Infrastructure Engineering - Theses
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ItemHumans’ decision-making during emergency evacuations of crowded environments: behavioural analyses and econometric modelling perspectives( 2017)Modelling evacuation behaviour of humans has become an increasingly important topic due to the growth of urban populations and mass gatherings as well as the increasing frequency of emergency incidents in environments that host large numbers of humans. Emergencies are relatively rare occurrences with high potential impact and safety-related implications. Thus, preparedness for them has the potential to save lives by preventing injuries during the evacuation process and accelerating the overall process and leading people to safety in the least possible amount of time. The research on this topic ultimately aims at developing predictions tools that could facilitate evacuation planning and optimisation by producing measures such as total evacuation times for each given condition. This would enable authorities and planners to evaluate the effectiveness of their evacuation policies, identify potentially problematic locations and vulnerabilities in their venues and propose measures that can accelerate the discharge of occupants should an incidents occurs in the environment. Such applications could range from simply advising occupants as to how they should conduct themselves in case of an incident, to estimating the safe occupancy rate of venues (particularly in mass gatherings and special events) and thus managing the demand accordingly, to optimising the architectural design of the environments in ways that best support the efficient discharge of occupants. The problem is interdisciplinary by nature and has attracted the attention of researchers in various fields, including ergonomics and fire safety, applied physics and mathematics, behavioural sciences and transport engineering. The problem at hand is also highly multifaceted and entails many aspects such as computational capacities and the versatility of the models. The most crucial component of such practice is arguably the accuracy of modelling that is inextricably linked with the humans’ behaviour element and how accurately it can be replicated by the models. Given the safety-related implications of evacuation models, it is of paramount importance to minimise the extent and likelihood of inaccurate estimates that could potentially culminate in misguided designs or suboptimal policies (contradicting the primary purpose for which such models are intended). Ensuring that the behaviour of evacuees in simulated practices are replicated accurately enough is, however, a highly challenging task. The modeller deals with a problem related to humans’ decision-making behaviour which is intrinsically complex, in addition to the fact that the behaviour is this context is particularly rare and is not observed on a day to day basis. This leaves modellers with a paucity of data for model development, calibration and verification purposes. Given that the human behaviour in emergencies is not yet well understood, more often than not, the modellers have resorted to formulating “intuitive” assumptions whose accuracy have yet to be scrutinised based on empirical observations. This has left a range of mysterious theoretical assumptions in this field of research largely unverified and thus subject to debate and scepticism. I argue that the empirical knowledge in this research field has lagged notably behind the theoretical advancements and model formulations, calling for more extensive empirical research in this field in order to bridge this gap. Furthermore, by analysing the existing empirical literature in this field, I argue that the research has been distributed in a relatively imbalanced way in terms of addressing various aspects of human behaviour relevant to this research area. More empirical knowledge has been acquired in relation to the aspects of behaviour that are more convenient in terms of data collection, namely the “walking behaviour” and momentary “collision avoidance” decisions of people. Whereas, higher levels of escape decision making like the directional wayfinding choices or choices of activities are in comparison far less understood. These less explored aspects of behaviour often entail a heightened cognitive load (compared to instantaneous and largely subconscious walking decisions) and pose additional levels of complexity for experimentation, data extraction and modelling. However, I argue in that gaining an accurate understanding of these aspects and developing models that can echo them adequately in the modelling process is at least as important as modelling the walking behaviour from a practical standpoint. In this study, I focused on modelling and understanding the directional (or wayfinding) choices of humans during evacuations that are often referred to as “tactical decisions”. The study is predominantly empirical. In carrying pout this study, a major underlying question was to choose the experimentation method that best suits this problem. As explained