Brisbane River plume using a numerical model. It also sought to answer the following questions: 1) What is the seasonal behaviour of the Brisbane River plume, particularly during flood seasons, and 2) What are the impacts of external forces acting on the Brisbane River plume? It is anticipated that the knowledge gained from this research will promote a better understanding of the Brisbane River plume behaviour in Moreton Bay.

Full Text, Thesis (Masters), Master of Philosophy (MPhil), School of Engineering, Science, Environment, Engineering and Technology, Over the years many studies have been completed on the carrying capacity of specific recreational activities. These studies generally focus on the factors and interactions that are limiting the growth of an area and what barriers need to be removed to allow for this growth. This study looks specifically at the perception of carrying capacity of Gold Coast beaches and the way in which they are used by tourists and locals. For the purpose of this study the definition of Beach Carrying Capacity is the perceived number of people that can fit comfortably on a beach, including the surf zone, before adversely affecting an individual person’s beach recreation experience and/or the surrounding environment. Beach usage encompasses all activities participated along any adjacent infrastructure including parks and oceanway, sandy beach and surf zone areas including swimming, surfing, walking, sunbaking and picnicking. During the research period a short questionnaire was produced and applied to a range of people along various Gold Coast beaches and within Griffith University. The questionnaire looked at what people used the beach for and how they perceived the crowding on the beaches. Results showed that the carrying capacity on Gold Coast beaches, by the survey respondents’ perceptions, has already been reached on some of the Gold Coast’s most popular beaches. The study then looked at and compared the results from the Portugal study (da Silva, 2002) to those obtained on the Gold Coast. Results showed that the survey data collected from the two locations does not differ greatly. Perceptions of beach carrying capacity and the general activities people used the beach for were uniform in both study locations. This study highlights the importance of beach monitoring as it allows us to determine what people are using the beach for and how they would like them to be used. The information obtained about how people are using the beaches will provide valuable data to coastal councils and

Full Text, Thesis (PhD Doctorate), Doctor of Philosophy (PhD), School of Engineering, Science, Environment, Engineering and Technology, Estuaries are of immense importance to many communities. It has been estimated that 60 to 80 % of commercial marine fishery resources depend on estuaries for part, or all of, their life cycle. The characteristics of estuarine flow, water quality and sediment conditions are important as they play a critical role in the functionality and health of these systems. This study utilised both field data and numerical modelling technique to help enhance our understanding of the physical processes of a very shallow subtropical estuarine system. This study first quantified various salt flux components within the shallow subtropical estuarine system Coombabah Lake in Gold Coast, Queensland, Australia to better understand the system’s physical processes for assisting future management decisions in this ecologically and economically significant region. Residual water transport was identified as the dominant factor influencing residual salt transport, which alternates direction frequently. This study then developed a new simple and robust traversing system to measure flow properties within estuarine bottom boundary layers to estimate two important parameters used in numerical modelling of aquatic systems: bed shear stress and bed roughness height. Four commonly-employed techniques: (1) Log-Profile; (2) Reynolds stress; (3) Turbulent Kinetic Energy; and (4) Inertial Dissipation used to estimate bed shear stresses from velocity measurements were also compared. Bed shear stresses estimated with these four methods agreed reasonably well; of these, the Log Profile method was found to be most useful and reliable for the unstratified conditions studied. A three-dimensional hydrodynamic model with unstructured meshes utilising the MIKE3 FM modelling system and simulated the hydrodynamic regime was set up for Coombabah Lake to assist with enhancing our understanding of the hydraulic properties within this shallow sub-tropical estuarine system. The sensitivity of calibration parameters of a

We have developed a conceptual model to assist integration between physical geographical sciences, institutional frameworks and management in the context of coastal wetlands. Wetlands are key interconnected systems that will respond early to climate change and especially to associated sea-level changes. A major constraint on management of wetlands is the lack of congruence between the ecosystems and the institutional frameworks that govern their management: connectivity in coastal systems is overlain by institutional fragmentation. We introduce a model that facilitates integration of physical geographical (biophysical) information into the legislative, planning, policy and management process. It consists of interconnected parallel subprojects in science and in planning with strong cross-links with stakeholders at all levels, founded on long-term and trusting relationships. We also show progress that has been made in applying the model, with an Australian example. It is concluded that the approach has potential to move towards the goal of sustainable management but that it urgently needs to evolve, so as to meet the challenges of climate and associated changes.

Full Text, Thesis (PhD Doctorate), Doctor of Philosophy (PhD), School of Engineering, Science, Environment, Engineering and Technology, Coombabah Lake is a sub-tropical, semi-urbanised, shallow lagoon in southern Moreton Bay (Australia), recognised nationally and internationally as an important conservation and habitat zone. However, significant increases in urban development have occurred within the lagoon catchment in recent times, raising concerns over the sustainability of the lagoon ecosystem. This is typical of many estuarine environments which are ecologically and economically important waterways that often become surrounded by urban development and therefore experience degradation of water and sediment quality. The processes controlling the distribution of organic matter and nutrients in estuaries are especially important in understanding their chemical cycling. Consequently, the assessment and understanding of biogeochemical processes and other influential factors is essential for the effective management of estuaries. This study is a multi-disciplinary investigation of biological, physical, and biogeochemical processes occurring in the surface sediments and overlying waters of Coombabah Lake and the adjoining creek. The primary aim of this study was to investigate physico-chemical and biogeochemical processes occurring over various patial and temporal scales and improve the understanding of Coombabah Lake and similar shallow sub-tropical systems. Spatial variability of physico-chemical surface sediment variables and the sources and distribution of surface sediment organic matter were investigated to provide an understanding of the physico-chemical and ecological processes driving the lagoon system. Lagoon sediments were characterised by generally fine sediments with predominantly sandier sediments occurring within the northern region and muddier sediments occurring within the southern region. Although some sediment locations had elevated nutrient concentrations in comparison to adjacent lagoon sediments, nutrient concentrations within the lagoon were generally typical of Australian estuari

Unmanned Aerial Systems (UAS) is recognised to be the next revolution in aviation as information technology matures in the aerospace sector. UAS systems are multidiscipline systems as they integrate several disciplines, e.g. avionics, flight control, aerodynamics, structures. The design and optimisation of these vehicles can be multi-modal, non-convex or discontinuous, with multiple local minima and with noise. Traditional gradient based optimisation method might fail to find true optimal solutions or Pareto Fronts. This paper explores the design and coupling of Meta-model Assisted (MMA) with Multi-Objective Evolutionary Algorithms (MOEA) for Unmanned Aerial Systems (UAS) design. Results indicate an improvement on optimisation performance and both practicality and robustness of the method in finding optimal solutions and Pareto trade-offs between the disciplines.

Full Text, Thesis (PhD Doctorate), Doctor of Philosophy (PhD), School of Engineering, The knowledge and understanding of sediment transport is essential for the development of effective management strategies for nutrient and sediment loading in estuarine systems. Estuarine suspended sediment (in high concentrations), has the ability to adversely impact upon surrounding ecosystems, such as the Great Barrier Reef, Australia. Due to a recent decline in water and sediment quality, it has recently been mandated that a number of tropical, coastal estuarine systems in Queensland, such as the Fitzroy River estuary, have their sediment loading reduced. In order to meet these requirements, a greater understanding of the sediment transport dynamics and driving processes (such as flocculation and settling velocity) needs to be achieved, and the accuracy of estimation improved. This research project was motivated by the need to improve the general accuracy of field measurements for estuarine suspended sediment transport and dynamics. Field-based measurements (especially settling velocity) are necessary for the parameterisation of sediment transport models. The difficulty in obtaining accurate, in situ data is well documented and is generally limited to methods that isolate a water sample from its natural environment, removing all influences of estuarine turbulence. Furthermore, the water samples are often extracted from points (Eulerian) where the history of the suspended particles is generally unknown. These sampling methods typically contain intrinsic errors as suspended sediment transport is essentially Lagrangian (i.e., flows with the net motion of flow-field) in nature. An investigation into different drogue systems conducted in parallel with a study into the tidal states of the Fitzroy River estuary led to the development of a novel Lagrangian drogue device, the LAD. Additionally, the water-tracking ability of the LAD was tested and found to accurately follow a parcel of estuarine water over a slack water period. Therefore the LAD was deployed in the Fitzro

Full Text, Thesis (PhD Doctorate), Doctor of Philosophy (PhD), School of Engineering, Hydraulic lock structures have been used for hundreds of years to control and maintain water levels in waterways. The most common are gated water regulation structures used to catch and divert water, and form an essential and critical part of many flood control and agricultural schemes. Although there are clear economic advantages to building the structures, they can contribute to major water quality problems for the waterways they influence (i.e. increased residence times and a change in mixing ability). Further, in most cases, the methods previously used to assess how the structures and their operations influence the flow regimes between the two connected systems were limited, thus hydraulic designers rely on simple formulations, existing literature and experience. Consequently, the objectives of this thesis were to undertake a detailed field study and develop a methodology and computer simulation tool to calculate the flow through a hydraulic structure connecting two water bodies so that future designs can be undertaken based upon sound knowledge. To demonstrate the outcomes of this thesis, the methodology and model were applied to an existing hydraulic structure (referred to as Structure C). Structure C is used to connect and exchange water between the tidally dominated section of the Nerang River estuary and an artificial lake system (Burleigh Lakes) on the Gold Coast, Australia. The gates of this structure open four times each day (once during each semi-diurnal tidal phase) and remain open for a period of 2 hours, allowing alternative and partial exchange between the two water bodies. To gain a better understanding of the dynamics of each waterbody under the influence of the structure, a series of detailed field experiments were initially undertaken to understand and quantify the exchange of water and its mixing ability. Tide gauges deployed within the lake indicated a water level change during each opening of up to 22 cm, equating to 413,600 m3 of water enter

Full Text, Thesis (Masters), Master of Philosophy (MPhil), School of Engineering, The prediction of coastal groundwater movement is necessary in coastal management. However, the study in this field is still a great challenge due to the involvement of tidal-groundwater interactions and the phenomena of hydrodynamic dispersion between salt-fresh water in the coastal region. To date, numerous theories for groundwater dynamic have been made available in analytical, numerical and also experimental forms. Nevertheless, most of them are based on the zeroth-order shallow flow, i.e. Boussinesq approximation. Two main components for coastal unconfined aquifer have been completed in this Thesis: the vertical beach model and the sloping beach model. Both solutions are solved in closed-form up to higher order with shallow water parameter ([epsilon]) and tidal amplitude parameter ([alpha]). The vertical beach solution contributes to the higher-order tidal fluctuations while the sloping beach model overcomes the shortcomings in the existing solutions. From this study, higher-order components are found to be significant especially for larger value of [alpha] and [epsilon]. Other parameters such as hydraulic conductivity (K) and the thickness of aquifer (D) also affect the water table fluctuations. The new sloping solution demonstrated the significant influence of beach slope ([beta]) on the water table fluctuations. A comprehensive comparison between previous solution and the present sloping solution have been performed mathematically and numerically and the present solution has been demonstrated to provide a better prediction