A. Ahmed-Zeki, G. Roads
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.
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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
David Snape and Brian Simmons
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:
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.
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.
John Phillips, Yu Sheng, Jennifer Henderson
The main iron ore body at Cockatoo Island in the West Kimberleys forms a cliff face plunging steeply into the sea. It was mined by BHP down to low tide level, but the tidal range of 10 metres hampered operations. Being a very pure and sought after ore, various investigations were made to determine methods of extracting the ore below the sea. A coffer dam into the sea was investigated with the conclusion that the soft marine sediments and apparent artesian groundwater in the foundation posed a major risk and high costs.
The mine was sold to a smaller company who proceeded to win useful ore from the island. They also eyed off the undersea ore and approached GHD to use soft ground technology developed for the Derby Tidal Power Project. The soft marine sediments and apparent artesian groundwater conditions were investigated.
The paper describes the design processes involved to achieve dam stability in a space limited by lease boundaries and the desire to maximise the amount of ore that could be accessed. A key to the process was the development of construction techniques and core placement procedures that could cope with the tidal range. Timing aspects were crucial and were controlled by observations of an extensive array of instruments installed for control purposes.
This paper presents the findings of experimental investigation of internal erosion by the process of suffusion within embankment dams and their foundations.
Suffusion is the process by which finer soil particles are moved through constrictions between larger soil particles by seepage forces. Soils susceptible to suffusion are usually described as internally unstable. Understanding of the suffusion process is important to the assessment of the risk of internal erosion in an embankment dam and its foundation. Suffusion results in a coarser soil structure, leading to increased seepage, progressive deterioration of the dam or its foundation, and a higher risk of toe instability. Suffusion within the protective filter of a dam may result in a coarser filter, rendering it ineffective in protecting the core materials from erosion.
Two types of suffusion tests, namely the downflow test and the upflow test, have been conducted at the University of New South Wales. The downflow test aims at identifying the types of soils that are susceptible to suffusion, whereas the upflow test aims at identifying the hydraulic gradient at which suffusion is initiated. This paper presents the initial findings of the downflow test. Eighteen downflow tests have been carried out on fourteen clay-silt-sand-gravel soils. The Kenney and Lau (1985, 86) method, which is commonly used for assessing the internal stability of coarse-grained soils, appears to be too conservative when used to predict the internal stability of silt-sand-gravel or clay-silt-sand- gravel soils, whereas the Burenkova (1993) method appears to provide better predictions. Further testing is required to define more accurate criteria for determining the internal stability of broadly-graded clay-silt-sand-gravel soils.