ANCOLD Bulletin No.114 (April 2000)
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Papers 2000
2000 – Risk Assessment and Dams – Is it Safe?
Learn moreS.G. McGrath
The use of risk analysis for dam safety is becoming more widespread. Dam owners are increasingly aware of the need for information on current and emerging practices from the world scene to determine how to proceed with the use of risk assessment. The paper summarises the findings of a Churchill Fellowship study into risk assessment for dam safety management. Dam owners, regulators and consultants from the United Kingdom, France, the Netherlands, Norway, Sweden, the United States and Canada were consulted for the study. Conclusions are drawn from the findings and recommendations made for future development.
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Papers 2000
2000 – Revising the Method for Estimating Probable Maximum Precipitation in Tropical Australia
Learn moreDavid Walland
The entire historical record of rainfall archives held by the Bureau of Meteorology over the region of Australia affected by tropical storms has been examined and the extreme storms have been extracted. From this database, we account for site specific effects (moisture and topography) from each of the storms, allowing us to compare storms amongst each other. This then allows us to construct a theoretical maximum precipitation in a generalised sense. By then returning the site specific information for a particular region, we can infer the probable maximum precipitation at this location.
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Papers 2000
2000 – Embankment Dam Rehabilitation with Granular Filters
Learn moreMark Locke, Buddhima Indraratna, Phillip Cummins and Gamini Adikari
ABSTRACT: Australia has a large number of older embankment dams, which have been in service and performed adequately for over 50 years. However, current industry practice in embankment dam design predicts that the granular filters within these dams may not be adequate. This may require refurbishment of the dam by retro-fitting a new filter to ensure the continued safety of the structure. This paper outlines the potential problems with older embankment dam designs, and the reasons for constructing a new filter. Potential problems may include inadequate or non-existent filters, risk of failure due to earthquake, piping, or excessive foundation seepage. Design methods for granular filters are described briefly, concentrating on whether an existing filter is adequate, and the potential improvement by constructing a new filter. Construction issues for placing filters on existing dams are also discussed.
A new analytical method, developed to describe the time dependent erosion and filtration within embankment dams, is described briefly. The model predicts particle erosion, transport and retention based on fundamental fluid mechanics and geotechnical concepts. The application of this model to the design of filters for new and existing dams will be described. The predictions of such analytical modelling can give a designer a significantly clearer picture of the purpose of a granular filter, the extent of core erosion that can be expected, and the effect of retrofitting a new filter to an existing dam.
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Papers 2000
2000 – Tailings Dam Rehabilitation at Kidston Gold Mines
Learn moreP.J. Ritchie and N.A. Currey
Kidston Gold Mines commenced operations in 1984 and built a dam to safely store the tailing waste from the ore processing. The dam was progressively raised 5 times (3 downstream and 2 centreline lifts) and has an active surface area of 310 hectares; stores 66 Mt of tailing and is 32 metres high at its maximum height. The dam was decommissioned in September 1997.
Rehabilitation planning for the tailing dam commenced in 1994 with an 11 hectare direct revegetation trial established in March of that year. A 40 ha trial was established in 1998. Both sites have been the subject of intensive scientific research by the (University of Queensland) Centre for Mined Lands Research group. This research assisted in understanding the issues of revegetation stability and sustainability, biological cycling, soil chemistry and surface erosion.The aims of rehabilitation is to meet the Queensland Department of Mines and Energy (DME) key closure criteria. These include; creating a stable landform, not only for the dam wall structure but also of low surface erodibility, maintenance of acceptable downstream water quality by controlling poor quality seepage and runoff and by meeting an acceptable final end land use criteria for the structure.
Ongoing research is addressing the long term hydrology of the tailing dam with an aim towards understanding the overall water balance. Three consulting groups are involved in what is considered to be a novel approach. Evapotranspiration rates from pasture and tree species have been measured during the 1999 wet and dry season. This information, along with climatic and soil suction data is then used as one of the key parameters for the unsaturated zone modeling. One output from the “Soilcover” model is seepage into the saturated zone in the tailing dam. Water movements in the saturated zone are being modelled using Modflow. The acid oxidation potential for the dam is also being evaluated in light of the long term water movements in the saturated and unsaturated zones of the dam. This process will allow short and long term prediction of dam seepage quality and quantities.
The geotechnical stability of the final dam wall structure as defined by the Factor of Safety, ranged from 2.0 to 2.3, which meets the long term DME recommended stability target FOS of 1.5 for slopes.
In order to evaluate the impact of metal toxicities in grazing cattle, a grazing trial has been established on the pasture covering the surface sediments of the tailing dam. This work is being supported by the Qld EPA, Qld DME, Qld Health and the NRCET, and will assist in understanding metal uptake in grazing animals on rehabilitated mined lands.
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Papers 2000
2000 – The Victorian Water Industry Seismic Network: Risk Management and Emergency Management Outcomes
Learn moreW.G. Peck
The Victorian Water Industry Seismic Network was substantially upgraded in 1999. This paper will look at the design and outcomes of the seismic network from a risk management and emergency management perspective. Funding issues for a diversified network providing benefits to a range of clients within the one industry group will also be discussed.
Prior to 1999 the Victorian seismic network had been developed on an ad hoc basis resulting in an incomplete level of seismic coverage throughout the state. The upgraded network now provides sufficient coverage to provide an intensity based alarm service for all contributing Victorian Water Authorities.
Community expectations of essential service providers such as the water industry are that they will carry out their own risk management to provide for service continuity and sustainability and that they will contribute to emergency management processes because it is in their own best interest to do so.
The risk management model looks at creating resilient communities through planning for the four R’s. Reduction, Readiness, Response and Recovery. The Seismology Research Centre’s Earthquake Preparation Alarm and Response system (EPAR) deals with the four R’s in relation to seismic hazard.
The EPAR system contributes to the risk management processes of identifying risks and vulnerability’s; potential consequences; and mitigation opportunities. The EPAR system additionally contributes to the emergency management processes of crisis response, impact assessment and recovery.
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