R.J. Nathan and P.E. Weinmann
Selected aspects of the guidelines dealing with the estimation of dam safety floods are being
considered for revision as part of a larger overhaul of “Australian Rainfall and Runoff”. One section
that warrants attention is the guidance provided on estimation of the Probable Maximum Flood
(PMF). The section of the current guidelines that deals with this issue received little attention in the
last revision as the focus was on estimating floods for risk-based design, that is on floods of known
annual exceedance probability. However, it is now common to jointly consider both risk-based and
standards-based components in the design process, and this has highlighted problems associated with the manner in which the PMF is defined and estimated. This paper examines the current problems involved with estimation of the PMF, and presents concepts and practical estimation approaches that could be considered for incorporation in the guidelines. The purpose of this paper is to promote discussion and elicit feedback from industry to aid the revision process.
The Aviemore Dam was built in the late 1960’s and is located on the Waitaki River in the South Island of New Zealand. It is comprised of a 56m high earth dam and a concrete dam housing the power plant and spillway. The dam is located across the Waitangi Fault. This fault was considered to be an ‘inactive’, normal fault at the time the dam was built. The dam is owned and operated by Meridian Energy Ltd.
This paper is in two parts. The first is to introduce the owners Dam Safety management processes. The second discusses the application of these processes to a State of the Art investigation of the faults near the dam, the derivation of seismic loads and the assessment of the dam for seismic loads including potential movement on the Waitangi Fault affecting both the earth dam and the reservoir.
Notable features of the work will be described including:
• Trenching studies in glacial materials and utilising new dating methods
• Discovery that recent fault movement has occurred
• Estimation of seismic ground motion and fault movement loads for a magnitude Mw 7.0 earthquake under the dams.
• Assessment of the earth and concrete dam performance under extremely high ground motion and fault movement loads.
• Assessment of overtopping risk resulting from seiche waves on the lake due to the uplift of the major part of the lake floor.
• The conclusions of the Seismic Safety Evaluation of Aviemore Dam
• The owner’s response at various stages in the project.
The decision-making landscape has shifted markedly over the last 10 years with the implementation of COAG micro-economic reforms. These reforms have seen the separation of regulatory functions from commercial / service provision functions – yielding benefits to all stakeholders. However, the fragmented regulatory framework for dam owners (in Queensland at least) has resulted in potential conflict between price regulation and major dam safety decisions such as spillway upgrades.
This paper examines the scope for conflict in the two regulatory frameworks (pricing and dam safety) and the implications for dam owners, water users and potential new investors in the water infrastructure.
Legislation specifically addressing dam safety was passed into law by the New Zealand Government on 12 August 2004 as part of the Building Act 2004.
Government, local authorities, and the dam industry have debated the need for specific dam safety legislation in New Zealand since the late 1980’s. The previous legislative framework addressing dam safety in New Zealand included civil law, the Resource Management Act 1991 and the Building Act 1991. The provisions regarding dam safety within this legislation were implied rather than specific.
In 2001, as part of the Building Act Review, various government departments reviewed current dam safety regimes in New Zealand. One of the objectives was to address issues related to lack of clarity with regard to regulatory responsibility and inconsistency in the application of the current law. The New Zealand Society on Large Dams (NZSOLD) along with owners and Local Government representatives has participated in this process. The following paper is an update on the progress of dam safety legislation, outlining the evolution and structure of the dam safety provisions within the new Act. Some brief comparisons are also made to current Australian legislation.
The PT Kelian Equatorial Mining (KEM) Gold Mine is located in the foothills of Central Kalimantan in Indonesia, only 3km south of the equator. Namuk Dam was completed in September 1991, to receive tailings from the gold mine that commenced commercial production in January 1992. Mining operations ceased in mid-2003. Progressive closure of the mine has been underway since 2003, but processing of ore stockpiles will continue to the end of 2004.
KEM and the local Government formed a Mine Closure Steering Committee, supported by four Working Groups to provide assistance and guidance to KEM in achieving responsible closure of the mine.
Engineering aspects of the Namuk Dam closure included flattening of the downstream slope to withstand overtopping in the event that the spillways should fail or be blocked for whatever reason. The design also required large rock to be placed as an apron over the tailings upstream of the dam as a security precaution against potential sabotage. This is intended to deter illegal mining of tailings, which could potentially initiate breach of the dam, and to protect the dam from malicious damage.
Dam safety planning is a team game. There are many players involved and there is a need for information to be shared and actions to be properly coordinated. The State Emergency Service is the legislated combat agency for flooding in New South Wales and is responsible for planning for and conducting the warning and evacuation of communities at risk from floods, including floods affected by dams. The successful execution of these responsibilities is dependent upon the continuing development of a strong, cooperative relationship between the dam owners and managers, dam regulators and emergency managers and the effective incorporation of community expectations in dam safety planning.
This paper explores some of the ways that this relationship can help to meet well accepted community expectations in respect of risk to life and property and outlines progress made in dam safety planning to date. The emergency response aspect of dam failure planning is still a relatively immature field in Australia, and it follows that there are lessons to be learned as we proceed. In that context, the paper also describes some of the difficulties the State Emergency Service has encountered in its role as the response planning agency and suggests some guiding principles to enhance future interactions between the key stakeholders.