Infrastructure Engineering - Research Publications
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ItemScaling from process timescales to daily time steps: A distribution function approach(American Geophysical Union, 2005-02)A new temporal scaling method applicable to many rainfall-runoff-erosion models is presented. The method is based on the probability distribution approach used in a number of spatial hydrological models, and it uses statistical distributions of rainfall intensity to represent subdaily intensity variations in a daily time step model. This allows the effect of short timescale nonlinear processes to be captured while modeling at a daily time step, which is often attractive due to the wide availability of total daily rainfall data. The approach relies on characterizing the rainfall intensity variation within a day using a probability distribution function (pdf). This pdf is then modified by various linear and nonlinear processes typically represented in hydrological and erosion models. The statistical description of subdaily variability is thus propagated through the model, allowing the effects of variability to be captured in the simulations. This results in pdfs of various fluxes, the integration of which over a day gives respective daily totals. The method is tested using 42 plot years of daily runoff and erosion plot data from field studies in different environments from Australia and Nepal. Significant improvements in the simulation of surface runoff and erosion are achieved, compared with a similar model using average daily rainfall intensities. The probability-based model compares well with a subhourly (2 and 6 min) model using similar process descriptions. This suggests that the probability-based approach captures the important effects of sub–time step variability while utilizing commonly available information. It is also found that the model parameters are more robustly defined using the probability-based approach compared with the daily effective parameter model. This suggests that the probability-based approach may offer improved model transferability spatially (to other areas) and temporally (to other periods).
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ItemHydropedology: Synergistic integration of pedology and hydrology(American Geophysical Union, 2006-05-09)This paper presents a vision that advocates hydropedology as an advantageous integration of pedology and hydrology for studying the intimate relationships between soil, landscape, and hydrology. Landscape water flux is suggested as a unifying precept for hydropedology, through which pedologic and hydrologic expertise can be better integrated. Landscape water flux here encompasses the source, storage, flux, pathway, residence time, availability, and spatiotemporal distribution of water in the root and deep vadose zones within the landscape. After illustrating multiple knowledge gaps that can be addressed by the synergistic integration of pedology and hydrology, we suggest five scientific hypotheses that are critical to advancing hydropedology and enhancing the prediction of landscape water flux. We then present interlinked strategies for achieving the stated vision. It is our hope that by working together, hydrologists and pedologists, along with scientists in related disciplines, can better guide data acquisition, knowledge integration, and model-based prediction so as to advance the hydrologic sciences in the next decade and beyond.
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ItemStochastic modelling of annual rainfall data(Conference Design, 2006-01-01)Rainfall data are generally required in computer simulations of rainfall-runoff processes, crop growth and water supply systems. The length of historical climate data is usually not long enough to describe the complete range of variability that might be experienced during the life of a water resources or agricultural project. Using the statistical characteristics of historical data, it is possible to generate many sequences of data that better represent the climatic variability. In developing the stochastic models, the data are generally assumed stationary in the broad sense and any long-term fluctuations in the data are ignored. Typically, only in monthly, daily and sub-daily models, is the seasonal variation within a year considered explicitly in stochastic models. However, there is a growing interest and concern about the role of interdecadal variability in climate and its influence on rainfall. One approach is to identify any long-term fluctuations in the observed rainfall and model them explicitly. Empirical Mode Decomposition (EMD) was used to identify any low frequency fluctuations in annual rainfall data from 44 sites in Australia. The results did not allow easy identification of low frequency fluctuations in the data. As a means of aiding interpretation of the EMD results, the following ploy was adopted. The AR1 model, the most widely used model for the generation of annual rainfall data, was used to generate stochastic data based on the statistics of the observed sequences and the EMD analysis was performed on the stochastic data sets. The results of the analysis comparing both the historical and generated data showed that, in general, both the data sets have similar low frequency characteristics except for Perth.
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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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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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ItemObject-based classification of ikonos imagery for mapping large-scale vegetation communities in urban areas(MOLECULAR DIVERSITY PRESERVATION INTERNATIONAL-MDPI, 2007-11)Effective assessment of biodiversity in cities requires detailed vegetation maps.To date, most remote sensing of urban vegetation has focused on thematically coarse landcover products. Detailed habitat maps are created by manual interpretation of aerialphotographs, but this is time consuming and costly at large scale. To address this issue, wetested the effectiveness of object-based classifications that use automated imagesegmentation to extract meaningful ground features from imagery. We applied thesetechniques to very high resolution multispectral Ikonos images to produce vegetationcommunity maps in Dunedin City, New Zealand. An Ikonos image was orthorectified and amulti-scale segmentation algorithm used to produce a hierarchical network of image objects.The upper level included four coarse strata: industrial/commercial (commercial buildings),residential (houses and backyard private gardens), vegetation (vegetation patches larger than0.8/1ha), and water. We focused on the vegetation stratum that was segmented at moredetailed level to extract and classify fifteen classes of vegetation communities. The firstclassification yielded a moderate overall classification accuracy (64%, κ = 0.52), which ledus to consider a simplified classification with ten vegetation classes. The overallclassification accuracy from the simplified classification was 77% with a κ value close tothe excellent range (κ = 0.74). These results compared favourably with similar studies inother environments. We conclude that this approach does not provide maps as detailed as those produced by manually interpreting aerial photographs, but it can still extract ecologically significant classes. It is an efficient way to generate accurate and detailed maps in significantly shorter time. The final map accuracy could be improved by integrating segmentation, automated and manual classification in the mapping process, especially when considering important vegetation classes with limited spectral contrast.
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ItemImproved capital procurement through increased use of quantitatively-based decisions(Department of Civil Engineering, National Taiwan University, 2008)The procurement of major capital projects always involves significant risk and uncertainties and this is one of the primary causes for the variations from expected outcomes. This paper outlines the delimitation between strategies for making complex decisions using quantitative analyses as opposed to the techniques and applications currently being used by project and construction managers. Various approaches have been developed and adopted by researchers and practitioners to improve the quality of critical project decisions to maximise benefits. Strategic frameworks and organisational hierarchies are frequently deemed as an optimal solution from the perspective of industrial participants, while numerous researchers indicate decisions with quantitative evidences, underpinned by proper choice of technique, will add additional benefits over current industrial practices. It is asserted that improved decisions can be made through the additional use of quantitative approaches. This paper reports the finding of a study that has identified where the increased use of quantitative approaches may assist project and construction managers and proposes a mechanism to confirm the potential benefits.