in the literature review chapter, I classified the data collection and experimentation techniques in this field to seven major categories, a number of which could be potentially used for the question in hand here. Each method offered certain advantages and disadvantages. I study the problem using two general sources of empirical observations: hypothetical-choice data and data extracted from controlled laboratory experiments with actual crowds (which I refer to as “realistic” choice experiments or often as “field-type laboratory” experiments). The hypothetical-choice data was simply gathered by generating fixed sets of directional choice scenarios, visualising them in the form of simple pictures and surveying a sample of subjects one by one. The choice scenario conceptualise trade-offs between “social factors” and “physical factors” of the environment and elicit the prioritisation of respondents between these factors. This decision trade-off was then imitated in a more realistic simulated evacuation experiment where decision makers had to interact with actual crowds in an actual confining environment for making escape decisions. Their decisions were extracted at the level of individuals using the video-analyses of the experiment footage. The choice data obtained from both contexts were structured in an identical way and were analysed using econometric choice modelling techniques. The findings of this study are two-fold, divided into behavioural findings and econometric-related findings. The analysis results provided novel insight into the escape behaviour of humans, allowing me to revisit a number of conventional theoretical assumptions and statistically test them based on empirical observations. In particular, I examined the assumption of “herding behaviour” and “social attraction and repulsion effects” deeply entrenched in the literature. The conclusion was that these assumptions did not perfectly hold true and could in least terms be regarded as overgeneralisations of complex behavioural phenomena that could affect the accuracy of our predictions. Also the disaggregate nature of our data allowed me to address in depth the question of individual differences in this context that had largely been downplayed by previous studies. The close connection established between the hypothetical and realistic choice data also provided interesting findings about how the responses that people state as to what they would do in hypothetical escape scenarios could actually materialise when they make the actual decisions in more realistic contexts. This connection led to findings that not only did offer insight into the possible relevance of the hypothetical choice methods (or virtual-reality experiments in more general terms) in this particular context (with major implications for choosing research directions for future studies in this field) but also could be of the interest of the researchers in the field of experimental economics and econometrics. The modelling practices reported in this study were performed while considering the prospect of the outcomes leading to practical applications. I intended the models reported in this study to be implementable to evacuation simulation tools. The models, as a result, were kept parsimonious and the parameters were kept fully generic. As a practical application of this study, these models were integrated with a social-force model of walking. This dual-layer model is capable of simulating crowd evacuation process in complex environments that entail the choice of direction. Given that the parameters of the directional choice model convey behavioural interpretations, the model has also the potential to provide behavioural insight into the evacuation behaviour from a system perspective (i.e. based on aggregate measures) through computer simulation and manipulation of the simulated behaviour through varying the level of these parameters. A preliminary analysis of this kind has also been reported in the thesis.
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ItemDevelopment of design tools for direct geothermal systems( 2015)Direct geothermal energy systems use the earth as a heat source or sink to provide heating and cooling for buildings. In these systems, a heat pump is employed to transfer heat from a building to the ground and vice versa by circulating water (sometimes with antifreeze) through Ground Heat Exchanger (GHE) pipes buried in the ground. By reducing the electricity demand for heating/cooling applications, these systems have the potential to significantly reduce both electricity consumption and greenhouse gas emissions. GHEs come in two basic configurations: closed loop and open loop systems. The focus of this thesis is on horizontal and vertical closed loop GHEs. The total length of a GHE has a significant influence on the efficiency of heat transfer between the circulating water and the surrounding ground and hence the efficiency and cost of a direct geothermal system. Despite the importance of the GHE to system performance, there are no Australian (and few international) field experiments on