Infrastructure Engineering - Theses
Now showing items 1-12 of 363
Rigid Barrier with a Gabion Cushion Subjected to Boulder Impact
Protection against rockfalls occurring alongside landslides contribute to the major part of the disaster management budget in many counties like Switzerland, Japan and Hongkong. Protective structures are usually built over disaster trajectories to safeguard lives and properties. Reinforced concrete barriers that are fitted with gabions are one common form of installations to provide the protection. Few experimental investigations involving impact testings of a rigid reinforced concrete barrier which was fitted with a gabion cushion cover have been reported in the literature. But these investigations were limited to studying the localised actions of impact. The change of structural response behaviour of the barrier as a whole by the presence of a cushion layer is typically not within the scope of the reported investigations. Design methodologies that have been developed are typically limited to overly simplified calculations based on applying an equivalent static force to the barrier. To fill this knowledge gap full-scale pendulum tests have been conducted by the authors on a barrier that was fitted with a gabion cushion layer. The structural response behaviour of the barrier, contact force and tensile strains in the longitudinal reinforcement were of interests. Results recorded from the tests were compared with results from control experiments which were without the protection of any cushion materials. The introduction of a layer of cushion is shown to be able to have the deflection demand on the structure reduced by more than 70% when the amount of energy delivered by the impact is kept constant. An analytical procedure employing the Hunt and Crossley contact model, Swiss code model and two-degrees-of-freedom (2DOF) system modelling technique is presented for evaluating the flexural response demand behaviour of the cushioned barrier. The proposed analytical procedure is shown to be able to predict the reduced deflection demand with a reasonable degree of conservatism. At the end of the thesis, a simple hand calculation procedure featuring the use of design charts is presented for engineering applications. The procedure is illustrated by a worked example which is based on a realistic rockfall scenario.
Wind-wave extremes in a changing climate from atmosphere and wave model ensembles
Marine offshore structures and operations, as well as coastline defences, rely on accurate estimates of the design sea state, defined as the maximum significant wave height which can be expected over an N year period. To find design sea state estimates, Extreme Value Analysis (EVA) statistical approaches are commonly used. However, due to the paucity of data available for extreme sea states, and the consequent challenges in modelling such phenomena, design sea state estimates are characterized by large confidence limits, which further complicate strategies and policies for resilient design of marine structures and operations. Furthermore, an additional challenge is posed by a changing climate, which introduces further uncertainties in the prediction of future design sea states. The present work deals with the EVA statistical uncertainties of ocean surface wind speed and significant wave height, developing and testing a novel ensemble approach to EVA. It then applies this novel approach to estimate future changes in extreme significant wave height by the end of the 21st Century. In this way, the present thesis finds, for the first time, statistically significant changes in extreme wave height in distributed regions of the ocean. Such an approach has the potential to be further refined with higher resolution models and new climate model projections, which would significantly improve global estimates both from past and future model ensembles. In parallel, this work finds an inconsistency in the trends of wind and wave mean climate throughout the 20th Century from climate models and reanalyses, questioning our confidence level as to a possible climate change signal for ocean surface wind speed and wave height. However, the work finds general agreement between datasets and statistical approaches, for a Southern Ocean wind speed and wave height increase over the last part of the 20th Century, that is also projected to further increase by the end of the 21st Century.
