... is commonly applied to collaborative actions to bring about sustainable environmental governa... more ... is commonly applied to collaborative actions to bring about sustainable environmental governance. ... Within water resources management, conditions and components of social learning have ... of studies however address social learning in river basin management in developed ...
A trial to artificially destratify part of the water column of the Swan-Canning Estuary took plac... more A trial to artificially destratify part of the water column of the Swan-Canning Estuary took place over four weeks in 1997. Destratification was attempted with bubble plumes created by pumping compressed air through a porous pipe near the bed at a location in the upper estuary. The purpose of the trial was to determine whether the resultant bubble curtain could mix the water column, thereby altering the extent of upstream and downstream mixing and the vertical structures of salinity, temperature, dissolved oxygen and turbidity. The destratification trial was monitored using three techniques: vertical profiles taken on several days at selected stations along the estuary, fine scale profiles in the vicinity of the bubble curtain on one day, and continuous water column profiles taken 1 km upstream of the curtain. The seasonal upstream propagation of brackish water underneath a residual freshwater discharge was affected by the magnitude of freshwater discharge and tidal elevations. Superimposed upon diurnal and semi-diurnal tides were non-tidal water level changes induced mostly by variations in barometric pressure. These caused large changes in the salt wedge position. Destratification by the bubble curtain was compromised by these large oscillations, which limited the exposure of the salt wedge region to the mixing action of the bubble curtain. Complete vertical mixing of the water column was observed up to 30 m either side of the curtain on 30 October. Disruptions to the density stratification were not evident beyond 350 m of the curtain. In the immediate vicinity (30 m) of the curtain, deficits of dissolved oxygen in bottom waters were generally reduced or obliterated and a naturally turbid plume of water near the bottom of the estuary was mixed through the water column. The effects of the bubble curtain on dissolved oxygen, turbidity and temperature were, however, similar to those for salinity, with mixing confined to around 30 m from the curtain and no effect observed further than 350 m away. The upper Swan River estuary, although relatively narrow and strongly vertically stratified, is unsuited to destratification using bubble plumes. Cycling of spring and neap tides and non-tidal water level changes, together with freshwater inflows to the estuary, strongly limit the longitudinal extent of mixing by bubble curtains.
Estuarine residence times regulate not only biomass, but also phytoplankton succession. In the Sw... more Estuarine residence times regulate not only biomass, but also phytoplankton succession. In the Swan River estuary, Western Australia, dinoflagellate and marine diatoms tend to dominate during periods of low flow and high residence times, whereas the faster-growing freshwater diatoms and chlorophytes are associated with higher flow rates. Modifications to the estuary and its catchment area over the last century have considerably reduced residence times and may favour dinoflagellate and marine diatom dominated populations. Anecdotal evidence also suggests a greater regularity of summer blooms dominated by these groups in recent years.
The occurrence of blue-green algal blooms within the Goulburn-Broken catchment has been identifie... more The occurrence of blue-green algal blooms within the Goulburn-Broken catchment has been identified as a priority ecological issue of concern to stakeholders. This study reports the findings of an ecological risk assessment designed to assess the risks associated with algal blooms within the catchment, and how those risks might be affected by factors associated with irrigation. The likelihood of bloom occurrence was assessed through numerical modelling of four ecosystems. Phase 1 of this project identified two case study systems: Lake Nagambie / Goulburn Weir, and the lower Goulburn River. In addition, another two systems (East Goulburn Main Channel, Lake Mokoan) were modelled to assist in validation of the assessment technique. Modelling enabled integrated examination of a number of environmental stressors, including nutrients, temperature, light, and flow regime within each system. The potential impact of these stressors on the likelihood of algal blooms was investigated. Level of filterable reactive phosphorus (FRP) was identified as the primary factor influencing the likelihood of algal blooms, and any future or current irrigation developments that increase the levels of FRP should be assessed carefully as they may increase the likelihood of bloom formation. As current concentrations are relatively low, the magnitude of environmental perturbation required to increase bloom risk is quite large. However, it should also be noted that a lack of site-specific data makes risk prediction very uncertain. Further monitoring, and possibly modelling, of the case study sites and alternative proxy sites may assist in reducing this uncertainty.
