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Gideon Steyl, Ralph Holding, Lis Boczek
A Monte Carlo method for assessing liner systems is applied with outcomes demonstrating the range of discharge that could occur over the liner interface. The Monte Carlo approach allows for variation of fill material over the liner system and includes the assessment of a second compacted zone either above or below the liner zone. In this paper clay liners were evaluated due to regulatory guidelines and it could be demonstrated that similar performance to a 1 m clay liner could be attained using compacted material to reduce discharge over the liner interface. The approach applied in this paper allows for at least a worst-case quantification of seepage risk which could be included in liner selection criteria or presenting liner options to regulators.
Now showing 13–24 of 27 search results:
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2020 Papers
2020 – Monte Carlo Geospatial Approach to Liner Design Principles in TSFs
Learn moreGideon Steyl, Ralph Holding, Lis Boczek
A Monte Carlo method for assessing liner systems is applied with outcomes demonstrating the range of discharge that could occur over the liner interface. The Monte Carlo approach allows for variation of fill material over the liner system and includes the assessment of a second compacted zone either above or below the liner zone. In this paper clay liners were evaluated due to regulatory guidelines and it could be demonstrated that similar performance to a 1 m clay liner could be attained using compacted material to reduce discharge over the liner interface. The approach applied in this paper allows for at least a worst-case quantification of seepage risk which could be included in liner selection criteria or presenting liner options to regulators.
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2020 Papers
2020 – When the bottom-line impacts dam safety: Case studies of commercial realities leading to increased risks
Learn moreJames Thorp, Ryan Singh, Jiri Herza
Responsible management and operation of tailings and water storage facilities comprises a series of activities and projects that must be delivered within the commercial realities of the organisation and operation context of the facility owner. All projects are constrained by several variables, which are commonly represented by the Project Management Triangle of Scope, Time, and Cost. These variables are often finite and mutually exclusive, and delivery of the required outcome is accomplished by successfully managing each variable. The activities (variables) associated with the long-term dam safety are sometimes omitted to meet the immediate project requirements. In addition, the commercial realities, such as a selected project delivery model, can have a significant impact on dam safety risks through the allocation of risk, ability of the key decision makers, and the undue commercial pressures applied by each project delivery model. This paper presents several case studies where the project and commercial realities have led to decision making that impacted dam safety and increased the risk presented by the storage facility. While the immediate impact of these decisions may appear to be minimal, all stages of a tailings or water storage facility’s life span are impacted. This paper presents learnt lessons with the aim to prompt both owners and consultants to reconsider their commercial processes and project delivery strategies and limit unforeseen risks to the safety of tailings or water dams.
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2021 Papers
2021 – Regulatory risk – a proposed framework for contractual accountability of the Crown of regulatory changes
Learn moreArnold Dix
Regulatory risk for large civil engineering projects such as dams and hydropower schemes can be larger than the engineering risks. The seriousness of project regulatory risks is rarely acknowledged publicly and almost never dealt with contractually. The recent adoption by the World Bank of the FIDIC/ITA Emerald Book contractual framework introduces geotechnical baseline reports as a contractual mechanism for managing ground risk in World Bank hydro projects. Regulatory risks created by government agencies and utilities due to changing project requirements can likewise be managed by adopting the concept of geotechnical baselines to regulatory impositions as a baseline report.
Government agencies changing regulatory burdens mid project can fairly be held accountable for the
burdens of those changes by establishing regulatory baselines at the earliest stages of a project. By
contractually embedding regulatory risk baselines, governments and their agencies can adjust their
payments to reflect the changed cost in delivering an agreed project caused by regulatory changes. In this way the compensation for delivering a project more closely aligns with its value and cost. A regulatory baseline report in reducing project exposure due to regulatory change driven costs is a new tool in more efficient and competitive project delivery.A transparent mechanism for costing regulatory change risk and apportioning it in accordance with pre agreed mechanisms, is an innovation of great use to the dam and hydropower sector.
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Guidelines
ANCOLD Guidelines on Risk Assessment (July 2022)
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Please note only available in hardcopy format.The ANCOLD Guidelines on Risk Assessment were published in 2003. They have served the Australian dam community very well and are referenced internationally. Risk assessment is now the principal approach to manage engineering risks at water dams and now a developing practice for tailings dams.
These new guidelines on risk assessment replace the 2003 publication. They include updates to several sections taking account of developments in risk analysis methods and risk evaluation, from experience in applying those guidelines. As for ANCOLD (2003), these guidelines are directed to the practical application of risk assessment, as an aid to better dam safety management. Risk management is the end objective – risk assessment is a means to that end.
These guidelines have been produced by a Working Group of six members, all with significant experience with risk assessments for dams. A Reference Committee of sixteen members has been engaged throughout the development of the Guidelines.
The Working Group and Reference Committee include representatives of dam owners, consultants, universities, and regulators of dam safety. Six Australian states and the ACT were represented. Members and associates of ANCOLD have also provided input through risk workshops held with annual conferences.
Dam owners, decision-makers and analysts need to consider the current state of development of risk assessment in deciding how best to use and apply the process in reaching decisions on dam safety, having regard to their specific overall business risk management needs, and their community and legal responsibilities.
