Since the research and development work carried out by the (then) Metropolitan Water Sewerage and Drainage Board for the strengthening of Manly Dam in 1979/80, there has been over twenty years of continuous improvement in the application of advanced post-tensioned anchors for gravity dam rehabilitation.
Up until the Manly Dam remedial works, concerns had been increasing as to the long-term viability of available anchors. Sophisticated monitorable and restressable anchors, with superior corrosion protection afforded by greased and sheathed strands, were developed initially in test-bed conditions. This style of anchor has subsequently been used extensively throughout Australia on dam upgrades.
This paper compares the claims made by the designers with the demonstrated outcomes of installations that have been achieved, with particular emphasis on dams now owned by the Sydney Catchment Authority and Sydney Water Corporation. The original commitments to economy, aesthetics and rapidity of construction have been borne out by experience, with additional environmental advantages also being achieved. With the confidence built up from many successes in the strengthening of older dams, the time appears right to revisit the construction of new dams using the same style of post-tensioned anchors as the primary stabilising force.
G. A. Pickens, J. O. Grimston
The Opuha Dam Project is a multipurpose water resources development, for irrigation and other uses. The 50 m high irrigation dam incorporates a 7.3 MW hydro installation, enhances summer low flows downstream, increases potable water supply security, is a significant recreational facility and provides flood attenuation. Opuha Dam was the first large dam permitted under NZ’ s Resource Management Act, for which sustainability is the cornerstone. It was also built under a design-build contract arrangement. Although breached by a flood during construction, the dam was successfully completed and performance has met or exceeded expectations. Experiences of potential value to future developments are outlined including the positive features of design- build. Technical features which contributed to the cost-effectiveness and performance of the project, are described, including downstream reregulation to enable “on-off’ peak hydro operation, Obermeyer type spillway gates to maximise flow capture for hydro and a stepped service spillway.
Allan Crichton, Jon Williams, Anthony Ford
Wivenhoe Dam was constructed in the early 1980’s and is the largest source of water to the southeast Queensland region. The dam also provides significant flood mitigation benefits to the large communities in the Brisbane valley including the cities of Ipswich and Brisbane. Changes in the methods of determining the probable maximum flood, which is the design flood for the dam, have meant that the dam was not capable of passing the significantly larger design flood event. The feasibility study undertaken to assess the most appropriate method of upgrading the flood passing capacity identified more than 240 options. These options were short-listed and the capital cost and consequences costs determined for each of the short listed options.
This paper describes the process used to identify the options to upgrade the flood passing capacity and the method used to assess the consequences costs, which are primarily the costs of flood damage resulting from each of the options. The consequences costs for each option are the costs associated with changing the flow conditions in the river downstream of the dam. For example the option to upgrade the dam to pass the design flood is a benefit to the community however if this benefit is achieved by installing large gates or a fuse plug that operates frequently the scheme may increase the costs to the community.
The preferred option initiates at the lowest probability of occurrence of all those analysed — average return period of 10,000 years. There will be opportunities during the Environmental Impact Assessment process to test acceptability of this initiation level — a more frequent occurrence would be a lower capital cost solution. The EIA process may require a solution with a higher initiating level. Informal talks with the regulator have indicated a preference for the less frequent initiation level.
M.A. Foster, R. Fell, R. Davidson, C.F. Wan
The probability of failure of embankment dams by internal erosion and piping can be estimated using historic performance, and event tree methods. Event tree methods are preferred for all except preliminary assessments, because they can better model the characteristics of the dam. This paper provides guidance on how to estimate the conditional probabilities within the event tree based on an understanding of the process involved, the historic performance of dams, and experience in recent risk analyses. This includes methods for representing the reservoir water level; assessing the likelihood that piping initiates; assessing the likelihood that erosion will be controlled by the filters or transition zones; and assessing the likelihood of development of a pipe and breach. The paper will be useful for those carrying out risk analyses and will also have relevance to those who are assessing piping of dams using traditional methods.
Thomas Zink, Michael Howat, Clive Anderson, Richard Davidson
This paper describes the refurbishment of Diversion Gate No 2 at Roxburgh Dam on the Clutha River, New Zealand. This 53m high concrete, gravity dam constructed in the 1950’s had three diversion gates fitted with stoney rollers which when opened into flow allows the rollers to disengage from the gate precluding subsequent closure. Diversion gate No. I was sealed off with a concrete plug. The remaining two diversion gates are required to provide additional flow control flexibility at the dam. Key aspects of the refurbishment design and construction include the system used to remove silt from upstream of the gate, and the condition of the gate itself and the concrete diversion channel after nearly fifty years of service. Brief details of the commissioning testing are also presented.
P.A. Maisano, P.A. Miskell
Design and construction issues relating to Cadiangullong Dam were reported to ANCOLD at
the 1998 Conference on Dams.’ First filling of the dam occurred in July 1998. Monito
ring of installed thermocouples, piezometers, joint and crack meters, movement targets and
seepage measurement devices, has been regularly undertaken by the dam owner and
reviewed by the designer. Annual inspections over these first 3 years of service, with
condition/performance reporting by the designer, has been undertaken in terms of the
Piezometers revealed excessive foundation uplift pressures near the right abutment.
Pressure relief holes drilled into the foundation were subsequently shown to have been successful in lowering foundation uplift pressures. Stability analyses confirmed the dam to
be stable under the new uplift regime.
The paper presents the performance of the structure and the reservoir in meeting the
designer’s and owner’s expectations as an assured process water supply for the Cadia Hill
Gold Mine, one of Australia’ s largest gold mines.
As one of the first roller compacted concrete (RCC) dams to use grout enriched RCC as an
impermeable facing to the upstream face and a durable surfacing to the stepped spillway,
the paper will also provide a performance review of this material which has since been
adopted on a number of other RCC dams worldwide.