Damon Miller and Grant Jones
Mt Buller Alpine Resort has significant constraints on its capacity to store and supply potable water during times of peak demand, which impacts the ability to sustain and grow visitation to the resort, limiting optimal functioning and future development of the resort.
A proposed new 100 megalitre dam would primarily supply the resident and visitor populations with a reliable potable water source while also maintaining through snowmaking, the Resort’s amenity and functionality during winter for skiing and snow-play.
Standard dam engineering criteria of technical feasibility and environmental impact influenced the site selection and design of the new off-stream storage whilst additional key drivers unique to an alpine resort, framed around impact to existing skiable terrain and resort functionality, were critical to satisfy the resort stakeholders. The need to minimise the visual impact of the dam and integrate with the resort environment was also of high importance.
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William Ziegler and Heather Middleton
This paper presents the collation of over 20 years of data on vertical and horizontal movements around Cataract Dam in the Southern Coalfield of New South Wales, reporting subsidence that continues 25 years after extraction in the area ceased. The occurrence of increased vertical movement over old goaf areas as the result of extraction in the same seam at greater than 1km distance has been observed. Together with a change in the behaviour of measured head of water 6 years after extraction ceased in the area. These points raise the question, how long should subsidence monitoring continue after extraction has ceased in areas of important infrastructure?
Wark, Bob; Thomas, Louise
This paper discusses the rating curves developed for several case studies from the Pilbara and Kimberley, including the Harding Dam, Moochalabra Dam and Ophthalmia Dam. The paper will discuss the impact of underestimated rating curves on the design of infrastructure. An example has occurred at Harding Dam where the pump station was designed to be inundated at a 1:100 AEP and this is now estimated to occur at a lower AEP. The paper will also discuss methods to improve the accuracy of rating curves and the challenges associated with determining accurate rating curves.
JN Rossouw, AHM Görgens and PC Blersch
Shallow lakes or reservoirs generally exist in either of two stable states; a clear water state dominated by rooted water plants, or a turbid state dominated by free floating algae. A dramatic event can switch a shallow reservoir from one state to another. Voëlvlei Dam, a relatively shallow off-channel storage reservoir in the Berg River catchment, South Africa, switched from a stable, clear water system to a turbid, algal dominated system when it was severely drawn down during a drought in the mid-2000s.
It appears that there is tipping point beyond which a shallow reservoir can switch from one stable state to another and that there are buffers that maintain it in a specific state. Voëlvlei Dam is a good example of what such a switch might be (low water levels and high wind mixing) and what buffers (change to bottom-feeding fish species) may maintain it in the new state. It is only by understanding the hydrodynamic behaviour of a shallow reservoir that one can predict what these switches and buffers could be. Complex hydrodynamic modelling and comprehensive fish monitoring will facilitate more informed decision making and better management of reservoirs.
This paper describes the mechanisms that lead to the switch and how it can be prevented by developing an understanding of the hydrodynamic behaviour of shallow reservoirs through hydrodynamic water quality modelling.
Andrew Richardson, Stephen Farrelly and Phil Farnik
In 2012 an update to the Portfolio Risk Analysis (PRA) was undertaken by State Water Corporation for its 18 major dams in New South Wales. The updated portfolio level risk analysis of all the dams has taken account of the completion of major components of the 2006 dam safety upgrade program, while also incorporating continued engineering research into dam safety performance. This paper will provide an overview of the approach, the challenges faced in the process and it will highlight the innovative advances made representing industry best practice. Some future implications and directions will also be discussed.
The three main components of the PRA update in 2012 have included a significant amount of dam break hydraulic modelling including revised hydrology and flood inundation mapping delivered in-house by State Water with consultant support. The Consequence Assessment was developed with a spatial link to natural flooding and dam failure consequences by Sinclair Knight Mertz (SKM), while the third element in producing the event trees, risk analysis and PRA reports was undertaken by consultants GHD. Peer review of the PRA process and reports and additional technical review of the failure modes and event trees by a panel of industry experts provided the necessary independent input and oversight required by the NSW Dams Safety Committee.
State Water’s PRA update builds on the large body of work undertaken for and since the last PRA in 2002. The update process has applied a systematic and quantitative approach across the Portfolio that provides a robust basis for managing dam safety risk. The results of the PRA have identified further work required to investigate and assess the need for dam safety upgrade options for non-compliant dams. State Water’s investment in the PRA has produced a risk-based position on each dam in the portfolio that can be used to identify a range of measures in a revised dam safety upgrade program for the future.
Shane McGrath, Phillip Cummins, and David Stewart
Dam owners and regulators now commonly use risk assessment techniques to assist with decision making for an individual dam or a portfolio of dams. In many cases risk assessment is used to select an optimal course of action in relation to ongoing safety performance of dams, including the achievement of public safety objectives. However, whilst it is an important tool, the use of risk assessment alone is not sufficient to establish that a dam is “safe”.
In modern organisations, business objectives are achieved through a systematic approach to management which described simply sets out what needs to be achieved, how the required outcomes will be delivered and audits the process and results.
In hazardous industries such as mining, chemical, nuclear and dams, it is necessary to reliably achieve business objectives such as product volumes, unit costs and workplace health and safety alongside public safety objectives. In the dams industry, dam safety management systems are now being implemented to document how the organisation satisfies its corporate and business objectives, governance responsibilities and risk management processes.
It is also common in hazardous industries that a “safety case” is required by regulators to demonstrate that the owner has identified what could go wrong at its facility, what controls are in place and that there is a system in place to ensure that the controls are reliable. Whilst dam owners may rely on a dam safety risk assessment to meet regulatory obligations and demonstrate due diligence, the results of risk assessments are not routinely documented sufficiently to satisfy a “safety case” and therefore will not fully meet the organisation’s requirements.
Many dam owners are also responsible for the safety management of other hazardous facilities, such as urban water and mining corporations which typically manage hazardous chemical installations and hazardous or toxic waste disposal. For such organisations, the corporate awareness and processes should already exist to extend the “safety case” philosophy to the management of their dams.
This paper sets out the importance of a dam “safety case”, the essential elements of a safety case and its relationship to the dam safety management system.