2013 IEEE International Symposium on Information Theory, 2013
ABSTRACT It is a well known result that the Kraft inequality is a necessary and sufficient condit... more ABSTRACT It is a well known result that the Kraft inequality is a necessary and sufficient condition for the existence of a uniquely decodable code. This paper provides an inequality which is a counterpart of the Kraft inequality in Error free Perfect Secrecy (EPS) system. Our inequality is a necessary and sufficient condition for the existence of an EPS system. It also illustrates some necessary and sufficient conditions for an EPS system to achieve the minimal expected key consumption.
2009 IEEE International Symposium on Information Theory, 2009
In this paper, we show how to construct a factor graph from a network code. This provides a syste... more In this paper, we show how to construct a factor graph from a network code. This provides a systematic framework for decoding using message passing algorithms. The proposed message passing decoder exploits knowledge of the underlying communications network topology to simplify decoding. For uniquely decodeable linear network codes on networks with error-free links, only the message supports (rather than the message values themselves) are required to be passed. This proposed simplified support message algorithm is an instance of the sum-product algorithm. Our message-passing framework provides a basis for the design of network codes and control of network topology with a view toward quantifiable complexity reduction in the sink terminals.
Scale functions play a central role in the fluctuation theory of spectrally negative Lévy process... more Scale functions play a central role in the fluctuation theory of spectrally negative Lévy processes and often appear in the context of martingale relations. These relations are often complicated to establish requiring excursion theory in favour of Itô calculus. The reason for the latter is that standard Itô calculus is only applicable to functions with a sufficient degree of smoothness and knowledge of the precise degree of smoothness of scale functions is seemingly incomplete. The aim of this article is to offer new results concerning properties of scale functions in relation to the smoothness of the underlying Lévy measure. We place particular emphasis on spectrally negative Lévy processes with a Gaussian component and processes of bounded variation.
For 0 < y < 1, let Ur(t) = t -I I~ 1 {B,>~I ds. The questions addressed in this paper are motivat... more For 0 < y < 1, let Ur(t) = t -I I~ 1 {B,>~I ds. The questions addressed in this paper are motivated by a result due to Strassen: almost surely, llm sup,_o~ Ur(t)= 1-exp{-4(7, -1-1)}. We show that Strassen's result is closely related to a large deviations principle for the family of random variables Ur(t), t>0. Also, when y=l, Ur(t)~O almost surely and we obtain some bounds on the rate of convergence. Finally, we prove an analogous limit theorem for discounted averages of the form 2Ig ~ D().s)lts,>~} ds as 2 $ 0, where D is a suitable discount function. These results also hold for symmetric random walks.
A participatory approach was used to develop a Bayesian network model for assisting integration o... more A participatory approach was used to develop a Bayesian network model for assisting integration of water resource management in the Kongulai catchment in the Solomon Islands. This catchment provides 40–60% of the water for Honiara, the capital, and management is complex, with sparse data and many competing uses including drinking, domestic, agricultural, and industrial uses for both water and land
The investigation of multiple sources in household water management is considered overly complica... more The investigation of multiple sources in household water management is considered overly complicated and time consuming using paper and pen interviewing (PAPI). We assess the advantages of computer-assisted personal interviewing (CAPI) in Pacific Island Countries (PICs). We adapted an existing PAPI survey on multiple water sources and expanded it to incorporate location of water use and the impacts of extreme weather events using SurveyCTO on Android tablets. We then compared the efficiency and accuracy of data collection using the PAPI version (n = 44) with the CAPI version (n = 291), including interview duration, error rate and trends in interview duration with enumerator experience. CAPI surveys facilitated high-quality data collection and were an average of 15.2 min faster than PAPI. CAPI survey duration decreased by 0.55% per survey delivered (p < 0.0001), whilst embedded skip patterns and answer lists lowered data entry error rates, relative to PAPI (p < 0.0001). Large-scale household surveys commonly used in global monitoring and evaluation do not differentiate multiple water sources and uses. CAPI equips water researchers with a quick and reliable tool to address these knowledge gaps and advance our understanding of development research priorities.
