The role of judgement in risk assessments as applied in dam safety management has been the source of considerable debate in recent years. With regard to risk analysis of dams, and while there is general agreement that judgement is an essential element of the process, essentially two schools of thought have emerged. One view holds that, in the assignment of probabilities, reliance can be based on collective engineering judgement that is anchored to a knowledge base. The second view holds that judgement should be based on the knowledge that is revealed by an appropriate amount of analysis. The paper, written from the perspective of the latter view, explores some of the underlying issues in this debate.
The role of judgement in risk evaluation, the process of judging the significance of risk, is considered to be equally important. However, the process of making value judgements and statements of principles is complex and often beyond the sphere of engineering. The third issue addressed in the paper concerns the search for answers to the question, “How good is the assessment?”
A strategy designed to ensure that an existing dam continues to perform effectively will include:
This paper will explore each of these issues and how they may be applied to dams in a variety of situations. These situations include water supply reservoirs, flood retarding basins, levees and wastewater lagoons. While each situation is different, the underlying principles will remain consistent. The range of situations encountered by Victorian Water Authorities provides the inspiration for the development of an efficient approach to the management of the safety of dams.
P. J. N. Pells and M. Hunter
The potential for generating acid leachate from waste dumps is a major consideration in many metalliferous and coal mines. This paper describes the construction of the highest embankment dam in Indonesia for the sole purpose of storing potentially acid producing waste under water. The paper discusses the features of embankment dam design peculiar to an open pit mining environment which involves moving more than three times the total volume of earth and rock than in the whole of the Snowy Mountains Scheme.
Andrew Day, Rod Bridges and Corrado Fabbri
A joint venture between Astaldi SpA of Italy and Thiess Contractors Pty Ltd of Australia (ATJO) has just completed a 95m high roller compacted concrete (RCC) dam on the island of Sulawesi in Indonesia. The dam which includes 528,000m’ of RCC was completed in September 1999 and will provide hydro-electric power for a nearby nickel smelting operation.
One of the largest RCC dams built in the region in recent times, the construction presented a number of unique challenges in particular placing techniques to cope with the heavy rainfall in the area as well the logistics to this remote location. Other aspects which are addressed in the paper include production rates, RCC placing systems (Rotec), dam formwork systems, aggregate sources, RCC mixes and waterproofing (membrane).
After early problems with the river diversion, the works were accelerated and completed to a very tight program. To enable dam construction to commence prior to river diversion the wall was advanced as a series of separate monoliths which led to a number of RCC placing innovations.
Dr. Azam Khan and Dr. Anil Patnaik
Concrete dams are thinner than embankment dams and impose more concentrated loads on the foundation and abutments. A narrow valley with sufficient rock foundation is a typical site for concrete dam, which require a solid foundation that is relatively free of faults, shears, and major changes in foundation strength. Such discontinuities can overstress the concrete by causing some areas of dams to carry more loads than other areas. The measurement of deflections and use of finite element technique can predict the stresses in the concrete dams. A computer model is underdeveloped for prediction of deflections and stresses in Concrete Dam by using finite element. At the first stage of this study, measured deflections from Burrinjuck Dam are compared with the predicted deflections by using finite element. This paper outlines the deflections measured in the dam due to temperature variations and comparison of the measured thermal deflections with those predicted from a finite element analysis.
Brian Haisman, Clarke Ballard and Neville Garland
In early 1997 the Murray-Darling Basin Ministerial Council instigated a review of the operations of its primary reservoirs, the Hume and Dartmouth Dams, in response to concerns of floodplain communities below the dams, coupled with changing community values in relation to the in-stream environmental effects of dams. The review, completed in May 1999, achieved a consensus between parties advocating what are on the surface irreconcilable objectives for the management of the water resource. Foremost competing objectives were flood mitigation, consumptive water use, and environmental health of the river system, plus subsidiary objectives related to recreation, hydro-electric generation, salinity management, tourism and the like. The keys to success were firstly, creation of a community-based Reference Panel which took on a steering role coupled with extensive consultation, and secondly a determination to describe situations wherever possible by means of factual information. The paper describes the identification and evaluation of issues, the consensus building process, the intensive hydrology and economic modelling undertaken, and the development of a comprehensive set of flow parameters which could be viewed as surrogates for environmental outcomes. Conclusions and recommendations are drawn for future reviews of similar dams.