These guidelines also require consideration by dam safety regulators, who need to decide what part risk assessment can play in the discharge of their responsibilities. Deciding on the tolerability of risk is one of the functions of regulators.
ANCOLD continues to believe that the use and further development of risk assessment using studies of the traditional engineering standards-based approach as an input, as proposed in these guidelines, offers the potential for significantly improved dam safety management.
Risk assessment methods are continuously developing. ANCOLD recognizes that detailed aspects of these guidelines will be overtaken by developments within a few years and urges practitioners to keep abreast of new knowledge. Nevertheless, the framework and generic guidelines in this publication are essentially as detailed in ANCOLD (2003) and are expected to remain valid for many years.
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2007 Papers
2007 – Planning to secure South East Queensland’s future water infrastructure
Learn moreRussell Paton and David Murray
The South-East Queensland Regional Water Supply Strategy is securing future water supplies, which includes a regional water grid and new water storages. The Queensland Government’s contribution to future water supplies includes Traveston Crossing Dam on the Mary River, Wyaralong Dam on the Teviot Brook, and Bromelton Offstream Storage and Cedar Grove Weir on the Logan River.
Queensland Water Infrastructure (QWI) was established by the Queensland Government in June 2006 to progress feasibility studies, design and construction of this new water infrastructure. QWI commissioned SunWater to investigate much of this infrastructure to preliminary design level for the impact assessment process and as supporting information for potential alliance partners for the delivery of the projects. The work undertaken included extensive geotechnical investigations, hydraulic modelling, hydrologic modelling and design activities. This paper outlines the investigations associated with the preliminary design of this infrastructure and process of risk and opportunity identification to establish the program and budgets for these projects.
Stage 1 of Traveston Crossing Dam is to be constructed by the end of 2011, with a storage capacity of 153,000 ML providing a yield of 70,000 ML each year. The design adopted for the dam consists of a roller compacted concrete structure across the valley floor with an earth embankment section on the left abutment. In order to limit inundation upstream and mitigate flooding in Gympie, a gated spillway on the right abutment has been adopted. The Traveston Crossing Dam has an estimated project cost of $1,700 million.
The design developed for the Wyaralong damsite provides a reservoir with storage capacity of 103,000 ML and a yield of 21,000 ML each year when operated in conjunction with Cedar Grove Weir. Preliminary designs have been prepared for three types of dam, which are all considered technically feasible for the site. They are a roller compacted concrete dam, an earth and rockfill dam and a concrete faced rockfill dam. The Wyaralong Dam has an estimated project cost of $500 million.
The Bromelton Offstream Storage, of earthfill construction, provides a storage capacity of 8,000 ML and Cedar Grove Weir, a sheet pile structure, provides a storage capacity of 1,000 ML and both are to be constructed by the end of 2007.
Keywords: Planning, Traveston Crossing Dam, Wyaralong Dam, Bromelton Offstream Storage, Cedar Grove Weir, Queensland, risk.
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2012 Papers
2012 – Estimating Individual Risk
Learn moreKelly Maslin, Mark Foster, Len McDonald
A key requirement of assessing the tolerability of dam safety risks is the assessment of individual risk. The ANCOLD Guidelines on Risk Assessment provides guidance on acceptable levels of individual risk and some general guidance on the calculation of individual risk.
Individual risk is a key measure in the consideration of the tolerability of risk, ALARP and development of risk mitigation works. It is essential that there is consistency in the approach to estimating individual risk used across the dams industry.
This paper reviews the approaches taken to estimating individual risk across the dams industry both locally and internationally as well as the experience of other industries.
The paper includes a review of the various methods for estimating the vulnerability of individuals subjected to flood inundation based on historical fatality rates as well as identification of the individual most at risk
The paper then describes a method that has been developed based on the principles used for assessing individual risk due to other hazards, such as landslides. The method includes consideration of a range of factors such as warning time, temporal variation and vulnerability of the individuals most at risk. The method developed provides a transparent, defensible and pragmatic approach to estimating individual risk. Practical guidance and examples are also provided on the application of the method.
Keywords: individual, risk, exposure, fatality
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2008 Papers
2008 – Estimating construction flood risk
Learn morePeter Hill, Phillip Jordan, Rory Nathan, Emily Payne
Abstract: There are a number of issues that need to be considered when deriving estimates of floods used to assess construction flood risk. This paper outlines the derivation of seasonal flood frequency curves and highlights the important differences in seasonality across Australia and the variation with the exceedance probability. Examples are provided as to how these seasonal frequency curves are used to estimate the construction flood risk during a particular construction activity in a safety upgrade for an existing dam or construction of a new dam. The paper also touches on the issues associated with estimating consequences for assessing construction flood risk.
