Bob Wark, Colin Bradbury, Michael Somerford and Michelle Rhodes
The Harvey Dam project is a major component of the Water Corporation’s Stirling-Harvey Redevelopment Scheme, which was developed to provide potable water to Perth. The scheme will deliver 34 GL/annum or about 10% of Perth’s supply. The project timetable was tight. The decision to proceed with the scheme, made in June 1998, required Harvey Dam to be ready to impound water by June 2002.
Construction of the Harvey Dam was complicated by the following:
These and other issues required the development of risk management strategies for the project. The construction risks were allocated within the contract to provide for an equitable sharing of risk between the Contractor and the Principal. The paper describes the development and implementation of the risk management strategies and what lessons have been learnt from the process.
J.H. Green, P.E. Weinmann, G.A. Kuczera, R. J. Nathan and E.M. Laurenson
Assigning an Annual Exceedance Probability (AEP) to the Probable Maximum Precipitation (PMP), and subsequently to the PMP Design Flood, is an integral part of the risk assessment process for large dams. Laurenson and Kuczera (1998) conducted a review of existing PMP risk estimation practices in Australia and concluded that, in the absence of any better information, the work by Kennedy and Hart (1984) provided the most appropriate estimates to adopt but with the proviso that the method should be viewed as interim pending the outcomes of ongoing research.
This paper gives an overview of a joint research project that is working towards obtaining credible estimates of exceedance probabilities of extreme rainfalls using the concept of storm arrival probability and storm transposition probability. It also outlines the work to be carried out over the next 12 months that will culminate in the combining of the outcomes of the two components and the application to test catchments. Finally, the paper discusses desirable follow-up action to promote the adoption of the research results by practitioners.
Richard R. Davidson, Shane McGrath, Adrian Bowden, Andrew Reynolds
Goulburn-Murray Water (G-MW) manages thirteen major dams for the State of Victoria. As part of its Dam Improvement Program (DIP), five priority dams were identified for detailed safety and performance evaluation. Over the last three years, the design reviews have been completed and a series of dam safety issues have been identified which pose societal and financial risk. Substantial financial resources will be required to be applied over a considerable period to bring these dams into compliance with established international and Australian standards. Which of these dam safety issues should be addressed first? In what sequence and with what urgency should the actions be implemented? Can cost-effective interim targets be set? How can the remaining eight
dams, which could also pose societal and financial risk, be prioritised for future detailed investigation? To answer these questions a quantitative risk assessment approach was used. The approach utilised expert engineering and consequence panels and included input to and review of the process and outcomes by a stakeholder reference panel reporting directly to the Board of G-MW. The implementation of a strategic risk management process has now begun to progressively and systematically reduce the dam safety risk across the entire dams portfolio. This process recognises that available funding for risk reduction measures is very limited, so the highest risks are reduced in an incremental fashion to achieve interim risk targets and eventually meet contemporary dam safety standards.
Tim Waldron, K D Murray and Allan Crichton
The City of Hervey Bay is a growing tourist community that is located a comfortable 3½ hour drive north of Brisbane. To meet the growing water demands of the community, Wide Bay Water Corporation required the raising of its sole water supply – Lenthalls Dam.
At the time of the option study, Queensland dam owners were aware of their obligation to manage their dams to minimise adverse environmental impacts but detailed Environmental Flow Objectives were still being developed.
This required a solution for the raising of Lenthalls Dam that provided maximum flexibility while, at the same time, being cost effective.
A range of solutions and new technologies were investigated. Using a Risk Management methodology, the Crest Gate system developed in South Africa was adopted.
Subsequently, draft Environmental Flow Objectives have been set and the use of a gated system has been beneficial in meeting post-winter flow objectives.
Awoonga Dam is located near the town of Gladstone in central Queensland. The dam is on the Boyne River, and supplies water for domestic and industrial use in the Gladstone area. It is also used for recreation including swimming, boating, fishing, sailing and water skiing.
Awoonga Dam was completed in 1984. It has a storage capacity of 289,000Ml, and a submerged area of 3,450ha. The dominant land use in the catchment area is open grazing and includes the Mount Castle Tower National Park. A limestone quarry is also adjacent to the reservoir
The Gladstone Area Water Board (GAWB) own and operate Awoonga Dam. In 1999, the decision was made to raise the existing structure using a staged construction program.
Included in the first stage was the protection of a limestone quarry, which is operated by Frost Enterprises Pty Ltd, and is adjacent to the reservoir. The quarry would be partially inundated unless some form of protection was provided.
This paper provides an outline of the investigation undertaken, the options considered and the solution provided to protect the quarry, hereafter referred to as Frost Quarry.
David Brett, Anton van Velden and Phil Soden
The Main Creek Tailings Dam is a 60m high earth and rockfill dam constructed during the early 1980’s to store tailings from the Savage River Mine on Tasmania’s west coast. The dam served the mine well for nearly 20 years, storing around 32 million m3 of tailings, but has required raising due to the expanded mining plans of the current operators, Australian Bulk Minerals (ABM). ABM believe that the mine could require a further 60 million m3 of tailings storage over the next twenty years at increased production levels. This could be stored in the Main Creek Dam by raising it by around 35m. In the medium term this scale of raising would be feasible using waste rock product from ongoing mining but in the short term of several years an interim solution would be required. The feasibility of upstream construction on the tailings beach was reviewed and found feasible for
a maximum 12m in 4 lifts.
Of critical concern were
The paper discusses the investigation and design phases of the dam and describes the issues arising during construction recently completed over the period January to April 2002. The use of pore pressure, shear strength changes and tailings beach movement monitoring to control construction is discussed.