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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.

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2006 Papers

2006 – ALARP Considerations for Dam Safety – Are We There Yet?
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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.
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2014 Papers

2014 – Beyond Quantitative ALARP – Re-Focussing Paradigms for Dam Safety Risk Management in a Changed Legal Environment
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Dennis C. Green

Current good practice for risk management as represented in ANCOLD guidelines emphasises risk reduction beyond tolerable risk levels to As Low As Reasonably Practicable (ALARP). Risk reduction reflected in key design parameters such as the spillway design flood is monitored on a quantitative basis, while the guidelines also draw attention to a number of non-quantifiable measures.

Recent work health and safety legislation in Australia does not at first appear to relate to dam safety, but it mandates elimination of risk, and, if that is not possible, then it mandates reduction of risk So Far As Is Reasonably Practicable (SFAIRP). It is tempting to believe that this is equivalent to ANCOLD’s approach to ALARP, but the devil is in the detail of the legislation. This paper argues for a change to a more systematic presentation of recording of decisions on dam safety risk management, lest the legislation expose dam owners unwittingly to liability when they thought they were following good practice. In particular, the re-focussing of ANCOLD Guidelines to align more recognisably with the new legal paradigm, including preparation and adoption of a Safety Case, is recommended.

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2015 Papers

2015 – Sweet Smell of Successful Risk Management
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Jason Fowler, Robert Wark

Tropical Forestry Services (TFS) currently (2015) leases Arthur Creek Dam from the West Australian state government and utilises the water source to drip irrigate its Indian sandalwood (Santalum album) plantation. Arthur Creek Dam is located approximately 70 km south west of Kununurra in the East Kimberley region of Western Australia. TFS grows and processes the sandalwood to produce oil that is used extensively in the global fragrance perfume market. TFS took over the lease of the 26 m high zoned earth core and rock fill dam in 2007 and has systematically carried out remedial works to the structure to lower the f-N curve below the ANCOLD “Limit of Tolerability” and to well within the ALARP zone. This paper describes the proactive risk management approach TFS has undertaken to address dam safety issues. It also specifically describes the most recent management issue, being the outlet pipe refurbishment.
A number of dam safety issues were identified during the initial surveillance and subsequent annual surveillance inspections. Issues include insufficient spillway capacity, seepage from the right abutment and deterioration of the steel outlet pipe. The remedial works to the outlet pipe were completed in late 2014 and involved close collaboration between TFS, the contractor and the designer. The outlet pipe re-sleeving operation was complex as the dam had to remain in operation and the water level could not be artificially lowered. In addition, the original outlet pipe was asymmetrical along both the vertical and horizontal axes, close to the bulkhead gate structure. Contingency measures were employed to enable the dam to remain in operation with 3 DN 400 HDPE siphon pipes installed.
The completion of the refurbishment of the outlet pipe by sleeving the pipe reduced the risk posed by this structure by an order of magnitude. Planned future risk reduction measures include the treatment of seepage within the upper right abutment and rebuilding the crest. These actions will further reduce the risk of dam failure through piping and overtopping of the dam crest.
Keywords: risk, ALARP, outlet pipe, re-sleeving.
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2016 Papers

2016 – The Use of a Safety Case to Demonstrate ALARP
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Shane McGrath, Stuart Richardson, Mark Arnold

Melbourne Water Corporation has recently completed a complex safety upgrade of Greenvale, an extreme consequence category dam. An assessment concluded that the residual risks were As Low as Reasonably Practicable (ALARP). However, given the uncertainty associated with the calculations the estimated residual societal risk was not comfortably below the limit of tolerability. Melbourne Water has experience with preparing hazardous industry safety cases for its water treatment chemical storages and decided to trial the methodology for Greenvale Dam. This paper describes the approach taken in hazardous industries to construct safety cases and how his was adapted to demonstrate that dam safety risks are ALARP.
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2016 Papers

2016 – Would Bowties and Critical Controls Contribute to the Prevention of High Consequence / Low Frequency Dam Failures?
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Russell Mills PhD,Rebecca Freeman, Malcolm Barker

The global mining industry lives with the risk of catastrophic events such as water storage or tailings dam failures as part of its daily operations, and has developed a number of approaches to enable mine management to understand the nature of the risks and the ways in which they are being managed. One such approach involves the use of bowties for the understanding of the hazards and risks. Building from bowties, the second approach involves the selection and management of controls critical to the prevention or mitigation of the catastrophic event. The Australian mining industry is a world leader in this regard and the purpose of this paper is to illustrate how bowties are constructed, how risks can be semi-quantitatively estimated, how critical controls are selected and managed, and how, if all this is done well, risks can be demonstrated to be as low as reasonably practicable (ALARP).

