Stuart Macnish, Natarsha Woods, Michael Dixon
What happens when the people that undertake early environmental investigation stay on as part of the delivery team throughout the design and construction phases of a major project such as the Wivenhoe Alliance?
Often, the early investigation for projects, particularly in the case of environmental impact assessments and approvals processes, is carried out independently of the construction team. In the case of the Wivenhoe Alliance, these issues were set out in the scope of the project itself and delivered by the same team during construction.
The benefits and outcomes have been impressive not only for the project, but for SEQWater and the local community into the future. Improved biodiversity values, increased water quality protection, safety improvements, and value for money are only some of the key benefits experienced.
Individuals within the team also benefit. Environmental professionals are able to implement their
knowledge ‘on-ground’ and progressively improve practices in an area of constant change due to
construction initiatives and timeframes.
This paper explores the specific areas in which the involvement of environmental professionals throughout early investigation and planning, design and construction have benefited the Wivenhoe Alliance and the outcomes that have resulted from this innovative approach.
The Ross River Dam was first commissioned in 1974 and raised in 1976. The 8200 m long
embankment was not fitted with chimney filters and has suffered extensive desiccation cracking since it was raised. A significant component of the dam upgrade is the retrofitting of filter zones to ensure the embankment meets current dam safety guidelines.
This paper describes the process of investigation of the existing desiccation cracks and the use of Hole Erosion Tests (HET) and No Erosion Filter (NEF) tests to validate the design of the retrofitted filter. A significant challenge in the design is to provide a cost effective solution given the 7500 m length of embankment requiring treatment. Assessment of flow rates within cracks and expected piping erosion along the cracks was used to assess the required drainage capacity. This assessment of expected flow capacity allowed the deletion of the coarse filter in the design reducing the filter requirement from a triple filter to a single fine filter. Results of this assessment were incorporated into the Risk Assessment based design validation process.
Sonny Connors, Shaun Nugent, Brett Taylor, Brian Walford
The Tarong coal-fired power station near Kingaroy in southern Queensland discharges ash to a storage facility of 42,000 ML capacity, impounded by a 48 m high-zoned earth and rockfill dam embankment. The embankment was constructed in 1980–81. In recent years, Tarong Energy Corporation (TEC) has investigated a number of options for a new storage facility as the remaining capacity of the existing ash dam storage diminishes. TEC determined that the existing facility should be upgraded to provide additional storage capacity for the short term. At the same time, there emerged a requirement to improve the long-term seismic resistance of the embankment. Enlarging the existing spillway cut provided the material for a 400,000 m3 weighting zone and, by reducing the design flood freeboard, extended the ash disposal capacity by several years without a need to raise the embankment. Challenges included significant foundation seepage and deteriorated riprap. The paper describes the issues, risks, adopted criteria, investigation undertaken, and implementation of the upgrading works. Innovative approaches to the provision of future storage capacity are outlined.
Construction of the Lake Buffalo Dam was completed in 1965. It was to be a temporary dam, required to operate for several years, then act as a cofferdam for the construction of a much larger dam downstream. This larger dam was never built and a risk assessment completed by Goulburn Murray Water (G-MW) in 2001 identified several dam safety deficiencies at Lake Buffalo were among the highest priorities for risk reduction measures across the G-MW dams portfolio. Specifically it identified Lake Buffalo as having inadequate flood capacity and there were also concerns about transverse cracking within the embankment.
This paper describes the detailed investigation and analysis of the embankment cracking including assessing the potential for piping through an embankment having deficient filters and known transverse cracking. The design features of the upgrade are also described including the design of the a filter buttress, a parapet wall raise, Computational Fluid Dynamics (CFD) modelling and spillway anchoring. Construction was completed in 2003.
The Ross River Dam was constructed in 1974 following design by the State Government, including
hydraulic model testing, by SMEC. The maximum spillway discharge at that time was 1100 m3/s.
Latterly, the dam and spillway have come up for a comprehensive review given that the dam is in an extreme hazard category because of its location only a short distance upstream of the city of
Townsville. The revised hydrology has produced outflow hydrographs peaking at over 4 000 m3/s – more than three and a half times the original – to be passed through the 130 ft (39.62 m) wide
The paper describes the hydraulic modelling planned and carried out to determine changes needed to handle such high discharges. The modelling was to provide for the installation of radial gates and piers, and study of the water level, pressure and dissipation conditions in the dissipator for several key discharges through the range to PMF. Pressure measurements included transients, consideration of the potential for uplift of the basin floor slabs, the integrity of the walls to handle the differential loads, and, as a major consideration, the energy conditions in the flow exiting the dissipator and the integrity of the rock downstream to avoid erosion. Each of these aspects will be addressed in the paper both from the modelling and interpretation standpoint and from the civil structural analysis standpoint, together with a description of the strengthening works required to achieve a satisfactory outcome.