Jim Walker, Sergio Vallesi, Neil Sutherland, Peter Amos, Tim Mills
The Tekapo Canal is a 26km long hydropower canal owned by Meridian Energy Ltd in New Zealand. Completed in 1976, the canal is 40m wide, 7m deep and has a capacity of 120m3/s. The canal was constructed from compacted local glacial soils with a compacted silt lining sourced from till deposits.
During 2007 and 2008 the canal showed signs of leakage where it crossed over a twin barrel culvert structure. In October 2008 a diver inspection identified depressions and sinkholes on the invert of the canal above the culvert. Approximately 6m3 of silty gravel lining material had settled. Testing showed direct and rapid connections between lining defects and seepage outflows at the culvert outlet headwall. Subsequent ground penetrating radar survey confirmed the presence of voids above the culvert barrels. Diver placed filling of the defects with granular materials was immediately implemented, and a series of remedial actions over the next four months were required to arrest deterioration and enable the canal to remain operational.
The paper describes the initial response to this situation and the immediate measures taken to prevent failure. It also describes the medium term and ongoing measures implemented to maintain the safety of the canal while permanent remediation requirements are assessed. The lessons learned from this event, and their impacts on Meridian’s Dam Safety Assurance Programme (DSAP) are also discussed.
Immediate response measures included ongoing filling of lining defects with filter gravel, intensive land based and diver surveillance of the canal, planning and resourcing for emergency contingency actions in the event that a risk of breach developed. Medium term measures included arresting leakage by placing a low permeability blanket of silty gravel over the damaged area using a concrete pump, and constructing external buttresses capable of safely withstanding large discharges should deterioration of the canal structure occur.
These short and medium term remedial measures were completed with the canal full and in operation and continue to perform well 20 months later. Continuing risk mitigation measures include enhanced surveillance and monitoring (land based and using divers), localised treatment of defects, as well as ongoing monitoring and review of the Dam Safety management regime and sustained Emergency Management preparedness.
Now showing 1-12 of 41 2974:
After a period of drought for many years, inflows during May and June 2009 resulted in releases from North Pine Dam. These releases resulted in deaths of fish downstream of the dam wall including lungfish. The Australian Lungfish is a protected species under the Environmental Protection and Biodiversity Conservation Act 1999 (Australian Government). The events of 2009 have shown, however, that a proactive response supported by sound knowledge is required to minimise lungfish losses from flood events and other dam operations activities. A framework has been developed for the management of lungfish populations in Seqwater storages. The framework centres on a Seqwater Fish Management Policy, and four broad strategies that are considered necessary for addressing fish management in Seqwater storages: Fish Management, Storage Operations, Communication, and Research. These strategies are being used as a basis for identifying, planning and managing a range of actions designed to ensure that impacts to lungfish are minimised. Seqwater intends to develop the framework further to include long term management initiatives such as implementing viable technologies for preventing lungfish strandings, habitat protection and restoration activities that support viable lungfish populations, as well as establishing priorities for managing risks to other aquatic vertebrates in Seqwater storages, including other protected species, recreationally and commercially important species; e.g. turtles , carp, mullet, etc.
Ben Greentree, David Bamforth, Matthew O’Rourke and James Willey
A series of relatively small floods occurring between end of construction in 1978 and late 1980s caused extensive and dramatic rock erosion to the very steep unlined section of the Googong Dam spillway. Following a review of hydraulic performance at larger floods, the spillway’s future erosion potential was evaluated and it became clear that extensive remedial work was required. A detailed design was developed comprising the retro-fitting of a full concrete-lined chute, the raising and extension of the spillway chute walls, strengthening of the upstream training walls and excavation of a large plunge pool. The Googong Dam has an ANCOLD hazard rating of ‘extreme’ because of its location upstream of Queanbeyan and Canberra.
In early 2008, the Bulk Water Alliance (BWA), comprising ACTEW Corporation Ltd, (in cooperation with ActewAGL) (the Owner), GHD Pty Ltd (the Designer) and Abigroup Contractors Pty Ltd in joint venture with John Holland Pty Ltd (the Constructors) was formed to deliver a package of water security projects for the ACT, one of which is the Googong Dam Spillway Upgrade.
After preparation of a construction methodology and target outturn cost (TOC), the project was approved by the Actew Board and construction commenced in February 2009. Completion is due in late 2010. A number of significant geotechnical, structural and logistical challenges were encountered during construction, resulting in major changes to the construction methodology necessitating design changes. The changes were incorporated within the original TOC, without instigating scope change contractual claims and while still maintaining spillway functionality in line with Owner operational requirements.
This paper presents delivery phase challenges that necessitated construction methodology and design changes to achieve best for project outcomes; how these challenges were overcome through genuine innovation reliant on a collaborative effort by all the Alliance partners; and how the contractual framework of the Alliance was essential for the change management process to be successful.
Karen Riddette, David Ho
Recent dam safety reviews of a number of Australian dams have identified that the arms of raised radial gates may be partially submerged by extreme flows which exceed the original design flood for the dam. Various design solutions have been proposed to secure and strengthen the radial gates, however an important concern is the potential for flow-induced vibration. Under extreme flood conditions, flows near the gate arms will be high-velocity, free-surface, with a steep angle of attack on the arm beams. Traditional hand calculations for computing vibrations are of limited applicability in this situation, and there is little published data available for this combination of flow conditions and arm geometry. A detailed study using CFD modelling of the potential for vibration around radial gate arms was carried out for Wyangala Dam. This paper presents the results of the validation and reveals some interesting flow patterns and vortex shedding behaviour.
Assessment of flow-induced vibration in radial gates during extreme flood
Keirnan Fowler, Peter Hill, Phillip Jordan, Rory Nathan, Kristen Sih
Although there are considerable uncertainties in the science of climate change, there is a growing recognition of the importance of the issue. Incorporation of climate change impacts is now required in policy guidance from several government authorities and it is prudent risk management to consider the effects of climate change in planning for water resource infrastructure, including assessment and design of dam upgrades. This paper describes the potential impact of climate change on extreme flood estimates and provides a case study for Dartmouth Dam in south-eastern Australia. Three inputs to flood estimation were considered according to the projected impact of climate change; namely design rainfalls, modelled losses and initial reservoir level. The relative influence of each of these factors is explored. Rainfall and losses had a similar (and opposite) influence on results and for this dam the reservoir level prior to the flood event had the largest influence on results. This case study demonstrates that the insights of climate modellers and hydrologists need to be integrated in order to provide defensible estimates of the impact of climate change in flood hydrology studies. Credible projections of changes in design rainfall intensities are required for the full range of exceedance probabilities across Australia.
Application of Available Climate Science to Assess the Impact of Climate Change on Spillway Adequacy
David Ryan, Peter Richardson, William Steen
Ibis Creek Dam, a referable dam and classified as a mass concrete gravity structure, was constructed in 1906 to supply water for both tin ore processing and the local township of Irvinebank. Irvinebank is a small township near Atherton in North Queensland and is situated about 3 km downstream of the dam. The mill ceased operation in 1990 but the township of Irvinebank remains reliant on the dam for water supply.
In 1996 the dam was raised about 1 m and strengthened by the addition of mass concrete on the crest and downstream face.
One recommendation of the Safety Review conducted in 2009 was that an investigation be made of the strength of the lift joints and the shear capacity of the connection between the Stage I and Stage II concrete sections. The investigations revealed that the structure was not constructed as had been originally assumed and the overall stability of the structure had been overestimated.
This paper details the investigations and remedial works proposed to strengthen the structure so that it complies with current design standards.