This paper sets out key themes and presents an example for a tailings dam failure to illustrate the role of bowties and critical controls in management of catastrophic events. It will also highlight the role of bowties in the anticipated introduction of a Safety Case approach to dam risk management. Bowties provide a useful tool for the transfer of risk management knowledge from the designer, to allow dam owner / operators to better understand their risks and to recognise the link between design and operational controls and how they are used to manage those risks to ALARP.
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2018 Papers

2018 – A Logical ALARP Risk Procedure
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Kate Robilliard, Kristen Sih

The As Low As Reasonably Practicable (ALARP) principle was established in the Australian Dams
community in the ANCOLD Guidelines on Risk Assessment in 1994. Since that time, dam owners have been focused on reducing their societal risk to below the ANCOLD Limit of Tolerability (LoT) through dam safety upgrades and are now considering how to justify an ALARP position. This paper presents a framework that provides a systematic approach to assembling the inputs, applying a process and documenting the outcomes of an ALARP assessment. It is a pragmatic approach that aligns with the safety case, which is a legislated requirement for Major Hazard Facilities in Victoria.
The framework has been applied to two dams in Melbourne Water’s portfolio with differing societal risk, size, uses and criticality to the water supply system. It has highlighted the importance of dam safety governance, documentation of procedures, defensible technical analysis and an ongoing engagement with leading industry practice, in demonstrating risks are ALARP.
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2020 Papers

2020 – Challenges in applying new guidelines to existing tailings dams projects
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Michael Ashley, John Phillips

New guidance and publications relating to tailings dams have been released recently by many jurisdictions across the world as an initial response to recent, well-documented, catastrophic tailings dam failures. The application of new guidelines retrospectively to existing tailings projects can introduce complex challenges, especially for sites with a long and often not well documented history. Challenges can be difficult to overcome while balancing time, cost and risk objectives.

This paper explores the impacts of changes between the 2012 and 2019 revisions of the ANCOLD Guidelines on Tailings Dams and potential implications for existing facilities.

The most significant update between the 2012 and 2019 revisions of the guidelines relating to design practices is the additional detail and guidance on seismic stability analyses and static liquefaction. Guidance on the application of new guidelines for tailings dam designers, owners and regulators is required to provide a consistent approach to manage the risk.
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2020 Papers

2020 – Dam Safety Due Diligence demands SFAIRP not ALARP
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Richard M Robinson, Siraj Perera, Gaye Francis

Due diligence has become endemic in Australian legislation and in case law, to the point that it has become, in the philosopher Immanuel Kant’s terms, a categorical imperative. That is, our lawmakers seem to have decided that due diligence is universal in its application and creates a moral justification for action. This also means the converse, that failure to act demands sanction against the failed decision maker.

This applies to dam safety management which represents the archetypical high consequence – low likelihood event. It is now essential to have positively demonstrated safety due diligence in a way that can withstand post-event judicial scrutiny. Presently the only way this can be done is by using the notion of criticality and precaution, not hazard and risk. The test is not that of risk acceptability (as low as reasonably practicable or ALARP), rather it is that no further reasonably practicable precautions (so far as is reasonably practicable or SFAIRP) are available, and that what results is not prohibitively dangerous.

This paper will document the difference between the two approaches and how to positively demonstrate safety due diligence. It also discusses the definition of ALARP as stated in ANCOLD’s Guidelines on Risk Assessment 2003 and the relevance of the safety case principle for dam safety management.
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2020 Papers

2020 – Implications of NSW Dams Safety Regulation 2019 on dam safety risk management
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Mark Pearse, John Pisaniello, Sam Banzi, Peter Hill

