D.N.D. Hartford and R.A. Stewart
It seems perfectly logical, obviously desirable and apparently sensible to prioritise dam safety reviews, deficiency investigations and capitalised remediation projects in terms of risk. However, our experience in attempting to apply the various deterministic and risk- based approaches in prioritising dam safety activities has revealed that, while it may appear to be quite logical and desirable to prioritise in terms of risk, it is rather less feasible than it appears.
This paper explores why different prioritisation processes can lead to different priority rankings across the same portfolio of dams. B.C. Hydro’s Preliminary Risk Exposure Profile process, which utilises the best and most robust attributes of risk analysis process at the preliminary level but avoids the pitfalls associated with estimating risks which will often have little or even no basis is presented. The paper explains how this process provides a “fail-safe” backup which will identify non-conservative and erroneous facility risk estimates; thereby allowing for correction in a timely fashion. The paper also raises some awkward philosophical issues which the profession will have to address in order to permit confident dam safety decision-making on the basis of risk analyses. Not the least of these is the following issue – “If preliminary estimates of risk are reasonably good, then there should be little need for more detailed risk analysis for confident and defensible decisions concerning making or not making dam safety improvements”.
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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.
Gary Gibson, Wayne Peck, Ian Landon-Jones and Kumara Arachchi
One of the first seismograph networks designed specifically to record local earthquakes was installed about Sydney in 1958. This network was converted to telemetry in 1983. In 1992, Sydney Water Corporation upgraded the network, integrating the functions of earthquake location and magnitude, measurement of the response of structures to earthquake motion, and provision of information for emergency response. The response function has been developed over the past six years, and is now an “Earthquake Preparation, Alarm and Response” system that provides customised information very soon after any significant event.
R J Westmore and P J Cummins
Wartook Reservoir is owned and operated by the Wimmera Mallee Rural Water Authority in western Victoria. The reservoir was constructed in the period 1887 to 1890 on the Mackenzie River within the Grampians National Park. It has a capacity of 29400 ML, is the sole supply of water to the City of Horsham, and also supplies stock, domestic and irrigation water to the Wimmera and Mallee Regions of Victoria.
The embankment is 1100 m long, 12 m high and is constructed of loose to medium density silty fine sands which are susceptible to liquefaction during a seismic event due to the combination of high pore water pressures and low density. Active seepage from the embankment and foundations render the embankment susceptible to failure by piping.
The outlet works were constructed of sandstone masonry and comprise a tower and cut-and- cover conduit buried within the embankment. Inflow of fine sands from the embankment into the masonry tunnel render the embankment susceptible to failure by piping through the joints in the masonry tunnel.
Design concepts for the rehabilitation of the embankment, outlet and spillways have been developed jointly between Wimmera Mallee Water and SMEC Victoria adopting a risk based approach. The design involves partial rehabilitation of the works, providing acceptable levels of risk to the Authority and community, at an economically justifiable cost.
I A Howley, G S Smith and D J A Stewart
Over the past decade the role of dam ownership in Victoria, and indeed Australia, has changed from one of owners, constructors and operators of large civil assets, to managers of structures on behalf of owners of the entitlements to water. This is part of the key business focus to dams management in Victoria.
This position has been heavily influenced by regional water reform policies, such as the Murray Darling Cap, and its effects in Northern Victoria, and COAG Agreements.
Dam owners now run service driven businesses, with a clear separation of roles and responsibilities from the traditional, engineering focused organisations which were established in an environment of resource development. The environment is now one of maintenance, service delivery, structure maintenance and long term business viability for ultimate community benefit.
By using Goulburn-Murray Water as an example, the current model of dams management in Victoria is outlined, together with possible future directions for the rural water industry in Victoria.
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.