Mechanobiological investigation of bone fracture healing under Ilizarov circular fixators
Ilizarov circular fixator (ICF) is an external bone fixation device used by orthopaedic surgeons in treating variety of bone defects. Despite the fact that ICFs are being used for over seven decades, the interplay between ICF mechanics and biology of fracture healing remains poorly understood. The roles of ICF configurations on processes within the fracture site during fracture healing such as cell differentiations, solute (e.g. cell, growth factors etc.) transport and angiogenesis have not been explained well yet. Furthermore, how the interplay between ICF and other mechanical factors such as fracture geometry and loading affect these processes remains unclear. This knowledge gap in the mechanobiology of fracture healing under ICF is a barrier to address clinical problems associated with ICFs. Consequently, treatment failures and complications are significant with ICF treatments (around 10 – 30 %). This thesis intends to address this knowledge gap by conducting systematic mechanobiological investigations of fracture healing under ICFs. In this research, various computational models to simulate various aspects of fracture healing under ICFs were developed. In developing the models, various novel methodologies and modelling techniques were adopted. Firstly, unlike in most previous studies, a fully coupled fracture healing prediction model of fractured bone stabilized with ICFs, including soft tissues and mechano-regulation was developed to simulate early stage mesenchymal stem cell (MSC) differentiations. Secondly, a model combining both mechano-regulation and bio-regulation was implemented to simulate healing of fractures stabilized with ICF under dynamic loading. Thirdly, a new regulatory model considering level of vascularity and local tissue strain was proposed and implemented to simulate angiogenesis and fracture healing under ICF. Finally, a methodology using computational modelling in conjunction with engineering reliability analysis was implemented to investigate the role of uncertainties in mechanical parameters on fracture healing under ICFs. All computational models were developed based on the theory of porous media and continuum mechanics. The models were first validated using experimental data and subsequently used for fracture healing predictions. Mechanical experiments involving measurement of bone interfragmentary movements (IFM) using an advanced 3D optical measuring system (ARAMIS) were conducted in this research for model validation purposes. Wherever possible, the predictions of the models were corroborated by experimental and clinical data. Through systematic analyses, this thesis contributes to the existing body of knowledge by providing new insights into the mechanobiology of fracture healing under ICFs. This thesis elucidates the following mechanobiological aspects of fracture healing under ICF that have not been systematically studied so far: 1. The effects of ICF configuration, loading and fracture geometry on the early stage mesenchymal stem cell (MSC) differentiations during fracture healing; 2. The roles of physiologically relevant dynamic loading on cell differentiations and cell / growth factors transport within the early stage fracture site; 3. The effects of subject specific factors (i.e. body weight, fracture geometry and ICF configuration) on angiogenesis and optimal time dependent weight bearing levels for bone fractures treated with ICFs; and 4. The effects of uncertainties in mechanical factors (i.e. fracture geometry, weight bearing and ICF configuration) on fracture healing under ICF. In addition, the models presented in this thesis could potentially be used for further systematic investigations and in clinical settings for designing and comparing ICF treatment strategies.
An integrated method for groundwater vulnerability assessment using a DRASTICL model and a green algae ecotoxicity test
The world population could reach 9.8 billion by the year 2050 (UN, 2019). The rising world population presents the challenge of water and food security for human development. As a result, excessive use of agricultural chemicals (both fertilisers and pesticides) which in most cases are toxic not only for the humankind but also for the environment, is putting significant stress on the groundwater levels and the water quality. Groundwater (GW) pollution from agriculture is particularly significant in partially and totally groundwater-dependent ecosystems, as these ecosystems provide habitat for various endangered flora and fauna. Even though the importance of GW systems is well recognised, groundwater pollution vulnerability assessment models and groundwater pollution quantification techniques have experienced slight changes over the last 10 years and in most cases, the use of agricultural chemicals is assumed to be safe in the absence of sufficient data and evidence. The existing models produce an annual GW Vulnerability map and there is little to no monitoring of groundwater for these chemicals due to difficulty with identifying the representative samples and the high analytical cost. Therefore, this thesis aims to develop a novel approach to understand the seasonal variations in groundwater vulnerability and used the modified model to identify the representative sampling bores and also explores an algal ecotoxicology test as for the pesticides in water, that can be used as a fast and inexpensive pre-screen to identify samples above a certain level of toxicity for detailed chemical analysis.
