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.
Increasingly, owners of ageing dams are having to reconcile with the notion of involving others in decisions affecting the management of their dams. Previously recognised as ‘expert’ exclusive arenas, doctors, lawyers, scientists and engineers are now expected to respond to enquiring consumers and communities. Individuals and communities are expressing their need to share responsibilities.
Events at Hume Dam provide an illustration of the potential challenges and opportunities that all Dam Owners may face. This paper is a narrative of the processes of involving the wider ‘community’ in the Hume Dam remedial work project. It remains for the stakeholders to rate the effectiveness of the process.
David Dole and Brian Haisman
The Murray-Darling Basin Commission recently created River Murray Water, an internal business unit, as a step towards the micro-economic goals of the COAG Water Reforms.
The assets which regulate the River Murray, have a replacement value around $1.4 billion. They range from the 4000 gigalitre Dartmouth Dam in the headwaters, to the 7.5 kilometres of barrages near the Murray mouth and are presently held in trust for the Contracting Governments of the Basin Initiative by one or other of the three riparian states. River Murray Water is bringing the assets together into a single, integrated business with the aim of securing long-run sustainability, funded through pricing for services provided. Broad institutional and pricing principles are described along with the special challenges of an inter-government environment.
These challenges are being met by adopting clarity and simplicity as driving principles, supported by best practice asset information. The paper describes the upfront development of explicit guiding principles and policies, including risk management and dam safety; coordination of activities; generation of life cycle information; and introduction of contestable service provision for the business.
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.
One of the most important issues during design and construction of an earthfill dam is how to secure a dam against unwanted events which may occur as a result of water flow (uncontrolled seepage, leakage & piping) through the dam.
Although earthfill dams are the largest by volume compared with other types of dams and they are designed to cope with seepage, their integrity is most sensitive to the effects which may be caused by it. The reason being that the earthfill materials are generally extremely heterogeneous and only one “unwanted” pocket is enough to create problems.
Another critical area is the foundation. In many situations it is not possible to avoid the complex geology which includes faults and joints as part of the foundation. An additional complication may be the presence of dispersive clay in the foundation.
In the area of tailings dams, the problems with seepage are slightly reduced as in most cases, tailings provide a degree of sealing. Tailings dams are very often designed as leaky dams. However, there is a hidden danger in approaching the design this way as at any stage of their lives they can retain water.
This paper presents two case histories of repairs carried out to tailings dams suffering leakage. One case describes leakage through the embankment wall while the other describes seepage through the foundation which contains dispersive soil.
M O’Reilly, S A L Read and P F Foster
Electronic (bubble) tiltmeters provide an up-to-date technique for continuously monitoring the deformations of dam and dam-related structures. Tiltmeters, with a sensitivity of (10Imm per length), are currently used in New Zealand at the high concrete gravity Waitaki Dam, and the Ohau A Powerhouse, as well as a short-term installation in the high concrete gravity Aviemore Dam.
This paper outlines the performance of the tiltmeters over a period of up to 7 years. They have been used to monitor the reactions of structures to loading changes such as headwater level variation, and to monitor ongoing performance, including the definition of annual thermal cycles. The results are compared with other monitoring techniques (e.g. plumblines, conventional surveying) to illustrate the usefulness and applicability of tiltmeters to dam safety programmes, either in conjunction with standard monitoring options, or in particular where such options may not be practicable.