Tommie Conway, Katherine Miller, Peter Hill
The ‘Black Saturday’ fires of the 7th of February 2009 and the continuation of fires over the following weeks had devastating human, environmental and financial costs for Victoria. Many of Melbourne’s water supply catchments and assets were burnt and the major harvesting catchments were seriously threatened. This paper highlights the need for owners and managers of catchments, dams and associated infrastructure to better understand and plan for the potential impacts of fire, given its predicted increased likelihood and severity due to climate change.
The paper will share Melbourne Water’s recent experiences of the fire, the scale of the impact to the business in terms of assets damaged and catchments affected, the extent of the burn and the threat that was faced. It will describe Melbourne Water’s experience with the United States Burnt Area Emergency Response (BAER) team to expediently map the severity of the fires, to identify areas of concern and prioritise fire recovery works. Of interest to those involved in risk management will be the discussion of the construction flood risk analysis at Tarago Reservoir which was revisited due to severe fire damage to the catchment.
Keywords: fire impact, Melbourne’s water catchments, BAER team, hydrology, Tarago, construction flood risk analysis
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Thomas Vasconi, Glen Fergus
Abstract: This paper describes the design of an 80 m-high stepped chute spillway, in gabion material, that will be constructed on a tailings storage facility dam of a mine in South East Asia. This dam, constituted of two cells, will be raised progressively via a series of intermediate crest elevations as mining proceeds, and each lift will be equipped with an operational spillway. The design of such spillways was challenging since it had to integrate local topography configuration, dam design, water balance, wall raise sequence and structure interdependency parameters. The design included flood routing, spillway sizing, stepped spillway design, followed by hydraulic and civil/geotechnical computations. Challenging design aspects included optimizing the stepped spillway structure costs in light of the structure’s short service (estimated to be less than 5 years), and ensuring the stability component. The design incorporates an innovative solution which allows reduction in the rockfill quantity of up to 40% with associated cost benefits, and sustainability in terms of material usage. The lessons learnt in applying this innovative design are useful for other sites requiring adaptive construction and short service life spillways.
Keywords: tailings dam, stepped spillway, hydrology, hydraulics, mine water management, gabions.
Dr Azan Khan, Ahmad Nasir, Kumud Kandel, Jaya Kandasamy, Hadi Khabbaz, Mahub Ilahee
Cracking in the clay core of embankment dams is important to dam safety because it can cause seepage through transverse cracks and with excessive seepage cracks may begin to erode the soil on the sides of the crack. If there are no filters to control this erosion, the erosion may progress to form a pipe, eventually leading to breach of the dam. Recent climate change has resulted in long term drought conditions in various parts of Australia, especially west of the Dividing Range. The prolonged drought conditions can lead to the loss of moisture content in the clay core causing cracking of the core material. The current research is investigating a relationship between long term drought condition and loss of moisture content in the clay core. This paper presents the loss of moisture content in the clay core of three dams in Australia due to global warming. A rigorous finite element modelling has been conducted to capture the moisture content changes in a typical large clay core dam.
Keywords: clay core, dams, climate change, moisture content
There are many international guidelines, state regulations and technical standards relating to tailings disposal. In addition, the larger mining companies have their own in-house standards and design rules with competent personnel in charge of their operations. Sound embankment design methods can be used by most designers familiar with earth dam design.
The paper gives a listing of many of the current sources of information and guidance available, with some comments by the author on their perceived relevance to the Australian mining industry. Despite the availability of a number of other guidelines at the time, the need for Australian Guidelines was recognised in the mid 1990s and the reasons for the development of the 1999 ANCOLD Tailings Guideline are explained.
Perhaps the best recognition of the need for the original ANCOLD guideline is the degree to which it has been adopted since publishing the 1999 edition. It is in almost universal use in the Australian mining industry and is recognised as providing appropriate and acceptable standards by all state governments. Its use is recognised and sometimes even specified by a number of neighbouring countries and it is also recognised internationally when used by Australian companies with overseas operations.
The reasons for this wide acceptance are described. However, there are some areas where more recent developments have led to the Guidelines becoming dated and improved international guidelines have been published since 1999. The need for a revised ANCOLD guideline and its elevance is then described.
Keywords: Tailings, dams, mining, guidelines
Khanh (Ken) Nguyen, Peter Allen
There is community concern regarding the potential for dams to fail and threaten lives. In Queensland, the Water Supply (Security and Reliability) Act 2008 provides for the regulation of dams whose failure could cause loss of life. Other consequences of dam failure such as interruption of services, economic loss and damage to the environment would also be of paramount importance for the safety management of our dams in the current climates of change.
In 2003, the Bureau of Meteorology (BoM) revised the Probable Maximum Precipitation (PMP) estimates for both short and long durations of extreme rainfalls for northern Australia. As a consequence, the majority of cases resulted in a significant increase of extreme flood estimates for many river catchments in Queensland. Subsequent studies by the BoM have investigated the potential impact that climate change might have on PMP estimation.
This paper examines the current progress of the Queensland Spillway Upgrade Program, by discussing the current regulatory environment and identifying a number of hydrological issues which may require further investigation for Queensland conditions.
Keywords: Spillway Upgrade, Acceptable Flood Capacity, Flood Discharge Capacity.
Gavan Hunter, Chris Chamberlain, Mark Foster
Hinze dam, an extreme hazard storage, is under the authority of Seqwater (Southeast Queensland) and is principle potable water storage supplying the Gold Coast. Hinze Dam Stage 3, presently under construction, involves raising the existing embankment almost 15m to a maximum height of 80m.
The foundation geology on the right abutment of the main embankment comprises of a deeply weathered sequence of greywacke and variably silicified greenstone and chert. The deeply (and variably) weathered soil profile below the right abutment of the existing embankment presented an unacceptable piping risk for the embankment in its existing condition. Contributing factors included: 1/ the highly erodible extremely weathered greywacke and presence of continuous defects in the weathered soil mass; 2/ the extremely weathered greenstone in direct contact with highly fractured, highly permeable silicified greenstone and chert bodies aligned normal to the dam axis which provide continuous seepage paths through the foundation.
Works were required as part of the Stage 3 raise to address the foundation piping risk. Significant issues for design included: 1/ the depth of weathering extended up to 25to 40m into the foundation.; 2/ extremely weathered and highly erodible greenstone was present below the right abutment of the embankment and extended down to the lower abutment some 50 to 60 m below the existing dam crest; 3/ the reservoir level could not be drawn down during construction and the probability it would be near full supply level during the works was high; and 4/ the variability of strength in the greenstone form soil to extremely high strength presented challenges for excavation.
The options assessed to address the piping risk included a plastic concrete cut-off wall and an upstream blanketing option. The plastic concrete cut-off wall (220m long and up to 50m deep) and deep filter trench was the selected option. The cut-off wall had been successfully completed ahead of time and below budget. The innovative design required excavation through earthfill core of the embankment under full reservoir level and use of a purpose built trench cutter (by Bauer Foundations Australia) for the variable excavation conditions.
Keywords: dam safety, piping, risk assessment, cut-off wall.