Shallow geothermal systems: individual and district applications
Worldwide energy use is expected to rise due to an increase in population and global warming. About half of this energy use is for space heating and cooling for buildings, where electricity (mostly derived from fossil fuels) and natural gas are the most common sources of energy. To achieve long term energy sustainability, electricity and natural gas consumption needs to be reduced. One way to achieve this reduction is by utilising shallow geothermal system or ground source heat pump (GSHP) system technology. This technology utilises the ground as a heat source or a heat sink to provide sustainable heating and cooling for buildings. The use of this technology has been growing worldwide. However, information and high-quality datasets of GSHP systems are still rare in Australia, leading to installations with low efficiency and high installation costs. This research aims to contribute to the understanding of GSHP systems under Australian climatic, cost and emission conditions, including how to improve their viability and uptake. The first part of this research aims to address this lack of availability of quality datasets. To do this, a full-scale monitoring project was undertaken. This thesis presents the performance data from 10 monitored residential and small commercial GSHP system installations in the greater Melbourne area. The measured data reveals that a GSHP system can perform well under Melbourne climatic condition, with an estimated coefficient of performance between 2 and 4.9. One common trend in all of the monitored properties is that they are used only around 10 to 20% of the year, which is much smaller compared to the expected usage based on typical design methods. For this reason, a more detailed comparison was conducted for two properties with the lowest and highest system usage. The comparison indicates that the differences in the usage patterns imposed by the occupiers can significantly impact the potential cost-effectiveness and environmental benefits of the GSHP system. This suggests that in general, a GSHP system can be an alternative heating and cooling options under Melbourne climatic and geological conditions, but they have to be designed, installed and used appropriately. Otherwise, this may lead to an inefficient system with a long payback period. One potential explanation behind the moderate GSHP system usage described above is the temperate climatic conditions of Melbourne, which requires only moderate heating and cooling. For these conditions, a hybrid combination between GSHP and conventional systems may be preferred to maximise the benefits from both systems. A hybrid GSHP (HGSHP) system means a GSHP system that is sized to provide the baseload thermal energy for a building and this system is supported by a conventional system during the hottest and coldest days of the year. This leads to the next part of this research where an HGSHP system design method is proposed with the objective that considers both costs and emissions by using a Pareto optimum approach. This analytical study is extended to cover different climatic, cost and emission conditions across several Australian cities. The results reveal that HGSHP systems can have a lower lifetime cost than GSHP or conventional systems. However, this hybrid system mix with the lowest lifetime cost is not necessarily the same as the one with the lowest lifetime emission. Overall, this research may provide a basis on which decisions about whether to install an HGSHP system with the objective to minimise their lifetime costs or emissions. A solution which considers both factors with equal weight is also provided herein. The last part of this research considers the possibility to combining several individual HGSHP systems into a district arrangement. This is called a district HGSHP system and this is possible because buildings are located close to each other in the urban area. The results indicate that district HGSHP systems can reduce capital and operational costs compared to individual HGSHP systems. The highest financial savings occur when buildings with significantly contrasting thermal load patterns are combined together, for example, combining heating dominant with cooling dominant buildings. Combining more buildings lead to higher financial savings, but this follows the law of diminishing returns. Altogether, the findings from each chapter are expected to contribute incrementally to improving our knowledge of GSHP system technology as well as providing more real-life performance data. The insights from this research may also be applicable to other locations with similar climatic, cost and emission conditions. Further, based on the outcomes of the work covered in this thesis, stakeholders may be able to make more informed decisions on design, installation and operation of GSHP systems. These should also allow the development of more appropriate public policy to encourage the growth of the shallow geothermal industry.
Development of Advanced Timber-based Prefabricated Panelised Systems
This thesis aims to develop advanced timber-based panelised prefabrication in an impactful manner. The research approach involved the establishment of close collaborative industry-partnerships which were then leveraged to best satisfy the critical needs faced in industry, resulting in targeted in-depth advancements across a range of areas. Five core areas for detailed advancement were identified, namely: manufacturing processes, waterproofing, wall systems, design methods (including optimal configuration selection) and floor systems. Within each core area, the pressing limitations of most immediate commercial need were investigated and addressed in detail. Consequently, the original contributions to knowledge are as follows: - Full evaluation and assessment of advanced automated manufacturing technologies and processes available for complete timber-based panelised systems; - Development and successful commercial adoption of a purpose specific prefabricated panel to panel waterproofing solution to replace on-site work; - Development and implementation of a significantly more material and cost-efficient panelised timber-based wall system for mid-rise buildings, namely stiffened engineering timber walls with post-tensioning; - Corresponding mathematical modelling via the computationally efficient exact finite strip method based upon the Wittrick-Williams algorithm with appropriate orthotropic material models and strength limits; - Development of associated design curves, configuration specific post-tensioned strength reduction factors and optimal configuration selection methods; - Development of a panelised stressed-skin timber floor system through reductive-design with increasing material efficiency whilst also reducing the number of manufacturing processes required for competitive commercial adoption. As a result, this development of knowledge, process and product innovations, is spurring and enabling the growth of research in, and industry adoption of, advanced timber-based panelised prefabrication.
