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.
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J. H. Green and P. I. Hill
Early Probable Maximum Flood (PMF) studies and spillway adequacy assessments for Hume Dam adopted the standards based approach of the time. Since then considerable work and thought has gone into the estimation of extreme floods – both the philosophy and the practice. These changes include the general change in emphasis away from a standards based approach and towards risk assessment; the move towards an AEP-neutral approach for the transformation of extreme rainfalls to extreme floods; and the redefinition of both the PMP and the PMF.
This paper details the effect these and other changes to extreme flood estimation techniques have had on the perceived adequacy of the Hume Dam spillway to pass extreme floods.
Steve Everitt, Ron Fleming, Lelio Mejia
The Electricity Corporation of New Zealand Ltd (ECNZ) is strengthening its Matahina Dam which is an 80 m high, 400 m long rockfill dam impounding a 60 million cubic metre reservoir. The strengthening is to ensure the dam will withstand potential fault displacement within the dam foundation.
ECNZ’s management of the project is described from the design and consents phase through to construction. Key issues are discussed which have contributed to the success of the project such as management structure, the International Review Board, the design process and risk management.
A dam owner is often surprised to learn that his dam has been listed on a heritage register. This is often the first indication that the dam has heritage significance.
This paper discusses the different types of heritage listing and what the implications are for an owner. It suggests that a prudent owner will find out whether he needs a heritage conservation plan, particularly where redevelopment or remedial work at the dam is contemplated. The paper describes the content of a typical conservation plan for a large dam and how it is implemented.
A safety review of the Corin dam has identified several deficiencies including an inadequate spillway capacity. A hydraulic model test, included in the review indicated that the construction of a 1.3m wave wall along the top of the dam was required to prevent overtopping during the flood of 10,000 years.
The original post tensioning anchors installed along the spillway crest were also identified as unreliable due to inadequate corrosion protection measures.
This paper presents safety assessment and aspects of the construction of the remedial works for Corin Dam. As part of the safety review, the condition of the dam was reviewed against the risks of piping, slope instability, flood and seismic forces. The paper also discusses the long term effects of the acidic leakage on the grout curtain and on the integrity of the core.
The risk associated with the flooding during anchor installation and the discovery of a gap formation between the clay core and the concrete spillway wall are also considered.
Mark Foster, Robin Fell and Matt Spannagle
This paper describes a method for estimating the probability of failure of embankment dams by piping. The so called “UNSW method” is based on the results of an analysis of historic failures and accidents of embankment dams. An estimate of the probability of failure of a dam by piping is made by adjusting the historical rates of failure by piping by applying weighting factors which take into account the dam zoning; filters; age of the dam; core soil types; compaction; foundation geology; dam performance; and monitoring and surveillance. The method is intended for preliminary assessments only and is ideally suited as a risk ranking method for portfolio type risk assessments to identify which dams to prioritise for more detailed studies and as a check on event tree methods.