Anna Hams, Lindsay Millard, Elizabeth Jackson, Zara Bostock, Helena Sutherland
The Queensland dam regulator requires that dam safety risk during construction must not increase from its existing profile. The Stage 2A upgrade of Ewen Maddock Dam required excavation of its homogeneous embankment to retrofit chimney and filter blankets, and also the construction of a concrete parapet wall. Due to the constraints of the embankment profile and a constricted site, it was necessary to excavate the downstream face of the embankment. This excavation increased the risk of embankment failure due to overtopping, piping and instability. This paper discusses the measures taken to manage those dam safety risks, and includes:
● use of a temporary system consisting of six large siphons to regulate the lake level to a Restricted Full Supply Level (Restricted FSL). This encompassed the optimisation of lake level and capacity of siphons required to balance competing risks; dam safety, environmental, community and water security. This optimisation was based on a probabilistic assessment of hydrological inflows and lake levels, the development of a flow management plan;
● implementation of a Dam Safety Management Plan which outlined the roles and responsibilities for
managing dam safety during construction at each pre-determined lake level trigger levels. This includes how the contractor was involved to ensure quick response from the “eyes and ears on the ground”; and,
● development of recommended construction methodologies including a “rolling front” and placing
filters vertically to increase production, maintain quality and limit the extent of embankment excavation underway.
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Richard Mannix, Michael Cawood, Joseph Matthews, Siraj Perera
Guidance material available to dam owners both domestically and internationally on testing dam safety emergency plans (DSEP) and running exercises is relatively general in nature. Guidance specific to dams that assists owners to design risk informed exercise scenarios tailored to their dam(s) total risk profile and the broader context in which the consequences of dam and operational safety failures would materialise, is limited.
This paper presents a framework that guides dam owners through a progressive scenario development process that enables the systematic identification of both dam and operational safety matters that require exploration as part of DSEP exercising. This level of rigour in guidance material has, until now, been missing and is particularly relevant in the context of dam owners demonstrating due diligence and SFAIRP imperatives while also bringing dam safety management closer to achieving the safety case.
Reena Ram, Siraj Perera, Mark Pearse, John Pisaniello, Shane McGrath, Joanne Tingey-Holyoak, Peter Hill
Dam construction in Victoria commenced in the 1850s and there are over 8,000 dams currently regulated by the Department of Environment, Land, Water and Planning (DELWP). Dam ownership spans across state owned water utilities and local government authorities to privately owned hydro-electricity generators and farmers.
Victoria was one of the first states in Australia to adopt risk-informed principles in the management and regulation of dam safety. A recent review of the State’s dam safety regulatory framework included a comparative analysis of Victoria’s dam safety arrangements with other regulatory regimes within Australia and overseas, including a total of 16 jurisdictions. A similar review was conducted in 2010.
The objective of the 2019 review was to examine the effectiveness of dam safety regulation in managing dam safety risks in Victoria and to assess the extent that dam safety regulation was consistent with good practice so that improvement opportunities could be identified.
This paper discusses the processes adopted in comparing various regulatory models, identification of good international practices and opportunities to achieve improved public safety outcomes for dam owners and regulators. In particular, it outlines how the State’s journey in progressively reducing dam safety risks over the years can be further strengthened.
Mark Pearse, Mark Foster, Peter Hill, Sam Banzi, Muhammad Hameed, Benson Liu
Determining which risk control measures are required is one of the top issues for dam owners as they contend with limited resources generally and capex in particular. The key issue addressed in this paper is how a dam owner can both identify the control measures that they should implement and demonstrate that they are acting reasonably and responsibly. The Framework developed in this paper provides a practical and transparent way to address the relevant matters that are required to be considered under common law, work, health and safety (WHS) legislation and the NSW Dams Safety legislation for determining whether a risk control measure is reasonably practicable. It provides dam owners with a transparent and defensible way of both identifying the controls and demonstrating that they are acting in a reasonable and responsible manner.
Dr Mark Leonard
The quantification of the 85% and 95% hazard fractiles, as required by the ANCOLD 2019 Guidelines for design of dams, is investigated. It is found that there are four independent sources of uncertainty in the PSHA input models that have a significant effect on the hazard. So all four need to be quantified, particularly for Extreme and High A consequent dams. It is also found that the uncertainty of many of the other parameters, which are routinely included in probabilistic seismic hazard assessments, have minimal effect on either the mean or the higher fractiles so do not necessarily need to be routinely included. The complexity of the input models required to satisfy the new standards are substantially higher than those routinely used in prior decades.
Claudia Smith, Shannon Dooland, Adam Broit, Rachel Jensen, Samantha Watt
The estimation of real consequences from dam failure that directly link to the overall likelihood of the failure is a challenging task, particularly in data sparse locations. Previous regional methods have often relied on simplistic assumptions without consideration of the true joint probability of the volume of flow in the downstream tributaries of concurrent catchments. As a result, concurrent downstream flooding directly impacting the consequence in dam break assessment scenarios may be misrepresented. More recently, the adoption of streamflow-based joint probability has become the standard, particularly where consequence estimation is used within the context of risk assessment. This paper progresses the work completed by others to establish a practical treatment method based on rainfall analysis where suitable streamflow information is unavailable. A case study is also presented where this method has improved the understanding of the risk profile associated with a coastal storage based on a better estimate of the likely flood concurrence within the storage and downstream catchments.