Over the last 30 years, the demand for water storages in Queensland’s Mary’s River has grown significantly. As a result of this growth in demand it was decided to raise Borumba Dam, the major storage on the system, in two stages The first stage was to be approximately 2 metres in I997 and the 25 metre raising be required in about 2010.
Borumba Dam was completed in 1964. It is a 43 metre high concrete faced dam with a 32 metre long on the left abutment. The first proposal for initial raising was to install a two metre high air-inflated rubber dam on top of the existing crest. However, it was determined that this method of raising presented a number of prob and a new solution was sought.
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Brian A Forbes and Jon T Williams
The 43 metre high Cadiangullong Dam was constructed during 1997-1998 to supply untreated water for the Newcrest Cadia gold mine near Orange in NSW. The placement of the 110,000 m3 of RCC was performed without expensive thermal control techniques in an area of extreme climate conditions. Thermal finite element studies were undertaken during design to assess the effect of the climate extremes on construction and assist in the design of contraction joints. An RCC mix with sand proportions in excess of 50% of the fully crushed aggregate by weight was used to eliminate segregation. This also had the effect of requiring a low compaction effort to achieve density but exhibited a sheared surface texture if placed over wet. Following full scale trials the conventional concrete facing was superseded during the early stages of construction with an in situ modified RCC facing. The modified RCC consisted of a grout enriched internally vibrated RCC (GE-RCC) to provide a durable, impervious upstream face. This paper discusses the details of these three aspects and provides design, construction and performance data to date.
As New Zealand’s largest dam owner, ECNZ has actively managed dam safety since its inception in 1987. During this time it has managed several major dam safety issues and enhanced its dam safety management practices. This has occurred in an environment of organisational change and increasingly competitive commercial pressures.
The change in emphasis from a primarily technical emphasis to dam safety towards a commercial focus is described together with details of highly rated dam surveillance system, some continuous improvement initiatives, and recent enhancements to the dam safety programme. The position of responsible ownership in regard to risk and legal requirements is also discussed.
Andrew Pattle and Bram Knoop
This paper provides an outline of a process that can be used to optimise regular dam surveillance and monitoring activities. The process is applicable for a wide range of dam types that an owner/operator may be responsible for. Basic assessments are made of inherent reliability and potential consequences of failure using key factors such as construction features, foundation conditions and observed performance. The key factors are combined to give a relative risk ranking for each dam. These rankings are used to determine specific dam monitoring schedules. The process focuses the monitoring effort on those dams that are perceived to constitute the greatest portion of the overall risk. The methodology is simple and provides a cost-effective framework for setting appropriate resourcing levels for dam monitoring.
Leonard A McDonald and Chi Fai Wan
A risk assessment has been undertaken as part of a comprehensive review of the safety of Hume Dam. Use of risk assessment techniques, to assist in evaluating the safety of existing dams, is a relatively recent trend. Hume Dam was a particularly challenging subject for the application of risk assessment techniques at their present stage of development. The challenge lay in the number and diversity of dam elements to be analysed, in the number and complexity of the potential failure modes and in the fact that there were significant safety issues under normal operating conditions.
This paper outlines some of the key lessons learned from that phase of the risk assessment that was concerned with estimating the chance of dam failure. Some of the issues discussed have not previously been addressed in the literature and some demonstrate a clear need for improved analysis procedures.
David Watson and John Adem
For several years risk management has been promoted by the Victorian Department of Natural Resources and Environment – Water Agencies as the key mechanism for the effective and efficient business management of dams. As part of an extensive water reform program, the Victorian Government announced in October 1997, a financial assistance package for the water industry which included funding for dam improvements covering a majority of large dam owners in the State. One of the conditions for receipt of these improvement funds was the need for each water authority to undertake a Business Risk Assessment of all significant and high hazard dams under its responsibility.
This paper discusses the Business Risk Assessment document based on a framework developed by Water Agencies after consultation with the industry and expands on the following reasons why the document was produced: