Chris Nielsen, Irene Buckman
As individuals, we are concerned about how a risk affects us and the things we value
personally. We may be willing to live with a risk if it secures us certain benefits and if the
risk is kept low and clearly controlled. We are less tolerant of risks over which we have little
ANCOLD’s risk assessment guideline (2003) identifies an individual risk threshold as being
one where “the dam safety risk to an individual should be close to the average background
risk of the population”. This is a principle of equity, where “all individuals have
unconditional rights to certain levels of protection” (HSE, 2001). The definition of
population at risk applied to Queensland’s referable dams (DNRME, 2018), being
individuals within a residence or workplace and typically not participating in any risky
activities such as driving a vehicle or walking through flooded waters, provides further
justification of this right.
In practice addressing societal risk tolerances and duty of care considerations may result in
individual risks being substantially lower than the thresholds. This may not always be the
case and, irrespective, should not distort the purpose of the individual risk tolerance test;
the principle of equity that drives individual risk tolerability has foundations in our societal
values and is easily and widely understood as a core value. This should be succinctly
described when justifying expenditure on risky infrastructure such as dams.
This poster describes aspects to consider when selecting a threshold individual risk
tolerance. Subject to site-specific considerations of the particular age group of individuals
most at risk, the wider benefit of the dam to society and ALARP, a single threshold
individual risk tolerance of less than 10-5 per annum (or 1 in 100,000 years) would appear
The aspects described are elaborated in the revised Guidelines on Safety Standards for
Referable Dams, soon to be published on the Queensland Government website (RDMW,
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Now showing 1-12 of 37 3483:
Zara Bostock, Helena Sutherland
Ewen Maddock Dam is located approximately 12.0 km west of Caloundra, in the Sunshine Coast area of Southern Queensland. The dam is a homogeneous earthfill embankment dam 10.5 m high and 724 m long. The dam was originally built between 1973 and 1976 and later upgraded in 1982 to raise the ogee spillway crest by 2.44 m to the current Full Supply Level (FSL) of 25.38 m AHD.
Seqwater is undertaking a staged upgrade of Ewen Maddock Dam to address deficiencies identified during the Acceptable Flood Capacity (AFC) Review (GHD, 2010). The consequence category assigned to Ewen Maddock Dam is ‘Extreme’ with a downstream Population at Risk greater than 1000.
Stage 1 construction was completed in 2012 to manage the seepage underneath the dam to reduce the risk of piping and improve embankment stability. Stage 2A involved retrofitting a filter in the existing embankment and raising the dam 1.61 m to 30.11 m AHD using a reinforced concrete parapet wall. Stage 2B involves spillway upgrade works and was split from 2A due to approval constraints.
Stage 2A construction was completed in April 2021, navigating various project and dam safety challenges. This paper presents some practical ways dam safety and risk was managed on the ground from the perspective of both the designer and owner.
Chris Nielsen, Ron Guppy, Gary Hargraves, Robert Fowden
Dam safety upgrade projects of major dams typically involve a large capital investment. It is important that expenditure decisions are based on sound criteria, both technical and non-technical. Independent peer review of technical matters plays a key role in meeting design, construction and safety objectives within practical financial constraints and assuring robust, resilient and reliable project outcomes.
An independent technical review is recommended for all dam projects.
The Queensland dam safety regulator has developed guidelines associated with technical review for dam safety projects that considers scope and limitations, expertise and governance. The guidelines are informed by literature, recent projects, a commission of inquiry, internal and external review and industry feedback. The guidelines are being implemented across major dam safety upgrade business cases through preparation of terms of reference by the Queensland Government’s business planning and implementation entities, who maintain the responsibility of providing assurance to state government projects, as well as the state’s major dam owners.
The terms of reference, supported by the underlying principles in the guidelines, provide a platform for consistent and appropriate application of technical assurance to dam projects in Queensland. Among other matters, governance is highlighted as a critical factor for success as well as clarity of the roles, responsibilities and reporting lines of all parties. The application of both guidelines and terms of reference to recent projects is discussed.
Sonel Reynolds, Alex Gower, Bob Wark
During the outlet works upgrade in 2017 it was found that the valve pit and stilling basin at Mundaring Weir were not founded on rock. Based on these observations and the arrangement of the spillway and outlet works, it was considered that during significant spillway overflow events, a high velocity jet could displace the stilling basin slabs, erode the underlying material, and progress to failure of the outlet pipe and valve pit. A comprehensive risk assessment was conducted to estimate the likelihood of stilling basin slab uplift, erosion of the underlying material, and failure of the outlet works. A geotechnical investigation was undertaken comprising drilling nine boreholes and a program of geophysical downhole logging. Computational Fluid Dynamic (CFD) modelling was used to determine the pressure fluctuations and turbulence intensity over the spillway slab which could lead to uplift. The erodibility of the rock mass material below the stilling basin slabs was assessed using the outcomes of the geotechnical investigations and CFD output, with analyses based on the Kirsten Index and eGSI. A net benefit analysis was conducted to assess whether preventative remedial works were justified. Through this process it was demonstrated that the business risk was low and risk reduction measures were not justified.
Alberto Scuero, Gabriella Vaschetti, John Cowland
Efficiency in water supply reservoirs, even more so in pumped storage reservoirs, requires good water management and minimisation of water losses. With climate change affecting the quantity of water available for supply and power generation, minimising water losses is becoming more and more crucial, and the most efficient way to achieve this critical objective is to line the reservoir with a watertight geomembrane system. With more than 60 years of use, flexible geomembrane systems have proven to be a dependable technology for new construction as well as for rehabilitation. Efficiency can also be increased by covering the reservoir with a floating geomembrane cover to minimise evaporation losses, and by adding value to the reservoir with the installation of floating photovoltaic panel farms on the surface of the reservoir, to provide or increase electrical power generation. This paper addresses these two aspects of efficiency: water loss minimisation, by presenting concepts and advantages of geomembrane liners, and concepts and application
of floating photovoltaic farms with a case history in a water supply reservoir. The concept of a floating
photovoltaic farm on a pumped storage reservoir, and information on available guidelines for geomembrane systems and floating photovoltaic panels, are also presented.
Reza Asadi, Mahdi M. Disfani, Behrooz Ghahreman-Nejad
Rockfill, a granular material with particle sizes usually in the range of 2 cm to 1 m, is commonly used as the main construction material in a range of civil engineering applications such as water and tailings retaining embankment dams. Rockfill’s complex behaviour mainly stems from its inherently large particle size grading on one hand and its discrete and heterogeneous nature on the other hand. The investigation of mechanical behaviour of rockfill requires expensive and time-consuming laboratory testing in large apparatuses, which are scarce. This highlights the importance of numerical investigation techniques such as Discrete Element Method (DEM) in better understanding of rockfill properties. In this paper initially a concise and comprehensive overview of effective parameters on Rockfill behaviour are presented followed by the discussion on analytical and numerical methods for investigation of the mechanical behaviour of Rockfill.
Finally, a combination of Replacement and Bonded-Particles (clusters) methods is proposed so the effects of particle shape and breakage, which are among the most effective parameters, can be adequately investigated. The preliminary results of DEM modelling are also presented which show a good agreement with the expected micro-mechanical behaviour of rockfill.