A completely new dam safety regulation framework was introduced into NSW in November 2019. The new framework addresses all aspects of dam safety management. The implications for dam owners in respect of risk reduction measures (RRMs) that will need to be undertaken have been the matter of debate and are the focus of this paper. The Dams Safety Regulation 2019 requires that dam owners eliminate or reduce the risk posed by their dams but “only so far as is reasonably practicable” (SFAIRP). This is a change from the previous Dams Safety Committee requirement that risks should be reduced as low as reasonably practicable (ALARP). The previous guidance around the extent and timing of risk reduction has been removed and dam owners are now required to determine what is ‘reasonably practicable’. These changes were anticipated to save hundreds of millions of dollars from the reduced cost of risk reduction measures across the state of NSW. These savings appear unlikely to materialise given that dam owners are likely to be highly cognisant of the need to meet the common law expectation that RRMs should be implemented unless the costs associated with the RRMs are grossly disproportionate to the benefits gained. The key changes in the new regulatory framework are identified along with the legal and financial implications in regard to RRMs followed by next steps that should be considered by dam owners in NSW. Many of the implications are applicable to other dam owners who operate under common law (including all states of Australia and New Zealand).
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2020 Papers

2020 – The Safety Case
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Shane McGrath, Mark Arnold, Josh Rankin, Gavan Hunter

Greenvale Dam is a critical storage for the supply of potable water to Melbourne. The dam had been upgraded through current risk management techniques, and an ALARP assessment completed at that time. However, it was decided that a more comprehensive demonstration of ALARP was warranted to satisfy the dam owner’s duty of care. Since there is no comprehensive guidance in the dams industry for owners and their advisors to reference, the safety case approach used extensively in other hazardous industries was adopted. Considering the approaches used by Victoria’s Worksafe, the Institution of Engineers Australia and the National Offshore Petroleum Safety and Environmental Management Authority (NOPSEMA), the key components of the safety case for Greenvale dam were identified then developed to provide a logical, structured and comprehensive argument for the safety of Greenvale Dam. This paper provides an overview of components of the safety case developed for Greenvale Dam, the use of safety cases for dams and where process improvements could be made.
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2021 Papers

2021 – Risk analysis and safety upgrade of Mangrove Creek Dam; SFAIRP assessment under Dam Safety NSW regulations
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Vicent Espert, Peter Buchanan, Colleen Baker, Malcolm Barker, Mark Locke

Mangrove Creek dam is an 80 m high CFRD constructed between 1976 and 1982 for water supply to the NSW Central Coast area, and is currently operated by Central Coast Council (CCC). The dam is classified as a ‘High A’ Consequence Category dam for both Sunny Day and Flood breach in accordance with ANCOLD guidelines.

Previous assessments of the dam identified that it would not be able to safely pass the ANCOLD Fallback flood capacity of the PMP flood in its current configuration. As such, the dam has been operated at a restricted full supply level for many years.

In 2020, GHD was engaged by CCC to develop a concept and detailed design to increase the spillway capacity using a standards-based approach to achieve the flood capacity fallback position. The first phases of this contract also required GHD to undertake additional investigations and analyses of various aspects of the dam and spillway to confirm the scope of works for the upgrade. During this review, it became evident that although the spillway capacity does not meet the ANCOLD fallback position, the Annual Exceedance Probability (AEP) of the existing capacity was relatively low and could potentially be deemed acceptable from a risk-based position.

A Risk Assessment was subsequently undertaken, with a SFAIRP assessment developed based on the new Dam Safety NSW guidelines. This assessment may be the first one to be completed for a major dam using the Dam Safety NSW guidelines. This paper discusses the different outcomes for a standards-based ‘Fallback’/’Simplified’ criteria and risk criteria based on DS NSW regulations, as well as the investigations developed to maintain confidence in the assessment. In addition, it describes a practical case for the application of SFAIRP criteria to a major dam.

In the case of Mangrove Creek Dam, the application of the new DS NSW Guidelines resulted in the dam being assessed as acceptable in its current state, with the FSL returned to the original design level. The outcome provided significant savings to the client, by avoiding costly upgrade works and avoiding disruption to the operation of the storage – a real success story.
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2013 Papers

2013 – A case study: how to minimise risks associated with a portfolio of non-revenue generating dams
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Monique de Moel and Gamini Adikari

Parks Victoria manages over 4 million hectares of parkland and a portfolio of over $1.9 billion worth of infrastructure assets. Within this portfolio, Parks Victoria is responsible for a large number of dams and their associated structures. Consequence category of these dams varies from Extreme to Very Low. Parks Victoria recognised that these assets required a dam safety management and monitoring program. The development of a program commenced with a portfolio risk assessment in 1998 which progressed to detailed design reviews of a selected number of dams and the initiation of an ongoing dam safety and surveillance program. This initial work identified the need for dam safety upgrade works within this asset portfolio which Parks Victoria has been progressively addressing. In 2012 Parks Victoria identified that a review of the risk profile of the dams was warranted. The review included consideration of alternative options such as staging of works, reducing storage volume and decommissioning, as well as non-technical considerations such as increasing the recreational use and the environmental value of these assets. This paper outlines the approach adopted by Parks Victoria in developing and improving its dam safety program and how it has assisted in minimising dam safety risks. Specifically, Parks Victoria’s approach of adopting measures that recognize the purpose and benefits of the individual storages, whilst being sympathetic to the requirements of the other infrastructure within its diverse portfolio of assets is highlighted. Since this work commenced in 1998, Parks Victoria have been successful in the development of an effective dam safety and management program which has resulted in the reduction of risks associated with this portfolio of assets.
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2013 Papers

2013 – Quipolly Dam safety upgrade
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Peter A. Ballantine

In view of the need for a safety upgrade for the Quipolly Dam and the plans of Liverpool Plains Shire Council for future growth in water supply, the Council took the opportunity to increase the storage capacity of the dam by raising the full supply level by 2.0 m. In 2009, the Council appointed GHD to design the upgrade in accordance with the ALARP principle.
The design of the dam included an innovative vertical crest wall, embedded into the embankment, a concrete-lined auxiliary spillway placed over the embankment adjacent to the existing spillway and the installation of Hydroplus Fusegates in the existing spillway channel.
This paper describes the design of the upgrade works.
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2010 Papers

2010 – Regulating Dam Safety: How do we compare?
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Kristen Sih, Peter Hill, Susan Ryan, Siraj Perera

Although ANCOLD provides guidance on good dam safety practices, in Australia it is the State and Territory Governments’ role to protect the public from dam safety incidents and in many cases these jurisdictions have legally binding regulations in place that dam owners must adhere to. This paper presents a comparative analysis of the dam safety regulations currently in place for Australian states, as well as selected international jurisdictions. The limit of applicability of the regulations, number of dams regulated, content of the regulations and powers and responsibilities of the regulator are all compared. It was found that there is a large range within each of these categories with regulatory approaches varying from light-handed and objective based, to highly prescriptive. The extent to which risk management principles are used in the regulations for each jurisdiction has also been investigated. It was found that in jurisdictions where higher hazard category dams account for a higher proportion of dams being regulated, risk analysis is included in the regulations. Finally, the ANCOLD societal risk criteria and ALARP considerations have been compared and contrasted with those from international jurisdictions and other hazardous industries.
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2011 Papers

2011 – Western Australian Dam Safety Challenges for ANCOLD Part 2
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Michael Somerford and Steven Fox

The Water Corporation of Western Australia has been implementing the risk assessment process promulgated by ANCOLD for 12 years. This approach has been central to a $310 million dam safety remedial works program that has reduced life safety risk across the Water Corporation’s portfolio of dams by an order of magnitude. However, whilst this process has provided a rational basis to prioritise dam safety upgrades, there are still questions that have not been fully answered and further development of the application of risk assessment to dams is desirable.

This paper revisits some of the key concerns that remain evident with the process and argues that unless further guidance is provided it may be that dam safety upgrades have effectively “hit the wall”; and upgrade programs commenced may never be completed as envisaged by ANCOLD.

2011 – Western Australian Dam Safety Challenges for ANCOLD Part 2
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2011 Papers

2011 – Hume Dam Spillway Southern Junction Filter and Drainage Works
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Rod Westmore, Andrew George& Robert Wilson

A 2007 risk assessment of Hume Dam concluded that the dam did not satisfy the ANCOLD societal risk criteria for existing dams. The Spillway Southern Junction (SSJ) and its associated failure modes was one of the main contributors to the risk profile.

Upgrade works at the SSJ involved the retro-installation of additional filter and drainage materials in the 40m high embankment immediately downstream of the tower block and central core wall by installation of more than 10,000m of secant caisson drilled columns backfilled with filter and/or drainage materials.

This paper describes the design and construction issues associated with the upgrade works, the equipment and methodologies developed to achieve the principal design objectives of coverage and connectivity of filter and drainage columns, and optimisation of compaction of the backfill materials. It also describes how these requirements were met whilst minimising adverse affects such as vertical deviation, excessive vibration, subsidence of secant filter columns during construction, and clay smearing of the perimeter of individual columns.

Hume Dam Spillway Southern Junction Filter and Drainage Works

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Search Results: “” — Page 1

Kate Robilliard, Kristen Sih