Visual indoor localisation using a 3D building model
With the emergence of the global navigation satellite system (GNSS), the performance of outdoor localisation has become excellent over the years. Applications like navigation, location-based services and augmented reality demand seamless localisation capabilities in all environments. However, a single technology that can satisfy the needs of localisation in indoor spaces is absent to date. The major limiting factor in the large scale adoption of indoor localisation systems is the overhead cost of installation and maintenance of dedicated local infrastructure. Consequently, infrastructure-independent indoor localisation has become a focus of research during the past decade. The ubiquity of smartphones with integrated cameras has resulted in a renewed interest in infrastructure-independent visual localisation approaches for the indoor environments. However, the existing visual approaches face two challenges that restrict the wide applicability of such approaches. Firstly, current visual simultaneous localisation and mapping (SLAM) approaches, where the challenge is the drift caused by the accumulation of errors. Loop closing is a solution to eliminate drift but it poses a limitation in the practical application of visual positioning. For navigation purposes, revisiting the same location might be impractical. The second challenge for the existing visual approaches is the requirement of an initial location. The existing visual approaches that are independent of the initial locations require either the construction of large database of images with known location or a 3D reconstruction of the indoor environment in the form of depth images or 3D point clouds. However, the creation of a database of images with known locations and the acquisition of additional data for large indoor spaces is a challenge due to the cost, time and post-processing involved. This research presents approaches to address the two above-mentioned challenges of the existing visual approaches by using a 3D building model that is usually available through the building information modelling process or can be generated with little effort from existing 2D plans. The motivation of using BIM for this research comes from the fact that BIMs of modern buildings are readily available, as they are jointly maintained by the constructors and facility managers. The research can be broadly classified into two parts. The first part proposes a novel 3D model-based visual tracking approach called BIM-Tracker. BIM-tracker uses the 3D building model to perform a drift-free localisation and addresses the challenge of accumulation of error. Localisation is performed by integrating image sequences captured by a camera, with the 3D building model. A comprehensive evaluation of the approach with photo-realistic synthetic datasets shows the robustness of the localisation approach under challenging conditions. Additionally, the approach is evaluated on real data captured by a smartphone, and achieves an accuracy of ten centimetres. Similar to the requirement of many visual approaches, BIM-Tracker depends on the availability of the initial location. The second part of the research proposes a deep learning-based method called BIM-PoseNet to estimate the initial location. The requirement of image-based reconstruction of the indoor environment is eliminated by using a 3D building model, thereby addressing another challenge of the existing visual approaches that estimate the initial location. BIM-PoseNet is based on training a CNN with synthetic images obtained from the 3D indoor model to regress the location of a real image taken by a camera. In addition, the uncertainties of camera location estimates are modelled by adopting a Bayesian CNN, as uncertainty provides an indication of confidence and trust in an estimated location in the absence of ground truth. Furthermore, the use of sequences of synthetic images is explored to exploit the spatio-temporal information from the images to improve the performance of BIM-PoseNet by using recurrent neural networks. The results of the qualitative and quantitative experimentation of the proposed approaches with photo-realistic synthetic and real datasets indicate the proposed research addresses the two major limitations of the existing visual indoor localisation approaches. In addition, the proposed research demonstrates the potential of visual indoor localisation as a single technology for achieving an infrastructure-independent localisation.