The Swan River estuary, Western Australia, has undergone substantial hydrological modifications s... more The Swan River estuary, Western Australia, has undergone substantial hydrological modifications since pre-European settlement. Land clearing has increased discharge from some major tributaries roughly 5-fold, while weirs and reservoirs for water supply have mitigated this increase and reduced the duration of discharge to the estuary. Nutrient loads have increased disproportionately with flow and are now approximately 20-times higher than pre-European levels. We explore the individual and collective impacts of these hydrological changes on the Swan River estuary using a coupled hydrodynamic-ecological numerical model. The simulation results indicate that despite increased hydraulic flushing and reduced residence times, increases in nutrient loads are the dominant perturbation producing increases in the incidence and peak biomass of blooms of both estuarine and freshwater phytoplankton. Changes in salinity associated with altered seasonal freshwater discharge have a limited impact on phytoplankton dynamics.
The procedures involved in model development may be set out as a ten step process, beginning with... more The procedures involved in model development may be set out as a ten step process, beginning with defining the purpose of the model and ending with evaluation of the appropriateness and utility of the completed model. This process, recently outlined by Jakeman et al. [Jakeman, A.J., Letcher, R.A., Norton, J.P., 2006. Ten iterative steps in development and evaluation of environmental models. Environmental Modelling and Software 21, 602–614], is often iterative as model development is a continuous process that refines and improves the intended capacity of the model. Here, the ten steps of model development are critiqued and applied using a process-based biogeochemical model of aquatic systems, with examples from two case studies: a model of phytoplankton succession and nutrient concentrations in the Swan-Canning Estuary (Western Australia) and a model of sediment and nutrient transport and transformation in the Fitzroy Estuary and Keppel Bay (Queensland).
... is commonly applied to collaborative actions to bring about sustainable environmental governa... more ... is commonly applied to collaborative actions to bring about sustainable environmental governance. ... Within water resources management, conditions and components of social learning have ... of studies however address social learning in river basin management in developed ...
A trial to artificially destratify part of the water column of the Swan-Canning Estuary took plac... more A trial to artificially destratify part of the water column of the Swan-Canning Estuary took place over four weeks in 1997. Destratification was attempted with bubble plumes created by pumping compressed air through a porous pipe near the bed at a location in the upper estuary. The purpose of the trial was to determine whether the resultant bubble curtain could mix the water column, thereby altering the extent of upstream and downstream mixing and the vertical structures of salinity, temperature, dissolved oxygen and turbidity. The destratification trial was monitored using three techniques: vertical profiles taken on several days at selected stations along the estuary, fine scale profiles in the vicinity of the bubble curtain on one day, and continuous water column profiles taken 1 km upstream of the curtain. The seasonal upstream propagation of brackish water underneath a residual freshwater discharge was affected by the magnitude of freshwater discharge and tidal elevations. Superimposed upon diurnal and semi-diurnal tides were non-tidal water level changes induced mostly by variations in barometric pressure. These caused large changes in the salt wedge position. Destratification by the bubble curtain was compromised by these large oscillations, which limited the exposure of the salt wedge region to the mixing action of the bubble curtain. Complete vertical mixing of the water column was observed up to 30 m either side of the curtain on 30 October. Disruptions to the density stratification were not evident beyond 350 m of the curtain. In the immediate vicinity (30 m) of the curtain, deficits of dissolved oxygen in bottom waters were generally reduced or obliterated and a naturally turbid plume of water near the bottom of the estuary was mixed through the water column. The effects of the bubble curtain on dissolved oxygen, turbidity and temperature were, however, similar to those for salinity, with mixing confined to around 30 m from the curtain and no effect observed further than 350 m away. The upper Swan River estuary, although relatively narrow and strongly vertically stratified, is unsuited to destratification using bubble plumes. Cycling of spring and neap tides and non-tidal water level changes, together with freshwater inflows to the estuary, strongly limit the longitudinal extent of mixing by bubble curtains.
