K. Chandler, D. Gill, B. Maher, S. Macnish and G. Roads
SEQWater is the major supplier of untreated water in bulk to Local Governments and industry in the South East Queensland region of Australia, through ownership of Wivenhoe, Somerset and North Pine Dams. Wivenhoe Dam (Lake Wivenhoe) is located on the Brisbane River in Esk Shire. The storage provides both flood mitigation and water supply storage to Brisbane and Ipswich. The water supply storage capacity at full supply level is 1,160 GL. An additional 1,450 GL of storage above full supply level is used for flood mitigation.
Changes to the estimation of extreme rainfall events has resulted in significant increases in the estimates of the PMF since the original design of Wivenhoe Dam. To upgrade the flood security of Wivenhoe Dam, SEQWater has formed an alliance with Leighton Contractors, Coffey Geosciences, MWH and the NSW Department of Commerce.
This paper details the alliance delivery method, the latest estimates of the PMF based on the GTSMR method and details of the two preferred options being finalised by the Alliance.
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This paper presents the findings of experimental investigation of internal erosion by the process of suffusion within embankment dams and their foundations.
Suffusion is the process by which finer soil particles are moved through constrictions between larger soil particles by seepage forces. Soils susceptible to suffusion are usually described as internally unstable. Understanding of the suffusion process is important to the assessment of the risk of internal erosion in an embankment dam and its foundation. Suffusion results in a coarser soil structure, leading to increased seepage, progressive deterioration of the dam or its foundation, and a higher risk of toe instability. Suffusion within the protective filter of a dam may result in a coarser filter, rendering it ineffective in protecting the core materials from erosion.
Two types of suffusion tests, namely the downflow test and the upflow test, have been conducted at the University of New South Wales. The downflow test aims at identifying the types of soils that are susceptible to suffusion, whereas the upflow test aims at identifying the hydraulic gradient at which suffusion is initiated. This paper presents the initial findings of the downflow test. Eighteen downflow tests have been carried out on fourteen clay-silt-sand-gravel soils. The Kenney and Lau (1985, 86) method, which is commonly used for assessing the internal stability of coarse-grained soils, appears to be too conservative when used to predict the internal stability of silt-sand-gravel or clay-silt-sand- gravel soils, whereas the Burenkova (1993) method appears to provide better predictions. Further testing is required to define more accurate criteria for determining the internal stability of broadly-graded clay-silt-sand-gravel soils.
Gregg Barker B.E. (Hons.) GradIEAust
Dam safety emergency plans (DSEPs) are typically produced for individual dams. For owners of a large portfolio of dams, this approach creates document control difficulties, requires excessive time and effort and can lead to confusion when a single emergency affects multiple dams having individual DSEPs. Hydro Tasmania has developed a single DSEP which is applicable to its portfolio of 54 referable dams. The DSEP contains generic emergency response procedures, is applicable to a whole range of generic dam safety incidents, uses a simple colour-coded flowchart-action list format, has a two-stage emergency response, retains all necessary dam-specific information and can be easily adapted to any organisational structure. This approach was found to have benefits in document control, flexibility in the management of the emergency response and short lead time in terms of having DSEPs which cover an entire portfolio of dams.
N. Vitharana, P. Mendis, G. Kusuma and T. Ngo
In 1998, ANCOLD Guidelines entitled “Guidelines for Design of Dams for Earthquake” was issued. The Guideline mainly deals with the seismic aspects of dams and only a basic reference is made to the seismic assessment of intake towers in Section 8.3. Although the much needed and pioneering step taken to introduce this Guideline is to be appreciated and it has covered the seismic aspects of dams, some confusion does exist amongst dam / structural engineers in assessing the seismic performance of concrete intake towers. This is mainly due to the fact the behaviour of reinforced concrete intakes towers is quite different from that of earth or concrete gravity dams. This confusion could potentially lead to gross overestimate of the inertia loads on concrete intake towers resulting in unnecessary expenditure in investigation and remedial works.
The energy dissipation due to inelastic hysteresis behaviour of concrete members results in a great reduction in the inertia loads compared with those calculated with traditional “elastic” analysis methods. This consequently results in significant reductions in bending moments and shear forces on the tower and its foundation. It is very important to understand the basic behaviour of reinforced concrete, considering the composite action of concrete, longitudinal & hoop reinforcing steel, before embarking in sophisticated dynamic analysis the outputs of which are highly dependent on the input parameters.
The authors have developed a methodology in which the hysteresis energy dissipation due to the inelastic behaviour of concrete intake towers is considered. Various criteria were defined for serviceability and ultimate failure modes such as excessive deflection, spalling of concrete, buckling of reinforcing steel. The confinement effect of hoop steel on the core concrete is also considered.
This paper will present the fundamental aspects of seismic behaviour of reinforced concrete structures with practical cases as applied to intake towers. The results showed that the current methods adopted by various Dam Authorities in Australia are cursory and the energy dissipation aspect should be considered, in conjunction with expert advice, before undertaking any remedial works.
Bill Hakin, Peter Buchanan, Doug Connors, Darren Loidl
To allow greater flexibility in their generation and hence a better response to the peaks in electricity demand, Southern Hydro decided to increase the Full Supply Level of Dartmouth Regulatory Dam by 3.5m using labyrinth Fusegates.
The Regulating Dam is located on the Mitta Mitta River, approximately 8 km downstream of Dartmouth Dam. It 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.
Although this is the second Fusegate project in Australia it is unique in that difficult access conditions determined that construction in mild steel would be the most appropriate. Initial civil works involved construction of a flat sill to replace the Ogee spillway crest so that it could support the Fusegates. The installation contractor devised an ingenious method for installing the huge structures over the top of the gate-house which blocks direct access to the spillway. Design was very much undertaken with the installation method in mind to ensure a high quality project with minimum contractual risk.
This paper discusses the construction stage of this very interesting spillway modification.
Cold water pollution occurs downstream of many Australian dams when water is released from well below the surface layer of a stratified reservoir during spring and summer. Water temperature can be depressed by 8 °C or more and this may impact negatively upon the survival and growth of native Australian fishes.
After many years in the ‘too hard basket’, mitigation of cold water pollution below dams is receiving increasing attention in Australia. Hume Dam is a case in point. Hume Reservoir, one of the largest irrigation reservoirs in Australia, has a high throughput of water (short residence time) and receives unseasonably cold water from Dartmouth Dam on the Mitta Mitta River and the Snowy Mountains Hydro Scheme on the Murray River.
The maximum possible discharge temperature below Hume Dam may be constrained by geomorphic and climatic features beyond human control. Specifically, the relatively short residence time of water may limit the extent to which it can heat up in the reservoir prior to discharge downstream. Here I present a heat budget for Lake Hume and address the question, “How much can we improve the thermal regime below Hume Dam.”