fully operational systems that study GHE heat transfer in the ground in detail. Therefore, there is little data available which allows the assessment of available design tools and how well these predict performance. Based on a critical review of current design methods, this research aims to improve current design techniques by performing field experiments using instrumented pilot geothermal systems. The ultimate goal of this research is to increase the performance and reduce the cost of direct geothermal systems, by improving the understanding of GHE heat transfer. To pursue this goal, in this research, a full scale horizontal geothermal system with more than 200 temperature sensors was installed at Main Ridge (80km from Melbourne) and a full scale vertical system with more than 100 sensors was installed at the Walter Boas Building at the University of Melbourne. Ground and GHE temperatures were measured at various depths within and around the GHEs to observe the effect of thermal loading on the ground. Heat flux has been applied to the GHEs using either heat pump(s) capable of extracting and rejecting heat to the ground or electrical heating elements. Two new robust numerical models have been developed on the basis of the experimental results. The first is the Horizontal Conductive Flux and Energy System (HCFES) that has been developed specifically for horizontal GHE modelling using ExcelTM. Although this model is useful, it has a few drawbacks. Therefore, the second model, a more Generalized GHE model referred to as the GGHE model has been developed to cover a much broader range of GHE geometries to include both horizontal and vertical systems as well as energy piles. These models have been validated against the experimental results. The results of this research suggest that the models developed may form the basis for better design practice through the adoption of a less empirical approach. There is a potential to significantly improve GHE efficiency, especially with regard to the steps provided within the GGHE model. The models developed create a potential to lessen the degree of conservatism in design and reduce the installation cost of the GHEs. This thesis also presents details of the equipment used in the experimental work and provides a framework for future experimental studies of direct geothermal energy systems.
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ItemLinking freshwater flows, salt wedge dynamics and black bream dispersal in the Mitchell River sub-estuary( 2014)For fish species with a planktonic larval stage, transport from the spawning ground to juvenile habitat is a critical aspect of their life history. While certain physicochemical features of the upper estuary, such as the estuarine turbidity maximum, are beneficial to larval survival, dispersal of larvae to suitable recruitment habitat is also important. This dispersal process is influenced by hydrodynamics, egg buoyancy, and larval behaviour. In estuaries, especially where strong stratification is present, variation in currents may occur over scales of centimetres to metres. Vertical variation in salinity can cause large current variations over short vertical distances. For small organisms in aquatic environments, hydrodynamics provides a large physical influence on their transport. Larvae, however, are not passive particles and may behave in ways which alter their location in the water column. The dominant research paradigm frames behaviour as an important feature in determining larval dispersal patterns, despite the magnitude of hydrodynamic influences. This study examines the balance between hydrodynamics and larval behaviour in determining the dispersal patterns of larvae of black bream (Acanthopagrus butcheri), an estuarine dependent species endemic to southern Australia. The study utilises a biophysical modelling approach, informed by empirical studies in both the field and the laboratory, to explore the dispersal of black bream larvae in the Mitchell River sub-estuary, part of the Gippsland Lakes in South-eastern Australia. The thesis begins with a review of literature in the field of biophysical modelling of fish early life history, noting that data assimilation and the integration of empirical data collection and modelling are growing needs. The importance of collecting species-relevant data on the ontogeny of behaviour is also highlighted. The literature review is followed by an empirical field study, which identified the Mitchell River sub-estuary as a micro-tidal system with an extensive salt-wedge that varied with river flow, and extended from the river mouth up to 18 km upstream. Average flows during the spawning season range from around 15 to 55 m3/s, and a flow of approximately 50 m3/s was required to flush the salt wedge from the river. The water column exhibited large vertical salinity stratification, even at flows up to 40 m3/s. Pronounced velocity variation was observed between parcels of water above and below the halocline. The field data also provided observations against which to calibrate and validate the hydrodynamic component of the