Shane Papworth, Stuart Richardson, David Dreverman, Mel Jackson
A prominent element of the operational environment of a dam is its interaction with the community.The management of public recreational use of irrigation storages is an increasing challenge for Goulburn-Murray Water and the Murray Darling Basin Authority. The upper Murray storages have been significantly affected by the unprecedented low water resource availability which has caused an increasing conflict between the primary use of the dam to supply irrigation water and the secondary benefit of recreation and tourism use by the local communities. Many difficult management issues (media, community relations, political interest) arise from the local community, rather than just from operation of the dam itself.
An increasing awareness of the dire water resource position in recent years has coincided with an ever increasing appreciation of the environmental and social impacts of recreational use. For the storages along the Murray system, effective management is further complicated by complex agency and authority responsibilities, communities and interest groups effectively ‘in competition’ for the water resource.
To better manage these issues, ‘Land and On-Water Management Plans’ have been developed for Lake Mulwala and Lake Hume. Developing the Plans has not been without controversy, but ultimately the Plans have proved to be a simple and successful means of planning for and achieving agreed land and water management outcomes. This in turn is fostering a positive spirit of cooperation and communication with communities currently under considerable stress as a result of prolonged drought.
This paper describes the process, pitfalls and learnings to come out of the development of the Land and On-Water Management Plans.
Key words: Environment, community, irrigation dams, recreational use, planning
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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.
David Ryan, Simone Gillespie
The Burdekin Falls Dam is the largest of the 19 dams owned by SunWater. The dam is located on the Burdekin River at AMTD 159.3km, approximately 210 km south of Townsville and supplies water for irrigation, urban and industrial development in the lower Burdekin Region. The dam has such unique features as the largest spillway of any dam in Australia and a catchment area of 114,770 km2, which is equivalent to about 1.7 times the land area of Tasmania. It is proposed to raise the dam to provide a more certain water supply for the North Queensland region. This paper outlines the features of the existing structure, the influence of the revised hydrology since the time of its construction and the options considered in the planning and design of the raised structure.
Keywords: Burdekin Falls Dam, unique features, spillway, fuse plug.
Steve O’Brien, Christopher Dann, Gavan Hunter, Mike Schwermer
One of the principal geotechnical issues identified for the Hinze Dam Stage 3 project was the potential for internal erosion and piping within the extremely complex geology at the right abutment. A plastic concrete cut-off wall was selected as the best solution to reduce the risk of piping to acceptable levels and careful planning of this work was required to manage a range of key project risks that included complex technical challenges, potential risks to dam safety, the environment, the surrounding community as well as delivering the works on a tight construction schedule to an agreed budget value. Construction of the 220m long and up to 53m deep cut-off wall, the largest wall of this type constructed to date within Australia, was undertaken by Bauer Foundations Australia and completed in January 2009. A major key to the success of the project was the planning and risk reduction measures that were undertaken during both the design and construction phases, a summary of which is presented in this paper.
Keywords: Cutoff Wall, Plastic Concrete, Hinze Dam.
In 2003, the Bureau of Meteorology revised the Probable Maximum Precipitation estimates and rainfall temporal patterns for Tinaroo Falls Dam using the Revised Generalised Tropical Storm Method. Based on the revised floods, the dam was assessed as having an ‘Extreme’ Flood Hazard Category rating. Subsequently a comprehensive risk assessment was undertaken in 2008 and this assessment recommended the dam be upgraded to pass the Fallback AFC which is the PMF event. The current spillway has a capacity for a flood with an AEP of 1 in 200. To achieve the AFC the concrete gravity Main Dam requires stabilising with post-tensioned anchors. The crest of the homogenous Saddle Dam needs to be raised by 300 mm and a filter and weighting zone needs to placed on the downstream face
Keywords: Tinaroo Falls Dam, mass concrete gravity dam, post-stressed anchors, Barron River, filter, weighting zone
Gavan Hunter and James Toose
Hinze Dam, an extreme hazard storage, is under the authority of Seqwater (Southeast Queensland) and is the principal potable water storage supplying the Gold Coast. The Stage 3 raise, presently under construction, involves raising the embankment almost 15m to a maximum height of 80m.
The central core earth and rockfill embankment is founded on competent greywacke rock within the valley floor and left abutment. On the right abutment it is founded on extremely weathered greywacke and rockfill stability berms were constructed upstream and downstream on this weak foundation.
Key issues for the design of Stage 3 embankment raise on the right abutment were: 1/ removal of the existing downstream stability berm and deep excavation at the toe of the Stage 2 embankment to connect into the blanket filters under the downstream shoulder; 2/ the soil strength properties of the weathered greywacke foundation and the presence of pre-sheared defects with strength properties significantly below the strength of the soil mass; and 3/ undertaking the works while the reservoir remained in operation and close to full supply level.
It was not possible to undertake large scale excavation at the downstream toe of the right abutment as the factor of safety for the excavation condition was below the design criterion for slip surfaces extending back to the upstream shoulder. The innovative design solution was for a staged excavation and back fill operation up the right abutment. In this ay the stability requirements were achieved by a 3-dimensional buttressing support and reduced the time that critical excavation sections were exposed.
The construction risk is being managed under a dam safety management plan. Key elements of this plan include instrumentation monitoring and increased surveillance for early detection of a potential incident, a series of trigger levels and responses to these levels, a clear hierarchy of contacts and adequate preparation for a dam safety emergency (including materials, personnel and equipment).
The embankment construction is presently in progress. The most critical sections have been successfully completed without incident and displacements are within the predicted range. Communication and planning within the Alliance between the designers and constructors has been a key element in the successful construction works to date.
Keywords: construction risk, embankment design, embankment construction, dam safety management