This paper provides the insight of one practitioner into the process and application of Dam Safety Risk Assessment. The ANCOLD Guidelines on Risk Assessment provide a reasonably comprehensive outline of the key tasks involved in the risk assessment process. The intent of this paper is not to rehash the Guidelines but rather to discuss some of the practicalities of completing a dam safety risk assessment and highlight some key learning’s gained from a wide range of projects for a number of different owners.
The paper includes a brief overview of each component of the risk assessment process as well as some of the advantages and disadvantages of the various approaches to completing a risk assessment project.
2011 – Dam Safety Risk Assessment – A Practitioner’s Perspective
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T. Mortimer, J. McNicol, P. Keefer, W. Ludlow
CS Energy’s Kogan Creek Coal Mine located in the Surat Basin in Queensland, services the 750MW coal fired, Kogan Creek Power Station. Strip mining generates large volumes of mine waste which is typically used to construct waste dumps. Recent work at the mine has focused on using mine waste to construct an ash storage facility to store ash that is piped over 5 km from the power station as a dense phase slurry. The use of mine waste to construct the ash storage facility provides significant cost and time savings, however a range of design, construction and operation issues needed to be addressed to operate a facility of this type.
This paper describes some of the key design, construction and operation considerations for the ash storage facility. Design considerations include pipeline transport through environmentally sensitive areas, addressing the stability of the embankment and the use of a partial LLDPE geomembrane lining system to reduce the risk of seepage from the storage. Construction considerations include post construction (pre ash deposition) floor treatment to reduce potential settlement. Operational considerations include ash slurry deposition, water management of the decant pond and progressive rehabilitation of the final landform.
2011 – Design, Construction and Operation of a Partially Lined, Ash Storage Facility Constructed from Mine Waste
G. Hadzilacos, ML. Ng, K. Taske, A. Small and B. Loney
Alteration of flow patterns by constructing a dam may have an irreversible impact on ecosystems depending on the timing, duration and frequency of these flows. As part of an Environmental Impact Study, carried out for a proposed mining operation in Australia that included an earth dam on a pristine ephemeral creek, an appropriate waterway management scheme was proposed that required the establishment of measurable instream flow requirements. This paper describes an environmental flow analysis (EFA) carried out to identify flow regimes that achieve the desired ecological outcomes for the affected waterways. The EFA methodology was based on the range-of-variability approach using a calibrated rainfall-runoff model to form the hydrologic basis. The study established a relationship between flow components and ecological variables based upon which the flow requirements were estimated using a simple methodology.
2011 – A case study of an initial Environmental Flows Assessment for an earth dam on a pristine stream in Cape York
Nanda Nandakumar, Janice Green, Rory Nathan, Kristen Sih& Robert Wilson
A detailed assessment of hydrologic risk was undertaken for Hume Dam. Data available and relevant to the hydrologic risk assessment were collated and assessed. The catchment was divided into 35 different sub-catchments, each with its own set of parameters that characterised the local hydrologic response. Recorded streamflow was used to calibrate the flood response of selected gauged sub-catchments, and a combination of historic and synthetically-derived data was used to validate the model and loss parameters. The 35 models were combined into a single catchment-wide model. A Monte Carlo approach was adopted for the validation of the models and the derivation of Hume Dam inflow and outflow frequency curves. A range of PMFs which satisfy ANCOLD’s definition of the PMF were also estimated. The PMPDF outflow was estimated to be 7,600 m3/s which can be passed by the dam. Depending upon the assumptions made, the peak PMF outflow was estimated to be in the range from 10,300 m3/s to 14,900 m3/s
2011 – Assessment of Hydrologic Risk for Hume Dam
M. A. Hariri Ardebili, M. Akbari and H. Mirzabozorg
This paper presents a study on the effects of incoherence (considering the Harichandran and Vanmarcke coherency model) and wave-passage (considering various wave velocities) on the nonlinear responses of concrete arch dams . A double curvature arch dam was selected as numerical example, the reservoir was modeled as incompressible material and the foundation was modeled as a mass-less medium. Ground motion time-histories were artificially generated based on a Monte Carlo simulation approach. Four different models were considered in the generation of ground motions; Uniform excitation; Just incoherence effect; Just wave passage effect; and finally take into account both incoherence and wave passage effects. It was revealed that modeling incoherency can have significant effect on the structural response of the dam by modifying the dynamic response of uniform excitation and inducing pseudo-static response. Also, it was concluded that incoherency effect overshadow wave passage effect and results caused by wave passage effect are close to the results of uniform excitation.
2011 – Comparison of wave passage and incoherence effects on nonlinear non-uniform excitation of concrete arch dams
Alex Gower, Graeme Mannand Peter Hulcup
The Water Corporation is the principal dam owner in Western Australian with a portfolio of 70 dams. Many of these dams are more than 30 years old and were designed and constructed prior to the writing of most occupational health and safety legislation and associated regulations and standards. Achieving compliance with these regulations and standards on the older assets has led to increasingly complex procedures and increased costs to undertake what were previously routine inspection, operation and maintenance tasks. In some cases achieving compliance has become impractical and modification to the assets is required.
This paper discusses a range of different safety issues, hazards and challenges faced at dams in Western Australia. These include prevention of falls from height, rescue of injured personnel within intake towers and drainage galleries and public access on the dams. Solutions adopted to improve safety and security for operators and the public are presented.
2011 – Safer Access at Water Corporation Dams