Direct geothermal energy: reducing the poultry industries’ carbon footprint
A Ground Source Heat Pump (GSHP) system is a type of highly efficient renewable energy system which utilizes the ground as the heat source when heating and as the heat sink when cooling. Since the initial installation cost of GSHP systems can be relatively high, hybrid GSHP systems can be designed to reduce the initial cost by coupling with other energy technologies, including solar technology. One promising area where hybrid GSHP systems can be applied to is in the rural industries which has high requirement for heating and lack of reticulated gas infrastructure and land availability. This research aims to contribute to the development of hybrid GSHP system with horizontal ground heat exchangers (GHEs) suitable for the rural industry, with poultry sheds in Australia investigated as cases studies. A full-scale instrumented hybrid geothermal system for the poultry shed in Peats Ridge was then designed and built to verify, demonstrate the performance. Providing 80 kW heating, the ground heat exchanger field consists of 12 horizontal trenches at the depth of 1.5 m totalling 4,800 m of ground loop and 400 m of pond loop in a nearby pond submerged at a depth of 4 to 6 m. This work then investigated energy efficient solutions for poultry sheds in Australia. The space heating and cooling demand cycles of a typical poultry sheds in Peats Ridge, NSW, Australia have been simulated in detail, using TRNSYS 18. It is found that heating systems, operational schedule (raising batches of chicks) and ventilation strategies have a great impact on energy consumption. An optimum scheduling strategy was developed, and energy demands were minimised. Furthermore, this work contributed to the improvement of the design of hybrid geothermal system with horizontal GHEs. As hourly simulation of GSHP with horizontal GHEs is not yet available in major commercial software packages, Artificial Neural Network (ANN) models were proposed, which can potentially be generally applied to similar sheds at different locations and under different climate conditions, with readily available and limited types of input data, hourly heating loads, accumulated heating loads and ambient air temperature. Trained with simulated data from a verified TRNSYS model, the ANNs can predict the performance of GSHPs systems with identical GHEs even under climatic conditions (and locations) that has not been specifically trained for. This represents a major advance in this area. With only limited input data and showing a high accuracy (no more than 5% error in most cases tested), the presented ANN is 100 times computationally faster than TRNSYS model and 10,000 times faster than comparable Finite Element models. Finally, to reduce the lifecycle cost and greenhouse gas (GHG) emissions of heating the shed, multi-objective optimisation regarding hybrid geothermal-solar-gas heating systems are investigated. In these systems, the baseload heating demand is satisfied by GSHPs, with solar photovoltaic panels providing the electricity needed to drive the pumps and LPG gas boilers toping up the balance of the heating. This study investigated and optimised lifecycle cost along with GHG emissions arising from the three components of these hybrid systems, considering three different electricity offsetting scenarios. The results indicated that a considerable reduction in the lifecycle heating costs (up to 55%) and GHG emissions (up to 50%) can be achieved when optimised hybrid systems are used for heating. The Pareto front solutions for this hybrid geothermal-solar-gas heating system were also determined. By comparing the Pareto front solutions in different scenarios, it has been identified that the shave factor, a measure of the proportion of GSHP to the overall heating system, has the highest impact when to comes to reducing the lifecycle cost, while the size and utilisation of solar PV panels contributes more to the lifecycle GHG emissions. The findings obtained from this study can contribute to the design and optimisation of hybrid geothermal systems to reduce its lifecycle cost and carbon footprint as well as assist in wide spreading the application of GSHPs for the rural industry.
Auxetic Armour System for Protection Against Soil Blast Loading
Extreme loading threats arising from terrorism, war zones, natural disasters, and even accidents, require specialised protection in order to limit and prevent death and damage to infrastructure and vehicles. In particular, soil blast loading is of concern due to the increased loading imparted by the dual phase explosive/soil mix. Smart, more efficient structures are required to better protect against these kinds of threats. Auxetics, structures and materials with a negative Poisson’s ratio, are one such novel structure which have seen increasing research as protective structures. Their counterintuitive nature means they contract under a compressive load and vice versa. This phenomenon draws materials towards the point of impact and can lead to increased energy absorption, indentation resistance, and fracture toughness. This research investigates the auxetic oval structure for its protective capabilities with a focus on energy absorption. Quasi-static and dynamic testing was conducted on samples to quantify the response over strain rates ranging between 0.001-100 /s. It was found that the auxetic oval structure displayed the classic stress-strain response for energy absorption with a flat plateau stress region. However, fracture was present in the experiments and shown to negatively affect the energy absorption. A Hybrid design utilising another auxetic geometry, the re-entrant honeycomb, was developed to remedy this issue. Digital image correlation (DIC) was also used in the analysis of the experiments