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The regulatory environment for dams in Queensland will change when the new provisions of the Water Act 2000 are proclaimed in late 2001 or early 2002. The definition of a ‘referable dam’ has shifted from a simple height and storage criteria to one that requires a population at risk (PAR) before dams are considered referable. Additionally hazardous waste dams such as tailings dams will no longer be considered as referable dams and under the Act regulatory control will be transferred to the Environmental Protection Agency.
Referable water dams will be assigned a Failure Impact Category of 2 if they have a PAR greater than 100 and a Category of I if they have a PAR greater than or equal to 2 and less than 100. This has required the development of guidelines for the assessment of ‘population at risk’. These guidelines have been written to suit a wide variety of dam impact situations and a range of dam owner resources. The guidelines require certification of the failure impact assessment by a Registered Professional Engineer in the state of Queensland.
The Queensland Dam Safety Management Guidelines have also been re-written to make them more amenable for reference in dam safety conditions.
New dams will require development permits to be issued under the Integrated Planning Act and will have development permit conditions applied in accordance with their Failure Impact Category. There is a range of transitional provisions for existing dams.
This paper covers all of the above issues as well as providing an indication as to how these statutory guidelines relate to the various ANCOLD guidelines.
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.
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.
P L Campbell, J W Walker and J T Mills
The results of a questionnaire on deformation surveys sent to dam owners around the world are presented. An analysis of the large variation in current international practice is made. The link between geodetic surveys and displacement instrumentation is established. The comparison with practice within a recent major New Zealand dam owner is drawn and a deformation survey policy is developed. Recourse is made to dam safety guidelines. Application of the policy is then described for a selection of differing types of hydraulic structures. It is shown that with the application of the policy a more rational approach resulted, surveys better reflected actual performance and there was better integration with the overall dam safety monitoring programme.