Since the guidelines were published much has been learnt about the critical issues that drive environmental concerns for both dam practitioners and the broader community arising from the construction of new dams, dam upgrades or altered operational strategies. The objective of this companion volume to the Environmental Guideline is to increase environmental awareness by encouraging more sustainable planning, design, construction and operation inputs to large dams. As such this companion volume complements rather than replaces the existing guideline. These are not exhaustive reviews of current knowledge but rather serve to raise a level of awareness on a range of issues that need to be considered at the various stages of planning, constructing, operating and decommissioning a storage with respect to environmental concerns. The Guidelines are intended to be regularly updated to reflect the changing regulatory environment as well as increasing technical knowledge about environmental management.
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The Guidelines were prepared to bring together knowledge about earthquakes in Australia following the devastating Newcastle magnitude Mw 5. When the Guidelines were issued, it was recognised that over time there would be improved data and tools to help the designer.
This has indeed been the case and ANCOLD decided that it would be timely to update its Guidelines to incorporate the significant advances made in the understanding of earthquakes, seismic hazard assessments, analysis and design.
The Working Group convened to produce these updated Guidelines, replacing the Guidelines, was composed of representatives from dam owners, State dam safety regulatory agencies and private consulting practices.
Because of the seismic hazard uncertainty and the associated structural response, these Guidelines encourage the use of risk-based methods for assessing existing dams and for the design of new dams. However, the deterministic approach is also covered for those owners who prefer to use it. It is a significant development for dam engineering in Australia and will be a valuable resource. As with all ANCOLD Guidelines, this guideline is not a design code or standard and has been produced for the guidance of experienced practitioners who are required to apply their own professional skill and judgement in its application.
Users must keep abreast of developments in the design of dams and appurtenant structures for earthquake and take those developments into account when using these Guidelines.
The Guidelines will again be reviewed when knowledge and practice have developed to a point when an update is required. Shane McGrath.
A Working Group and a separate Expert Review Panel were formed in to review the Guidelines with the intention of preparing a document that was not only more in line with the current thinking but would also be widely adopted and used by practicing dam engineers. Although the working stress method, with associated Factors of Safety, approach was agreed amongst the team, it took considerable time and effort to reach consensus on the details, in particular chapters four through to six. The issue that took most effort to resolve was how the Factors of Safety relate to the level of certainty of the inputs, including knowledge of the foundations, loads, strength of materials and assumed mechanically feasible failure surfaces. The notes to Table 6. One thing the drafting team agreed on early, and unanimously, was the importance of the concrete gravity dam design team having a thorough understanding of the foundation conditions, the development of a detailed geological model of the foundations and an understanding of the kinematically feasible failure mechanisms.
Gated spillways which can be operated to control the outflows A small primary spillway that restricts the outflow During a large flood the ability of a dam to attenuate a flood may be exceeded resulting in the need to release water to maintain the safety of the dam itself. The ANCOLD Guideline brings together improved appraisals of the earthquake loadings that a dam may suffer and then describes appropriate methods for analysis and evaluation. However, they require that the user will be a professional dam engineer with significant experience who is able to use sound engineering judgement in the application of the guidelines. Indeed, without the application of such judgment, the procedures themselves could lead giudelines results that have serious shortcomings. The resulting tailings water generally needs to be treated to remove heavy metals and reduce acidity before being released back into the natural environment.
Guidelines on the Consequence Categories for Dams (October 2012)
AUSTRALIAN NATIONAL COMMITTEE ON LARGE DAMS INCORPORATED