Dr Judy Henderson
Against a background of several decades of increasingly polarised and acrimonious debate, the World Commission on Dams (WCD) was established in 1998 with a two year mandate to review the development effectiveness of dams, assess alternatives for water resources and energy development and develop internationally acceptable criteria and guidelines for future decision- making. This report discusses the role of large dams in development and the challenges of water resource management in the future. T the work program of the WCD is outlined and progress to date on fulfilling its mandate.
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Now showing 1-12 of 33 2963:
Jim Walker, Murray Gillon and John Grimston
Karapiro Dam is at the end of a cascade of hydropower dams on the Waikato River in New Zealand’s North Island. The 52m high, high hazard, arch dam retains the lake for a 96MW power station at its downstream toe. Safety reviews recommended a re-evaluation of the dam stability under seismic loading.
Dam owner, Electricity Corporation of New Zealand (ECNZ), commissioned consultants Tonkin & Taylor Ltd to carry out a series of studies and investigations which provided better understanding of the dam’s safety status. Investigations located a previously unrecorded continuous low strength thrust fault underlying the left abutment. This provided the potential for movement of the left abutment gravity blocks under earthquake loading, with adverse effects on arch dam and reservoir safety. Investigations showed the abutment cut off walls to be lower than the PMF lake level. High groundwater levels and erodible pumiceous soils were found at the left abutment. These findings prompted ECNZ to implement stability enhancement works.
This paper describes the studies and investigations, peer review process, and design and construction of enhancement works.
Anthony Moulds and Anthony M Watson
The selection of lightning protection equipment will always remain within the cost versus benefit, or risk management area. As more and more monitoring equipment becomes electronic and microprocessor based, we need to have a better understanding of the ways to protect it, and maintain the data flow.
Recent experience has shown that utilising the Australian Standard (NZS/AS 1768-1991) Lightning Protection, in conjunction with a six-point plan, will go a long way to providing total integrated protection for both structures and contents. However, no matter how much protection is applied, damage due to lightning may still occur. For dam surveillance instrumentation the aim ultimately is to protect the transducer ‘in the ground’ or ‘in the dam’, because generally these instruments are inaccessible and non-replaceable without prohibitive drilling and retrofitting costs.
The six-point plan was applied initially to designing lightning protection for a large, well- instrumented RCC dam, completed in 1991. The protection proved to be not as good as was hoped. The paper describes how the lightning protection at the dam was subsequently developed. This experience, which has pointed the way to achieving a good level of protection at a reasonable cost, has been applied to a number of other, instrumented dams.
The paper outlines the integration of Environmental Risk Management in Goulburn- Murray Water with previous work on Dam Safety, Business and Occupational Health and Safety risks. This has now been followed by the development of an Environmental Management System (EMS) to provide an environmental risk management framework for the whole Authority.
An Environmental Audit in 1997 identified deficiencies in some areas of environmental management and questioned the Authority’s ability to demonstrate due diligence. This led to a decision to develop and implement an EMS based on the International Standard ISO 14001.
Examination of Goulburn-Murray Water activities, associated environmental aspects and impacts, (and the consequences arising), led to the establishment ofan environmental risk register. Analysis and assessment of the risks to produce a ranking Jrom low to very high is described. Refinement to a significant risk register (high and very high risks), and consolidation into a list of generic risks based on major activities, functions and asset categories is described.
Based on this risk profile for the Authority, the Environmental Policy and Objectives were revised, and a methodology for identifying Environmental Targets was developed. Environmental Risk reduction is then delivered through the implementation of target driven Environmental Management Programs (EMPs).
Major system elements described include an emergency response plan, a legal register, an authority / responsibility matrix, a document control system, procedures, forms, training, auditing, and reporting.
The paper describes some of the practical issues encountered and the lessons learned with a focus on the activities of the Headworks Business. A prospective view of implementation and culture change issues is given.
Peter Allen, Don Cock, Garry Grant and John Ruffini
The paper examines the performance of the Brisbane River and Pine River real time flood management system for the operation of Somerset Dam, Wivenhoe Dam and North Pine Dam during the 1999 flood event.
The February flood event, which was about 80% of the magnitude of the disastrous 1974 flood event upstream of Wivenhoe Dam, was the first major flood event to be managed by the system and it performed very creditably. The overall flood management system comprises:-
A network of 125 ALERT type rainfall and river height stations throughout the catchment; A data management system to facilitate data collection and data validation;
The paper describes the system and gives details of the performance of the system during the February event. It details the performance of the dams during the event and how this was optimised to maximise the safety of the dams and minimise impacts on those downstream.
Ahmad Shayan, Robert J. Wark and John Waters
The Canning Dam concrete gravity structure located in Western Australia has shown an upward movement of 18.3 mm and lateral upstream movement of 14.2 mm over the past 15 years of monitoring. These movements have been associated with considerable cracking of the upper parts of the dam and the upper gallery. Investigations have shown that the cause of the cracking was a strong alkali-aggregate reaction (AAR) in the concrete, brought about by a deformed granitic rock. Extensive horizontal and vertical cracking in the upper part of the dam wall has necessitated the removal of the section above the floor of the upper gallery level, and construction of a new reinforced concrete section to act as head beam for post-tensioning of the rest of the dam wall.
A set of small diameter cores were taken from the various parts for diagnostic purposes, and a vertical core of 100 mm diameter was taken through the whole thickness of the wall for the determination of the strength properties, alkali content and residual expansion potential. Based on these, a post-tensioning stress of 1.5-2.0 MPa has been calculated for restraining the residual expansion of the concrete. The spillway bridge structure which is part of the dam wall has also shown mild signs of deterioration. The piers and abutment walls and the deck were surveyed for corrosion activity and extent of AAR. This work showed that the spillway bridge structure was sound and only needed maintenance. The performance of a triple blend concrete mix containing a high volume of fly ash (45%) and silica fume (5%) developed for the replacement of the old concrete is also discussed.