C Lake and J Walker
Meridian Energy is the owner and operator of a chain of hydro dams on the Waitaki River in the
South Island of NZ. It operates a Dam Safety Assurance Programme which reflects current best
practice; consequently it has focused primarily on managing civil dam assets. Advances in plant control technology have allowed de-manning of our power stations, dams and canals through centralised control. The safety of our hydraulic structures is increasingly reliant on the performance of Dam Safety Critical Plant (DSCP) – those items of plant (eg water level monitoring, gates, their power and control systems, and sump pumps) which are required to operate automatically, or under operator control, to assure safety of the hydraulic structures in all reasonably foreseeable circumstances.
Recent dam safety reviews have highlighted that the specification and testing of our DSCP is based on the application of ‘rules of thumb’ which have been established through engineering practice (eg. “monthly tests”, “third level of protection”, “backup power sources”, “triple voted floats”). The
adequacy of these engineering practices is difficult to defend as they are not based on published
criteria. The realisation that such rules may not be relevant to the increased demand on, and complexity of, DSCP led us to ask “Which belts and braces do we really need?” The current NZSOLD (2000) and ANCOLD (2003) Dam Safety guidelines give little guidance regarding specific criteria for the design and operation of DSCP.
Meridian has identified the use of Functional Safety standards (from the Process industry, defined in IEC 61511) as a tool which can be applied to the dams industry to review the risks to the hydraulic structures, the demands on the DSCP, and utilise corporate “tolerable risk” definitions to establish the reliability requirements (Safety Integrity Levels) of each protection, and determine lifecycle criteria for the design, operation, testing, maintenance, and review of those protections.
This paper outlines the background to identifying Functional Safety as a suitable tool for this purpose, and the practical application of Functional Safety Analysis to Meridian’s DSCP.
Peter J Burgess, Delfa Sarabia, John Small, H. G. Poulos and Jayanta Sinha
The assessment of settlement behaviour of clay core rock fill dams has always been a challenge for dam designers and geotechnical engineers. The method of construction and the material properties of the clay and rock fill materials used in the dam construction have a significant influence on the inter-zonal interaction and the load transfer that occurs within the dam. At times this load transfer can lead to excessive differential and total settlements. The paper presents a case study of a major dam that experienced large settlements during and after construction. An elaborate analysis has been carried out by modelling the sequences of construction by using a finite element program (PLAXIS).
The paper describes the influence of the degree of compaction and moisture control on non-linear deformation characteristics of clay core. High vertical strains in the wet placed region of the core and low strains in the dry placed regions were analysed for possible shear development between the core and shell. The rock fill for the dam embankment consists of quartzite, metasiltstone and phyllite material. These materials have apparently undergone deformation with increasing height of the dam due to softening and crushing as saturation of the embankment took place. The effect of soil consolidation and strength gains have been considered in the analysis and are discussed. The settlement behaviour of the dam including these effects has been analysed, and compared with the historical post-construction settlements.
This paper is intended to provide valuable information for dam engineers handling clay core rock fill dams – especially where there is excessive settlement of the core.
Roger Vreugdenhil, Joanna Campbell
The dams industry is immersed in a changing environment. It is one of many industry sectors in Australia becoming acutely aware of the impacts of ageing practitioners and a competitive labour market. Shortages of skills and labour are impacting on all participants. The constraints around recruitment and retention are further amplified for dam owners in some States by increasing expenditure regulation and accountability.
People choosing to leave or retire from the dams profession per se does not necessarily pose a problem. Instead, problems arise if insufficient transfer of valuable knowledge has occurred prior to their departure, if the rate of replenishment is inadequate to cope with current and future industry workload, and if there is no innovation around what workforce is involved. Future work will likely be characterised by remedial works for existing dams rather than new dam construction, with an increased focus on environmental restoration, and optimisation of operations and maintenance to minimise losses and maximise productivity. These tasks require a great level of skills in leadership and innovation, equal to any level previously applied to this industry.
Organisational goals and decisions have to be realised through people and it appears that many people are taking up their roles differently than in the past. The authors, both Generation X, contend that the core issue is as much a challenge of imagination as it is a crisis of human resourcing. Greater imagination is required around: the image presented by the profession; retention and replenishment of personnel; appropriately connecting people of different generations to their individual roles; developing leaders comfortable with the sentient aspects of organisation life and capable of collaboration; and sustainable management of knowledge.
Peter Allen, Malcolm Barker, Shane McGrath and Chris Topham
Are we there Yet? The question we all ask in Tolerability of Risk. The answer is in the journey, which we are all on as owners, regulators or designers.
A number of authorities in Australia are applying risk assessment for the evaluation of dam safety upgrades in accordance with the October 2003 ANCOLD Guidelines on Risk Assessment. A fundamental requirement for the evaluation of risk below the limit of tolerability is the use of the As Low As Reasonably Practicable(ALARP) principle. In making a judgement as to whether an ALARP position may have been reached, ANCOLD suggest the evaluation of a Cost to Save a Statistical Life, good practice, level of existing risk, social concerns, affordability and duration of risk. ANCOLD also suggests consideration of the USBR Criteria for evaluating risk. Recent guidelines on the Acceptable Flood Capacity for Dams developed by the Queensland Dam Safety Regulator provide further insight into the application of ALARP.
The objective of the paper is to make dam owners, regulators and designers aware of some current practice regarding the evaluation of ALARP in Australia, highlight the challenges of applying this principle and to encourage further discussion.
A brief overview of dam surveillance is given from a South African perspective and more specifically the perspective of the Department of Water Affairs and Forestry (DWAF). DWAF’s Ten Commandments for the design of dam monitoring systems serve as introduction and this is followed by a summary of the design steps. The various parameters that can be measured and the South African preferences are discussed briefly followed by a synoptic description of crack and joint monitoring in South Africa. This provides the background for DWAF’s recent developments in 3-D Crack-Tilt gauges. Some of DWAF’s achievements as well as some of the blunders made by the author during the past 30 years are illustrated by means of a few case histories.
Leonard A McDonald
Dam safety regulators look for evidence in support of the safety status of dams and to justify the need for safety improvements. Instrumentation and monitoring have a key role in providing the needed evidence.
In New South Wales, the Dams Safety Committee [the DSC] is the regulator of dam safety. The purposes of instrumentation and monitoring from the viewpoint of the DSC are set out, along with the current regulatory requirements in New South Wales. The relationship of instrumentation and monitoring to the tolerability of risk is discussed. There are remarks on some special considerations for a regulator and on the contemporary trend to remote sensing for the capture of information. Two case studies are described to show how instrumentation and monitoring has improved the understanding of dam behaviour. Some pitfalls to avoid are listed from DSC experience. Finally, there is an outline of matters that a regulator would see deserve attention if ANCOLD does undertake preparation of a guideline document on instrumentation and monitoring.