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.
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R.J. Nathan, P.E. Weinmann and P.I. Hill
Current practice for estimation of design floods is typically based on the “design event” approach, in which all parameters other than rainfall are input as fixed, single values. Considerable effort is made to ensure that the single values of the adopted parameters are “AEP-neutral”, that is, they are selected with the objective of ensuring that the resulting flood has the same annual exceedance probability as its causative rainfall. While this approach represents current best practice in Australia (and overseas), it does suffer from a number of limitations.
This paper describes the development and application of a Monte Carlo (or joint probability) framework which offer an alternative to the design event method. This technique recognises that any design flood characteristics (e.g. peakflow) could result from a variety of combinations of flood producing factors, rather than from a single combination. The approach mimics “mother nature” in that the influence of all probability distributed inputs are explicitly considered, thereby providing a more realistic representation of the flood generation processes.
The advantages of the technique are illustrated by application to a hypothetical dam located on a real catchment. The manner in which standard design inputs are incorporated are discussed, as is the relationship of the approach to current guidelines.
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.
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.
Tony McCormick, John Grimston, Robin Dawson
Project Aqua is a proposed hydroelectric and irrigation resource sharing development on the Lower Waitaki River in New Zealand’s South Island. The NZ $1 billion project aims to deliver approximately 540 MW peak power at an economically viable price, while minimising environmental and social impacts. Application of traditional hydro concepts in historical studies for the same reach has not provided an economic solution. The current proposal challenges conventional thinking in many areas with innovative concepts allowing a significantly lower cost while not sacrificing safety or flexibility.
Development of storage may involve high social and environmental impacts. No significant storage is needed for Project Aqua as the operation of existing upstream dams can be modified to provide for peaking demand and maintenance of minimum flows. The river intake offers innovative features with its very low profile structure. The concept allows a departure from the traditional barrage or dam diversion and maintains an open braid for jet boat and fish passage. This concept has proven to be a major feature in the overall project progression to the current stage.
The largest impact component of the scheme is the eight canals designed to carry 340 cumecs over 63 km through six power stations. Cuts and fills form the canals with locally derived materials used for the embankments and lining. Expensive lining has been minimised by balancing flow exchange with groundwater through the cut and fill sections.
Feasibility design has been completed and resource consents are currently being sought. This paper will cover the significant design features and impacts.
R.I. Herweynen and A.M. Hughes
Hydro Tasmania has a number of dams which were designed and constructed in the 1950-70s
with fully grouted, post-tensioned anchors. The method used was leading edge in its day,
however, it does not achieve the cable protection of modern methods which provide two barriers
against corrosion and are monitorable. Hydro Tasmania has developed and employed an
innovative program to ascertain the integrity and remaining life of the cables and to prepare
long term management plans for its cabled dams.
An international panel was set-up to provide guidance on the overall issue, assist in developing
a sound methodology for assessing the corrosion of the anchors and advise on long-term
monitoring. To focus the efforts, Catagunya Dam was adopted as the pilot dam, as the stability
of this dam is very much dependent on the integrity of the anchors. This paper will provide a
brief overview of the project to date but will focus in detail on the main components of the
corrosion assessment of the anchors, namely:
The paper also provides a brief summary of the instrumentation installed at Catagunya Dam to
assist with the long-term monitoring of the dam.