Kristen Sih, Peter Hill, Susan Ryan, Siraj Perera
Although ANCOLD provides guidance on good dam safety practices, in Australia it is the State and Territory Governments’ role to protect the public from dam safety incidents and in many cases these jurisdictions have legally binding regulations in place that dam owners must adhere to. This paper presents a comparative analysis of the dam safety regulations currently in place for Australian states, as well as selected international jurisdictions. The limit of applicability of the regulations, number of dams regulated, content of the regulations and powers and responsibilities of the regulator are all compared. It was found that there is a large range within each of these categories with regulatory approaches varying from light-handed and objective based, to highly prescriptive. The extent to which risk management principles are used in the regulations for each jurisdiction has also been investigated. It was found that in jurisdictions where higher hazard category dams account for a higher proportion of dams being regulated, risk analysis is included in the regulations. Finally, the ANCOLD societal risk criteria and ALARP considerations have been compared and contrasted with those from international jurisdictions and other hazardous industries.
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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
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.
Jiri Herza, Nihal Vitharana, Alex Gower
The Western Australia Water Corporation plans to increase the storage capacity of Millstream Dam, which is located near Bridgetown in the south west region of WA. The existing dam is an 18 m high zoned earthfill embankment constructed in 1962. The dam suffered a block heave of the foundation at the downstream toe during the first filling, probably attributable to high foundation pore water pressures. The dam upgrade will be challenging due to complex and unfavourable foundation soils coupled with these artesian pressures.
The dam is founded on lateritic soil, which is a common weathering profile throughout the region. These soils formed in a tropical environment of fluctuating water tables, severe leaching and translocation of iron oxides over many millions of years. As a consequence some of the lateritic horizons at Millstream Dam have been modified such that they exhibit behaviours that are not consistent with conventional constitutive models and correlations. These are attributed to a complex structure of the soil microfabric, which comprises clay particles bonded together into larger aggregates. The clayey aggregates are also bonded to each other, forming a porous matrix of silty or sandy appearance characterized by low dry density and high void ratio, which may nevertheless disintegrate on working.
Comprehensive geotechnical investigations and extensive laboratory testing have revealed that the foundation materials display characteristics of clayey and granular soils. Under shearing, these soils demonstrate high initial strength, which gradually reduces as the inter-aggregate bonds are broken and the relative position of the aggregates changes. Several soil samples also exhibited significant contractive behaviour on shearing generating high pore pressures under undrained conditions.
This paper presents the investigation and design methods used in the foundation design of the Millstream Dam upgrade with emphasis on unusual behaviour of the foundation media.
Challenges in dam design on lateritic soils
Dr Adam Butler, Robert Rigg, Glen Hobbs
The cost of maintenance is a serious problem. Preventive Maintenance is a good strategy if implemented well, but can led to unnecessary costs if items are replaced unnecessarily. Predictive maintenance can augment preventative maintenance by using real time instrumentation to monitor conditions. These techniques have been effective at recognizing the symptoms of impending machine failure
Glen Hobbs and Associates (GH&A) recently analysed pressure and displacement data from hydraulically actuated hoisting equipment of a large emergency closure fixed wheel gate. Data analysis enabled GH&A to pin-point causes of the gate malfunction. Anomalies in the data waveform corresponded to impacts and squeeze points in the system. Furthermore, comparing recent test data with older data highlighted gate deterioration over time.
Testing, analysis and trending of data enables asset managers to better predict the point at which maintenance really needs to be performed and shows that careful analysis of relevant data can help solve multi-faceted problems.
Keywords: Operations, Maintenance, Asset Management, Gates.
Brendan Sheehan, Chris Topham, Alan White, Rowenna Lagden
Darwin Dam is a 21m high embankment dam constructed on a geologically complex foundation that includes karst limestone features. The dam retains the top 15m of Lake Burbury on Tasmania’s west coast, and borders the Tasmanian Wilderness World Heritage Area. Defensive design of the dam addressed the key failure modes of piping through the complex foundations of limestone, sandstone, gravels and silts, and guarding against sinkholes forming in the limestone foundations. During construction, a comprehensive range of instruments were installed in the dam and foundation, as a long term means of monitoring this structure. A range of surveillance data has been collected since lake filling and this data, along with historic geological investigation information, was used to develop a three dimensional (3D) geological model of the dam and
foundation with phreatic profiles. The software used was a commercially available geographical information system. This tool has assisted Hydro Tasmania to better understand and manage the dam. The paper outlines the need for a 3D model, the methodology for development of the model, resources required, limitations and lessons learned. The benefits of the model, such as aiding understanding of foundation behaviour, assisting with interpretation of surveillance data, supporting decision making, and potential use during incident response are also discussed.
Keywords: Three dimensional, computer model, karst foundation, geology, hydrogeology ,dam surveillance