A survey of spillway gate systems and operations has recently been completed by dam organisations in Nth America, Australia and New Zealand. The survey sought to identify typical arrangements for spillway gate systems and common features pertaining to reliability such as system redundancy, actuation methods and back-up systems, gate and hoist types, remote and local operation, gate testing programmes, and human factors.
Sixteen organizations responded, covering sixty two dams and nearly four hundred gates. This Paper reports on the preliminary analysis of the data, providing an overview of the industries’ approach to spillway gate operation and control.
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Tony Qiu and Brian A. Forbes
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.
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.
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.
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.
Sydney Catchment Authority (SCA) has been progressively enhancing its asset management capability for dams and other headworks infrastructure since 1999. A key to the development of the integrated asset management system has been the application of asset condition assessment and Failure Modes, Effects and Criticality Analysis (FMECA) across the water supply mechanical and electrical assets. This has provided vital data necessary to:
• Identify all the mechanical and electrical assets
• Update the computerised maintenance management system database (MAXIMO)
• Determine asset criticality against a range of factors
• Allow review and rationalisation of maintenance work plans
• Upgrade the System Management Plans
Asset management features as a key result area within the SCA’s Corporate Business Plan. Integrated asset management is achieved by cascading corporate outcomes, strategies, objectives and responsibilities down through divisional and team work plans to individual staff members. This paper covers a range of issues that have a bearing on the day-to-day integrity of the infrastructure required to deliver bulk raw water to the SCA’s customers.
The management of maintenance at Warragamba Dam is used as an example to demonstrate the effectiveness and practicality of the application of the contemporary asset management system.