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Andrew Pattle and Bram Knoop
This paper provides an outline of a process that can be used to optimise regular dam surveillance and monitoring activities. The process is applicable for a wide range of dam types that an owner/operator may be responsible for. Basic assessments are made of inherent reliability and potential consequences of failure using key factors such as construction features, foundation conditions and observed performance. The key factors are combined to give a relative risk ranking for each dam. These rankings are used to determine specific dam monitoring schedules. The process focuses the monitoring effort on those dams that are perceived to constitute the greatest portion of the overall risk. The methodology is simple and provides a cost-effective framework for setting appropriate resourcing levels for dam monitoring.
One of the most important issues during design and construction of an earthfill dam is how to secure a dam against unwanted events which may occur as a result of water flow (uncontrolled seepage, leakage & piping) through the dam.
Although earthfill dams are the largest by volume compared with other types of dams and they are designed to cope with seepage, their integrity is most sensitive to the effects which may be caused by it. The reason being that the earthfill materials are generally extremely heterogeneous and only one “unwanted” pocket is enough to create problems.
Another critical area is the foundation. In many situations it is not possible to avoid the complex geology which includes faults and joints as part of the foundation. An additional complication may be the presence of dispersive clay in the foundation.
In the area of tailings dams, the problems with seepage are slightly reduced as in most cases, tailings provide a degree of sealing. Tailings dams are very often designed as leaky dams. However, there is a hidden danger in approaching the design this way as at any stage of their lives they can retain water.
This paper presents two case histories of repairs carried out to tailings dams suffering leakage. One case describes leakage through the embankment wall while the other describes seepage through the foundation which contains dispersive soil.
David S. Bowles, Andrew M. Parsons, Loren R. Anderson and Terry F. Glover
This paper summarises the Portfolio Risk Assessment (PRA) process that was implemented for SA Water’s 17 large dams, the information obtained from the PRA, and its use by SA Water. The PRA was designed to provide a baseline assessment of the existing dams and an initial prioritisation of future investigations and possible risk reduction measures. The PRA comprised a reconnaissance-level engineering assessment and risk assessment. These assessments were performed for floods, earthquakes, and static loading. Various structural and non-structural risk reduction measures were developed and evaluated. Information from the PRA can be used to provide inputs to capital budgeting, due diligence and liability evaluations, contingency planning and business criticality assessment, evaluation of loss financing and insurance programs, and a firm basis for monitoring and surveillance, operations and maintenance, and emergency preparedness planning.
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.
David Watson and John Adem
For several years risk management has been promoted by the Victorian Department of Natural Resources and Environment – Water Agencies as the key mechanism for the effective and efficient business management of dams. As part of an extensive water reform program, the Victorian Government announced in October 1997, a financial assistance package for the water industry which included funding for dam improvements covering a majority of large dam owners in the State. One of the conditions for receipt of these improvement funds was the need for each water authority to undertake a Business Risk Assessment of all significant and high hazard dams under its responsibility.
This paper discusses the Business Risk Assessment document based on a framework developed by Water Agencies after consultation with the industry and expands on the following reasons why the document was produced: