2005 – Use of Risk Based Design Validation for Justification of the Ross River Dam Upgrades
Malcolm Barker, Jon Williams and Chi Fai Wan
The Ross River Dam, designed in the early seventies, does not meet current dam safety criteria for overtopping and piping within the embankment or the foundation. The dam comprises a 40m long concrete overflow spillway flanked by a central core rockfill embankment of 130 m on the right bank and 170m on the left bank with a 7620 m long left bank earth fill embankment, which has no internal filter zones for piping protection. The embankment was extensively assessed and treated for foundation deficiencies in 1982, and further assessed in 2000-2002 for appropriate upgrade options.
This paper describes the process of validation of the detailed design using Risk Based Design Criteria.This process included data mining for historical performance and original design intention,comparison of the original design against current and historical investigations and assessment of the upgrades using the large volume of data available from previous work. A design team comprising specialist hydrologists, hydrogeologists, geologists, geotechnical and dams engineers worked within a risk assessment framework at all stages of the design to ensure the design was validated using the design Validation Model. This process incorporated assessment of crest level based on flood risk and wave overtopping, review of 2D and 3D seepage models to assess piping and foundation erosion potential, assessment of fissured soils within the embankment foundation for structural stability and evaluation of spillway model testing for potential spillway failure modes.
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2005 Papers
2005 – Investigation to Pursue Innovation
Learn moreBarton Maher, Richard Rodd
Changes to the estimation of extreme rainfall events resulted in significant increases in the estimates of the PMF since the original design of Wivenhoe Dam. To upgrade the dam to meet these new requirements, SEQWater (owner and operator) formed an Alliance with Leighton Contractors, Coffey Geosciences, MWH and the NSW Department of Commerce.
The option selected for the upgrade works included the construction of a new secondary spillway, upgrade of the existing gravity section, radial-gated spillway, and strengthening of the dam crest.
Value management was key throughout the project ensuring the Alliance was continually looking to
improve practices, increase cost-effectiveness and create innovative solutions for design elements of the project.On numerous occasions when the design was challenged, the Alliance made ‘best for project’ decisions to carry out additional investigations or design work to pursue alternatives. As an example, the powerful tool of Computational Fluid Dynamics was used in the analysis and design of flow deflector plates on the existing spillway, which were an alternative to the originally designed gate locking pins. The investigation and development of this alternative resulted in significant cost savings and a more effective design solution.
This paper presents aspects of the design carried out by the Wivenhoe Alliance, lessons learned, and the way continual investigations during construction provided value for money solutions.
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2005 Papers
2005 – Ross River Dam – Hydraulic Design Considerations for the Spillway Upgrade
Learn moreEric J Lesleighter and Peter F Foster
The Ross River Dam was constructed in 1974 following design by the State Government, including hydraulic model testing, by SMEC. The maximum spillway discharge at that time was 1100 m3/s.Latterly, the dam and spillway have come up for a comprehensive review given that the dam is in an extreme hazard category because of its location only a short distance upstream of the city ofTownsville. The revised hydrology has produced outflow hydrographs peaking at over 4 000 m3/s –more than three and a half times the original – to be passed through the 130 ft (39.62 m) widespillway.
The paper describes the hydraulic modelling planned and carried out to determine changes needed to handle such high discharges. The modelling was to provide for the installation of radial gates and piers, and study of the water level, pressure and dissipation conditions in the dissipator for several key discharges through the range to PMF. Pressure measurements included transients, consideration of the potential for uplift of the basin floor slabs, the integrity of the walls to handle the differential loads, and, as a major consideration, the energy conditions in the flow exiting the dissipator and the integrity of the rock downstream to avoid erosion.Each of these aspects will be addressed in the paperboth from the modelling and interpretation standpoint and from the civil structural analysis standpoint, together with a description of the strengthening works required to achieve a satisfactory outcome.
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2005 Papers
2005 – Importance of Streamflow Monitoring for Sam Safety and Water Supply Security
Learn moreIan Cordery, Peter S. Cloke
Scientists advocate more hydrological monitoring but in most regions publicly funded monitoring is in
steady decline. The lack of measured data at dam sites means there are many designs for new dams and remedial work that are insufficiently supported by factual information. Unfortunately data –free modelling exercises will usually produce favourable results – favourable to the modeller’s purposes, but not necessarily favourable to the determination of physical reality or truth. In these days of the popularity of modelling it is common to find decisions being made based on model studies for which little or no local data were available for model calibration or verification. How can the ‘large dam’ fraternity encourage (ensure) more data use? Causes of lack of data are many. For example governments fund data collection but others need the data, and data collection is a long-term activity that produces few benefits in the short term. Some years ago it was shown that hydrological data collection and archiving provided benefits to the community of at least nine times the costs of the data.The real costs of comprehensive data collection are not large but examples will be given of the huge
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costs, mainly due to the need to allow for uncertainty, that result from unavailability of data. Those
who understand this problem need to explain it to their communities, politicians and CEOs in a clear,
unmistakably persuasive manner, and to demand an increase in data collection. If we do not, no one
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2005 Papers
2005 – DAM SAFETY, RISK AND COST-SHARING: REVIEW OF THE DAM SAFETY PROGRAM FOR WESTERN AUSTRALIA’S SOUTH-WEST IRRIGATION DAMS
Learn moreThis paper sets out the principles, practices and issues relevant to the sharing of
costs for dam safety upgrades in southwest Western Australia and other locations.
We review:
? the general principles (noting that in practice multiple conditioning factors
apply);
? the practical outcomes for cost sharing in Australian jurisdictions;
? the beneficiaries of the dams, the water and the safety upgrades;
? legacy costs (including IPART’s framework and whether this can be directly
applied to the southwest);
? the Bulk Water Service Agreement;
? the question of price impacts and affordability based on surveys of farm
performance, water use and profitability; and
? the pricing impact of treating safety upgrades as if Harvey Water owned the
assets itself.We examine the impact of applying economic allocation principles to this task and the
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impact of other criteria such as dam safety obligations, hazards presented by a large dam,
community expectations for public safety, the broader public safety, welfare and state and
regional economic benefits reliant on dam safety, significant community costs subsidised by
irrigation customers, State Government ownership, and the effects on bulk water prices
should customers be required to fully fund the necessary dam safety upgrading. -
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2005 Papers
2005 – Achieving Benefits from Instrumentation and Survey Measurements of Dam Behaviour
Learn moreJohn D Smart
The paper presents the recent trends in the use of instrumentation and
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survey measurements at Bureau of Reclamation (Reclamation) dams. The underlying philos
ophy that has influenced those trends is presented and discussed. Based on experience at Reclamation, several factors that are considered key to the effective use of instrumentation and surveys are discussed. Several conclusions are offered.