biophysical model. Next, the thesis documents the development of a vertically layered finite difference hydrodynamic model with baroclinic salinity for the Mitchell River sub-estuary. This model was validated using physicochemical observations. For computational efficiency, a one-cell wide straightened river bathymetry was adopted. The model captured spatio-temporal variation in water level, salinity and velocity in the longitudinal and vertical dimensions. A laboratory study of individual-level behaviours in larval black bream is reported next. In the laboratory black bream larvae were observed to increase in critical swimming speed with size up to a maximum of approximately 0.2 m/s for larvae around 1 cm in length. This is at the higher end of observed critical swimming speeds for larvae of marine demersal fishes, and is above velocities observed beneath the halocline in the Mitchell River sub-estuary. A baroclinic response was observed in late-stage larvae which were bottom associated until depths increased beyond 6 m. Young larvae were surface attracted, but were found significantly deeper in the presence of a halocline than in a homogeneous salinity water column. These observations provided individual-level data to inform a biophysical model of black bream eggs and larvae in the Mitchell. The thesis then details the development of numerical Lagrangian particle modelling software, incorporating modules for the inclusion of behaviours in response to salinity, depth, the presence of a halocline, and positive rheotaxis. A sensitivity analysis of each of the behavioural modules found that retention of particles within the model was more sensitive to the choice of behaviours influencing vertical position of particles than those influencing horizontal position. Results of the sensitivity analysis varied depending on whether the model was forced with high or low flow rates. Finally, using the biophysical model as a virtual laboratory, a series of virtual experiments are described. Longitudinal spawning location was found to be critical to retention of larvae within the sub-estuary. A pattern-oriented modelling approach determined that a biophysical model structure including egg buoyancy but no larval behaviour best explained empirical patterns of black bream egg and larval dispersal in the Mitchell River sub-estuary. This is in contrast to the findings from the laboratory study that black bream exhibit dispersal-relevant behaviour. In conclusion, this study, focussed on the development of a biophysical model, found that estuarine circulation in the Mitchell River sub-estuary provides a greater influence on the dispersal outcomes of black bream eggs and larvae than active behaviours exhibited by the larvae. Biophysical modelling techniques have been successfully applied in a morphologically and hydrodynamically complex system, however there remains scope for improvement, particularly through the use of a hydrodynamic model with a more flexible spatial discretisation to better resolve the estuarine bathymetry. Additionally, the extension of this modelling framework to other estuaries in southern Australia could reveal whether the findings of this study can be generalised to other estuaries which black bream inhabit.
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ItemQuantitative methods for hydrological spatial field comparison( 2006-08)This thesis addresses the current lack of comprehensive, quantitative methods for comparing hydrological spatial fields. Comparison of spatial fields is needed for assessing hydrological models and for data assimilation. The methods that are currently used for quantitative comparison generally fail to consider the spatial arrangement of element values within spatial fields. Instead, there is a dependence on qualitative methods (e.g. visual comparison) to undertake comparison of many aspects (e.g. intermediate scale features), but such methods are non-repeatable, often biased and difficult to report on. This thesis advances the comparison methods available for use with hydrological spatial fields. (For complete abstract open document)
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ItemModelling impact actions of spherical objects( 2013)Impact action is a very common phenomenon not only in mechanical systems and infrastructural buildings, but also in sporting activities. Such extreme events not only impose damages to structures, but also creates huge financial burden to society. For example, the quite high frequency of damaging hailstone impacts in urban areas in Australia is the most costly natural hazard as compared to earthquakes, cyclones and bushfires. Over the past decades, impact-contact mechanism has drawn a great deal of attention to both engineers and designers. Indeed, any structure that is vulnerable to impact by flying or fallen objects should be designed to have a minimum amount of capacity to counter impact actions. Current codes of practices for structure or structural element design are to check the static strength by assuming a prescribed quasi-static force. However, unlike designing