Changes to the Regulatory and legal environment have resulted in an increased focus on the
importance of proficient management of dams. Operation and maintenance manuals are now a
Regulatory requirement in Tasmania for all but very low hazard dams and are also required to ensure that dams are managed efficiently and safely. To meet these requirements Hydro Tasmania has developed the ‘Smart’ operations and maintenance manual.
Hydro Tasmania has a large portfolio of dams and as a result requires a large number of operations and maintenance manuals. This would result in an overwhelming array of information that is subject to evolving change if the traditional approach to the manual was adopted. To overcome this burden, a controlled electronic manual was developed to enable:
• Critical operation and maintenance information to be collated with minimal effort;
• Electronic hyperlinks to key existing operation and maintenance documents, reference
materials, and portals into operational data bases; and
• A means of updating and controlling information that is subject to change.
This paper will discuss how Hydro Tasmania developed its user-friendly operation and maintenance manuals in an innovative, unique and controlled manner to ensure prudent management of dams and to comply with Regulatory change.
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John Grimston Sally Marx Robin Dawson and Peter Thomson
The Wai-iti Valley is located in the northern region of New Zealand’s South Island. Water demand during summer in the Wai-iti Valley is greater than the available supply, resulting in water allocation restrictions and pressure on in-stream habitat and uses. Further, the summer water resource in the Wai-iti Catchment is currently over-allocated. Thus, since the mid 1980s, Tasman District Council (TDC) has been unable to grant new water permits to take water from either rivers or groundwater in the Wai-iti Catchment. Existing water permit quotas have been reduced where they were not being used, but despite this agricultural, horticultural and domestic use is frequently restricted during dry years.
Recently, the need for a community solution was identified for the Wai-iti Valley area. The Wai-iti Water Augmentation Committee (comprising representatives from the local community and TDC) was set up in 1995 to find the best option for the northernmost extent of the Wai-iti valley. A feasibility study for a community dam was completed in 2001 identifying small off-river storage dams as options. The proposed scheme is located in a tributary of the Wai-iti River and is essentially a water harvesting project where winter flows in the stream would be impounded and stored, and gradually released on a regular basis back into the stream and Wai-iti River system during dry summer periods.
The paper will cover the project’s economic objectives as well as community and environmental impacts and the consenting process under the Resource Management Act. Dam construction is planned to start in October 2004.
Robert Humphries, Caroline Minton, Andrew Baker and Mark Leathersich
There is a constant stream of criticism levelled at the perceived or actual adverse environmental
effects of large dams. These criticisms include prevention of fish migration, thermal and chemical and biological disturbance of downstream riverine habitats, silt trapping and drowning of terrestrial
habitats by flooding behind the dam wall. The beneficial effects of dams are rarely discussed, but
include aquatic habitat creation, catchment protection, flood mitigation, carbon sequestration and
protection of endangered species, amongst others.
Critics of large dams rarely present an analysis of the environmental costs and benefits of other water supply options, which include abstraction of shallow or deep groundwater, desalination of seawater, and reclamation of human or other wastewater.
In this paper we compare the environmental costs and benefits of water supply from large dams with
the common alternative options, and assess the relative sustainability of them all.
Keith Seddon, Craig Noske, Ian Duffield
This paper covers the investigation, design, construction and performance of a tailings dam at Mount
Thorley Warkworth (“MTW”), a Coal and Allied operated open-cut coal mine in the Hunter Valley, NSW.
A tailings disposal site was identified in one of the ramps through the mine-spoil piles. The “foundations” and abutments comprise uncompacted mine spoil to a depth of 40m below the haul road surface. The Stage 1 embankment at this site has a height of 70m.
The dam is a zoned rockfill embankment, constructed from mine spoil.
It was designed as a “leaky” dam. An innovative method of work packages was developed
for construction. The rockfill was delivered to the site by the mine. Spreading and compaction was carried out by a separate external contractor. Construction of the embankment was completed in a period of 5 months.
Filling of the storage commenced before the end of construction. Monitoring has included measurements of very large settlements, plus tailings level and piezometric surface. The monitoring results are presented and discussed.
David S. Bowles, Loren R. Anderson, Terry F. Glover, Sanjay S. Chauhan, Ronn S. Rose
A risk assessment was performed for the Sacramento District of the U.S. Army Corps of Engineers to explore the justification for imposing an operating restriction on Lake Success to reduce the probability and consequences of an Earthquake-induced dam failure. The potential for both a sudden overtopping failure and a delayed “seepage erosion through cracks” failure were considered.
The risk assessment focused on the seismic performance of the dam, the potential life loss and economic consequences of Earthquake-induced dam failure, and the estimated residual risk and degree of risk-based justification for the Existing operating regime, a range of Potential Operating Restrictions, and an Indicative Improved Warning and Evacuation System. Risk assessment inputswere supported by seismic deformation analyses under various Earthquake loadings and pool elevations, dam break-inundation modelling, and reservoir simulation.
Evaluations against tolerable risk guidelines from the USBR, ANCOLD, and the UK HSE, together with insights into the relationship between pool elevation and dam failure risk, provided important inputs for the decision to implement an operating restriction.
Brian Simmons, Glen Hobbs, S Muralitharan, Udaya Peeligama
Warragamba Dam supplies up to 80% of Sydney’s water needs and is currently undergoing a range of major infrastructure upgrades. The outlet works upgrade is one of these projects. The outlet works of the dam were constructed in the 1950s and consisted of four 2100mm pipes with isolating gate valves and needle control valves feeding two large aboveground pipelines running 27 kilometres east to Prospect Reservoir in Sydney’s western suburbs.
In the 1990s the then dam owner (Sydney Water) undertook a detailed and extensive risk analysis of the outlet works. The study resulted in a recommendation to remove the existing valves and replace them with a combination of emergency closure (guard) valves and isolating valves. Under the Sydney Catchment Authority (the present dam owner) work subsequently proceeded in 2004 as a design and construct contract with all aspects of construction and water supply risks identified. Stringent controls were developed and placed on work programs and pipeline shutdowns to ensure the safety of all involved and the integrity of the supply to Sydney.
The four outlets required eight large valves, which were manufactured in Germany and were required to meet stringent operational requirements.At the time of writing three of the four outlets have been successfully upgraded and commissioned.Work has commenced on upgrading the fourth outlet, which is due for completion by the time of the conference, approximately 20 months ahead of schedule.
This paper discusses the project from the initiation of the risk analysis study, through the consideration of options, development of the contract, and the supply, installation and commissioning of the large valves and pipe work. It highlights the role of risk assessment in selection of the preferred option and addresses some of the engineering challenges faced during the project.