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.
Wivenhoe Dam is being upgraded to safely manage any conceivable flood in response to a revision of rainfall predictions by the Bureau of Meteorology. These revisions have led to a substantial increase in estimates of the Probable Maximum Flood that the storage must be able to manage under the ANCOLD guidelines. Wivenhoe Dam, completed in 1985, is located about 80 km north west of Brisbane and is the major domestic water supply for South East Queensland.
The dam is owned and operated by SEQWater who are responsible also for North Pine and Somerset Dams. The upgrade is being undertaken as an Alliance contract with the member companies being SEQWater, Leighton Contractors, MWH, Department of Commerce NSW, and Coffey Geosciences. The upgrade involves construction of a second spillway, 165 m wide on the right abutment. This will be a fuse plug spillway requiring excavation of approximately 600,000 m3 of material.
Construction impacts on the community include noise and dust, blasting, and temporary road diversions/lane closures of the main Brisbane Valley Highway over about two years of construction.
This paper deals with a wide range of stakeholder, community consultation and environmental initiatives that have involved local residents, stakeholders and recreational users in the planning and implementation phases of this project. Several long-term environmental legacies are also discussed.
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
A. Crichton, J. Willey, G. Bell and A. Franzmann
Under the Snowy Water Licence and as a result of the Snowy Water Inquiry, Snowy Hydro Limited
(SHL) is required to release environmental flows into the lower Snowy River below Jindabyne Dam at lake levels as low as the minimum operating level (MOL). The construction of new outlet works is necessary to meet this requirement. The other issue driving the project is the limited spillway capacity. A new spillway is required to pass the design flood recommended in the guidelines of the NSW Dam Safety Committee. The design of the outlet works and new spillway has been completed and a contract to construct the works has been let and construction has commenced. This paper summarises the process used to develop the selected design arrangement. It includes discussion on the design of modifications to the existing spillway and the part played by the hydraulic model study in that design and discussion on the auxiliary spillway design and the design of the outlet works to pass a peak flow of 58 m3/s
The ANCOLD Guidelines for the Design of Dams for Earthquake (ANCOLD 1998) were developed by a working group convened by the author over the period 1993-1998.
Since the release of the guidelines there have been some important developments in the design of embankment dams for earthquakes, and it has become apparent some aspects of the guideline could be explained better.
This paper outlines some of these issues with a view to encouraging the Profession to use up-to-date methods.
P J Cummins, G S N Adikari, C Hill and A K Parkin
Yan Yean Dam has been a key component of water supply to the City of Melbourne since its completion in 1857. Of typical puddle core construction over deep alluvium, it has performed well over the years since, with the exception of the discovery of a piping tunnel in 1949, duly repaired with minimal risk. However, in the absence of an engineered filter, some potential for recurrence has remained, and this, coupled with a continuing outward creep of the downstream batter and the need to ensure compliance with current design practice, has driven the recent remedial program.
The original embankment was 9.6m high and almost a kilometer long, with 3:1 and 2:1 batters and a wide core, now modified by the placement of a 3-component full-height chimney filter and stabilising fill. Critical issues in the design of these remedial works are described herein, including foundation preparation, the evolution of the design slope, the cellular filter and its specification, and measures required for the preservation of historic structures. Because of the potential impact on public parkland and nearby housing, community consultation was a vital input that enabled good relationships to be maintained throughout the project.