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.
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.
P L Campbell, J W Walker and J T Mills
The results of a questionnaire on deformation surveys sent to dam owners around the world are presented. An analysis of the large variation in current international practice is made. The link between geodetic surveys and displacement instrumentation is established. The comparison with practice within a recent major New Zealand dam owner is drawn and a deformation survey policy is developed. Recourse is made to dam safety guidelines. Application of the policy is then described for a selection of differing types of hydraulic structures. It is shown that with the application of the policy a more rational approach resulted, surveys better reflected actual performance and there was better integration with the overall dam safety monitoring programme.
M.B.Barker and B.A. Vivian
Tumut Pond and Island Bend Dams are owned and operated by the Snowy Mountains Hydro Electric Authority. These dams, which are gated, have recently had significant electrical supply and control system upgrades. Subsequent reliability analyses performed for the gates provided unexpected results which highlighted issues concerning common mode failures and common cause failures associated with the mechanical systems. A further unexpected outcome of the analyses was the minor affect of human error and response to the emergency operating conditions of the gates in the event of electrical supply failure due to the over-riding mechanical system failures. This outcome was of benefit to the owners who had some concern that centralization of operation and consequent reduction in operating personnel would have an adverse effect on the reliability of the gates. The operation of the automatic control system is an ongoing issue for Island Bend where hunting of the gate operation is yet to be resolved. The preparation of the fault trees, development of failure probabilities and outcomes of the analyses are discussed in the paper which highlights some of the difficulties in design and operation of spillway gates, particularly where human response time is limited and automatic control is essential.
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.
The regulatory environment for dams in Queensland will change when the new provisions of the Water Act 2000 are proclaimed in late 2001 or early 2002. The definition of a ‘referable dam’ has shifted from a simple height and storage criteria to one that requires a population at risk (PAR) before dams are considered referable. Additionally hazardous waste dams such as tailings dams will no longer be considered as referable dams and under the Act regulatory control will be transferred to the Environmental Protection Agency.
Referable water dams will be assigned a Failure Impact Category of 2 if they have a PAR greater than 100 and a Category of I if they have a PAR greater than or equal to 2 and less than 100. This has required the development of guidelines for the assessment of ‘population at risk’. These guidelines have been written to suit a wide variety of dam impact situations and a range of dam owner resources. The guidelines require certification of the failure impact assessment by a Registered Professional Engineer in the state of Queensland.
The Queensland Dam Safety Management Guidelines have also been re-written to make them more amenable for reference in dam safety conditions.
New dams will require development permits to be issued under the Integrated Planning Act and will have development permit conditions applied in accordance with their Failure Impact Category. There is a range of transitional provisions for existing dams.
This paper covers all of the above issues as well as providing an indication as to how these statutory guidelines relate to the various ANCOLD guidelines.