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.
Now showing 1-12 of 26 2965:
M.A. Foster, R. Fell, R. Davidson, C.F. Wan
The probability of failure of embankment dams by internal erosion and piping can be estimated using historic performance, and event tree methods. Event tree methods are preferred for all except preliminary assessments, because they can better model the characteristics of the dam. This paper provides guidance on how to estimate the conditional probabilities within the event tree based on an understanding of the process involved, the historic performance of dams, and experience in recent risk analyses. This includes methods for representing the reservoir water level; assessing the likelihood that piping initiates; assessing the likelihood that erosion will be controlled by the filters or transition zones; and assessing the likelihood of development of a pipe and breach. The paper will be useful for those carrying out risk analyses and will also have relevance to those who are assessing piping of dams using traditional methods.
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.
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.
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.
P.I. Hill, D.S. Bowles, R.J. Nathan, R. Herweynen
With the growing emphasis on a risk-based approach to dam safety management, event tree models are increasingly being used as an analysis tool. The simple structure of event trees belies some of the more complex issues associated with their application to dam safety risk analysis. This paper outlines some of the basic principles of event tree analysis and then demonstrates how inappropriate construction of event trees, and particularly oversimplification, can result in a bias in the estimated risk and produce misleading results when used to assess the dam against various risk criteria. Issues considered include the partitioning of the loading event and the impact of conservative assumptions such as assuming the reservoir is initially at full supply level.