for wind and seismic actions, impact actions can be sensitive to the dynamic properties of both the impactor and target structure. Consequently, the forcing function should be obtained from adequate simulation of the collision between the impactor and target, and cannot be pre-defined. In spite of the experimental costs, isolated experimental studies on the impact action would not automatically provide all the information required to characterize the dynamic properties of the impactor and target structure. Repeated testings are required if the impact conditions are altered. Finite element analysis can be used to complement physical tests. However, this type of analysis is too time-consuming and numerical instabilities (e.g. negative volume, shootingnodes and hourglass) can be encountered. Thus, finite element analysis cannot fulfill the requirement of daily practical design applications. Clearly, there is a lack of reliable tools and generalized methodology that are amenable to practical applications. There is also a lack of integrated use of analytical simulations in conjunction with experimental investigations to facilitate the fundamental understanding of impact actions. Simulation of impact actions by the use of a two-degree-of-freedom (2DOF) lumped mass model is an expedient way to assess the effects of the impact. This modelling methodology is relatively computationally inexpensive and could provide accurate predictions provided all the input parameters (e.g. structural generalized properties K2 and m2, and contact spring property K1) have been well identified. The 2DOF modelling methodology is not new in dynamic modelling, but little attention has been paid to determine the representative values of K2, m2 and K1 for different structures and impact conditions. The first part of this thesis focuses on developing suitable idealised 2DOF lumped mass model for impact response analysis of beam/columns, slabs and dome-shaped structures/shells. Traditionally, an idealised deflection shape function based on modal analysis is used for generalization of the above-mentioned structures. Such assumption is only applicable to beam-typed structures. For plates or shells, the aspect ratio and subtended angle can be very influential on the deflection profiles caused by external loading. The first contribution of this thesis is the development of equations and charts for estimating the values of the generalized properties of rectangular plates and shells with aspect ratio of up to 4 and subtended angle of up to 180 degrees respectively. Comparative analyses between the results as obtained from finite element analysis by LS-DYNA and 2DOF model have been carried out to support the creditability and also identify the limitations of the analytical model. Based on the well established 2DOF model, displacement design charts were proposed and illustrated by case studies in place of dynamic analyses. Once the deflection value has been identified, an equivalent static force can be calibrated to emulate the bending moments associated with the impact actions. The basic 2DOF model was further developed to taken into account energy dissipation and contact nonlinearity (hence it is nonlinear inelastic 2DOF model). A tubular device was designed and custom built for measuring contact force generated by an impact. Unlike other experimental techniques which normally employ load cell or accelerometer, the proposed measurement methodology only requires displacement transducer to be mounted to the mid-section at the base of the target structure. The contact force is determined by displacement readings and dynamic force equilibrium principle (i.e. contact force = reaction force + inertia force). The key advantages of the proposed measurement technique are: (1) forcing functions including contact, reaction and inertia forces can all be measured; (2) the condition of contact between impactor and target would not be interfered by the instrumentations (unlike placing load cell on top of the target structure); and (3) forces induced by the impact of debris can also be measured (circumventing difficulties with attaching accelerometer to the impactor). Comparison between the indirect measurements from the proposed technique and direct measurements as obtained from the load cell indicates that the proposed technique can provide very accurate force predictions. By the use of the 2DOF model and a custom made inexpensive device, a proposed calibration procedure was introduced for determining the parameters characterising the nonlinear inelastic compressive stiffness properties of the impactor in relation to the target structure. Given the parameter values, the amount of contact force generated by a diversity of impact actions by the same impactor can be estimated reliably and accurately by the 2DOF model. The calibration procedure is emulated using cricket ball, golf ball, hockey ball, tennis ball and baseball as example spherical impactors. Although this methodology is demonstrated by low velocity impacts, it can be further developed to cover for conditions of high velocity impact.