Estuarine residence times regulate not only biomass, but also phytoplankton succession. In the Sw... more Estuarine residence times regulate not only biomass, but also phytoplankton succession. In the Swan River estuary, Western Australia, dinoflagellate and marine diatoms tend to dominate during periods of low flow and high residence times, whereas the faster-growing freshwater diatoms and chlorophytes are associated with higher flow rates. Modifications to the estuary and its catchment area over the last century have considerably reduced residence times and may favour dinoflagellate and marine diatom dominated populations. Anecdotal evidence also suggests a greater regularity of summer blooms dominated by these groups in recent years.
The occurrence of blue-green algal blooms within the Goulburn-Broken catchment has been identifie... more The occurrence of blue-green algal blooms within the Goulburn-Broken catchment has been identified as a priority ecological issue of concern to stakeholders. This study reports the findings of an ecological risk assessment designed to assess the risks associated with algal blooms within the catchment, and how those risks might be affected by factors associated with irrigation. The likelihood of bloom occurrence was assessed through numerical modelling of four ecosystems. Phase 1 of this project identified two case study systems: Lake Nagambie / Goulburn Weir, and the lower Goulburn River. In addition, another two systems (East Goulburn Main Channel, Lake Mokoan) were modelled to assist in validation of the assessment technique. Modelling enabled integrated examination of a number of environmental stressors, including nutrients, temperature, light, and flow regime within each system. The potential impact of these stressors on the likelihood of algal blooms was investigated. Level of filterable reactive phosphorus (FRP) was identified as the primary factor influencing the likelihood of algal blooms, and any future or current irrigation developments that increase the levels of FRP should be assessed carefully as they may increase the likelihood of bloom formation. As current concentrations are relatively low, the magnitude of environmental perturbation required to increase bloom risk is quite large. However, it should also be noted that a lack of site-specific data makes risk prediction very uncertain. Further monitoring, and possibly modelling, of the case study sites and alternative proxy sites may assist in reducing this uncertainty.
2013 IEEE International Symposium on Information Theory, 2013
ABSTRACT It is a well known result that the Kraft inequality is a necessary and sufficient condit... more ABSTRACT It is a well known result that the Kraft inequality is a necessary and sufficient condition for the existence of a uniquely decodable code. This paper provides an inequality which is a counterpart of the Kraft inequality in Error free Perfect Secrecy (EPS) system. Our inequality is a necessary and sufficient condition for the existence of an EPS system. It also illustrates some necessary and sufficient conditions for an EPS system to achieve the minimal expected key consumption.
2009 IEEE International Symposium on Information Theory, 2009
In this paper, we show how to construct a factor graph from a network code. This provides a syste... more In this paper, we show how to construct a factor graph from a network code. This provides a systematic framework for decoding using message passing algorithms. The proposed message passing decoder exploits knowledge of the underlying communications network topology to simplify decoding. For uniquely decodeable linear network codes on networks with error-free links, only the message supports (rather than the message values themselves) are required to be passed. This proposed simplified support message algorithm is an instance of the sum-product algorithm. Our message-passing framework provides a basis for the design of network codes and control of network topology with a view toward quantifiable complexity reduction in the sink terminals.
Scale functions play a central role in the fluctuation theory of spectrally negative Lévy process... more Scale functions play a central role in the fluctuation theory of spectrally negative Lévy processes and often appear in the context of martingale relations. These relations are often complicated to establish requiring excursion theory in favour of Itô calculus. The reason for the latter is that standard Itô calculus is only applicable to functions with a sufficient degree of smoothness and knowledge of the precise degree of smoothness of scale functions is seemingly incomplete. The aim of this article is to offer new results concerning properties of scale functions in relation to the smoothness of the underlying Lévy measure. We place particular emphasis on spectrally negative Lévy processes with a Gaussian component and processes of bounded variation.
