A. Ash, D. S. Bowles, S. Abbey and R. Herweynen
A preliminary risk assessment was undertaken of its three dams by the South East Queensland Water Board (SEQWB) in 1999. The risk assessment process used included a series of workshops that proved to be an important part of ensuring a worthwhile result. The combined expertise of the consultants together with that of staff from the Board and the Queensland’s Department of Natural Resources were used to improve the outcome. The results of the assessment showed that the process had both advantages as well as difficulties in comparison to a standards based approach for making dam safety decisions. Risk Assessment was seen to be a useful management tool for managing dam safety. It gave the owner the ability to quickly rank upgrade requirements or maintenance options on the basis of probability of failure, life safety risks and financial risks to the owner or economic risks to all stakeholders.
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Now showing 1-12 of 27 2964:
P.W. Heinrichs and R. Fell
Ben Boyd Dam, a 29 m high earthfill embankment built in 1978, has had an unusual history. In 1979, a number of seeps developed during first filling with water 5 m below FSL indicating unexpectedly high pressures. Investigations concluded the coarse filter permeability was very low due to excess fines. Remedial works in 1982 included a drainage filter beyond the toe and a new stability berm above. New piezometers were installed, including several in the blanket filters in the existing dam. These later indicated up to 10.5 m head in isolated areas within the filter. Pump out tests partially lowered the water level in the standpipes but in 1995 the water level rose by 4 m back to its previous high level. All this during a period of relatively low rainfall. Stability analyses were carried out and further investigations in 1999 concluded that apart from general leakage from the foundation abutment into the filters, the rise in pressures was due to leakage from a riser hole from one of the nearby foundation piezometers. A potential for piping along the piezometer tubes within the dam was also identified.
This situation was managed without resort to costly capital works, because it was concluded that the pressures from the vertical riser were not a potential failure mode, and potential piping failure would be adequately handled by the existing chimney drain, intersecting the piezometer tubes trench. Any potential piping failure would also give warning signs which increased frequency of monitoring (now in place) would pick up in time to allow lowering of the storage.
The Victorian Water Industry Seismic Network was substantially upgraded in 1999. This paper will look at the design and outcomes of the seismic network from a risk management and emergency management perspective. Funding issues for a diversified network providing benefits to a range of clients within the one industry group will also be discussed.
Prior to 1999 the Victorian seismic network had been developed on an ad hoc basis resulting in an incomplete level of seismic coverage throughout the state. The upgraded network now provides sufficient coverage to provide an intensity based alarm service for all contributing Victorian Water Authorities.
Community expectations of essential service providers such as the water industry are that they will carry out their own risk management to provide for service continuity and sustainability and that they will contribute to emergency management processes because it is in their own best interest to do so.
The risk management model looks at creating resilient communities through planning for the four R’s. Reduction, Readiness, Response and Recovery. The Seismology Research Centre’s Earthquake Preparation Alarm and Response system (EPAR) deals with the four R’s in relation to seismic hazard.
The EPAR system contributes to the risk management processes of identifying risks and vulnerability’s; potential consequences; and mitigation opportunities. The EPAR system additionally contributes to the emergency management processes of crisis response, impact assessment and recovery.
Glen Hobbs and Danny Azavedo
Recent years have seen a growing awareness and understanding of the factors that contribute to the reliability of spillway gates and the incorporation of reliability data into overall dam risk studies.
The study of a number of spillway gate failures shows that no one component or incident leads to gate failure, but rather a combination of factors have resulted in gate failure. A rigorous reliability assessment should consider all factors, not only the equipment condition and performance but the complete system, from the receipt of data through to the actuation of the gates. It should take into account issues such as human factors, poor design, maintenance history and policy. Unfortunately one of the main hindrances to quantifying gate reliability is the lack of information on spillway gate equipment and system performance and failures.
This paper considers a number of gate failures, then looks at some of the tools of reliability assessment and the role of human factors in gate reliability.
The paper then discusses a recent study of four gated dams. For this study a systems approach was adopted and human factors were considered. The results compare favourably with other similar critical structures, and show that for these well designed and maintained structures human factors are the limiting criteria in multiple gate operations. The study also shows that the probability of opening all the spillway gates at a dam improves with time (2-4 hours) during the flood operation, and it is considered that time based reliability provides a more meaningful and useful assessment of overall spillway gate reliability.
R. E. Saunders, J. Roberts, B. W. Omundson
Ross River Dam is located immediately upstream of the twin cities of Townsville and Thuringowa. The population at risk from failure of the dam is approximately 110,000. A recently completed risk assessment has confirmed earlier studies that the dam does not satisfy current safety criteria and presents high risk levels in a number of areas. Importantly, the risk assessment has enabled the extent of these risks to be clearly identified. This paper summarises the risk assessment highlighting notable methodologies employed and the key findings of the study.
P.I. Hill, D. Cook, R.J. Nathan, P.A. Crowe, J.H. Green, N. Mayo
This paper describes the development of a comprehensive approach to estimating the consequences of failure of a dam. The approach considers separately the consequences in terms of potential loss of life, economic loss and damage to the environment and the development and application of the method involved professionals from a wide range of disciplines. The method has been applied to 28 dams in NSW.