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ItemModelling of the Wnt signalling pathway and its role in colorectal cancer( 2011)Colorectal cancer is one of the most common forms of cancer and a leading cause of death in the western world (Parkin et al., 2005). Truncation of the tumour suppressor gene adenomatous polyposis coli (APC) (a key member of the intra-cellular canonical Wnt/β-catenin pathway) has been strongly linked with colorectal cancer (Kinzler et al., 1991b), being found in 85% of adenomatous carcinomas. During development, Wnt/β-Catenin signalling is known to regulate key cellular decisions, namely cell survival, proliferation and differentiation (Logan and Nusse, 2004, Cadigan and Peifer, 2009). The main function proposed for Wnt signalling is to regulate the cytosolic β-catenin concentration. However, recently other regulatory (Seo and Jho, 2007, Faux et al., 2008) and functional (Brembeck et al., 2006) roles have been proposed. Although many of the protein interactions in the Wnt/β-catenin pathway are now known, data on concentrations of the Wnt pathway components in mammalian cells are limited. This lack of quantitative data prevents a systems level approach via computational biology. This thesis presents a systems-level framework integrating experimental and computational techniques for the investigation of the Wnt/β-catenin pathway in cancerous and noncancerous mammalian epithelial cell lines. In order to acquire the experimental data necessary for system level modelling, new experimental techniques are developed in this thesis. These include a new fluorescence cytochemistry protocol employing 3D confocal microscopy and image processing techniques to determine cell volume and volume of cellular compartments in live cells, as well as a novel 3D confocal microscopy quantification technique to monitor spatial and temporal changes of specific target proteins in structurally intact cells. Using a previously published Xenopus cytosolic model of the Wnt/β-catenin pathway as a starting point (Lee et al., 2003), the Lee et al. 2003 β-catenin degradation experiment setup was repeated for mammalian epithelial kidney (HEK293T) cytosolic extracts, with β-catenin concentration quantified using Western blots. The experimental data acquired was integrated in a computational model to develop an initial cytosolic Wnt signalling model optimised for mammalian cells. To advance the Wnt model towards a whole cell system, cellular volumetric data was measured and used to calculate the total whole cell concentrations of five key Wnt pathway proteins: APC, Axin, GSK3β, β-Catenin and E-cadherin, for five mammalian cell lines (HEK293T, MDCK, Caco-2, SW480 and SW480APC) as quantified by Western blots. Applying the new 3D quantification technique, the dynamics of specific pathway proteins (i.e. β-catenin and N-cadherin) in intact HEK293T cells and L-cells were estimated under a range of Wnt perturbations (i.e. Wnt3A, partially purified Wnt3A (ppWnt3A), cycloheximide (CHX) and MG132). Computational models of Wnt pathway signalling are developed and results compared to the experimental data in order to formulate calibrated models of Wnt signalling. In the cytosolic experiment, the degradation dynamics of β-catenin is found to be significantly faster in the mammalian cells than that previously reported by Lee et al. (2003) for the Xenopus oocyte. Substantial differences in protein concentrations were also observed between mammalian cells and the Xenopus oocyte. In particular, it was found that the Axin level was much higher (>5000 times) in mammalian cells than the Xenopus oocyte, while the reverse was true for the APC level. It was also found that non-cancerous cells have a smaller APC:Axin ratio (APC:Axin<0.1) as compared to cancerous cells (APC:Axin>0.5), highlighting a potentially critical balance between these two scaffold proteins in Wnt signalling. 3D quantification of β-catenin dynamics for intact mammalian kidney epithelial cells (HEK293T) showed significant co-localisation at the cellular membrane. β-catenin degradation rates are consistent with the mammalian cytosolic extract experiment. Under Wnt 3A stimulation, Wnt activation dynamics are acquired, and 3D compartmental analysis reveals a sharp increase in nuclear β-catenin (compared to the increase in cytosol-membrane β-catenin) at the onset of Wnt stimulation. Spatial kinetics data is obtained for HEK293T and L-cells using a variety of perturbations (i.e. Wnt3A, ppWnt3A, MG132 and CHX). The sharp initial increase in nuclear:cytosol-membrane β-catenin ratio upon Wnt stimulation observed in HEK293T is only able to be reproduced in L-cells when stimulated with ppWnt3a. With L-cells having predominantly cytoplasmic β-catenin, this highlights the role of membrane localisation in β-catenin regulation. Furthermore, a potential synergistic effect was observed between Wnt stimulation and the inhibition of β-catenin degradation (with MG132). In both L-cells and HEK293T, only MG132+Wnt3A-stimulated cells were able to trigger a significant accumulation of β-catenin in the whole cell with no such accumulation observed in MG132+non-stimulated cells. These observations are contrary to reports indicating a significant β-catenin increase within an hour of Wnt3A incubation for L-cells (Hannoush, 2008) and requires further investigation. The approach adopted during this investigation is repeated iterations between computational modelling and experimental data collection to incrementally progress the model development and fundamental understanding of the Wnt signalling pathway. Future application of this methodology to colonic cells in crypts will provide a context for the interpretation of the cell model and cell data reported in this thesis, while establishing a platform for the interrogation of the role of Wnt signalling in colon cancer. It is hoped that a systems approach to signalling will eventually facilitate the prediction and development of optimal treatments for colon cancer.
