2006 – Effect of Geology on Dam Construction Projects in Iran
A. Uromeihy, P.G. Ranjith
In response to increasing potable water need and in order to control and collect precipitations, many dams have been constructed and many more are under construction in Iran. Due to the complex geology of the country, many of the dam sites face serious geological problems both during construction and in operation phases. The most predominant types of problems are water leakage and sediment deposition in the reservoirs. In order to define and classify the type of problem with regards to geological condition, the country is divided into eight zonesin whicheach zone demonstrates similar problem on the dam site location. It is found that the water leakage is related directly to either the presence of soluble carbonate rocks in the abutment or the presence of thick permeable material in the foundation. It is also shown that the sediment deposition in the reservoir is related to many factors but the geology of the watershed area has a major effect. Therefore it can be concluded that the geology has a great role in the construction of dams.
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2006 Papers
2006 – Hydraulic Flow Simulation – Five Years On: Lessons Learned and Future Challenges
Learn moreKaren Riddette, David Ho & Julie Edwards
Over the last five years in Australia, the use of computational fluid dynamics for the investigation of water flows through hydraulic structures has been steadily rising. This modelling technique has been successfully applied to a range of dam upgrade projects, helping to assess spillway discharge capacity and structural integrity, and giving insight into flow behaviours including orifice flow, shock wave formation and chute overtopping (Ho et al, 2006). Innovative and cost effective upgrade solutions have been implemented from numerical model studies including baffle plates (Maher and Rodd, 2005) and locking arrangements to protect radial gates from extreme floods.
This paper will begin with a review of recent dam engineering applications, including outlet flow through a fish screen, the performance of a fishway against hydraulic and environmental criteria and pipe flow in a large pumping station. Some of the difficulties and limitations of the modelling technique will be examined together with current research being conducted to address these issues and further validate the numerical results against published data. Some interesting results to date will be reported on elliptical crest discharge, boundary geometry, and model/prototype correlation.
With increasing computing power and software enhancements, the potential applications for numerical simulation in dam engineering continue to grow. This paper will also examine the future outlook and highlight some recent advances such as the thermal simulation of cold water pollution, air entraining flows and combined free-surface and pipe flow in a morning glory spillway.
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2006 Papers
2006 – PMP ESTIMATES – ARE WE KIDDING OURSELVES?
Learn moreJanice 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.
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2006 Papers
2006 – From Portfolio Risk Assessment to Portfolio Risk Management
Learn moreDavid 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.
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2006 Papers
2006 – Justification for an Operating Restriction in Spain Incorporating ANCOLD Guidelines on Risk Assessment
Learn moreManuel G. de Membrillera, Ignacio Escuder, David Bowles, Eduardo Triana, Luis Altarejos
The work herein presented is an application of the risk assessment process to retroactively estimate the justification of an operating restriction implemented on a Spanish Dam. Since the risk approach is not yet an established practice in Spain, the main objective of this case study is to show, the utility that risk assessment can have as a decision support tool for decisions on dam safety risk reduction investments.
An operating restriction has been imposed at this dam since its first impoundment. All studies, analysis and documents related to the safety of the dam and reservoir have been completed, as required by the Technical Regulation on Dam and Reservoir Safety (Spanish legislation, 1996). In addition, the structural corrective actions recommended in these evaluations are being implemented, so it is expected that the operating restriction can be removed in the near future.
In this context, the problem that has been formulated and solved comprises an evaluation, after more than 30 years since construction, of the operating restriction justification in terms of risk mitigation. In order to achieve the objective of the work, ANCOLD guidelines on Risk Assessment (2003) have been followed in addition to tolerable risk guidelines from several other countries and organizations.
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2006 Papers
2006 – Failure Modes Analysis as Applied at Rocklands Dam
Learn moreMarius Jonker, Malcolm Barker and Gary Harper
This paper provides a framework for conducting an effective Failure Modes Analysis. It explains the fundamental principals and methods of Failure Modes Analysis. The current international state of practice on Failure Modes Analysis is discussed, and the objectives, benefits and limitations of Failure Modes Analysis assessed. Guidelines are given on how to apply the outcome of Failure Modes Analysis in dam safety management and surveillance.The effective application of Failure Modes Analysis is illustrated in a case study where the process was applied in the safety review and risk assessment of Rocklands Dam for Grampians Wimmera Mallee RegionWater Authority in Victoria.
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