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
Conrad Ginther, Colleen Stratford
The Wyaralong Dam Alliance (WDA), a consortium of seven engineering and contracting companies, was contracted to design and construct the Wyaralong Dam, which impounds the Teviot Brook 14 km from Beaudesert in Queensland, Australia. The dam is an approximately 500 metre long, 48 metre high Roller Compacted Concrete (RCC) structure built on a foundation generally consisting of massive sandstone with intermittent conglomerate zones consisting of cemented gravels, mudclasts and sands. Geologic features of note with regard to dam stability and long term seepage at the site are dominated by downstream sloping bedding features and conglomerate zones. In addition to the bedding-related features, two predominant vertical to subvertical fracture sets exist. The condition of the vertical fractures ranges from tight and fresh at depth to highly weathered and filled with dispersive clay and gravels near the foundation surface. To provide a durable and effective long term seepage barrier for the dam, an extensive foundation cleaning and treatment operation was undertaken. This comprised drilling, blasting, and excavation of the majority of the highly weathered rock and dispersive materials supplemented by localized installation of small cut-offs and dental concrete and the construction of a double-line grout curtain installed using real time computer monitoring, the GIN methodology, and balanced, stable grout mixes.
Foundation Preparation and Seepage Barrier Installation at Wyaralong Dam Construction Project
Lesa Delaere, Ivor Stuart, Thomas Ewing, David Marsh
As part of Wide Bay Water’s commitment to minimising environmental impacts of its water supply weirs, a “Nature Like” Fishway is under development for the Burrum No 1 Weir. This project is a fishway offset provision for the raising of Lenthalls Dam in the upper reaches of the Burrum River in Hervey Bay. The Burrum No 1 weir forms the primary pumping pool for the Hervey Bay water supply and is located at the tidal limit of the Burrum River. Understanding fish biology and behaviour is critical to the effectiveness of the design of a fishway as much as the balance between the goals of maximising fish passage versus cost, construction and operational difficulties that a fish passage solution may present.
This paper presents the aquatic ecology of the project and the inter-relationship of fish biology and river flow frequency. It discusses the fish species of the Burrum River, their behaviour, seasonal migration and criteria for successful passage. It presents the analysis of river flows with respect to frequency and headwater/tailwater relationships to weir drownout, which was complicated by the tidal flow regimes downstream of the weir. These aspects were also applied in consideration of river behaviour; low flow characteristics for fishway operation during dry seasons and drought, and high flow characteristics during the wet season and floods.
The biological needs for successful fish passage for two very different river flow characteristics were analysed. This allowed targeted design criteria and fishway solution to be developed to provide maximum benefit without causing undue cost to the project.
Burrum Weir Fishway – Fish Biology and River Flows: Two Faces
Susan Ryanand Siraj Perera
This paper describes the benefits of the statewide risk reporting framework used in dam safety regulation in Victoria and its ongoing development. Key to this approach is a web-hosted reporting system and benchmarking process, established by the Department of Sustainability and Environment in collaboration with the Victorian water industry. This is the first time that such an approach has been used in Australia for publicly owned dams.
Sector-wide reporting on dam safety is central to the objective-based approach used by the Department in the governance and regulation of the water industry. Water corporations submit detailed annual reports on dam safety status. This incorporates ‘self assessment’ against performance criteria based on ANCOLD risk and dam safety management guidelines. These are collated to produce a statewide report of industry-wide results on the progress of dam safety management programs. This benchmarking process is providing a driver for on-going improvement and proving to be an effective tool for regulation of publicly owned dams.
The reporting framework has significantly advanced the understanding of dam safety risk across the water sector, with outputs easily understood by both dam safety practitioners and decision makers. It has improved monitoring and trend analysis of risk management practices, and is informing policy development on demonstration of the ALARP principle and decision-making about appropriate long-term dam safety levels.
David R Jeffery
In 2004 the Victorian Government announced the decision to proceed with Australia’s largest dam decommissioning project, the return of the 365,000ML capacity Lake Mokoan to a wetland.
The project has been completed and has resulted in significant river health benefits through liberating environmental flows in the Broken, Goulburn, Murray and Snowy Rivers. Decommissioning has allowed the recovery of water savings for return as environmental flow to the River Murray (30,000 ML/year) and Snowy River (21,000 ML/year).
With decommissioning complete, development of a significant wetland complex across the 8100 hectare site has commenced.
This project has been undertaken at a time when the Broken River basin was exposed to its worst drought conditions in over 100 years and within 11 years of the worst flooding experienced in the nearby Rural City of Benalla. These extremes of climatic conditions and their impacts on the local and irrigation communities have ensured considerable community and stakeholder interest in the decision to proceed with decommissioning and in the subsequent delivery of each of the project elements.
This paper provides an explanation of the drivers for the project, describes the process followed and some of the challenges experienced over the projects seven year life and presents some of the lessons learned along the way.
2011 – MOKOAN – RETURN TO WETLAND PROJECT