Karin Xuereb, Garry Moore and Brian Taylor
Assessment of dam safety requires estimates of extreme rainfall together with the temporal and spatial distributions of extreme rainfall. In order to satisfy dam safety requirements for dams in the west coast of Tasmania, the Bureau of Meteorology has developed the method of storm transposition and maximisation for application in this region.
Daily, as well as continuously recorded rainfall data for all Bureau of Meteorology and Hydro Tasmania sites in western Tasmania have been analysed and the most outstanding rainfall events over one, two and three-day durations in the region have been identified. Meteorological analysis of these events reveals that the most significant rainfall events in the west coast of Tasmania are caused by the passage of fronts, which are sometimes associated with an intense extratropical cyclone, with a westerly or southwesterly airstream.
A database of isohyetal analyses of the most significant rainfall events in western Tasmania has been established. These can be used either ‘in situ’ or transposed to estimate mean catchment rainfall. Storm dewpoint temperatures for the purpose of moisture maximisation have been determined.
Cumulative and incremental three-hourly temporal distributions for sites having continuous rainfall data or three-hourly meteorological observations have been constructed and design temporal distributions of extreme rainfall have been derived.
An objective method for adjusting for differences in the topography between the storm and target locations is proposed.
Yarrawonga Weir was constructed in the 1930’s and is located on the Victoria / New South Wales border, between the towns of Yarrawonga and Mulwala. Dam safety investigations revealed that the main embankment was founded on a very loose layer of sand that would be vulnerable to liquefaction even under the operating basis earthquake
This paper details the statutory approvals and community consultation processes that were employed and the benefits that they provided to the $13 million remedial works project.
Local communities can assist, be neutral or obstruct a project. By engaging the community in a positive manner it is possible to deliver excellent results without increasing costs.
M. Barker, B. Vivian, J. Matthews and P. Oliver
This paper discusses reliability issues of the fourteen 3.85m high by 7.89m wide radial gates at Glenmaggie Dam in Victoria and the twin 3.6m high by 16.5m wide drum gates at Little Nerang Dam in Queensland. The Glenmaggie dam radial gates are manually controlled using electrically driven (mains and diesel generator power supply) hoist motors with a petrol driven hydraulic pack for use in the event of complete electrical power supply failure. A detailed fault tree analysis was developed for the spillway gate reliability of the Glenmaggie Dam gates as part of the risk assessment for the dam, which was being completed at the time of publishing the paper. Each of the identified components of the spillway gates, including human error in operation was used to evaluate the probability of failure of a single gate or multiple gates for inclusion in the event tree to estimate the risk and assist the evaluation of the requirement for remedial works. The Little Nerang drum gates are fully automatic hydraulically operated gates with independent operating mechanics and a common override system in the event of automatic system failure. Drum gates are uncommon on dams and the system operation is discussed together with an assessment of the reliability and measures taken for handling operating risks during floods for the dam, which has some stability concerns.
Craig Johnson, Phillip Solomon, Nihal Vitharana
Tank Hill Reservoir is located approximately 25km north-east of Warrnambool and forms part of the fresh water supply for the town. It was built in the 1930’s by the construction of an earthfill dam across the natural breach of the crater of an extinct volcano. The reservoir is an offline storage with a small natural catchment and has a nominal capacity of 770ML at Full Supply Level (FSL). The reservoir is operated by South West Water Authority (SWWA).
Previous investigations had identified instability issues associated with the dam embankment and the necessity for remedial work to increase the stability of the dam embankment. SKM undertook detailed survey and investigations and the proposed upgrade works include the construction of a downstream stabilising berm incorporating graded filters and a drainage system. The condition of the outlet works was investigated as part of the project, with some of these works found to be in poor condition with a risk to the security of supply, necessitating the design of refurbishment of the outlet works. The degree of siltation of the reservoir was also assessed, and some loss of capacity due to siltation was noted.
Detailed investigations were performed to determine the optimum configuration of the stabilising berm and to locate and test suitable construction materials. The embankment interface filters were designed to satisfy modern filter design criteria and were incorporated in the embankment drainage system. The condition of the outlet works, including the intake standpipe, three offtake valves and the outlet conduit beneath the embankment, were assessed via manual and CCTV inspections. An operation review, incorporating the proposed upgrade works within the framework of ongoing operation of the reservoir for supply to downstream customers was also prepared, as was a construction risk assessment.
This paper will present “extremely useful practical information” for dam design engineers, owners and operators where the whole spectrum of dam safety issues is required for the successful completion of remedial works design and construction.
Stephen Newman, Kelly Maslin
Lake Bellfield is a reserve storage for the Wimmera Mallee Water (WMW) Stock and Domestic System in North Western Victoria, constructed between 1963 and 1967. The dam is located on Fyans Creek approximately 3 km upstream from Halls Gap in an area of high tourist value and is rated in the Extreme category under ANCOLD guidelines. The dam consists of an earth and rockfill embankment 745 m long with a maximum height of 57 metres and retains a reservoir with a storage capacity of 78,500 ML.
Previous studies and a subsequent physical model study confirmed that the existing spillway does not meet the requirements of the current ANCOLD guidelines. The current flood capacity is approximately 40% of the Probable Maximum Flood. A range of potential upgrade options to pass the PMF were evaluated with a 1.9 metre composite earthfill and downstream concrete parapet wall raise in combination with spillway lowering of 3.4 metres selected. Construction of this option was completed in early 2003.
This paper describes the key features of the investigation and design including:
The Diavik Dyke was constructed in 2001/2 in a major sub-Arctic lake in Canada’s Northwest Territories, to permit an open-pit diamond mining operation. The dyke, 3.9km long, was built in water up to 20 metres deep in a period of 17 months. For ten months of this period the lake was frozen. The project was notable for the extreme climate, discontinuous permafrost in the dyke foundations, very difficult logistics and the exceptional environmental constraints.
Project economics dictated a short construction period to permit the early generation of revenue from the mine. To confidently deliver a secure dyke within the time frame, the world’s most technologically advanced cut-off wall equipment was designed and fabricated in Germany.
This paper provides an overview of the dyke and focuses in more detail on the specialty equipment used for the cut-off wall and foundation treatment.