Michael Somerford, Alex Gower
The Water Corporation is the principal dam owner in Western Australian with a portfolio of 95 dams. In the absence of dam safety legislation in Western Australia the Corporation has adopted a policy of self regulation. This paper presents how the Corporation’s dam safety policy has been implemented with respect to dam instrumentation and monitoring. It includes a summary of the type of instruments used and experiences with automated data collection systems. The paper concludes that the Corporation does not see a need for a dam instrumentation guideline, however a document summarising current Australian practices and experiences would be of value.
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The Water Act 2003 established a new role for the Environment Agency, that of the Enforcement Authority for the Reservoirs Act 1975 in England and Wales. The transfer of this regulatory role from 136 Local Authorities has had a significant impact on the regulated community. Further change is heralded with the forthcoming introduction of Reservoir Flood Plans, Post-Incident Reporting and a review of current regulations. The improvements sought in reservoir safety may be at risk due to a growing skills shortage and increasing financial constraints imposed by owners.
This paper highlights the issues impacting on the reservoir industry in England and Wales and in recognising developments made by ANCOLD members the author seeks to understand how they are being responded to in Australia.
David M. Schaaf, P.E., Jeff Schaefer, Ph.D., P.E., P.G
The United States Army Corps of Engineers (USACE) has an inventory of over 600 dams. The main purpose of many of these dams is for flood control, but there are a significant number of dams primarily used for navigation. Additional benefits at many of these projects are provided through hydropower generation, recreation, and irrigation for farmers. Many of the dams are quite old and represent an aging infrastructure across the inventory. In addition, leaner budgets relative to the need for repairs across the aging system require that USACE invest wisely in order to efficiently use available funds to reduce the greatest risks across the inventory. Previously, individual projects with perceived deficiencies were evaluated separately by the responsible district. This evaluation was not compared in any programmatic way to other USACE dams being evaluated for deficiencies.
In order to improve the process of making risk-based decisions across the entire spectrum of USACE dams, the Screening for Portfolio Risk Assessment (SPRA) for the USACE Dam Safety Program was initiated during the summer of 2005. This effort represents the first level of a multiple phased effort to bring full scale risk assessment to the decision-making regarding making investment decisions associated with dam safety by linking engineering reliability with economic and life loss impacts on a relative scale. The SPRA effort involved the development of a tool for evaluating the relative life and economic risk of dam failures for a variety of deficiencies across the inventory of USACE dams. This paper will focus on the basic aspects of the evaluation tool as well as the process by which the screening was completed.
Janice H. Green and Jeanette Meighen
The Probable Maximum Precipitation (PMP) is defined as ‘the theoretical greatest depth of
precipitation that is physically possible over a particular catchment’. The PMP depths provided by
the Bureau of Meteorology are described as ‘operational estimates of the PMP’ as they represent the best estimate of the PMP depth that can be made, based on the relatively small number of large events that have been observed and our limited knowledge of the causative mechanisms of extreme rainfalls.
Nevertheless, the magnitudes of the PMP depths provided by the Bureau are often met with scepticism concerning their accuracy when compared to large rainfall events which have been observed within catchments and which are, typically, only 20% to 25% of the PMP estimates. The recent increases in the PMP depths, resulting from the revision of the Generalised Tropical Storm Method (GTSMR), have served only to entrench this cynicism.
However, analyses of the magnitudes of the storms in the databases adopted for deriving PMP depths show that these observed storms constituted up to 76% of the corresponding GTSMR PMP depths and up to 80% of the Generalised Southeast Australia Method PMPs for the storm location. Further, comparisons of the PMP depths to large storms observed in similar climatic regions around the world indicate that the PMPs are not outliers.
The results of these analyses are presented for a range of catchment locations and sizes and storm durations and demonstrate that the PMP estimates provided by the Bureau of Meteorology are reasonable and are not unduly large.
David S. Bowles
Portfolio Risk Management is a risk-informed approach for improved management of dam safety for a portfolio of dams in the context of the owner’s business. It can be used to identify ways to strengthen technical and organisational aspects of a dam safety program, and to provide valuable inputs to various business processes. Portfolio Risk Assessment is a decision-support tool, which is incorporated in Portfolio Risk Management. It can combine engineering standards and risk assessment approaches to provide a systematic means for identifying, estimating and evaluating dam safety risks, including comparisons with other industries. It should be periodically updated to provide a basis for managing prioritised queues of investigations and risk-reduction measures to achieve more rapid and cost-effective reduction of both knowledge uncertainty and risk.
Portfolio Risk Assessment is a standard of practice in Australia and is being applied by the US Army Corps of Engineers and others. When properly conducted and used within its limitations, the Portfolio Risk Assessment process is generally considered to be robust, adaptive, defensible for corporate governance, and to justify its cost through such benefits as increased dam safety funding, identification of failure modes that were not previously recognised, identification of opportunities for improved risk management, and more rapid “knowledge uncertainty” and risk reduction.
Legal and moral requirements necessitate an “equivalent to industry standard” approach to dam management by all dam owners. As an urban authority Central Highlands Water has a portfolio of dams with a broad range of classification and risk. ANCOLD Guidelines form the basis of our approach to dam management. Thus any guidelines developed can have significant affect on our budget and operation. Guidelines with requirements targeted at extreme and high hazard dams managed by large authorities with “deep pockets” may not be reasonable to impose upon low risk structures managed by lesser authorities. This does not mean smaller authorities want to do it on the “cheap” but budgets for such infrastructure can be hard to sustain. Consequently when guidelines are considered so too should the flow on affect to those who must implement them.