Infrastructure Engineering - Research Publications
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ItemThe value of water in storage: Implications for operational policies(Curran Associate Inc., 2018-01-01)With desalination plants becoming an increasingly common feature of water supply systems for major cities, the options for managing water security are now markedly different to past times when the short-term response to low water availability essentially revolved around reducing usage. The operation of desalination plants and other components of diversified water supply systems now enable operators to increase availability, essentially by producing water. The operation of such systems clearly impacts operational costs but, more subtly, also impacts future augmentation decisions. This can have major cost implications as there is a trade-off between the costs of operating a water supply system and the probability and timing of future augmentations that leads to important differences in the economics of reliably supplying water. This paper first summarises an economic analysis framework in which to explore the interaction of short (operational) and long (capital investment) term decisions towards maintaining water security. It then explores the implications of different operation approaches in Melbourne’s water supply system, assuming a planned augmentation pathway under conditions of low water availability. We assume augmentation decisions are prompted by critically low water availability events, rather than long-term reliability analysis. We show that the majority of the variation in cost of maintaining a reliable water supply is associated with impacts of operational rules on likely capital investment and that this results in a strong interaction between short and long-term decision making. The outcome of this work has implications for both operational decision making and augmentation planning for urban water supply systems. These implications are relevant to any water supply system where a climate independent water supply source, such as desalination, can be accessed.
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ItemDetection of a soil moisture and groundwater signal in ground-based gravity observations(Conference Organising Committee for the 40th Australian Conference of Economists, 2006)Gravity observations have the potential to provide an exciting new source of remotely sensed data to constrain the water balance in land surface models. This would result in more accurate soil moisture and flux predictions and correspondingly improved numerical weather prediction and global climate forecasts. However before existing or future (GRACE or GOCE) dedicated gravity satellites can be utilised in an operational setting it must be shown that a soil moisture signal is detectable in gravity observations. This is extremely difficult to show directly for the satellite observations due to the massive spatial scale involved (1000 km2or larger depending on accuracy requirements), so a ground-based field study of soil moisture, groundwater and gravity changes is essential in verifying the magnitude of the hydrological signal in gravity observations. This paper presents results from two field sites in the Kyeamba Creek catchment in NSW where soil moisture, groundwater and gravity have been monitored for one year. One is a hillslope site with no groundwater whereas the other is a valley site with a shallow water table. After correcting for earth tides and gravity meter drift, a gravity network adjustment is performed for two time periods chosen to capture the full range of subsurface water storage (autumn and spring). The adjustment improves the precision of the gravity estimates at each site relative to a hydrologically stable bedrock reference site. A t-test is performed on the gravity changes at the two sites and the valley site is found to have a significant change in gravity that corresponds extremely well to the predicted hydrologically induced gravity change. There are many complicating factors in a ground-based study, but nevertheless a hydrological signal (predominantly soil moisture) has been detected in the gravity observations of a valley site with a shallow groundwater table.
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ItemRecharge mechanisms in an Arid Zone River: Effects of channelisation(Conference Organising Committee, 2006)Arid zone, ephemeral rivers typically experience very high transmission losses. Most international studies have identified infiltration into stream sediments and subsequent percolation to the unconfined alluvial aquifer as the major cause of transmission losses. There is relatively little data regarding mechanisms and stores controlling transmission loss processes in Australian arid zone streams, particularly in regards recharge to the unconfined aquifer. This study reports on a field study of recharge mechanisms occurring in the Neales River of the Lake Eyre Basin (northern South Australia). Piezometric monitoring, numerical and analytical modelling were used to identify and quantify recharge to the unconfined aquifer during streamflow events in 2004-2005. Significant recharge only occurred in channelised reaches and rates of recharge did not show a clear relationship with stage but tended to be higher for flow events occurring after longer periods of no flow. Reaches lacking a single, well-defined channel are common in the anastomosing rivers of the Lake Eyre Basin. Piezometers monitoring the alluvial sediments at two locations lacking well-defined channels did not measure any development of a saturated zone in the alluvial aquifer following flow events. The data suggests that most percolation and recharge occurs through the bank, rather than the floodplain and this needs to be taken into account when estimating transmission losses for these river systems.