to confirm the presence of the rigid rotating square mechanism controlling the auxetic behaviour. Numerical models were then developed in finite element software LS-DYNA and validated against the stress-strain response and DIC analysis from the experiments. Further understanding of the energy absorption mechanisms were identified through the numerical models, including the locations of plastic energy dissipation. Parametric studies were then conducted from which different behaviour characteristics were tied to geometric features. Most results were intuitive, such as the plateau stress being tied to the thickness of the material between holes. However, additional insight was revealed about how the thickness negatively affected the Poisson’s ratio, i.e. thicker sections changed the load transfer response and thus negated the auxetic effect. Only one parameter, the oval ratio, was shown to directly affect the densification strain, which was due to the available space the holes could collapse in. Finally, load rate studies showed how the auxetic oval structure was characterised by uniform crushing for load rates up to 10 m/s. Above 200 m/s the auxetic displayed localised crush band formation. Soil blast loading was quantified through flying plate tests conducted with 0.5 kg TNT charges buried within an unsaturated soil. The impulse imparted to the plates can be used to determine the loading imparted to a protective structure. It was also used to validate numerical models of soil blast events in LS-DYNA using the Arbitrary Lagrangian-Eulerian (ALE) method. The soil model was populated with data from soil characterisation tests. Good agreement between the experiments and models was generally achieved. Further work on understanding the loading mechanism of soil blast was then conducted. It was determined that ~63% of the impulse was from the soil alone. Furthermore, the spatial and temporal loading was determined through additional numerical models, highlighting the localised nature of soil blast events. The final body of research investigated the auxetic oval geometry with soil blast loading considered. Simplified localised loading on long auxetic sections showed the benefit of a negative Poisson’s ratio over conventional positive Poisson’s ratio equivalent structures. This included an increase in relative energy absorption due to the ability to draw material towards the load point. Loading was then simulated recreating the failure scenarios of a vehicle subject to a soil blast event. This was conducted using simplified load models (ConWep) on the auxetic structure, and ALE loading on homogenised foam material models representing the auxetics. Both methods highlighted the benefits of the auxetic oval structure over conventional protective structures, including; reduced stress transmission, increased energy absorption, and decreased global body acceleration. In conclusion, the auxetic oval structure displays an ideal response for energy absorption, and the localised nature of soil blast is ideal for activating the main benefits of an auxetic structure though material densification and load redistribution.
Investigation of hyporheic flow through meandering rivers: Implications for nitrogen processing
Increased nitrogen loads have significant negative consequences in streams. The hyporheic zone of streams, where surface-subsurface water exchange happens, provides significant attenuation for nitrogen compounds from the fluvial system. From many geomorphic features that contribute to hyporheic flow, meanders are particularly important for these biogeochemical reactions. Meanders provide longer residence times to allow complete denitrification of various nitrate to nitrogen gas, which can support more significant improvements in water quality compared to other channel features that only allow for partial denitrification due to short residence time. From the published literature, it is evident that there is not enough understanding about the extent of temporal variation of meander driven hyporheic flow except for few theoretical studies that have been performed to investigate the physical behavior of water and solute movement. Therefore, this research aims to investigate how meandering morphology impacts on transport characteristics of water and dissolved solutes in the hyporheic zone and to identify primary mechanisms controlling the flow. This was achieved through a set of laboratory experiments and a three-dimensional numerical model developed for meandering stream. Laboratory experiments were conducted in a recirculating flume with a set of river discharges and meandering morphologies. Residence time distribution and downwelling water flux were determined by continuously monitoring the exchange of a conservative tracer (Rhodamine WT) introduced into the surface flow. The experimental results show that both; stream discharge and meander wavelength affect the residence time and water flux into the sediment bed, hence affecting the rates of biogeochemical reactions. Most importantly, change in stream discharge affects residence times in the hyporheic zone, but the importance of considering river flow conditions in modeling hyporheic flow through meanders has been neglected in previous studies. The three-dimensional model developed in this study is based on the combination of surface flow modeled with Reynold average Navier-Stokes equation and subsurface flow modeled with the Continuity equation for groundwater flow and Darcy’s law equation. This mathematical model was solved using COMSOL Multiphysics Modelling Software (will be referred to as COMSOL henceforth), and water transport characteristics in the hyporheic zone were estimated using a numerical particle tracing technique in COMSOL. The model predicted the observed residence time distributions of laboratory