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ItemModelling of canal water acidity due to acid sulphate soils: a case study of the Camau Peninsula, Mekong Delta, Vietnam( 2008)Acid Sulphate Soils (ASS) often cause acidic pollution in canal water, which negatively impacts on water quality, biodiversity and the livelihood of farmers and fishermen, especially the landless poor. The problem is particularly acute in the coastal zones, where people already suffer from the consequences of salinity intrusion. Reducing acidic pollution is important for improving agricultural and aqua-cultural production and also the living conditions of people living in coastal zones with ASS. This study aims at developing an analytical tool that can simulate the propagation of acidic pollution and that would allow planers and managers to develop water management options and other resource management measures to reduce acidic pollution in the canal network of a coastal zone. This study utilizes a systems approach, with a series of field, laboratory studies, in combination with statistical and GIS-based analyses and simulation modelling. Field and laboratory studies were carried out during 2001 - 2006 in Ca Mau peninsula, Mekong Delta, Vietnam, to fill in knowledge gaps on the source and amount of acidic loads from soil to the water surroundings, their interaction with saline water and their propagation in the canal network. Knowledge generated from this study was used in developing and validating a model to simulate the propagation of acidity in the tidal canal network with brackish water. Measured data showed that the acidic pollution in the canal network varies seasonally. The pH of the canal water was lowest (3 – 4.5) at the beginning of the rainy season and highest (7 – 7.5) at the end of the rainy season and during the dry season. The reduced dredging activities in year 2005 and 2006 may explain why the acidic pollution decreased in 2005 – 2006 compared with 2001 –2004. The most serious acidic pollution occurs when the two following conditions are present simultaneously: (i) The existence of newly dredged canals (and hence the deposition of the excavated spoils on the canal embankment) in areas with ASS (especially with a severe ASS); and (ii) little or a lack of water exchange from tidal flows. Field experiments showed that ASS embankments within 2-3 years after dredging represent a high acidity hazard because they can release into the canal a total acidity, mainly from runoff and seepage water, of up to 2.7 mol H+day-1 per meter length of canal embankment. Functional relationships were established allowing quantification of the daily acid load transferred from fields and canal embankments to the canal network. A laboratory titration experiment showed that saline water could buffer the effects of acidic pollution in the canal water. A new ACIDITY module was developed and was coupled to an existing hydraulics and salinity model (the Vietnam River Systems And Plains - VRSAP). The model was calibrated with measured data from 2003 and validated with data from 2005. The Model is the first of its kind able to simulate the temporal and spatial dynamics of changes of pH (as an indicator of acidity) at a regional scale, together with salinity and water flow characteristics in a tidal canal network with brackish water. The Model can be used to investigate the effects of different scenarios of water and other resource management options on the extent of acidic pollution in a coastal area. Analysis of simulation runs for various scenarios indicate that opening the two main sluices along the East Sea at high tide in one day every week in May and June for saline water intake, combined with widening the canals that connect these sluices to the West Sea can eliminate the acidity problem in the study area. Large scale dredging of canals of ASS in fresh water zone should be avoided as it can create severe acidic pollution of the canal water.