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ItemNo Preview AvailableRiparian tree water use by eucalyptus coolabah in the Lake Eyre Basin(Conference Organising Committee, 2006)The Lake Eyre Basin (LEB) is characterised by enormous stream flow variability, low rainfall, saline groundwater and at times saline surface water; conditions that demand flexible tree water use strategies in the riparian zone. In the lower reaches of the Diamantina River, the water sources and extraction patterns of Eucalyptus coolabah were examined using isotope data from xylem, soil water, groundwater and surface water. Additionally, soil chloride and matric potential data were used to infer zones of water availability for root uptake. It was found that despite their elevated salinity, groundwater and soil water formed a large proportion of the transpiration flux, with little contribution from standing pools of surface water. At two sites located on the dry floodplain, the data indicated E. coolabah relied substantially on groundwater with a salinity exceeding 30,000 mgL-1Cl. However, some dilution with fresher soil water was evident at most sites, highlighting the importance of flooding in replenishing soil water. Water extraction primarily occurred in the unsaturated zone where a compromise between salinity and source reliability was required. However, E. coolabah was found to have higher salinity tolerances than previously reported for Eucalyptus species.
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ItemNo Preview AvailableEquifinality and process-based modelling(American Geophysical Union, 2018-11-26)Equifinality is understood as one of the fundamental difficulties in the study of open complex systems, including catchment hydrology. A review of the hydrologic literature reveals that the term equifinality has been widely used, but in many cases inconsistently and without coherent recognition of the various facets of equifinality, which can lead to ambiguity but also methodological fallacies. Therefore, in this study we first characterise the term equifinality within the context of hydrological modelling by reviewing the genesis of the concept of equifinality and then presenting a theoretical framework. During past decades, equifinality has mainly been studied as a subset of aleatory (arising due to randomness) uncertainty and for the assessment of model parameter uncertainty. Although the connection between parameter uncertainty and equifinality is undeniable, we argue there is more to equifinality than just aleatory parameter uncertainty. That is, the importance of equifinality and epistemic uncertainty (arising due to lack of knowledge) and their implications is overlooked in our current practice of model evaluation. Equifinality and epistemic uncertainty in studying, modelling, and evaluating hydrologic processes are treated as if they can be simply discussed in (or often reduced to) probabilistic terms (as for aleatory uncertainty). The deficiencies of this approach to conceptual rainfall-runoff modelling are demonstrated for selected Australian catchments by examination of parameter and internal flux distributions and interactions within SIMHYD. On this basis, we present a new approach that expands equifinality concept beyond model parameters to inform epistemic uncertainty. The new approach potentially facilitates the identification and development of more physically plausible models and model evaluation schemes particularly within the multiple working hypotheses framework, and is generalisable to other fields of environmental modelling as well.
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ItemSalt and water flux in an arid zone intermittent river: The role of the floodplain environment(Conference Organising Committee, 2006)Exchange between the surface water and local groundwater systems in intermittent rivers is not well understood, however the ecological functioning of these riverine environments can be dependent on the degree of interaction between the two domains. Spatial and temporal changes in the isotopic (δ18O/δ2H) and major ion composition of the floodplain aquifers in the lower reaches of the intermittent Diamantina River, South Australia, along with hydrologic data and sedimentary analysis, are used to identify localized groundwater recharge following flow events. The approximately synchronous response of groundwater levels to surface water events over two years (encompassing the recession of one major flood involving substantial floodplain inundation and two smaller events) particularly in near channel locations, indicates connectivity between surface water and local groundwater systems. The increase in δ18O/δ2H values and decrease in the salinity of groundwater <100m from the river subsequent to major flooding indicates event recharge of the shallow alluvial aquifers. Over time, groundwater compositions return to more saline and isotopically depleted values, considered here to be base conditions. Groundwater salinity and isotopic compositions of the mid and outer floodplains varied little over the course of the study period despite flood inundation and change in groundwater head. Sedimentary analysis of the predominantly silt and clay floodplain surface indicates the potential of these soils to develop seals and thus limit infiltration of flood waters. Thus event recharge was limited to near bank areas or zones of preferential infiltration over the course of the study period. CFC dating and isotopic data give some indication that sustained recharge to the floodplain groundwater system occurs during successive large flood events or wet years.
