South East Queensland Water Corporation (SEQWater) as owner and operator is proceeding with an upgrade of the flood capacity of Wivenhoe Dam. SEQWater has formed an Alliance with Leighton Contractors, Coffey Geosciences, Montgomery Watson Harza (MWH) and the Department of Commerce-NSW (formerly DPWS, NSW) to upgrade Wivenhoe Dam. This paper presents feasibility level investigation and design activities for an upgrade option, comprising a large labyrinth auxiliary spillway at the right abutment of the dam, for supplementing the existing gated spillway in handling the Probable Maximum Flood (PMF) event. This right abutment auxiliary spillway option incorporates Hydroplus type concrete fuse gates. The investigation so far has proved the technical viability of this option, however, ranking along with the other three options against various criteria will lead to the selection of the preferred upgrade option.
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.
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.
Hydro Tasmania has recently upgraded the control systems for the spillway gates of three of its dams, Clark Dam, Meadowbank Dam and Liapootah Dam. The upgrades followed internal reliability assessments that highlighted high reliance on operator attendance, single points of failure and operational difficulties on each of the three gate systems.
The three gates are of contrasting types. Clark Dam Spillway Gates are submerged orifice type radial gates, operated by wire rope hoists. Meadowbank Crest Gates are flap type gates, held by 10 hydraulic cylinders per gate, a design that has had a difficult operating history. Liapootah is a floating drum gate. The upgrades for each gate therefore required different solutions, albeit within a common basis of design framework. The solutions arrived at are innovative, and meet or exceed worlds best practice.
All three gates are now fully automatic, with PLC control. The use of PLC’s significantly enhances the reliability of the gates. Extensive use is also made of the PLC in monitoring key systems. For example, an impossibly rapid lake level rise detected by one transducer, but not its duplicate, will be alarmed but ignored to avoid unnecessary discharge. All systems incorporate appropriate redundancy. The PLC systems also provide some automatic functional testing functionality and enhance remote alarms and local fault finding.
Mechanical systems were modified to facilitate automation and increase reliability. Stand by power sources used include auto-start diesel genset, DC batteries and a micro hydro generator.
The design and implementation of each of the upgrades was carried out by the Electrical and Mechanical Group of Hydro Tasmania’s Consulting Division, in conjunction with Generation Division’s Project Management Group.
Arthur Yapa, Tom Bowling and Peter Watt
Hydro Tasmania uses an electronic inclinometer to monitor the face deflections of nine of its CFRDs. The inclinometer is lowered down a steel pipe attached to the upstream face of each dam. The inclinometer was designed and constructed by the University of Tasmania and was first used on Cethana Dam when it was completed in 1972.
The success of its use on Cethana Dam lead to its use for the long term monitoring of eight subsequent CFRDs constructed by Hydro Tasmania.
After 25 years of successful operation some irregular readings of face deflection became apparent. This paper describes the investigation of the irregular readings that had been obtained, the assessment of other methods of observing concrete face deflection, and the refurbishment of the inclinometer using modern electronic components.
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.