The report of the World Commission on Dams (WCD), issued in November 2000 was the result of a world-wide study of the development and effectiveness of dams. This paper describes a parallel but much smaller study, specifically relevant to the Asia-Pacific Region, carried out simultaneously for the Asian Development Bank (ADB) by a multi-disciplinary consortium of consulting organisations, whose work was reviewed by an Advisory Panel. This study comprised an analysis of performance compared with design expectations in case studies of four dams spread across the Region and constructed at different times between 1970 and 1999, supplemented by a literature survey. Although the case studies were conducted independently of WCD and to different Terms of Reference, they used similar methodologies, and the results were submitted to WCD to increase their knowledge base. The ADB study’ s recommendations take a somewhat different form to those of the WCD, but there is no conflict between the recommendations of the two studies.
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Now showing 1-12 of 26 2965:
Lelio Mejia, Murray Gillon, Jim Walker, Tom Newson
This paper describes the criteria for developing seismic loads for the safety evaluation of dams of two New Zealand owners. The criteria were constrained to satisfy the requirements of the NZSOLD Dam Safety Guidelines and to be consistent with international practice in countries with levels of seismicity and socio-economic development similar to New Zealand. In selecting the criteria, dam seismic load standards from several countries were surveyed and summarized. The selected criteria follow a standards-based approach to the seismic safety evaluation of dams. Guidelines for the use of deterministic and probabilistic procedures to develop seismic loads were formulated as a function of the Potential Impact Classification of a dam. In addition to the traditional deterministic definition of evaluation earthquakes, the selected criteria allow the use of a probabilistic definition in cases where the deterministic definition yields very low probability evaluation events.
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.
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.
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.
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.