2018 – Dam Safety Management of Junction and Clover Dams: A Risk Based and Observational Approach
Steven O’Brien, Christopher Dann, Timo Mantyvirta
Junction and Clover Dams are central spillway slab-and-buttress dams located in Victoria. Previous safety reviews and assessments of the dams concluded that neither dam met modern dam design standards and remedial works were recommended, including infilling the slab-and-buttress dams with mass concrete to sustain seismic loadings. These conclusions were based largely on the assessed seismic hazard at the site, the results of response spectrum analyses and observed conditions of the dams including alkali-aggregate reaction of the concrete. AECOM used current seismic hazard assessment techniques, conducted concrete investigations and testing, assessed long term surveillance monitoring results and used modern finite element techniques to demonstrate that no upgrade works were required at either dam resulting in a significant saving for AGL.
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2018 Papers
2018 – Understanding Transverse Deformation for Zoned Embankment Dams
Learn moreBeth Scott, Jamie Campbell
Deformation Survey is a simple and widely implemented technique to identify the early signs of dam failure and is regularly undertaken on many dams. Thanks to advances in equipment and more accurate survey records, there is now a better understanding of measurement and movement of embankments and previous records.
However, the “expected” range of transverse deformation and implications for failure modes of dams is not particularly well researched or understood.
This paper collates a case history of transverse deformation for a number of Tasmanian dams and examines the relative behaviour of the embankment dams. From this the “expected behaviour” of an embankment dam can be estimated and related to key influencing factors, such as observed settlements, height and age of the dams, and thereby providing guidance on when transverse deformation is considered unusual for similar dams.
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2018 Papers
2018 – Localised Repairs of Spillway Concrete Scour at the Base of a 42 m High Arch Dam
Learn moreOliver Giudici
A common concern for large spillways is erosion/abrasion of the receiving plunge pool and potential impacts on the stability of the dam. An example of this was presented at the 2017 ANCOLD Conference in a paper that discussed the detection and repair of spillway scour erosion at the base of Devils Gate Dam, an 84 m high, double curvature arch concrete dam. The focus of this paper is the partial repair of scour and abrasion within another concrete lined plunge pool, at the base of Repulse Dam in Southern Tasmania.
Repulse Dam consists of a 42 m high double curvature concrete arch with post-tensioned abutments and an adjoining earth embankment with a reinforced concrete upstream face. The stepped dam crest acts as a free-overflow spillway which discharges onto a concrete apron designed to protect the valley sides and floor immediately downstream of the dam. The permanent tailwater rises part-way up the dam during high flows which lessens the impact on the apron.
Previous underwater inspections had not identified a pressing need for maintenance. However, an upcoming twelve month Repulse Power Station outage would generate constant spill and therefore a more thorough assessment of the spillway apron was undertaken. Inspection was limited to underwater methods due to the inability to lower the tailwater; the downstream lake forming the tailwater is solely regulated by a hydro-power station and this station was being refurbished at the time. Sonar scanning enabled the spillway apron condition to be mapped and revealed areas of exposed reinforcing steel and deposits of river rock and gravel. The information provided by the scan justified temporary disruption to the lakes and power stations which form the Lower Derwent Power Development in order to dewater the area and work safely below the spillway. This was necessary to expose the apron for detailed inspection in dry conditions and thereby make a full assessment of the need for concrete repairs prior to the station refurbishment.This paper presents a case study of the actual performance of a spillway apron below an arch dam and the inherent challenges in accessing and maintaining these types of structures when a permanent tailwater is present.
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2018 Papers
2018 – Exploring the Potential of Advanced Instrumentation in Physical Hydraulic Modelling for Spillway Design
Learn moreBen Modra, Stefan Felder, Laura Montano, Mathieu Deiber, Chad Martin, Craig Wiltshire, Michel Raymond, Barton Maher
Physical modelling of dam structures remains a preferred method for validating and improving dam designs. Flow behaviour in the approach and over the crest of a dam can be accurately studied with traditional methods such as pressure transducers, piezometers and current meters due to the relatively smooth and steady flow conditions. However, characterising flows within a stilling basin is far more difficult due to the complex, aerated and highly turbulent flow conditions. Recent work on detailed measurement of hydraulic jumps using a line-scanning Lidar was adapted for measurement of stilling basin surface profiles in a 1:50 scale model of Somerset Dam, QLD. Lidar was shown to be an effective and efficient tool for providing assessment of the toe jump, boil and flow into the downstream channel.
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2018 Papers
2018 – Assessing the Accuracy of a Two-Dimensional Hydraulic Model for Dambreak Analysis
Learn moreDaniel Sheehy, Dr Sharmil Markar, Dr David Newton
Two-dimensional hydraulic modelling technology has advanced significantly in recent years, providing powerful and flexible tools that are now routinely used for a wide variety of flood risk assessments. Assessing the downstream impacts of catastrophic dam failure represents an extreme test for the accuracy and stability of hydraulic models. Catastrophic dam failure can present an extreme risk to downstream infrastructure and public safety. Hence, it is important to have confidence in the estimated magnitude of potential impacts to design suitable, costeffective mitigation measures. The highly visual output of two-dimensional models adds credibility to their results. However, validation data for extreme hydraulic conditions is rarely available, resulting in uncertainty in the accuracy of model predictions and in the risks associated with dam failure. By validating numerical model results against analytical solutions for cases of simple geometry and also against realworld data, an improved level of confidence can be obtained in the accuracy of the model representation of these extreme hydraulic conditions. In this paper, we assessed the capability of the TUFLOW hydraulic modelling software package to accurately simulate an idealised dam break scenario by comparing the model results to analytical solutions. We also compared the model results for coastal inundation by a tsunami to real-world data from the 2004 Banda Ache (Indonesia) tsunami. The results showed that the HPC solver version of TUFLOW correctly captures the dam break flood fronts and the flood wave propagation and TUFLOW HPC is well suited for dam break flood modelling.
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2018 Papers
2018 – Integrating Climate Change into Dams Management Practices
Learn moreTusitha Karunaratne, Dr Jill Fagan, Dr Gamini Adikari
Global climate change will amplify existing risks, as well as create new risks for natural and human systems. Recent climate changes have already had widespread impacts on human and natural systems. Dams provide a range of economic, environmental and social benefits including irrigation, flood control, water supply, hydroelectric power, recreation and wildlife habitat and play an important role in human settlement. Adapting into the effects of climate change is vitally important for future management of dams. This paper uses the recent drought and floods in Victoria to illustrate the importance of considering the effects of climate change in design, operations, maintenance and emergency management of dams.
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