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.
Now showing 1-12 of 26 2965:
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.
Ian Millward-Brown, John Wall
Australian Governments have recently undertaken series of consequence studies for all of their major and some minor dams. The methods used for the analysis were along the lines of the “Rapid Appraisal Method” (RAM). However, the exercise highlighted the need for care in undertaking such evaluations if meaningful comparisons are to be made between the studies. Dam owners, regulators and consultants need to understand that within the RAM framework there can be considerable variations in evaluation procedures and outcomes. Care also needs to be exercised in using these studies for ranking dams for asset and refurbishment planning and programs.
Thomas Zink, Michael Howat, Clive Anderson, Richard Davidson
This paper describes the refurbishment of Diversion Gate No 2 at Roxburgh Dam on the Clutha River, New Zealand. This 53m high concrete, gravity dam constructed in the 1950’s had three diversion gates fitted with stoney rollers which when opened into flow allows the rollers to disengage from the gate precluding subsequent closure. Diversion gate No. I was sealed off with a concrete plug. The remaining two diversion gates are required to provide additional flow control flexibility at the dam. Key aspects of the refurbishment design and construction include the system used to remove silt from upstream of the gate, and the condition of the gate itself and the concrete diversion channel after nearly fifty years of service. Brief details of the commissioning testing are also presented.
Dr Bradford Sherman, Dr Phillip Ford, Allison Mitchell, Gary Hancock
Recent reports from the World Commission on Dams have highlighted the relative lack of knowledge regarding the release of greenhouse gases (GHGs) from reservoirs. In order to be considered eligible to receive carbon credits in the future, hydropower facilities probably will be assessed using some sort of life cycle analysis of net GHG emissions.
Unfortunately, empirical data regarding GHG emissions is available only for a few reservoirs none of which are located in temperate or semi-arid climates.
We report preliminary observations on the vertical distributions of methane and carbon dioxide in Chaffey Reservoir (Tamworth, NSW) and Dartmouth Reservoir, two temperate zone reservoirs located in southeastern Australia. In Chaffey, the diffusive methane flux from the hypolimnion to the epilimnion (where it is oxidised by bacteria) was estimated to be 220-1760 mg-CH, m’ d’. Operation of a destratification system released 43 t of CH, to the atmosphere in 3 days. The carbon dioxide flux to the atmosphere via the surface of Dartmouth was 21-168 mg-CO, m’ d’, and 530 mg-CO, m° d’ through the turbine. The impact on GHG emissions of common reservoir management techniques such as destratification and hypolimnetic oxygenation is discussed.
Allan Crichton, Jon Williams, Anthony Ford
Wivenhoe Dam was constructed in the early 1980’s and is the largest source of water to the southeast Queensland region. The dam also provides significant flood mitigation benefits to the large communities in the Brisbane valley including the cities of Ipswich and Brisbane. Changes in the methods of determining the probable maximum flood, which is the design flood for the dam, have meant that the dam was not capable of passing the significantly larger design flood event. The feasibility study undertaken to assess the most appropriate method of upgrading the flood passing capacity identified more than 240 options. These options were short-listed and the capital cost and consequences costs determined for each of the short listed options.
This paper describes the process used to identify the options to upgrade the flood passing capacity and the method used to assess the consequences costs, which are primarily the costs of flood damage resulting from each of the options. The consequences costs for each option are the costs associated with changing the flow conditions in the river downstream of the dam. For example the option to upgrade the dam to pass the design flood is a benefit to the community however if this benefit is achieved by installing large gates or a fuse plug that operates frequently the scheme may increase the costs to the community.
The preferred option initiates at the lowest probability of occurrence of all those analysed — average return period of 10,000 years. There will be opportunities during the Environmental Impact Assessment process to test acceptability of this initiation level — a more frequent occurrence would be a lower capital cost solution. The EIA process may require a solution with a higher initiating level. Informal talks with the regulator have indicated a preference for the less frequent initiation level.