Hydro Tasmania has recently developed a Dam Safety Emergency Plan, which covers 54 referable dams throughout Tasmania. A major contribution was the development of the Pieman River flood warning system. The flood warning system is a computer-based model that forecasts the hydrological situation of the catchment up to 48 hours into the future and alarms the appropriate personnel when a flood event is imminent. The Pieman River catchment experiences some of the highest average annual rainfalls in Tasmania and contains dams in the High Hazard category. The flood warning system was developed using Hydstra Modelling™ (formerly TimeStudio), which links directly to the Hydstra TSM™ database. This package offers powerful automation tools that enable the Pieman River flood warning system to operate, alert personnel and display results on Hydro Tasmania’s internal website with no manual involvement. With its maintenance free operation and user-friendly interfaces, the Pieman River flood warning system is an effective contribution towards the overall risk management package of the Pieman River Power Development
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Cairn Curran Dam is a 44m high zoned earthfill embankment located near Bendigo in central
Victoria. The dam is owned and operated by Goulburn-Murray Water.
A risk assessment had identified that the junction between the embankment and spillway wall was a weakness in regard to the potential for piping. Initial geotechnical investigations indicated a softened zone adjacent to the foundation.
The conceptual upgrade design was to excavate the downstream slope and place filter material and a rockfill weighting berm. A 2-D slope stability analysis gave unacceptably low factors of safety for this excavation. The three dimensional nature of the embankment/spillway interface and excavation geometry was identified as an important factor in the upgrade design.
A detailed geotechnical assessment was undertaken and a geotechnical model developed that
accounted for potential softened zones adjacent to the spillway wall, along the foundation, and within the embankment.
A 3-D limit equilibrium slope stability program was utilised to analyse the 3-D factors of safety. The
program employed an extension of Bishop’s method of slices to a 3-D ‘method of columns’. A 3-D
finite element analysis was also undertaken to estimate likely deformations of the embankment and cut slope during construction.
The development of the geotechnical model and subsequent analysis allowed the upgrade works to be undertaken with confidence.
M G Webby
Investigations of damaging blowback incidents at the headrace tunnel intake to Rangipo Power Station in the Central North Island of New Zealand are described. The blowback phenomenon is explained theoretically based on evaluation of the evidence available from the incidents and information obtained from the literature. A physical hydraulic model study is described in which this explanation of the blowback phenomenon was verified. The model was also used to devise a solution for the blowback problem.
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.
The RCC design review and construction supervision of the 60m high Tannur Dam in Jordan was carried out by GHD, Australia.
The 220,000m3 of RCC was placed during February-December 2000; change to the sloped layer method was made once the dam reached 15m height. It produced a 50% increase in placing rate and a considerable saving in costs.
The use of the method is the first known use outside of China, where it was developed during the construction of the 130m high Jiangya Dam in 1997-8. The sloping of the 300mm thick layers of RCC across the dam from bank to bank at grades between 5-8% ensures subsequent layers of RCC can be placed within the initial set time of the lower layer and hence the RCC is monolithic across the lift joint.
This paper briefly describes the project in Jordan and then gives specific details of the use of the sloped layer method. Typical results from the quality control testing during placement and subsequent coring and testing of the lift joints are also provided. The benefits of its use in adverse climatic conditions, such as extreme heat or rainfall and the ways it can be integrated with forming the upstream-downstream slope are also discussed.
The sloped layer method is a significant advancement, particularly for large structures, where lift joint cohesion, tensile resistance and RCC placing rates are vitally important.
There are many important dams and other structures on catchments smaller than 1000 km² with response times less than 24 hours, however these catchments have been largely overlooked in previous research into large and extreme floods. This paper is an initial step in “catching up” design practice for short duration rainfall events to the current best practice that is available for estimation of floods from rainfall events with durations of 24 hours and greater.
Two issues are specifically addressed in this paper. Firstly, a regional analysis of short duration rainfall depths is conducted to extend the frequency curve beyond an AEP of 1 in 100. Rainfall frequency curves are estimated for durations between 0.5 and 12 hours, using data from ten pluviograph sites around Australia. Secondly, sets of temporal patterns are derived that could be useful in joint probability analysis of short duration rainfall events. The effects of these new rainfall depths and temporal patterns on flood frequency curves are tested by applying them to rainfall-runoff routing models for three dams with small catchment areas.