Resource consents for Christchurch’s existing solid waste disposal facility at Burwood expire in May 2005 and the landfill must close. A new, state-of-the-art regional landfill is under construction at Kate Valley, which will accept solid waste from Christchurch and surrounding districts. Investigations and studies for the landfill have attracted considerable public attention, engaging public groups in discussions through resource consent hearings in 2002 and 2003.
The proposed landfill includes two embankment dams in a cascade arrangement below the landfill. The first is a 19m high sedimentation dam designed to retain silt runoff from the earthworks associated with landfill construction and operation, protecting the health of the stream and environment below the dam. The second is a 9m high dam performing dual roles of storing and supplying water for the landfill earthworks activities, and providing an additional safety buffer for silt control and containment of any accidental release of leachate at the landfill.
While the dams are relatively modest in size, they are being built to very high standards with strict peer review as a result of their association with the landfill project, and to minimise any community and environmental impacts. The design and construction of the landfill and dams is being completed using an innovative modified alliancing arrangement which provides the close working relationship that alliances are renowned for, while minimising up-front financial risk to the owner.
This paper deals with key aspects related to the landfill dams, such as community consultation and expectations, environmental impacts as well as the technical features. Construction is underway for the dams and the landfill at the time of writing of this paper.
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Peter Campbell, Phil Papas, Matthew McDonald
Southern Hydro is a private dam owner generating electricity from ten power stations in Victoria and five power stations in New South Wales. Amongst its assets are the Kiewa and Rubicon schemes comprising a cascade of dams in state forests and national parks. To manage the passing of sediment during desilting operations of these schemes, Southern Hydro has implemented a biological and water quality monitoring programme. A working group has been established to coordinate this activity and provide feedback to the wider community.
The paper describes how Southern Hydro manages environmental risks during the desilting operations to ensure standards are met and the community is assured rivers in good environmental condition. It also describes how the Environmental Working Group that was potentially an unwieldily group of wide membership has become an effective working team.
The decision-making landscape has shifted markedly over the last 10 years with the implementation of COAG micro-economic reforms. These reforms have seen the separation of regulatory functions from commercial / service provision functions – yielding benefits to all stakeholders. However, the fragmented regulatory framework for dam owners (in Queensland at least) has resulted in potential conflict between price regulation and major dam safety decisions such as spillway upgrades.
This paper examines the scope for conflict in the two regulatory frameworks (pricing and dam safety) and the implications for dam owners, water users and potential new investors in the water infrastructure.
Simon A. Treadwell, Michael Shirley, Rory Nathan, Kylie Swingler
The Murray Darling Basin Commission through its native fish strategy has embarked on a comprehensive program for improving fish health in the basin. The strategy is aimed at managing and mitigating a range of threats including loss of habitat, altered flow regimes and thermal pollution downstream of large dams.
To help identify the relative benefits of different management options SKM developed a numerical ecological model. The model produces an index score that provides a measure of condition for native fish under various habitat, flow and temperature scenarios. The model uses a series of preference curves that define habitat requirements, critical spawning periods, spawning temperature thresholds and upper and lower temperature limits for egg, larval and adult survival. An index score of 1 is applied if conditions are ideal and an index score of 0 is applied if conditions are intolerable. Different temperature time series and habitat extent can be modelled to generate condition scores related to each fish life-history stage. Comparisons between the natural condition and those related to various reservoir release regimes can be made, for example to examine the likely effects of cold water releases or the benefits that could be achieved through the use of multi-level outlets. This can be compared with the relative benefits of restoring habitat or changing flow regime.
The results from a case study examining the relative benefits to native fish from managing flow, temperature and habitat downstream of Dartmouth Dam will be presented.
Rapid increases in pore pressure measured in the embankment in 1987 and 1994 raised concerns regarding the internal stability and safety of Cosseys Dam. A comprehensive dam safety review indicated that the dam would not meed modern design standards and a broad range of options to upgrade the dam were evaluated assessing not only the technical design aspects, but also the construction impacts on the operation and reliability of the water supply network, the environment and the local community. A multi criteria selection matrix was used to assist in selecting the preferred upgrade solution. Extensive consultation was undertaken with the dam owner, dam operator, City Councils and local community to ensure that the upgrade solution would satisfy the technical requirements of the project while minimising construction impacts. The project enjoyed a positive profile throughout the duration of the construction
Russell Paton, Clancie Saverin
The Awoonga Dam Raising Project, completed in July 2002, consisted of raising the full supply level by 10 metres. As part of the project the discharge capability of the dam was increased to a maximum of 3210ML/day (37.2m3/s) to meet the environmental release requirements of the Boyne River Basin Resource Operations Plan. The final design incorporated the use of an existing intake tower and outlet works supplemented by an auxiliary inlet to meet this release.
Between January and February 2004 rainfall within the dam’s catchment resulted in inflows to the storage raising it to within 5m of the new spillway crest, historically its highest level. Subsequently, two environmental releases, which required full utilization of the dam’s discharge capacity, were made. These regulated releases created a precedent for the Boyne River, and were the first time flow passed through Awoonga’s auxiliary intake.
Throughout the releases, water levels and water quality downstream were monitored to determine the effect of the release on the stream and to ensure the community was not inconvenienced due to flooding. The MIKE11 model created for the recently completed Boyne River Flood Study was used to estimate water levels. Inspections were continuously carried out to ensure the intakes, pipework and discharge valves operated without incident and to monitor bank stability and fish movement during and after the releases.
The paper discusses the requirement to make the environmental release, and the infrastructure together with the operation and monitoring undertaken to facilitate it.