tracer experiments with an R2 of 0.95. Results show that there are two primary mechanisms driving hyporheic flow through meanders; 1) Lateral flow caused by channel slope at the scale of meander wavelength (Floodplain HE) and 2) vertical flow caused by surface water acceleration due to the curvature of the channel at the scale of channel width (Fluvial HE). This three-dimensional model was then used to study the effect of meander morphology on the hyporheic residence time distribution and water flux complemented by Taguchi orthogonal array design. Channel sizes considered in the simulations range from 1m to1000m in widths. We propose three empirical relationships to predict downwelling water flux and characteristics of residence time distribution (mean and standard deviation). Also, we found that the hyporheic residence time distribution induced by three-dimensional meanders follows a log-normal distribution. Meander wavelength has a significant effect on the hyporheic residence time as well as the downwelling water flux, demonstrating the importance of channel size on the hyporheic flow processes. However, the sinuosity of the river does not affect much on the time that water spends in the hyporheic zone but alters the volume of water entering the hyporheic zone. Most importantly, meanders produce significant vertical hyporheic flow in addition to lateral flow. Increasing the channel curvature (increased sinuosity or decreased wavelength) increases the vertical flow, hence higher downwelling water flux but the reduction in the residence time. Finally, we looked at how meander induced hyporheic flow influences on nitrogen processing. We consider a dimensionless number (Da, Damkohler number), defined as the ratio between the median residence time and the critical concentration of dissolved oxygen below which nitrogen removal reactions occur (reaching anaerobic conditions). Meanders, being large morphologic features, observed to provide high Da values (>20) suggest the availability of hyporheic regions with prevailing anaerobic conditions for nitrogen removal reactions. In recent decades, fate and transport of nitrogen in hyporheic zones have been significantly influenced by flow modifications, increased water pollution, and channel straightening. Increased straight channels and impervious surfaces confine the hydrological flow paths and residence times in the hyporheic zone, which may limit sufficient treatment. In order to support this important ecological service, implementing restoration solutions is vital. Understanding the underlying mechanisms and effects of urbanization on nitrogen transformation is a prerequisite for minimizing stream degradation and achieving restoration goals. Therefore, our findings can potentially be incorporated in river restoration practices and to design rivers as natural nitrogen filters. This study represents a step forward for the analysis of large-scale channel features and their residence times, which are less understood in previous literature but are very important for biogeochemical cycling in rivers.
Determination of oceanic extremes using a spatial ensemble of satellite data
In this thesis, the application of extreme-value analysis to long-duration (30-year) global altimeter and radiometer datasets is considered. In contrast to previous extreme-value analyses of satellite data, the dataset is sufficiently long to enable a Peaks over Threshold (PoT) analysis to be undertaken. When applied to altimeter data for wind speed and significant wave height, this analysis produces values consistent with buoy validation data and previous numerical model reanalysis datasets. The spatial distributions produced are also consistent with the model reanalysis data. However, the altimeter data shows a much greater fine-scale structure for wind speed, which is consistent with known tropical cyclone activity. Nevertheless, these results still show spatial variability of estimates as a result of relatively high statistical variability. The greater data density provided by radiometer measurements offers the potential to address altimeter under-sampling. However, issues associated with the radiometer’s inability to measure wind speed in heavy rain events appears to create an unacceptable “fair-weather” bias at extreme wind speeds. This renders the radiometer data of wind speed largely unusable for the investigation of wind speed extremes. The study also clearly demonstrates the limitations of the Initial Distribution Method (IDM) for extreme-value analysis, which is heavily biased by mean conditions. Based on these outcomes, the aim was to investigate approaches to reduce potential errors and the size of confidence intervals on the resulting estimates of extremes when applying the PoT approach to altimeter data. Therefore, a novel approach to the estimation of extreme-value ocean significant wave height is investigated, in which data from adjacent regions are pooled to form a spatial ensemble. The equivalent duration of this ensemble region is the sum of the duration of the data pooled to form the ensemble. To create such a spatial ensemble, data from regions to be pooled must be independent and identically distributed. ERA-Interim [“ERA” refers to ECMWF (European Centre for Medium-Range Weather Forecasts) ReAnalysis] global atmospheric reanalysis data are used to investigate the requirement of independent and identically distributed data on a global basis. As a result, typical spatial ensembles are defined for 18 regions of the world, and the 100-yr return period significant wave height is calculated for these regions. It is shown that the method can result in a reduction in the confidence interval for such extreme-value estimates of between 30% and 60%. The method is demonstrated both with ERA-Interim data and altimeter data.
