Swan Street Bridge Upgrade – Widening a 70-year old bridge

<p>The Swan Street Bridge is a reinforced concrete five-span arch bridge crossing the Yarra River in Melbourne, Australia. Constructed circa 1950, it provided four lanes of traffic and narrow pedestrian footpaths on both sides. The bridge forms part of a key route for vehicular access into the Central Business District, as well as pedestrian thoroughfare to the sporting and events precinct.</p><p>Substantial increases in traffic volumes meant the bridge had become a significant bottleneck and was hazardous for pedestrians. In response to this, a scheme was developed to widen the bridge – providing an additional lane of traffic and four-metre-wide Shared User Paths on both sides – all guided by an overlaying architectural vision created by the winner of a design competition.</p><p>This paper presents the structural technical solutions adopted for the strengthening and widening, which considered the original structural design, as well as the architectural intent for the widening.</p>

Ordinary kriging and genetic programming for spatial estimation of rainfall in the Middle Yarra River catchment, Australia

Rainfall maps with gridded data are frequently used as an important input for many hydrological models. In this study, two kriging-based interpolation methods (i.e., ordinary kriging (OK) and kriging with genetic programming (KGP)) and a deterministic interpolation method (inverse distance weighting (IDW)) are implemented to generate gridded rainfall maps from point rainfalls. The KGP is implemented as a new kriging method in which the genetic programming-based non-parametric variogram model is used with kriging. Rainfall records from existing 19 raingauges in the Middle Yarra River catchment, Australia are used for the analysis. The performance of each method is assessed through the cross-validation test. Results indicate that the kriging-based methods clearly outperform the IDW method. Among all the kriging-based methods, OK with the spherical variogram model yields the lowest prediction error and best estimates for all months. The KGP method gives an almost identical error to that given by the OK with the spherical variogram model for most of the months and a lower prediction error than that given by OK with the exponential or Gaussian variogram model. Thus, the KGP can be used in line with traditional kriging as a viable alternative technique for spatial estimation and mapping of rainfall.

Spatio-temporal spawning patterns of two riverine populations of the threatened Macquarie perch (Macquaria australasica)

Understanding species-reproduction dynamics is vital for the management of riverine fish. Information on the spawning ecology of the endangered Australian Macquarie perch (Macquaria australasica) is based largely on data gathered from lacustrine populations, with uncertainty on the applicability such data has for managing riverine populations. The current study presents a first description of spawning patterns of two riverine populations of Macquarie perch in Victoria, Australia, using egg counts recorded across multiple sites and periods within the species core spawning window. Spawning intensity was highly variable between study sites, with 96 and 82% of eggs collected from a single site in the King Parrot Creek and Yarra River respectively. We also found a strong positive association between spawning and water temperature. Our results provide an important account of spatio-temporal spawning patterns of riverine Macquarie perch populations and lend some support for the transfer of information from lacustrine populations (as demonstrated by spawning habitat and temperature association). Although the spatial and temporal constraints of the present study must be considered, the results provide opportunity for further testing of the environmental effects, and management options aimed at enhancing spawning of this endangered species.

Integrated conceptual modelling of faecal contamination in an urban estuary catchment

Urban stormwater is regarded as a key input of faecal contamination in receiving water bodies and therefore, a major concern for health risks associated with aquatic recreation. Wastewater leakages, cross connections and overflows, together with faeces washed from surfaces during rainfall events, are possible origins of faecal contamination which enter these water bodies through stormwater drains. This paper applies conceptual models to a case study of the Yarra River estuary to understand the relative importance of fluxes derived from an urban creek and the 219 urban stormwater pipes which drain directly to the estuary as compared with other inputs, such as the Yarra River itself. Existing hydrologic-microorganism models were used for the estimation of the inputs from riverine and urban stormwater fluxes. These predictions were applied as boundary conditions for a new, highly simplified, model which accounts for the transport and survival of faecal microorganisms in the estuary. All models were calibrated using a rich dataset, containing over 2,000 measured Escherichia coli concentrations. Mass balances from the riverine and stormwater models indicate the limited influence of urban stormwater drains on the estuary during dry weather; less than 0.05% to 10% (5th and 95th percentile; median 0.5%) of the total daily E. coli load entering the estuary was derived from urban stormwater drains. While wet weather contributions from stormwater drains could be more significant (2% to 50%; 5th and 95th percentile), the average contribution remained marginal (median 10%). Sensitivity testing of the estuarine microorganism model by switching off stormwater boundary conditions resulted in minimal model efficiency reduction; this may reflect the low average daily contribution from urban stormwater drains. While these results confirm previous studies which show that E. coli loads derived from stormwater drains are dwarfed by other inputs, it is essential to note that these results also demonstrate that some conditions reveal the opposite; high proportions from stormwater are possible when combined with low riverine inputs and high urban rainfall. Furthermore, this study focuses on the overall impacts of direct urban stormwater inputs on the faecal contamination levels within the estuary, and localized impacts would certainly require further investigation.