For 0 < y < 1, let Ur(t) = t -I I~ 1 {B,>~I ds. The questions addressed in this paper are motivat... more For 0 < y < 1, let Ur(t) = t -I I~ 1 {B,>~I ds. The questions addressed in this paper are motivated by a result due to Strassen: almost surely, llm sup,_o~ Ur(t)= 1-exp{-4(7, -1-1)}. We show that Strassen's result is closely related to a large deviations principle for the family of random variables Ur(t), t>0. Also, when y=l, Ur(t)~O almost surely and we obtain some bounds on the rate of convergence. Finally, we prove an analogous limit theorem for discounted averages of the form 2Ig ~ D().s)lts,>~} ds as 2 $ 0, where D is a suitable discount function. These results also hold for symmetric random walks.
A participatory approach was used to develop a Bayesian network model for assisting integration o... more A participatory approach was used to develop a Bayesian network model for assisting integration of water resource management in the Kongulai catchment in the Solomon Islands. This catchment provides 40–60% of the water for Honiara, the capital, and management is complex, with sparse data and many competing uses including drinking, domestic, agricultural, and industrial uses for both water and land
The investigation of multiple sources in household water management is considered overly complica... more The investigation of multiple sources in household water management is considered overly complicated and time consuming using paper and pen interviewing (PAPI). We assess the advantages of computer-assisted personal interviewing (CAPI) in Pacific Island Countries (PICs). We adapted an existing PAPI survey on multiple water sources and expanded it to incorporate location of water use and the impacts of extreme weather events using SurveyCTO on Android tablets. We then compared the efficiency and accuracy of data collection using the PAPI version (n = 44) with the CAPI version (n = 291), including interview duration, error rate and trends in interview duration with enumerator experience. CAPI surveys facilitated high-quality data collection and were an average of 15.2 min faster than PAPI. CAPI survey duration decreased by 0.55% per survey delivered (p < 0.0001), whilst embedded skip patterns and answer lists lowered data entry error rates, relative to PAPI (p < 0.0001). Large-scale household surveys commonly used in global monitoring and evaluation do not differentiate multiple water sources and uses. CAPI equips water researchers with a quick and reliable tool to address these knowledge gaps and advance our understanding of development research priorities.
The Swan River estuary, Western Australia, has undergone substantial hydrological modifications s... more The Swan River estuary, Western Australia, has undergone substantial hydrological modifications since pre-European settlement. Land clearing has increased discharge from some major tributaries roughly 5-fold, while weirs and reservoirs for water supply have mitigated this increase and reduced the duration of discharge to the estuary. Nutrient loads have increased disproportionately with flow and are now approximately 20-times higher than pre-European levels. We explore the individual and collective impacts of these hydrological changes on the Swan River estuary using a coupled hydrodynamic-ecological numerical model. The simulation results indicate that despite increased hydraulic flushing and reduced residence times, increases in nutrient loads are the dominant perturbation producing increases in the incidence and peak biomass of blooms of both estuarine and freshwater phytoplankton. Changes in salinity associated with altered seasonal freshwater discharge have a limited impact on phytoplankton dynamics.
The procedures involved in model development may be set out as a ten step process, beginning with... more The procedures involved in model development may be set out as a ten step process, beginning with defining the purpose of the model and ending with evaluation of the appropriateness and utility of the completed model. This process, recently outlined by Jakeman et al. [Jakeman, A.J., Letcher, R.A., Norton, J.P., 2006. Ten iterative steps in development and evaluation of environmental models. Environmental Modelling and Software 21, 602–614], is often iterative as model development is a continuous process that refines and improves the intended capacity of the model. Here, the ten steps of model development are critiqued and applied using a process-based biogeochemical model of aquatic systems, with examples from two case studies: a model of phytoplankton succession and nutrient concentrations in the Swan-Canning Estuary (Western Australia) and a model of sediment and nutrient transport and transformation in the Fitzroy Estuary and Keppel Bay (Queensland).
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Papers by Terence Chan