N. Vitharana, A. Gower, G. Bell and N. Petrovic
Churchman Brook Dam is a 26m high earthfill dam with a puddle clay core and impounds a reservoir of 2.2GL. Various remedial works have been undertaken since completion of construction in 1928. In September 2000, a sinkhole in the right abutment was observed during a routine dam inspection. Following this incident, detailed site investigations were carried out. These investigations revealed that there are soft zones and possibly voids formed in the upper part of the clay core.
A comprehensive dam safety study and a risk workshop undertaken in 2002/2003 showed the dam to be deficient in aspects associated with piping, spillway adequacy and outlet works condition. A rational geotechnical model was developed for the foundation utilising triaxial test data from 1980s and recent investigations. The existing spillway chute will be upgraded with a concrete liner attached to the existing chute incorporating no-fine concrete as a free-draining medium. This paper presents the various aspects of the remedial works currently being designed.
John Grimston, Robin Dawson, Maurice Fraser
Water supply for irrigation of horticulture and agriculture in New Zealand has gained considerable momentum since the mid 1990’s. The rapid growth of the wine industry in areas such as Marlborough (located at the top of the South Island) and dairy conversions in many areas of South Canterbury are prime examples of the pressure being applied to existing water supplies and sources and the increasing need for new irrigation supplies and security of supply.
The larger irrigation projects of the past were implemented by the government – schemes such as the Rangitata Diversion race and the Lower Waitaki irrigation project both on the east coast of the South Island. The 1990’s and early 2000’s has seen a largely hands off government approach to potential irrigation projects with the shift towards leaving it to market forces to build irrigation schemes. The result has been that due to significant larger project risks and capital cost requirements with often multi party stakeholder groups, only relatively small schemes have been implemented – the Waimakariri irrigation scheme and Opuha irrigation dam are a few examples. However, in recent years with the value of water increasing several significant irrigation projects promoted by private enterprise or progressive district councils with farmer groups are being investigated and a few may be close to implementation.
The recent drought conditions have focussed attention on the need for storages to maintain security of supply and, together with the balance with sustainability, the consenting environment in New Zealand and existing river/aquifer allocations, significant challenges to development are presented.
Specific case examples include the proposed Delta dam near Blenheim being developed by a private group of irrigators and the Bankhouse development being implemented by a private owner in the same Marlborough region.
This paper provides a background to irrigation in the South Island and describes these two proposed schemes and associated storage dams, together with an insight into the key issues related to the proposed projects.
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.”
This paper provides an insight into the management of reservoirs under drought conditions within the new water management frameworks established under the Council of Australian Governments (COAG) Water Reforms. Traditional approaches to the sharing of available supplies during drought are no longer appropriate as the roles of the resource regulator, infrastructure operator, and Government have been separated in the interests of providing certainty for water users and the environment. Recent experiences during drought in the Upper Mary River system near Gympie in Queensland has demonstrated the need to ensure the robustness of water sharing rules for reservoirs under the new framework if certainty is to be delivered.
Hydro Tasmania has recently upgraded the control systems for the spillway gates of three of its dams, Clark Dam, Meadowbank Dam and Liapootah Dam. The upgrades followed internal reliability assessments that highlighted high reliance on operator attendance, single points of failure and operational difficulties on each of the three gate systems.
The three gates are of contrasting types. Clark Dam Spillway Gates are submerged orifice type radial gates, operated by wire rope hoists. Meadowbank Crest Gates are flap type gates, held by 10 hydraulic cylinders per gate, a design that has had a difficult operating history. Liapootah is a floating drum gate. The upgrades for each gate therefore required different solutions, albeit within a common basis of design framework. The solutions arrived at are innovative, and meet or exceed worlds best practice.
All three gates are now fully automatic, with PLC control. The use of PLC’s significantly enhances the reliability of the gates. Extensive use is also made of the PLC in monitoring key systems. For example, an impossibly rapid lake level rise detected by one transducer, but not its duplicate, will be alarmed but ignored to avoid unnecessary discharge. All systems incorporate appropriate redundancy. The PLC systems also provide some automatic functional testing functionality and enhance remote alarms and local fault finding.
Mechanical systems were modified to facilitate automation and increase reliability. Stand by power sources used include auto-start diesel genset, DC batteries and a micro hydro generator.
The design and implementation of each of the upgrades was carried out by the Electrical and Mechanical Group of Hydro Tasmania’s Consulting Division, in conjunction with Generation Division’s Project Management Group.
Tony Qiu and Brian A. Forbes
The RCC design review and construction supervision of the 60m high Tannur Dam in Jordan was carried out by GHD, Australia.
The 220,000m3 of RCC was placed during February-December 2000; change to the sloped layer method was made once the dam reached 15m height. It produced a 50% increase in placing rate and a considerable saving in costs.
The use of the method is the first known use outside of China, where it was developed during the construction of the 130m high Jiangya Dam in 1997-8. The sloping of the 300mm thick layers of RCC across the dam from bank to bank at grades between 5-8% ensures subsequent layers of RCC can be placed within the initial set time of the lower layer and hence the RCC is monolithic across the lift joint.
This paper briefly describes the project in Jordan and then gives specific details of the use of the sloped layer method. Typical results from the quality control testing during placement and subsequent coring and testing of the lift joints are also provided. The benefits of its use in adverse climatic conditions, such as extreme heat or rainfall and the ways it can be integrated with forming the upstream-downstream slope are also discussed.
The sloped layer method is a significant advancement, particularly for large structures, where lift joint cohesion, tensile resistance and RCC placing rates are vitally important.