Keywords: construction flood, risk, seasonal hydrology, hydrologic loading
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2008 Papers
2008 – Towards responsible management of tailings facilities
Learn moreElizabeth Gardiner, Len Murray, David Gladwin
Abstract: The Mining Association of Canada has worked over the past 12 years to improve the management of tailings facilities. This effort began out of a realization that tailings present a major business risk to the mining industry, and that a series of major tailings failures around the world in the 1990’s were fundamentally indicative of need for improved care and management practices by tailings dam and facility owners and operators. MAC established and continues to sponsor the Tailings Working Group, which has assisted in development and publication of a three-volume set of guides to improve tailings management:
•“A Guide to the Management of Tailings Facilities”, initially published in 1998, updated edition published in 2008;
•“Developing an Operation, Maintenance and Surveillance Manual for Tailings and Water Management Facilities”, published in 2003; and
•“A Guide to Audit and Assessment of Tailings Facility Management”, published in 2008.
The three guides provide a strong message that the key to safe and environmentally responsible management of tailings is consistent application of sound engineering capability within an effective management framework.The documents are almost directly applicable to all forms of dams and are widely used for water dams. Also, because the documents are available in Spanish and French they have found wide use in International projects.
A brief comparison with published ANCOLD guidelines is provided.
Keywords: Management of tailings facilities and water dams, Operation, Maintenance and Surveillance, Auditing, risk, safety, guides
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2008 Papers
2008 – Structural risk from cracking in mass concrete monoliths
Learn moreRandy J James, Yuyi Zhang, Gabriela Lyvers, David Schaaf
Abstract: Following the flooding disaster in New Orleans, Louisiana, due to Hurricane Katrina in August 2005, the U. S. Army Corps of Engineers (COE) initiated a comprehensive program to survey, evaluate, and rank all dams and levees in the COE’s portfolio for risk of structural failure and associated economic consequences. One objective of this program is to improve safety and risk through efficient allocation of resources for rehabilitation efforts when needed. One area of great concern is internal stresses in aging concrete monoliths causing cracking. While some cracking in concrete monoliths is a common condition having little effect on the structural performance, extended cracking can lead to instability in parts of the monolith. Mass concrete monoliths generally are not reinforced, and cold joints at lift interfaces are a potential source of weak planes. Failure of concrete monoliths due to sliding instability along internal cracked planes can have serious consequences for loss of pool. This failure mode can occur quite suddenly, and detection of such cracking or the extent of such cracking is very difficult to establish from visual inspections or even core sampling. To help in this portfolio risk assessment, analysis methodology has been developed for establishing the structural risk due to cracking in mass concrete monoliths. Finite element modelling with automated mesh generation and employing advanced concrete constitutive relations for crack initiation, propagation, and arrest, are used to establish internal cracking. Monte Carlo based probabilistic analysis methods, directly coupled to the finite element analyses, are used to evaluate uncertainties and establish the probability of failure for increasing pool elevations and seismic hazards. The objective is to provide a probability of failure for possible pool elevations under current site conditions given that there is always some possibility of a range of seismic events that could occur at any given time.
Keywords: concrete dams, cracking, structural reliability, risk, and safety
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2009 Papers
2009 – Goulburn Weir Anchor Failure Investigation & Anchor Replacement Design & Construction
Learn moreBen Ross, Jason Brown, Richard Rodd
Goulburn Weir was constructed in 1891 forming Lake Nagambie on the Goulburn River, approximately 8km north of Nagambie in Victoria. It is a key asset in the irrigation network diverting water to 352,000ha in Northern Victoria. The weir was remodelled between 1983 and 1987, replacing 21 overshot gates with nine radial gates. A series of 28 post tensioned bar ground anchors were installed to secure the radial gate concrete support piers to the weir’s mudstone foundations. On 8 March 2006 during routine testing of the pier bar ground anchors, failure of one anchor occurred. It posed a possible risk to pier stability. Subsequently investigations into the cause of failure and its implications was undertaken consisting of a program of data review, site investigations, metallurgical testing, geotechnical investigation, design reviews and stability assessments. It was recommended to replace the failed anchor and 10 other under performing anchors with 8 cable strand anchors at the cost of approximately $1million.
Key words: Risk, bar anchor failure, stability assessment, anchor construction.
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2011 Papers
2011 – Awoonga Dam Acceptable Flood Capacity design – the anguish of erosion risk and implications for design
Learn moreMalcolm Barker, Toby Loxton
The Gladstone Area Water Board (GAWB) owns and operates Awoonga Dam, which is a concrete-faced rock fill embankment with a fixed crest concrete spillway on the left bank impounding a storage volume of 770,000 ML.
The current arrangement can accommodate the Probable Maximum Flood, allowing for flow over Saddles 3, 4 and 6 on the left abutment. A comprehensive study was carried out to evaluate the erosion potential downstream from Saddles 3 and 6 as well as other spillway options adjacent to the existing dam. One option was a radical approach including the removal of the Saddle Dam 3 and provision of downstream erosion protection works. This reduced the PAR and improved the overall dam flood capacity; however concerns were expressed about the environmental impact of possible erosion downstream from Saddle 3 for relatively frequent events.
A risk assessment showed that the erosion protection works downstream from the Saddle 3 or 6 were not cost effective and the preferred option for the upgrade was the closure of the Saddle Dam 3 with an auxiliary spillway created in Saddle 6,
This paper summarises the methods used and the outcomes from this study.
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