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
Anurag Srivastava, David S. Bowles, Sanjay S. Chauhan
DAMRAE is a software tool for performing the event tree risk model computations for dam safety risk analysis. It is being applied by the US Army Corps of Engineers (USACE) and undergoing continued development and testing at Utah State University. DAMRAE is designed to overcome the limitations of existing business risk analysis software. It includes a generalized algorithm for constructing and calculating event trees. A generic project framework provides functionality for considering risk reduction alternatives or a staged implementation of risk reduction measures including obtaining estimates of their cost effectiveness of risk reduction. Evaluations against USACE tolerable risk guidelines are made. A flexible capability exists for obtaining tabular and graphical presentations of estimated risks at different levels of detail.
This paper provides an overview of the structure and capabilities of DAMRAE. It also includes an example screenshots to illustrate its capabilities. Plans for future improvements are summarized.
Keywords: Dam Safety Risk Assessment, Event Tree Analysis, Risk Reduction Measures.
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.
Russell Paton, Peter MacTaggart, Lee Benson
The Nathan Dam project has been identified by the State Government of Queensland as a potential water supply option to facilitate future growth in central Queensland. The proposed storage is located approximately 69 km downstream of the township of Taroom and would have a storage capacity of 1,080,000 ML which would make it Queensland’s fourth largest storage.
The proposed dam arrangement includes a central concrete gated spillway section across the river in order to maximise the storage volume and limit the flood rise upstream such that flood levels at Taroom are not increased during major flood events. A high level fixed crest spillway, to assist in the passage of rare flood events, forms the right abutment portion of the dam wall. It is proposed that the bulk of the concrete sections of the dam be constructed using roller compacted concrete (RCC).
The investigations to progress Nathan Dam are complicated by the existence of the Boggomoss Snail (Adclarkia dawsonensis) within the proposed inundation area. The snail is listed as a critically endangered species under the Environment Protection and Biodiversity Conservation Act 1999 (EPBC Act), and a proportion of the snail’s known population is located on a Boggomoss (the colloquial name for an artesian spring) that will be inundated should the project proceed.
SunWater has engaged Australia’s foremost expert on land snails to design a translocation process aimed at relocating the species to alternative habitat outside the inundation area. The process will seek to not only protect the snail from the dam development, but to increase both its numbers and distribution thereby reducing risks to the currently isolated population from threats such as fire and predation. It is the first time in Australia that such a trial has been attempted, and SunWater is working closely with the Federal Department of Environment, Water, Heritage and the Arts (DEWHA) to ensure that the process is consistent with their policies and guidelines.
The paper will discuss the engineering and environmental challenges of the dam and how the Environmental Impact Study process can influence the delivery of a project.
Keywords: Nathan Dam, Environment, Engineering
John Prentice, Jim Barrett, Dr Martin Mallen-Cooper
Located in south-eastern Australia, the River Murray has provided almost a century of regulated water supply, bringing immense benefit to human welfare during this period. However a healthy river is recognised as being essential to its sustainable future. With this in mind, in March 2001 the Murray- Darling Basin Ministerial Council approved several actions including “a structural works program to provide passage for migratory fish, from the sea to Hume Dam”. The paper outlines progress to-date on this ambitious fishway construction program.
The program involves building fishways on twelve of the fourteen weirs on the river, and at the barrages. The criteria established, to enable passage for all native fish species known to regularly migrate, are detailed. The important lessons learned from earlier fishways, and confidence gained from the Torrumbarry Weir vertical-slot fishways constructed in the 1990’s, have been applied to the new designs. Part way through the program, important changes were made to the design criteria, and the reasons for doing so are described.The fishways constructed at the barrages near the Murray mouth, and their need to respond to estuarine and lake conditions, are recognised. In addition, Mildura and Euston Weirs vary from the other River Murray structures, and their special fish passage consideration is described.
In achieving a successful outcome to date, the important role of river managers, engineers and scientists working together with design consultants is acknowledged. A tri-State monitoring and assessment program has been established to enable the questions about the short and long term outcomes of the program to be answered. The beneficial results to date are detailed.
This paper outlines the steps and challenges involved in delivering this decade long program, scheduled for completion in 2011.
Keywords: Sustainable, fishways, fish passage, native fish, hydraulics, fish monitoring, Murray.
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.