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.
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S. Knight, B. Cooper and P. van Breda
Warragamba Dam was completed in 1960 and impounds Sydney’s main water supply storage. Hydrological studies in the 1980’s showed the existing spillway to be significantly undersized by modern standards. Considering the dam’s High Incremental Flood Hazard category, the current risk of dambreak is unacceptably high. This has resulted in a two-stage program to upgrade the dam to full Probable Maximum Flood (PMF) capability.
The interim (first stage) measures were completed in 1990 and involved a 5.1 metre raising of the dam crest and significant post-tensioning of the dam wall. Following many feasibility/option studies and detailed technical and environmental studies, a contract was let by Sydney Water Corporation (SWC) in late 1998 for the construction of an auxiliary spillway as the major (second stage) component of the flood security upgrading. The spillway will be a large capacity (about 18,000m*/s) concrete lined chute 700 metres long around the dam’s right abutment. In the upper curved section will be the largest fuse plug embankments in Australia (up to 14.5 metres high). The lower straight section will terminate with a flip bucket structure.
The NSW Department of Public Works and Services (DPWS) designed the earlier Interim Works, undertook the subsequent engineering option studies for the Major Works and carried out the concept design and technical specification for the new auxiliary spillway and associated dam modification works. This paper summarises the project, describes the main features of the concept design of the spillway and outlines the associated dam modifications.
David S. Bowles, Loren R. Anderson, Joseph B. Evelyn, Terry F. Glover and David M. Van Dorpe
A demonstration risk assessment was conducted on the 283-foot high rolled-earthfill Alamo Dam as part of a U.S. Army Corps of Engineers (USACE) Research and Development program. The existing dam and 19 structural risk reduction alternatives were evaluated for flood, earthquake and normal operating conditions. The paper summarizes the risk assessment process, results, findings and recommendations. It also provides an evaluation of the risk assessment process and recommendations for better positioning the USACE to use risk assessment for dam safety evaluation and decision support.
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.
Shane McGrath and Michelle Cowan
Goulburn-Murray Water (G-MW) is a Victorian rural water authority with responsibility for management of the major water systems within a 68,000 square kilometre region. Following a detailed business risk assessment undertaken in 1996, Goulburn-Murray Water developed a ten-year program to commence design reviews and address identified deficiencies at thirteen dams for which G-MW has responsibility.
In October 1997, the Victorian Government announced a $450 million regional water reform package, of which $35 million was provided for rural water authorities dam improvements. $18.5 million was allocated to G-MW on a ‘dollar for dollar’ basis. With contributions from G-MW customers, the current total funding amounts to $37 million.
This paper focuses on processes that G-MW has adopted to manage an accelerated program of dam design review and remedial work.
Michael Cawood, Roger Jones and Ken Durham
A methodology for local disaster management planning based on Australian/New Zealand Standard AS/NZS 4360:1995 — Risk Management has been developed as an out-working of a Flood Risk Study for Murweh Shire. The methodology has relevance to all local governments, particularly in view of National Disaster Relief Arrangements (NDRA) that now link the extent of NDRA funding available for a re-occurring natural disaster event to the existence of disaster mitigation actions or plans. This places a premium on actions being taken by local governments to mitigate public safety risk at community level.