Paul W. Heinrichs & John Bosler
Spring Creek Dam is a 16m high zoned earthfill dam with a central vertical concrete core wall storing 4700 ML for Orange City Council’s water supply. It was a 14.5m high dam constructed in 1931 and in 1947 was raised by 1.0m. In 1966 after a week of heavy rain following a long dry spell, an 80m section of the downstream face slumped but the dam fortuitously survived. In 1969 the dam was re-constructed but no internal drain/filter was installed.
Following the 1994 dam surveillance report, piezometers were installed in the downstream fill. Drilling for these revealed that a substantial portion of the zone downstream of the core wall was saturated. The piezometers recorded piezometric elevations that closely and rapidly followed the reservoir level. Subsequent site investigations identified pockets of very low strength fill immediately downstream of the core wall. It was concluded that the core wall was seriously compromised and the storage level was subsequently, significantly lowered, as an interim dam safety measure.
Dambreak studies indicated the dam is a high hazard and hydrological studies found that the spillway capacity was inadequate.
This paper details the problems involved, their analyses, and the remedial measures proposed at the concept design stage. These include a chimney filter/drain, a stabilising fill combined with embankment crest raising and the construction of a 3-bay fuse plug auxiliary spillway.
Mike Taylor, Paul Maisano and Rod Conway
Daylesford Dam forms an ornamental lake, known locally as Lake Daylesford, situated on Wombat Creek within the heart of Daylesford in Victoria. It is a focus of the local tourism industry and is vitally important to the Daylesford community as a recreational, social and environmental asset, with important heritage value.
On 24 October 2000, the 12m high embankment was overtopped following heavy rainfall and was in danger of breaching. This could have resulted in loss of the dam and lake, downstream damage to roads and the environment and possible loss of life. The overtopping of the dam prompted the Hepburn Shire Council, land manager for the dam, to initiate a safety review of the dam as well as the commissioning of a Dam Surveillance Program and a Dam Safety Emergency Plan.
The spillway is of the side-channel type with a 30m long concrete sill at the entrance discharging into a 5m wide unlined trough and chute. The existing spillway can only accommodate a peak flow of 24m3/s, which represents an AEP of less than 1 in 20. The required flood capacity in terms of the latest ANCOLD guidelines on spillway adequacy is for an AEP of 1 in 1 000 which equates to 120m3/s.
Following discussions with Hepburn Shire Council, and an evaluation of public usage of the Lake Daylesford area, it was assessed that the following constraints apply when considering options for increasing spillway capacity:
The proposed solution includes the following:
Tim Waldron, K D Murray and Allan Crichton
The City of Hervey Bay is a growing tourist community that is located a comfortable 3½ hour drive north of Brisbane. To meet the growing water demands of the community, Wide Bay Water Corporation required the raising of its sole water supply – Lenthalls Dam.
At the time of the option study, Queensland dam owners were aware of their obligation to manage their dams to minimise adverse environmental impacts but detailed Environmental Flow Objectives were still being developed.
This required a solution for the raising of Lenthalls Dam that provided maximum flexibility while, at the same time, being cost effective.
A range of solutions and new technologies were investigated. Using a Risk Management methodology, the Crest Gate system developed in South Africa was adopted.
Subsequently, draft Environmental Flow Objectives have been set and the use of a gated system has been beneficial in meeting post-winter flow objectives.
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.
Pieter van Breda, Alison White, and Greg Carmody
Site works on the $150 million Warragamba Dam Auxiliary Spillway project commenced in March 1999 and were completed in June 2002. Successful interaction with the local community, to achieve an equitable outcome, has been a feature of the communications strategy for the project.
The Auxiliary Spillway is located close to the village of Warragamba, a township of approximately 2,000 residents. The closest residence is about 200 metres from the site. The EIS and subsequent planning documents identified key localised environmental impacts that the project would impose. The main concern of local residents, including a local action group, was the impact on their amenity during construction of the Auxiliary Spillway, particularly in relation to noise, vibration, dust and traffic.
The conditions of approval for the project included a range of communication activities, of which the formation of a Community Liaison Committee (CLC) with an independent Chairperson was a key component. When the membership of the CLC was established the Sydney Catchment Authority (SCA) and chairperson agreed that it needed to fully represent the local community – and therefore included community representatives from Warragamba and two nearby villages, the Chamber of Commerce, the local action group, the local school, local council, the dam owner (SCA) and the project manager (AWT P/L).
The establishment of the CLC has proven to be very successful. It has been the voice of the community, with responsibility to act on behalf of the community and to keep them informed of progress on the project. When issues arose during the construction, the CLC were briefed on the particular matter. The CLC was instrumental in resolving these community issues and has allowed this $150 million civil project to proceed without community attributed delays.
Bill Hakin, Phillip Solomon, Peter Siers Bruce Goddard
Lyell Dam is located on the Coxs River near Lithgow NSW Australia. It was constructed in 1982 to supply cooling water to Delta Electricity’s Mt. Piper and Wallerawang power stations.
In 1994 the storage capacity of the dam was increased by 7,500 Ml by raising the embankment height and installing two 3.5m high inflatable rubber dams on an enlarged and slightly raised spillway sill. Two significant failures of the rubber dams in 1997 and 1999, led the dam owner to seek an alternative method of maintaining the increased Full Supply Level (FSL) whilst still providing spillway capacity for the design flood. Although the lost storage has a certain strategic value to Delta Electricity, the main reason for restoring the capacity to its former level was to preserve the environmental and recreational use of the reservoir for the local community.
Following a detailed review of options, Delta Electricity chose to regain the former FSL with the Hydroplus Fusegate System. Because of the freeboard available at Lyell dam it was possible to design the Fusegates such that none tip before the 20 000 AEP flood.
In order to derive accurate as-built levels and dimensions of the existing spillway, new laser scanning methods were utilised to create a digital 3-D model of its complex shape.
The water retaining concrete Fusegates were poured in-situ and designed without anti-crack reinforcement. This innovation was only possible by use of a special design mix and careful temperature control/monitoring during concrete placing.
This is the first installation of the Hydroplus Fusegate System in Australia. The paper examines the philosophy of approach and various unique methods used in the application of the System during the design and construction stages.