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.
J S Marsden, P H Jacob, R Nathan and L A McDonald
This paper relates to the conference sub-themes of Dam Safety Upgrades – Management of Risk and Due Diligence and Dam Construction.Specifically, it relates to the changing willingness of governments to fund risk reduction indams compared with risk reduction in other areas.
The cost of dam safety upgrades is just one of a portfolio of risk reduction strategies affecting the general community that governments are required to underwrite.
This paper examines the variation in acceptable risk standards between dam safety and other areas. This may be explained in terms of what is acceptable to the community and the courts. For instance, a corporation is likely to attempt to minimise its liability (which may differ to minimising risk for the community).
We also examine:
There is an increasingly well-established literature on the value of a human life and increasingly systematic approaches to the evaluation of risk and the setting of risk standards. Risk standards are particularly explicit in the area of dam safety – they set limits of tolerable risks for large-scale loss of life (eg. for existing dams, a loss of life of more than 10 persons with a probability of more than one in a ten thousand per annum is regarded as unacceptable under the Australian guidelines).
However, there are significant contrasts in what is tolerated as acceptable risk between different areas of government activity. To date,there appears to be no systematic evaluation of the portfolio of risks or a common view on what is acceptable levels.
Graeme Hannan, David Jeffery
Lake Mokoan is a 365 GL capacity off-stream storage in the Broken River basin in northern
Victoria. Lake Mokoan will be decommissioned to provide 44 GL of water savings to benefit the
River Murray and the Snowy River. The Victorian Government has committed to maintain
reliability of supply in the Broken River supply system by implementing a package of offset projects.
The paper describes the community engagement process implemented by Goulburn-Murray Water
to steer the selection and implementation of the offset projects.
A reference committee of Broken systems irrigators was established in late 2004 to provide advice
to Goulburn-Murray Water and the Department of Sustainability and Environment on the package
of offset measures to be implemented to maintain the supply reliability once the 365 GL capacity
Lake Mokoan was decommissioned, leaving the 40GL capacity Lake Nillahcootie as the sole
storage in the Broken River irrigation system.
A REALM based system simulation model was refined to test the sensitivity of the parameters
defining the system reliability and to assess proposed offsets measures. The paper describes the
modelling which was undertaken and the evaluation and ranking of offset projects priorities.
The community engagement process is described. The paper concludes with commentary of the
lessons learned from this process.
Andrew Evans, Michael Cawood, Jonathon Reid
Eildon Dam, Goulburn Weir and Waranga Basin in Victoria are owned and managed by Goulburn-Murray Water (G-MW). Eildon Dam and Goulburn Weir are situated on the Goulburn River, while Waranga Basin is an offstream storage supplied from Goulburn Weir.
In November 2004 a dam safety emergency exercise involving the establishment of a central Emergency Coordination Centre at Tatura as well as Emergency Operations Centres at each of these three dam sites was conducted. The exercise presented a variety of emergency situations in stepped time increments, including earthquake, mechanical failure, a hazardous material spill and a terrorism related incident. External agencies were not involved.
The exercise was part of an ongoing G-MW program designed to test and improve dam safety emergency planning and response systems for all of G-MW’s dams and highlighted areas where procedures, situational management and communications can be enhanced.
Outcomes aimed for in G-MW’s program are improvement in Dam Safety Emergency Plans and internal communications, together with clarification of roles, responsibilities and capabilities.
The valuable experiences learned from this dam safety emergency exercise and plans for a larger scale exercise involving other emergency management agencies will be shared with others through this paper.
Ian 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
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
Peter Hill, Kristen Sih, Rory Nathan, Phillip Jordan
This paper presents a number of innovative hydrologic investigations undertaken for the recent detailed design of upgrades for Ross River Dam in North Queensland. A key issue for estimating extreme floods in the tropics is the estimation of flood events of long critical durations. The implication is that there is an increased focus on estimating the correct volume (not only the peakflow). This paper describes the regional analysis of flow volumes that was used to validate the estimated flood volumes.
Another issue of considerable importance is the assumed relationship between inflows and initial reservoir level. The analyses described in this paper showed that inflows are independent of reservoir levels for the more frequent events but for more extreme events they are correlated. This has important implication on how the initial reservoir level is incorporated in the hydrologic analysis. The final aspect covered by the paper is the derivation of seasonal flood frequency curves. This is particularly important given the highly seasonal nature of rainfalls in the tropics and the results are important for assessing risks during construction and scheduling the upgrade works