The use of risk analysis for dam safety is becoming more widespread. Dam owners are increasingly aware of the need for information on current and emerging practices from the world scene to determine how to proceed with the use of risk assessment. The paper summarises the findings of a Churchill Fellowship study into risk assessment for dam safety management. Dam owners, regulators and consultants from the United Kingdom, France, the Netherlands, Norway, Sweden, the United States and Canada were consulted for the study. Conclusions are drawn from the findings and recommendations made for future development.
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Failure modes and effects analysis (FMEA) has been increasingly utilised to prioritise and investigate dam safety deficiencies. It can be used to enhance dam safety programmes. Dam Surveillance, O & M procedures, and emergency plans can all be evaluated for their effectiveness in detecting and mitigating the applicable failure modes for a dam. Experience with a workshop process to carry out this evaluation and some of the improvements that have been identified are described.
M. B. Barker and D. Holroyde
A detailed study was completed for the Stage 2 works of the Grahamstown Dam augmentation to investigate various alternatives for the slope protection of the Saddle Dam and Subsidiary Dam embankments, including a standards based and a risk management approach. The standards based approach required an evaluation of the slope protection level and least cost option based on the hazard rating of the dam. Due to the sand construction of the embankments, it was possible to apply a wave erosion model SBEACH to develop an economic risk model for optimising the slope protection alternatives. The erosion model included the effects of the wind direction, reservoir level and wind speed variation during flood events, embankment profile and material parameters. The risk management approach clearly showed that significant cost savings could be achieved by using the risk management approach. Furthermore, the cost curves indicated the sections of the embankments for which present capital works would not be economically justified and for which ongoing maintenance works would be economically advantageous.
Robert Wark, Nihal Vitharana and Michael Somerford
This paper reviews the history of dam remedial works on publicly-owned dams in Western Australia over the last 40 years. Projects have ranged from refurbishment of the facilities, through capacity upgrades to complete reconstruction. Major work has been undertaken on at least thirty dams. Most of these dams are now owned by Western Australia’s Water Corporation. The Corporation continues to undertake remedial works where necessary and now has a strategy in place for an on-going program of remedial works.
The paper outlines the scope of the work undertaken and why the work was required. The current status of the Corporation’s planning for an on-going remedial works program is also reported.
The entire historical record of rainfall archives held by the Bureau of Meteorology over the region of Australia affected by tropical storms has been examined and the extreme storms have been extracted. From this database, we account for site specific effects (moisture and topography) from each of the storms, allowing us to compare storms amongst each other. This then allows us to construct a theoretical maximum precipitation in a generalised sense. By then returning the site specific information for a particular region, we can infer the probable maximum precipitation at this location.
B. S. Sherman
Many large Australian dams currently lack selective withdrawal capabilities and release water mainly from deep within the hypolimnion. Deep-water releases coupled with the strong thermal stratification typical of Australian reservoirs results in discharge temperatures 10 °C or more colder than would normally be expected. Cold water pollution has impacted more than 1000 km of river habitat in Australia where it is known to impair spawning, feeding and survival of many native fishes.
This report reviews alternative approaches for the mitigation of cold water pollution below dams. The underlying theory and practical limitations of operation as well as field experience (including cost) with each of the methods are discussed. Two methods in particular, suface pumps and submerged curtains, appear to offer cost-effective alternatives to the expensive retrofitting of dams with multi-level outlet structures (estimated to cost $5-35m per dam for major dams in NSW). These methods are predicted to be capable of increasing discharge temperatures by 4-10 ° throughout the range of irrigation releases without any redirection of flows, i.e. hydropower releases can be maintained at present levels. This holds the promise of restoring more desirable temperatures over hundreds of kilometres of river.