N. Vitharana, G. Bell, J. Jensen and J. Sinha
When the storage was enlarged in 1971, Wyangala Dam provided a storage of 1220Gl. The original concrete gravity dam was completed in 1936 with an initial storage of 37.5Gl. The enlargement comprised the construction of a central core earth and rockfill dam utilising the existing concrete gravity as an upstream “toe” dam. At its deepest section, the toe (concrete gravity) dam is 60m high with a base length of 40m. The rockfill dam is 85m and the full supply level is at 75m. Two cylindrical reinforced concrete intake towers were constructed utilising the crest of the toe dam as their bases.
Screening level analyses commissioned by The NSW Department of Land and Water Conservation have recommended that detailed seismic assessment of the toe dam and intake towers be undertaken. In 2001, GHD Pty Ltd undertook inelastic time-history analysis using site-specific seismic loadings. Toe dam was modelled together with the rockfill dam using a 2-dimensional model. Intake towers were modelled incorporating the composite behaviour of concrete and reinforcing steel with limited concrete strains to prevent the loss of cover concrete and the buckling of longitudinal steel. Time-history analyses supplements by conventional pseudo-dynamic analysis procedures.
This paper described the constitutive modelling, structural analysis criteria, evaluation of hydrodynamic and dynamic earth pressures and the findings.
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Chas Keys and Steve Opper
As the legislated ‘combat agency’ for dealing with floods, the NSW State Emergency Service has had considerable experience in planning for flooding on the state’s rivers and in developing arrangements to help keep people safe when floods occur. This experience has been put to use over the past decade in the particular context of managing floods caused or exacerbated by dam failure. Some of the complexities of the dam-failure planning problem are explored in this paper, specifically as they relate to warning and evacuation tasks and to the issue of preparing communities for the extreme flooding which dam failure can be expected to cause. The points are made that warning is not just about mechanical alerting devices, evacuation is not restricted to commanding people to move, and public education requires a sensitive comprehension of the problems of disseminating information about rare and difficult-to-believe events.
Tom Ryan, Charles Todd and Simon Nicol
The potential impacts of cold water releases on the downstream thermal regime include: reducing the seasonal temperature range (lowering of the maximum and raising the minimum); reducing the diurnal temperature variation; rapid temperature changes; and delaying the seasonal warming of stream temperatures. Recent investigations have identified at least 20 large dams within Victoria, that have the potential to release cold water from below the hypolimnium. A monitoring program is currently being implemented in Victoria to identify the occurrence of cold water releases and to estimate the extent of the downstream impacts.
Cold water releases have been shown to impact the biological processes within aquatic ecosystems and consequently reduce the natural productivity. The physiological development of native freshwater fish can be impacted in a number of ways. Growth and reproductive development of adult fish is impacted while the survival of eggs and larvae can also be retarded. As a result, the sustainability and viability of native fish populations are greatly compromised.
Using stream temperature data from the Mitta Mitta River downstream of Dartmouth Dam, the decline of the native fish populations, due to cold water releases, can be demonstrated under current operating conditions. The decline in population numbers can be further demonstrated with the use of a simple age-based population model for Murray Cod. The spawning opportunity and survival of egg and larvae can be improved for Murray Cod by increasing the overall spring release temperatures by 2, 4, 6 and 8 oC. The population model adjusted for these thermal improvements, results in increased survival prospects for the Murray Cod population.
Russell Hawken, Peter Buchanan, Doug Connors, Bill Hakin
Dartmouth Regulating Dam is located on the Mitta Mitta River, approximately 8 km downstream of
Dartmouth Dam. The dam is a 23 m high concrete gravity structure with a 60 m long central spillway
section. The dam forms the storage required for regulating releases from the Dartmouth Power
Station back to the Mitta Mitta River, so as to satisfy environmental requirements. Dartmouth
Regulating Dam and Power Station are owned and operated by Southern Hydro Limited, the largest
hydropower generator in Victoria.
To allow greater flexibility in their generation and hence a better response to the peaks in electricity
demand, Southern Hydro investigated the possibility of increasing the full supply level of the dam.
After an initial assessment of the economic benefits a detailed review of raising options was
undertaken, including different proprietary products and conventional spillway gates. Following this
review it was concluded that the Hydroplus System would provide the greatest benefits when all
aspects of the raising were considered, including dam safety, long term reliability, maintenance and
This paper discusses the reasons for the raising of the full supply level, the approvals process
undertaken and the technical issues addressed during the design stage, including the required
modifications to the dam and the appropriate sizing of the Hydroplus Fusegates.
R.J. Nathan, P.E. Weinmann and P.I. Hill
Current practice for estimation of design floods is typically based on the “design event” approach, in which all parameters other than rainfall are input as fixed, single values. Considerable effort is made to ensure that the single values of the adopted parameters are “AEP-neutral”, that is, they are selected with the objective of ensuring that the resulting flood has the same annual exceedance probability as its causative rainfall. While this approach represents current best practice in Australia (and overseas), it does suffer from a number of limitations.
This paper describes the development and application of a Monte Carlo (or joint probability) framework which offer an alternative to the design event method. This technique recognises that any design flood characteristics (e.g. peakflow) could result from a variety of combinations of flood producing factors, rather than from a single combination. The approach mimics “mother nature” in that the influence of all probability distributed inputs are explicitly considered, thereby providing a more realistic representation of the flood generation processes.
The advantages of the technique are illustrated by application to a hypothetical dam located on a real catchment. The manner in which standard design inputs are incorporated are discussed, as is the relationship of the approach to current guidelines.
David J. Walland, Jeanette Meighen, Catherine Beesley, Karin Xuereb
The method for estimating Probable Maximum Precipitation in areas of Australia affected by tropical storms has been revised. The method that it replaces, designed in the 1970s is considered outdated and based on limited data.
The entire Bureau rainfall record has been examined objectively for the largest rainfall events. These events have been analysed and modified to enable storm transposition across a large region. The modifications are based on local topography, moisture and location. Once the storm data is transposed to a single location it can be meaningfully compared and used to construct an upper estimate on the possible rainfall. This estimate can then be used in conjunction with information about a specific catchment in order to estimate Probable Maximum Precipitation at that location.