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Within about ten years of the 1991 edition of the ANCOLD Guidelines on Design Criteria for Concrete Gravity Dams being published the Limit State design approach it proposed fell out of favour with Australian dam engineers.  The ANCOLD Executive recognised this situation and resolved that the Guidelines be revised to reflect the preferred design approach amongst Australian dam engineers.  A Working Group and a separate Expert Review Panel were formed in 2005 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.

It has not been an easy task for the Working Group and the Expert Review Panel.  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 6.4.1 and the discussion in Appendix A highlight this issue.

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. In keeping with this principle, this revision of the guidelines has the section on foundations at the front of the document.  There is a strong recommendation that the design team has expertise covering foundation geology and rock mechanics as well as the dam engineer.

These Guidelines provide a basis for design of concrete gravity dams in most situations. 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. It is recommended that less experienced dam engineers using these guidelines do so under the advice and guidance of an experienced dam engineer. It is the dam engineer who is responsible for the design.

On behalf of ANCOLD I would like to thank the members of the working group and all the other contributors that persevered in developing and bringing these Guidelines to fruition. They will be of great assistance to dam engineering professionals both within Australia and internationally.

ANCOLD has prepared these important Guidelines to provide a consistent method of categorising the consequences of dam failure so that resources can be allocated according to the potential effects of failure on the general community.

These Guidelines replace the ANCOLD Guidelines on the Assessment of the Consequences of Dam Failure issued in May 2000 and follow a similar approach.  However, they include quite significant changes aimed at providing enhanced description of Consequence Categories and making them easier and more consistent to use.

The Technical Working Group has made every effort to make these Guidelines straightforward to use by professional engineers and consistent with other ANCOLD guidelines.

However the complexity of determining the various parameters that make up each Consequence Category means that only experienced dam engineering professionals should interpret and use these Guidelines when making decisions that could impact on community safety, community cost and services, infrastructure, natural environment, heritage, and the owner’s and other businesses.

These dam safety guidelines are intended to apply to what might be termed conventional dams (eg. for water supply, irrigation, power and flood mitigation). Guidelines for dam safety management of tailings dams are published separately.

These guidelines have been developed by ANCOLD with the aim of promoting appropriate dam safety management practices in Australia. It is recognised that circumstances vary enormously from dam to dam and different administrative frameworks apply in each state. Some states have specific dam legislation while other rely on more general provisions. For these reasons, ANCOLD puts this guideline forward as an advisory document that must be interpreted by appropriately qualified and experienced professionals in each case. In no sense is it intended that they should be regarded as a standard.

The guidelines will again be reviewed when knowledge and practice have developed to the point where an upgrade is required. With this in mind, comment from users and others is welcomed.

The application of risk assessment involves a major philosophical addition to, and enhancement of the deterministic standards developed over many years for appropriate safety of dams. These guidelines are issued to provide more appropriate and consistent guidance within a risk process, for dam safety evaluation under floods. In applying them, it must be remembered that they are guidelines only to what is considered current acceptable practice and allow owners and practitioners flexibility to exercise professional judgment in all aspects. Indeed, without the application of such judgment, the procedures themselves could lead to results that have serious shortcomings.

This is a rapidly developing area with ongoing research in many related aspects. In view of this ANCOLD will review the guidelines periodically and, to that end, seek comments from users at every opportunity.