M.B.Barker and B.A. Vivian
Tumut Pond and Island Bend Dams are owned and operated by the Snowy Mountains Hydro Electric Authority. These dams, which are gated, have recently had significant electrical supply and control system upgrades. Subsequent reliability analyses performed for the gates provided unexpected results which highlighted issues concerning common mode failures and common cause failures associated with the mechanical systems. A further unexpected outcome of the analyses was the minor affect of human error and response to the emergency operating conditions of the gates in the event of electrical supply failure due to the over-riding mechanical system failures. This outcome was of benefit to the owners who had some concern that centralization of operation and consequent reduction in operating personnel would have an adverse effect on the reliability of the gates. The operation of the automatic control system is an ongoing issue for Island Bend where hunting of the gate operation is yet to be resolved. The preparation of the fault trees, development of failure probabilities and outcomes of the analyses are discussed in the paper which highlights some of the difficulties in design and operation of spillway gates, particularly where human response time is limited and automatic control is essential.
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For many years, engineers associated with the design, construction and operation of large dams have been undertaking environmental effects studies in association with their projects in the belief that they were thereby satisfying their obligation to the community whose interests they served. With increasing environmental consciousness of the community in developed countries, methods have been developed one by one for assessing environmental impacts of various kinds, and techniques have been developed for abating them.
However, the issue in November of the report of the World Commission on Dams (WCD) has focussed attention not only on the importance of bigger issues such as regional ecology, national economic disbenefits and social dislocation, but also on the vulnerability of dams to social and political hindsight.
This paper develops the above background, and shows why some excellently conceived techniques developed in the early 1970’s were capable of identifying almost all imaginable environmental impacts of dam projects, but were not applied in such a way as to deal adequately with the larger issues. It is argued that tools for dealing with all known issues now exist, but that responsible and competent application of the tools are not equivalent to successful application of them. d A new approach is suggested both to upgrade the quality of the decision and to make successful adoption of a soundly based decision more likely to withstand long term critical appraisal, by expressly recognising these decisions as ethical ones.
PJ. Cummins, P.B. Darling, P. Heinrichs, J.Sukkar
The Department of Land and Water Conservation, Town Water Treatment and Recycling Branch, had identified a number of local government council-owned dams throughout NSW with deficiencies. SMEC was engaged to undertake a portfolio risk assessment to assist in the development of an appropriate program of remedial works.
The portfolio risk assessment methodology relies on the development of consistent assessments of failure probability, consequence level and cost estimate for mitigation measures. This tool enables a large amount of data on a portfolio of dams to be drawn together so as to provide decision makers with a coherent and robust basis for the development of a program of remedial works.
Bill Hakin, Phillip Solomon, Geoff Hughes, Peter Siers
Lyell Dam is located on the Coxs River near Lithgow NSW Australia. It was constructed in 1982 to supply cooling water to Delta Electricity’s Mt. Piper and Wallerawang power stations.
In 1994 the storage capacity of the dam was increased by 7,500 MI by raising the embankment height and installing two 3.5m high inflatable rubber dams on an enlarged and slightly raised spillway sill.
Two significant failures of the rubber dams in 1997 and 1999, led the dam owner, Delta Electricity, to seek a more reliable way of maintaining the increased FSL whilst still providing spillway capacity for the design flood.
Following a detailed review of options, Delta Electricity chose to reinstate the storage capacity with the Hydroplus Fusegate System. The Hydroplus System consists of a series of fusible units that progressively tip off the spillway as flood magnitude increases, thereby forming a controlled breach in the spillway and providing for passage of the design flood. At Lyell Dam it has been designed such that no units tip until the 20 000 AEP flood. The System is designed to act as a normal free overflow spillway up until extreme events when it is required to commence operation. Key factors in the selection process were safety, reliability and operation/maintenance.
This is the first installation of the Hydroplus Fusegate System in Australia or New Zealand. There are currently 35 installations throughout the world. The System has wide application with dam owners either seeking to store additional water and/or to increase the capacity of their existing spillways for safety reasons in an economical and efficient manner.
This paper examines the decision and selection process adopted by Delta Electricity. It also presents a case study for the design and construction stages of this unique solution for Lyell Dam.
Peter Lilley, Kelly Deighton, Don Tate, Craig Scott
In recent years TrustPower has undergone a rapid transition from a part owner of three dams in the Kaimai ranges south of Tauranga and the Hinemaiaia and Wheao schemes near Taupo in 1998, to the present ownership situation. Today TrustPower owns 22 dams comprising a range of structure types, including arch, earthfill, rockfill, concrete gravity and a number of embankment canal systems. The dam classifications for the dam portfolio vary from small to large and the NZSOLD potential impact ratings vary from very low to high. The portfolio includes some of the largest dams in New Zealand, for example Matahina Dam a 70m high central core rock fill, Patea Dam an 80m high earthfill dam and Mahinerangi Dam a 40 m high concrete arch dam with concrete gravity abutments.
The dam structures vary significantly in terms of age, potential impact and risk to TrustPower . The Dam Safety Management Procedures (including monitoring and surveillance systems, inspections and reviews) that existed for each dam also showed considerable variation in comparison.
The approach adopted for dam safety management is described, and the interrelationship with commercial objectives and commonly accepted standard practices.
G. A. Pickens, J. O. Grimston
The Opuha Dam Project is a multipurpose water resources development, for irrigation and other uses. The 50 m high irrigation dam incorporates a 7.3 MW hydro installation, enhances summer low flows downstream, increases potable water supply security, is a significant recreational facility and provides flood attenuation. Opuha Dam was the first large dam permitted under NZ’ s Resource Management Act, for which sustainability is the cornerstone. It was also built under a design-build contract arrangement. Although breached by a flood during construction, the dam was successfully completed and performance has met or exceeded expectations. Experiences of potential value to future developments are outlined including the positive features of design- build. Technical features which contributed to the cost-effectiveness and performance of the project, are described, including downstream reregulation to enable “on-off’ peak hydro operation, Obermeyer type spillway gates to maximise flow capture for hydro and a stepped service spillway.