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ItemWhich theoretical distribution function best fits measured within day rainfall distributions across Australia?(Conference Organising Committee, 2006)Rainfall data at high temporal resolutions is required to accurately model the dynamics of surface runoff processes, in particular sediment entrainment. These processes respond to rainfall intensity variations over short intervals, yet measurement of rainfall intensity at sufficient resolution is available only at a limited number of locations across Australia. On the other hand there is good coverage of rainfall data registered at a daily time step, thus it is desirable to establish a means to estimate within-day distributions of rainfall intensity given the daily rainfall depth and other readily available hydrometeorological data (e.g. temperature, pressure). As a first step towards such a method, an investigation was conducted into the shape of the temporal distribution of high-resolution (6 minute) rainfall intensity within the wet part of rainy days (total rainfall depth > 10mm). This paper quantifies the skill of nine different theoretical distribution functions (TDFs) in fitting characteristics of measured rainfall that are most likely to drive sediment entrainment and transport on hillslopes. Skill is reported by two goodness-of-fit statistics: the Root Mean Square Error (RMSE) between the fitted and observed within-day distribution; and the efficiency of prediction of the 30 minutes of highest rainfall intensity (average intensity of the 5 highest intensity intervals). Four TDFs provided relatively poor fits to higher intensity rainfall (two and three parameter lognormal, two parameter Generalized Pareto and Gumbel), and also showed higher RMSE values. The remaining five TDFs performed equally well for both goodness-of-fit measures. Two of these TDFs are extreme value distributions (Generalized Extreme Value and Weibull) and in a strict statistical sense should not be applied to within-day rainfall intensity data. On this basis, the remaining three TDFs (gamma, exponential and the three parameter Generalized Pareto) were selected as suitable candidates to represent within-day rainfall distributions in Australia, in particular for hydrological models seeking to estimate runoff and erosion.
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ItemA web-based interface to visualize and model spatio-temporal variability of stream water quality(River Basement Management Society, 2018)Understanding the spatio-temporal variability in stream water quality is critical for designing effective water quality management strategies. To facilitate this, we developed a web-based interface to visualize and model the spatio-temporal variability of stream water quality in Victoria. We used a dataset of long-term monthly water quality measurements from 102 monitoring sites in Victoria, focusing on six water quality constituents: total suspended solids (TSS), total phosphorus (TP), filterable reactive phosphorus (FRP), total Kjedahl nitrogen (TKN), nitrate-nitrite (NOx), and electrical conductivity (EC). The interface models spatio-temporal variability in water quality via a Bayesian hierarchical modelling framework, and produces summaries of (1) the key driving factors of spatio-temporal variability and (2) model performance assessed by multiple metrics. Additional features include predicting the time-averaged mean concentration at an un-sampled site, and testing the impact of land-use changes on the mean concentration at existing sites. This tool can be very useful in supporting the decision-making processes of catchment managers in (1) understanding the key drivers of changes in water quality and (2) designing water quality mitigation and restoration strategies.
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ItemIntegrated modelling of spatio-temporal variability in stream water quality across victorian catchments(Engineers Australia, 2018-01-01)Degraded water quality in rivers and streams can have large economical, societal and ecological impacts. Stream water quality can be highly variable both over space and time, so understanding and modelling these spatio-temporal variabilities is critical to developing management and mitigation strategies to improve riverine water quality. However, there is currently limited capacity to model stream water quality due to the lack of understanding of the key factors driving spatio-temporal variability in water quality. To address this, a Bayesian hierarchical statistical model has been developed to describe the spatio-temporal variability in stream water quality across multiple catchments in the state of Victoria, Australia. We used monthly water quality monitoring data collected at 102 sites over 20 years. The modelling focused on three key water quality indicators: total suspended solids (TSS), nitrate-nitrite (NOx) and salinity (EC). It was found that both human-influenced catchment characteristics (land use) and other natural characteristics such as climate or topography are important drivers of spatial variabilities. The key drivers of temporal variability are changes in streamflow, climate and vegetation cover. These key drivers have been integrated into a spatio-temporal modelling framwork. These models can be applied at different spatial and temporal scales, and explain a reasonable proportion of spatio-temporal variation in the different water quality constituents. The extension and adaption of these models is currently underway to create an operational tool to forecast stream water quality responses to potential land use and climatic changes.
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ItemUsing a data-driven approach to understand the interaction between catchment characteristics and water quality responses(River Basin Management Society, 2016)