Peter Buchanan, Malcolm Barker, Paul Maisano, Marius Jonker
Kangaroo Creek Dam located on the Torrens River, approximately 22 km north east of Adelaide, is currently undergoing a major upgrade to address a number of deficiencies, including increasing flood capacity and reducing its vulnerability to major seismic loading.
Originally constructed in the 1960s and raised in 1983, recent reviews have indicated that the dam does not meet modern standards for an extreme consequence category dam.
The original dam was generally constructed from the rock won from the spillway excavation. This rock was quite variable in quality and strength and contained significant portions of low strength schist, which broke down when compacted by the rollers. The nature of this material in places is very fine with characteristics more akin to soil than rock. Review of this material suggests that large seepage flows (say following a major seismic event and rupture of the upstream face slab) could lead to extensive migration of the finer material and possible failure of the embankment. However, it is also envisaged that the zones of coarser material could behave as a rockfill and therefore transmit large seepage flows, which may result in unravelling of the downstream face leading to instability.
This paper addresses the design of the embankment raising and stabilising providing suitable protection against both these possible failure scenarios, which tend to lead to competing solutions. The final solution required the embankment to be considered both as a CFRD and a zoned earth and rockfill embankment.
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Assoc. Prof. Shu-Qing Yang
Next to air, freshwater has been always considered as a key resource, central for economic development and human’s basic needs. Currently the total population is about 7 billion, and by 2050, global population is projected to be 9 billion. An additional 10 more Nile Rivers are needed, and the water demand is increasing steadily and significantly. The dams industry has successfully solved the water deficit problems in many places for most of the time, but more and more countries and regions are gradually resorting to other emerging technologies like desalination, wastewater recycling and rainwater tanks etc. as they believe that a dam is the 20th century technology and has too many significant negative impacts. However, available data show that the global water consumption is only 5~6% of annual runoff, e.g., Australia’s water use is about 20km3, but the runoff lost to the sea is up to 440km3. A coastal reservoir is a freshwater reservoir inside seawater, aimed at the development of freshwater from the sea without desalination. The 1st generation of coastal reservoir has emerged in China, Singapore, Hong Kong and Korea successfully, but generally its water quality is not as good as that in inland dams. The 2nd generation of coastal reservoirs has been developed and its water quality is at least comparable with the water in existing reservoirs like Warragamba dam. The application of coastal reservoirs in Australia is discussed and the feasibility is investigated. The preliminary designs of coastal reservoirs in SE Queensland, Sydney, Melbourne, Adelaide and Perth show that the coastal reservoir is a feasible and effective technology for Australia’s water crisis.
D Stephens and P Hill
Dambreak modelling and consequence assessment is a key component of many dam safety related studies. The outputs from these assessments can be used to inform the consequence category, dam safety emergency planning, risk-based surveillance and dam safety risk assessment. These studies are complex, intensive and expensive to complete, and all too often there is a need to manipulate or extrapolate the results of these assessments to fit a purpose other than what they were intended for. This issue is particularly prevalent for risk assessment, where the likelihood calculations are directly tied to analysis of the key failure modes, but consequences may be taken from previous studies which were not informed by failure mode selection. The result of this mismatch may lead to inefficiencies and uncertainties in preparing the risk estimates. Subtle changes to the timing or scope of the original dambreak modelling and consequence assessments, at relatively small incremental cost, may help to prevent these issues arising for future studies. Advice is provided on specific issues such as the determination of the downstream extent of the dambreak modelling, selection of the dambreak modelling scenarios and reconciliation of the consequence assessment results with flood and seismic loading partitions for risk assessment. It is hoped that the advice provided will lead to an overall increase in the efficiency and value for money of these studies.
Mark Arnold, Gavan Hunter and Mark Foster
Following the dam safety risk assessment for Greenvale Dam in 2008, Melbourne Water implemented a 3.0 m reservoir level restriction on the operation of the storage as an interim risk reduction measure. The 3.0 m restriction coincided with the ‘as constructed’ top of the chimney filter in the main embankment. This interim action reduced the dam safety risk to below the ANCOLD limit of tolerability.
Dam safety upgrade works were undertaken in 2014/15 to bring the dam in-line with current risk based guidelines and to enable the removal of the interim reservoir restriction, bringing the storage back to full operating capacity. Greenvale Dam was required to remain operational throughout the works and this required careful consideration of the dam safety risk during construction.
Deep excavations were required within the crest and downstream shoulder of the embankments, that,, without adequate management, had the potential to increase risk to the downstream population. Excavations up to 18 m depth were required into the wing embankments for construction of full height filters from foundation to crest, excavations up to 7 m deep were required in the main embankment to expose and connect into the existing filters and secant filter piles up to 13 m deep were used to connect the new chimney filter of the wing embankments with the original chimney filter of the main embankment.
A key element of the design and construction of the upgrade works was managing dam safety during construction. Dam safety considerations included (i) design based decisions to manage the level of exposure; (ii) implementation of further restrictions on reservoir level by the owner Melbourne Water; (iii) construction methods to manage exposure; (iv) an elevated surveillance regime during the works and (v) emergency preparation measures including emergency stockpiles and 24 hour emergency standby crew. The construction based dam safety requirements were focused on early detection and early intervention, and were managed via the project specific Dam Safety Management Plan.
This paper focuses on dam safety management including the decisions made, actions taken and construction requirements and touches on how these relate to the key project features.
Extending the useful life of a dam to an extent well beyond what was envisaged by the original designer poses diverse challenges. In this paper, three case studies are described, one involving strengthening of two similar dams and two cases involving raising. In all three cases, the dams continue to provide a reliable source of supply in a water scarce country.
The Woodhead and Hely-Hutchinson Dams have substantial historical significance which guided the selection of restressable post-tensioned anchors as the preferred method of strengthening.
The Stettynskloof Dam was almost doubled in height by constructing a clay core rockfill embankment abutting the downstream face of the existing concrete gravity dam. The new structure was well instrumented to cover areas of concern but the dam was found to perform as largely predicted by the designers.
Keerom Dam faced both technical and regulatory challenges that were eventually overcome and the raising of the dam was able to proceed. A further raising will increase the utilisation of this valuable resource still further.
David Piccolo, Gareth Swarbrick, Garry Mostyn, Bruce Hutchison, Rodd Brinkmann
Hillgrove Resources owns and operates Kanmantoo copper mine some 44 km southeast of Adelaide.
An important feature of the mine is its tailings storage facility (TSF) which is fully lined with HDPE, and double lined at the base, fully under drained, has a secondary underdrainage system for leak detection and a multi-staged centralised decant system. This onerous design of the TSF was developed in consultation with DMITRE between 2007 and 2010 amid concerns of groundwater protection and effective water management.
The Authors were approached in 2010, following construction of the initial stage of the TSF, and charged with developing the design to increase storage from 13 to 20 million tonnes, as well as optimising the design and construction of future stages.
This paper presents the more interesting aspects of the design and construction optimisation between 2010 and 2016 including:
The design and construction approaches have been scrutinised and accepted by regulatory authorities, and implemented by the mine operator over a period of 6 years. The paper includes lessons learnt during the implementation process.