Understanding the Co-evolution of Land, Water, and Environmental Governance in Victoria during 1860 - 2016
There are many cases where the changes in government interventions have resulted in considerable negative consequences to social-ecological systems (SESs) instead of promoting improvement. Difficulties occur in guiding governance change to steer SESs onto desirable pathways. However, the linkage between the degradation of SESs and governance failure remains unclear. To address this gap, this research aims to understand the co-evolution of land, water, and environmental governance through the integration of policy into social-ecological system frameworks (SESFs). This research is presented into three chapters to answer the following three research questions: Research Question 1: How does land, water, and environmental governance steer the SES condition? Research Question 2: How have policy instruments for land, water, and environmental governance developed from 1860 to 2016 in Victoria, Australia? Research Question 3: How have the policy instruments for land, water, and environmental governance co-evolved? Is there any association with biophysical changes? Chapter 3 developed an SES framework by extending the SES frameworks proposed by Ostrom and Anderies. In the proposed framework, SES condition is viewed as the product of the accumulation of policy instruments used in land, water, and environmental governance to rule the interaction between and among components of biophysical and social systems. Policy instruments can help policy analysts explain the linkages between resources, resource users, and public infrastructure providers and which has a significant role in enhancing the robustness of SES. The framework provides a new way to develop a wider recognition and appreciation of dynamic, site-specific biophysical and social system conditions in influencing the government intervention, and in turn, have been shaped by them. In particular, the framework can help policymakers elucidate: 1. how the biophysical system has been understood in SES governance as represented by the relevant policy instruments; 2. how the social system has been set up in SES governance; and 3. how the synergies and trade-offs between the biophysical and social systems have been managed in the governance of the SES. It can help for systematically analyzing SES governance through the configuration of policy instruments. Chapter 4 used the proposed framework to investigate the evolution of policy instruments used in the land, water, and environmental governance in Victoria, Australia. The content analysis of Victorian Acts related to land, water, and environment practices between 1860 to 2016 was conducted. The investigation found that policy instruments to manage the behavior in resource utilization (substantive and procedural policy instruments) did not vary. However, they were differences in the circumstances in which they were implemented, in this case, differing interactions among components of the biophysical and social systems. The policy instruments held a particular focus in managing components of SESs in different periods and the evolution of each policy instrument has its pathway. Four regimes were identified in the evolution of policy instruments used in water governance: reserve, authority, information, and integration regimes. Whilst, policy instruments used in land governance experienced three regimes (authority, information, and integration regimes) and policy instruments used in environmental governance experienced two regimes (information and integration regimes). Chapter 5 associated the co-evolution of land, water, and environmental governance and biophysical changes. The co-evolution was analyzed by unpacking the integration of policy instruments used in land, water, and environmental governance. The integration was analyzed by examining the relationships between SES components covered in policy instruments. Represented by the subtle changes in their integration, the analysis showed the Victorian government’s learning process in adapting and accommodating the natural system and its desire to avoid signiﬁcant negative impacts on the land, water, and environmental conditions have resulted in the inclusion of the dynamic interaction within SES as the consideration in formulating its policy instruments. Comparing the co-evolution of policy instruments used in land, water, and environmental governance with state-wide changes within the biophysical system, it is found that there is a strong association between the integration of land, water, and environmental governance and the change in SES condition in Victoria from 1860 to 2016. This longitudinal study of Victoria land, water, and environmental governance developed a new way to explain the linkage between natural resources governance and SES condition. Re-constructing government intervention through policy instruments implemented in the land, water, and environmental governance, the study found the way policy instruments were designed and implemented varied with the state of understanding of the dynamic interactions within the SESs. Looking back over Victoria’s history in developing policy instruments used in land, water, and environmental governance, the study suggests that policy instruments should be formulated to address the interactions among components within SES, in this case, policy instruments as managers of interaction within SES. This is crucial to steer SES conditions onto desirable conditions.