Jon Williams and Chi Fai Wan
The Ross River Dam was first commissioned in 1974 and raised in 1976. The 8200 m long embankment was not fitted with chimney filters and has suffered extensive desiccation cracking since it was raised. A significant component of the dam upgrade is the retrofitting of filter zones to ensure the embankment meets current dam safety guidelines.This paper describes the process of investigation of the existing desiccation cracks and the use of Hole Erosion Tests (HET) and No Erosion Filter (NEF) tests to validate the design of the retrofitted filter.
A significant challenge in the design is to provide a cost effective solution given the 7500 m length of embankment requiring treatment. Assessment of flow rates within cracks and expected piping erosion along the cracks was used to assess the required drainage capacity. This assessment of expected flow capacity allowed the deletion of the coarse filter inthe design reducing the filter requirement from a triple filter to a single fine filter. Results of this assessment were incorporated into the Risk Assessment based design validation process
Howard and Opper
Dam safety planning is a team game. There are many players involved and there is a need for information to be shared and actions to be properly coordinated. The State Emergency Service is the legislated combat agency for flooding in New South Wales and is responsible for planning for and conducting the warning and evacuation of communities at risk from floods, including floods affected by dams. The successful execution of these responsibilities is dependent upon the continuing development of a strong, cooperative relationship between the dam owners and managers, dam regulators and emergency managers and the effective incorporation of community expectations in dam safety planning.
This paper explores some of the ways that this relationship can help to meet well accepted community expectations in respect of risk to life and property and outlines progress made in dam safety planning to date. The emergency response aspect of dam failure planning is still a relatively immature field in Australia, and it follows that there are lessons to be learned as we proceed. In that context, the paper also describes some of the difficulties the State Emergency Service has encountered in its role as the response planning agency and suggests some guiding principles to enhance future interactions between the key stakeholders.
J S Marsden, P H Jacob, R Nathan and L A McDonald
This paper relates to the conference sub-themes of Dam Safety Upgrades – Management of Risk and Due Diligence and Dam Construction.Specifically, it relates to the changing willingness of governments to fund risk reduction indams compared with risk reduction in other areas.
The cost of dam safety upgrades is just one of a portfolio of risk reduction strategies affecting the general community that governments are required to underwrite.
This paper examines the variation in acceptable risk standards between dam safety and other areas. This may be explained in terms of what is acceptable to the community and the courts. For instance, a corporation is likely to attempt to minimise its liability (which may differ to minimising risk for the community).
We also examine:
There is an increasingly well-established literature on the value of a human life and increasingly systematic approaches to the evaluation of risk and the setting of risk standards. Risk standards are particularly explicit in the area of dam safety – they set limits of tolerable risks for large-scale loss of life (eg. for existing dams, a loss of life of more than 10 persons with a probability of more than one in a ten thousand per annum is regarded as unacceptable under the Australian guidelines).
However, there are significant contrasts in what is tolerated as acceptable risk between different areas of government activity. To date,there appears to be no systematic evaluation of the portfolio of risks or a common view on what is acceptable levels.
Peter D Amos, Pip Nicolson, M Grant Webby, Murray D Gillon
To obtain a resource consent to build and operate any new water resource or hydro-electric development in New Zealand, the developer is required by the Resource Management Act (RMA) to consult with the community over the effects that the development could have, including describing how public safety risks will be avoided, remedied or mitigated. The community has the opportunity to respond to the authorities issuing the resource consent and influence the conditions attached to the consent.
The proposed Project Aqua Scheme in the South Island, New Zealand, comprised a 60 km long canal system to convey 340 cumecs flow from the Waitaki River across alluvial river terraces and through a chain of six hydro-power stations before returning the water back to the river. Each section of canal between stations would have contained between 4 and 6 million m3 of water within embankments up to 20m high. A breach of any one of these canals had the potential to flood farmland, residential buildings, highways, and other infrastructure, thereby posing a safety risk to local residents together with the potential for significant economic loss.
The paper describes the methodologies that were developed and used to assess the impacts, the measures proposed to avoid, remedy or mitigate safety risks and the public reaction to the associated report that was provided for public consultation prior to abandonment of the project. The methodologies used required adaptation of dam safety and consequence assessment practices usually applied to in-river dams, and applied here to the 60 km long length of canal embankment.
Stuart Macnish, Nikki Bennett
The $70 million upgrade of Wivenhoe Dam is being undertaken by the Wivenhoe Alliance, in close
proximity to the town of Fernvale, Queensland. As part of the Alliance’s commitment to delivering positive outcomes for the local community, it was decided part way through the project, to commit to delivering a ‘signature’ community legacy project. The team brainstormed a range of options and a decision-making matrix was used to choose the project that would best meet its objectives.
A partnership has been formed between the Alliance, Esk Shire Council and SEQWater to deliver a
master-planned project which incorporates elements such as a community information/service facility,upgrade of Fernvale Memorial Park, streetscape enhancements, improved parking and installation of shelters along the adjacent rail trail. These major partners, together with representatives of the local community, constitute the steering committee, which oversees planning of the project.
The project aims to encourage visitors to the area, to provide improved amenity and sense of pride for the region, and in turn encourage strong relationships for SEQWater in the area in which they operate. Due to tight time frames the partnership is managing the fund raising activities, community consultation and design processes in parallel.
This paper discusses the process by which the Alliance was able to deliver this remarkable project, within a short timeframe. It also discusses how the local community has been involved and the benefits, which have resulted.
Philip Styles, Brett Stephens, Stephen Perrett
The Wivenhoe Dam Spillway Augmentation Project involved the construction of an additional spill way on the right abutment of the main dam. The right abutment is located in massive sandstones and siltstones of Jurassic and Upper Triassic age.
Seismic refraction surveys and borehole drilling conducted at the design stage for the project indicated that part of the spillway area was likely to be marginally rippable to unrippable using a Caterpillar D9 bulldozer or equivalent. Further assessment and rock strength testing was conducted during the initial stages of excavation where D9 and D10 bulldozers were in operation. The results from this further work indicated that a section of the spillway extending from the proposed position of the ogee crest to approximately 100m further upstream were unlikely to be unrippable for a D9 dozer and marginally rippable for a D10.
Excavation options considered for this section included full scale blasting and load out, limited small scale ‘popping’ combined with ripping or the use of larger ripping equipment. Based on an assessment of cost-benefit, and given the availability of larger ripping equipment, it was decided touse a combination of D10 dozers and a Komatsu 475A bulldozer (D11 equivalent) equipped with single tine ripping tools. The use of this equipment proved successful with better than anticipated production rates being achieved. This resulted in significant cost and time savings for the project and reduced the likelihood of potential adverse impacts on the existing dam grout curtain, environment,travelling public and residents that may have occurred during blasting.