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.
Jenny Stewart, Murray Gillon
This paper describes decommissioning studies carried out as part of a dam safety improvement project by Coliban Water. The project results from a Portfolio Risk Assessment of 20 referable dams and the selection of 10 dams for safety improvements. Due to future water supply commitments and possible alternative supplies, eight of the reservoirs were subject to a decommissioning analysis as part of the dam safety options studied. The decommissioning studies included alternative uses, flora and fauna and other environmental issues, and European and aboriginal heritage studies.
As a result of the studies, five of the reservoirs will no longer be required for water supply. Two will be upgraded and handed over to others to manage as recreation sites and one will be decommissioned. Two are still being considered for either decommissioning or hand-over to others at a reduced capacity for habitat and heritage benefits.
Neil Gillespie, Chris Hansen
With the introduction of the Resource Management Act in 1991, two significant changes have meant a complete review has been necessary of the planning provisions for hydro generation facilities in plans prepared under the new legislation.
Firstly, the Resource Management Act 1991 introduced an ‘effects’ based approach to planning, as opposed to an ‘activity’ based approach that existed under the previous Town & Country Planning Act 1977. Secondly, the planning mechanisms available to hydro generators to provide for their facilities changed.
Contact Energy Ltd (Contact) is a significant hydropower generator based in Central Otago. The new Regional and District Plans prepared under the Resource Management Act 1991 now contain provisions controlling activities previously provided for by way of a designation. Contact has invested considerable time and effort into the plan preparation process to ensure their activities are not unduly restricted by the new plans.
This conference paper provides an overview of the changes to the planning associated with hydropower generation facilities, and Contact’ s experience in the plan preparation process.
Since the research and development work carried out by the (then) Metropolitan Water Sewerage and Drainage Board for the strengthening of Manly Dam in 1979/80, there has been over twenty years of continuous improvement in the application of advanced post-tensioned anchors for gravity dam rehabilitation.
Up until the Manly Dam remedial works, concerns had been increasing as to the long-term viability of available anchors. Sophisticated monitorable and restressable anchors, with superior corrosion protection afforded by greased and sheathed strands, were developed initially in test-bed conditions. This style of anchor has subsequently been used extensively throughout Australia on dam upgrades.
This paper compares the claims made by the designers with the demonstrated outcomes of installations that have been achieved, with particular emphasis on dams now owned by the Sydney Catchment Authority and Sydney Water Corporation. The original commitments to economy, aesthetics and rapidity of construction have been borne out by experience, with additional environmental advantages also being achieved. With the confidence built up from many successes in the strengthening of older dams, the time appears right to revisit the construction of new dams using the same style of post-tensioned anchors as the primary stabilising force.
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.
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.