Graeme Maher, Richard Herweynen, Martin Mallen-Cooper and Stuart Marshall
Increasing awareness of the environmental impact of dams means that fish passage is emerging as a critical issue for both existing and new dams in Australia.
The fish passage and outlet works for Wyaralong Dam, a new dam currently under construction, required accommodation of large ranges of head and tailwater levels. The solution that has been adopted, a bi‐directional fishlift using a single hopper with trapping for downstream fish movement occurring within the intake tower, is a world first. The solution required the innovative integration of a number of existing technologies to create a system which is necessarily complex, yet reliable and effective.
The paper incorporates discussion of the critical design constraints, the biology of fish passage, the process adopted to reach the concept solution and a description of the final design including its integration with the outlet works. A number of design issues and their solution are discussed in detail, particularly those associated with dealing with the complexity of the design constraints and how the components of the solution were integrated into a seamless design.
The paper will be of use to those involved in the process of providing fish passage on both existing and new structures that obstruct river flow.
A Bi-Directional Fishlift – An Innovative Solution for Fish Passage
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Glen Hobbs, Robert Rigg, Alan Hobbs, Adam Butler
Maintenance errors and associated non-conformances are becoming increasingly recognised as a source of system failures in a wide range of industries. Research in other industries has shown that errors often arise in response to local factors beyond the control of the maintainer. Various dam ‘incidents’ have been attributed to maintenance errors. In Australia we have been fortunate with few serious dam safety events. However, the dam operating and maintenance environment is changing dramatically.
A survey of dam maintenance personnel was recently undertaken in Australia. The survey was in the form of 49 questions that asked participants to state how frequently a situation occurred. This survey format has previously been used in other industries; thus allowing a comparison of dam maintenance with other high-risk industries such as rail infrastructure, oil and gas, and airline maintenance.
A number of ‘error-producing’ conditions have been identified and survey results indicate a high level of poor procedures/documentation and supervision; highlighting the need for accurate and appropriate manuals and supervision of tasks. These and other factors are leading to instances of maintenance non-compliance, which may threaten the reliability and safety of equipment. The survey has revealed that trade training needs to be addressed. However, occupational safety issues are low; indicating a positive approach to a safe working environment. The paper also discusses the responses to specific maintenance questions relevant to the dam industry.
Keirnan Fowler, Peter Hill, Phillip Jordan, Rory Nathan, Kristen Sih
Although there are considerable uncertainties in the science of climate change, there is a growing recognition of the importance of the issue. Incorporation of climate change impacts is now required in policy guidance from several government authorities and it is prudent risk management to consider the effects of climate change in planning for water resource infrastructure, including assessment and design of dam upgrades. This paper describes the potential impact of climate change on extreme flood estimates and provides a case study for Dartmouth Dam in south-eastern Australia. Three inputs to flood estimation were considered according to the projected impact of climate change; namely design rainfalls, modelled losses and initial reservoir level. The relative influence of each of these factors is explored. Rainfall and losses had a similar (and opposite) influence on results and for this dam the reservoir level prior to the flood event had the largest influence on results. This case study demonstrates that the insights of climate modellers and hydrologists need to be integrated in order to provide defensible estimates of the impact of climate change in flood hydrology studies. Credible projections of changes in design rainfall intensities are required for the full range of exceedance probabilities across Australia.
Application of Available Climate Science to Assess the Impact of Climate Change on Spillway Adequacy
David Ryan, Sean Fleming
The Connors River Dam and Pipeline Project comprises the construction of a 367,540 ML storage on the Connors River located in central Queensland and a 130 km pipeline capable of delivering annually 49,500 ML of high priority water to the rapidly expanding Central Queensland Coalfields. The dam also has the capacity to supply water for the downstream agricultural sector.
Key outcomes of SunWater’s recent business case investigations included the identification of a strategy that would deliver the project in parallel with the construction programs currently being developed by the coal mining sector, the delivery of a quality product with high certainty cost and the ability to supply water at a commercially attractive rate. Construction activity is currently scheduled to commence in mid 2011, with commissioning of the works early 2014.
The paper outlines the project details, the design features of the dam and pipeline and the contract strategy adopted in an attempt to deliver the project on time and within budget.
Keywords: Roller Compacted Concrete, Early Contractor Involvement, Design and Construction.
Rick Friedel, Len Murray, Gerrad Suter, James Penman, James Watt, Hendra Jitno
The Hidden Valley tailings storage facility (TSF) has set a new precedent in environmental management of tailings in Papua New Guinea (PNG). Modern mining in PNG arguably began with the development of Bougainville Copper in the late 1960s, and continued through to Ok Tedi, Porgera, Lihir, Misima (and others). These mines have proceeded with deep sea or riverine tailings deposition, rather than construction of a tailings dam to retain the mine waste within an impoundment; as is the practice throughout the majority of the mining industry.
The Hidden Valley TSF is comprised of two large earth and rock fill dams, raised by the downstream method. Starter dam construction was completed in 2009. At final height the Main Dam will be one of the highest tailings dams in the world. The dams are constructed of pit waste and therefore have the dual function of storing tailings and waste rock.
Construction of the starter dams and subsequent raises is complicated by conditions at the site. Water management was, and remains, the dominant issue. High rainfall, weak erosive soils, material availability, dense vegetation and remoteness of the site provide constant challenges to construction. The Observational Approach to construction was recommended by the designers and adopted by the mine operator. This involves a knowledgeable pre-assessment of what is likely to change and having contingency plans to deal with possible major issues. This approach allows changes to the design during construction so the “as-built” product is suited for the site, fit for purpose, and remains consistent with the overall intent of the design.
The TSF has been in operation since August 2009 and monitoring data of the structures has been collected during construction and operation. This data is reviewed to confirm design assumptions and assess dam performance.
Personnel involved with this project combined their experiences working in the PNG environment and dam building from other locations. This process led to close interaction between the mine operators, designers and construction teams. Team work and diligent construction practices were and will continue to be necessary to construct and operate the pioneering TSF in PNG.
Peter A Ballantine, Christopher V Seddon
Massingir Dam, constructed in the late 1970’s on the Olifants River in Mozambique, is a 48 m high zoned earthfill dam. Due to various safety concerns, the dam was operated at a reduced full supply level of 110 masl, compared to the design full supply level of 125 masl. Between 2004 and 2006 remedial works were undertaken, including the construction of a berm on the downstream face of the dam, grouting and drainage of the foundations and installation of the spillway crest gates. From December 2005 the storage level of the dam was allowed to increase.
On 22 May 2008, with the reservoir storage level at 122.43 masl and the gates on the outlet conduits closed, the reinforced concrete conduits failed at the downstream end, releasing an estimated 1,000 m3 /s of water into the Olifants River.
A 2-D finite element analysis was undertaken in order to establish the safe load bearing capacity of the as-constructed conduits. On the basis of the analysis, it was concluded that the original design did not take proper account of the pressure that would develop within the thick concrete sections of the conduit. In view of assumptions regarding the load paths, the reinforcement was not placed in the most appropriate positions.
This paper describes the events leading up to the failure of the conduit, presents the findings of the investigation into the failure and makes recommendations on the basis of the findings.