John D Smart
The paper presents the recent trends in the use of instrumentation and survey measurements at Bureau of Reclamation (Reclamation) dams. The underlying philosophy that has influenced those trends is presented and discussed. Based on experience at Reclamation, several factors that are considered key to the effective use of instrumentation and surveys are discussed. Several conclusions are offered.,
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Now showing 1-12 of 59 2970:
Peter Allen, Malcolm Barker, Shane McGrath and Chris Topham
Are we there Yet? The question we all ask in Tolerability of Risk. The answer is in the journey, which we are all on as owners, regulators or designers.
A number of authorities in Australia are applying risk assessment for the evaluation of dam safety upgrades in accordance with the October 2003 ANCOLD Guidelines on Risk Assessment. A fundamental requirement for the evaluation of risk below the limit of tolerability is the use of the As Low As Reasonably Practicable(ALARP) principle. In making a judgement as to whether an ALARP position may have been reached, ANCOLD suggest the evaluation of a Cost to Save a Statistical Life, good practice, level of existing risk, social concerns, affordability and duration of risk. ANCOLD also suggests consideration of the USBR Criteria for evaluating risk. Recent guidelines on the Acceptable Flood Capacity for Dams developed by the Queensland Dam Safety Regulator provide further insight into the application of ALARP.
The objective of the paper is to make dam owners, regulators and designers aware of some current practice regarding the evaluation of ALARP in Australia, highlight the challenges of applying this principle and to encourage further discussion.
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.
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.
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.
Ensuring compliance with the Regulator’s requirements is a cornerstone consideration for any water corporation in planning its risk minimisation strategies against dam failure. With the increased focus on due diligence and corporate governance however, there are emerging themes that are of equal importance for a water corporation in planning protections against its core risks to dam safety. These considerations include: