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R.M. Dawson, A. Orange

Karapiro dam is the last in a line of hydro-electric dams on the Waikato River, in New Zealand’s North Island. Investigations identified a potential deficiency in parts of the dam under seismic loading. Detailed investigations and analysis narrowed the deficiency to a low strength clay seam under the concrete gravity left abutment structure. An innovative approach was taken to solving the stability problems at minimum cost, without lowering the storage lake, which would have had significant environmental and social impacts. The process of design and construction was overviewed by an international board of review.

Construction was completed in three main stages with further investigation and design refinement between. The main contract was completed over about eight months and included detailed concrete mix and pour schedule design to control stress development due to temperature gradients for the 2000 + cubic metres of mass concrete placed. While the extent of work was relatively small, the quality control, programming, and presence of a full reservoir throughout demanded a high degree of communication and co-operation between the Principal, Designer and Constructor. Despite some surprises during construction, the project was completed within budget and formed strong bonds between all those involved. This paper briefly describes the design process, and focuses on construction, from the point of view of the Owner, Constructor and the Designer.

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2002 Papers

2002 – Karapiro Dam Stability Enhancement Project – Construction
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R.M. Dawson, A. Orange

Karapiro dam is the last in a line of hydro-electric dams on the Waikato River, in New Zealand’s North Island. Investigations identified a potential deficiency in parts of the dam under seismic loading. Detailed investigations and analysis narrowed the deficiency to a low strength clay seam under the concrete gravity left abutment structure. An innovative approach was taken to solving the stability problems at minimum cost, without lowering the storage lake, which would have had significant environmental and social impacts. The process of design and construction was overviewed by an international board of review.

Construction was completed in three main stages with further investigation and design refinement between. The main contract was completed over about eight months and included detailed concrete mix and pour schedule design to control stress development due to temperature gradients for the 2000 + cubic metres of mass concrete placed. While the extent of work was relatively small, the quality control, programming, and presence of a full reservoir throughout demanded a high degree of communication and co-operation between the Principal, Designer and Constructor. Despite some surprises during construction, the project was completed within budget and formed strong bonds between all those involved. This paper briefly describes the design process, and focuses on construction, from the point of view of the Owner, Constructor and the Designer.
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2003 Papers

2003 – BELLFIELD FLOOD SECURITY UPGRADE How we did it our way with minimal resources
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Bellfield dam is a 78,500 ML drought reserve storage for the Wimmera-Mallee Stock and Domestic System. The 800m long by 57m high zoned earth and rockfill dam is located on Fyans Creek upstream of the Grampians tourist town of Halls Gap in north western Victoria. The dam was built in the period 1963-67. Later in 2002-03 as part of a flood security upgrading (FSU) program, had its rock chute spillway deepened by 3.4m and its embankment crest raised by 1.9m to withstand a PMF.

To manage the FSU’s likely construction constraints and risks, Wimmera Mallee Water’s Headworks Group successfully undertook the upgrading by a mix of schedule of rates contracts and direct management.

This paper complements a companion paper by WMW’s design consultants, URS and describes why and how direct management was used, plus unconventional aspects of spillway deepening and the raising of a narrow dam crest with earthworks and a pre-cast parapet wall.
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2017 Papers

2017 – Construction Flood Risk Strategies for Dam Upgrades
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Colleen Baker, Sean Ladiges, Peter Buchanan, James Willey, Malcolm Barker

Dam Owners and Designers are often posed with the question “what is an acceptable flood risk to adopt during the construction of dam upgrade works?” Both the current ANCOLD Guidelines on Acceptable Flood Capacity (2000) and the draft Guidelines on Acceptable Flood Capacity (2016) provide guidance on the acceptability of flood risk during the construction phase. The overarching principle in both the current and draft documents is that the dam safety risk should be no greater than prior to the works, unless it can be shown that this cannot reasonably be achieved.Typically with dam upgrade projects it is not feasible to take reservoirs off-line during upgrade works, with commercial and societal considerations taking precedent. It is therefore often necessary to operate the reservoir at normal levels or with only limited drawdown. The implementation of measures to maintain the risk at or below that of the pre-upgraded dam can have significant financial and program impacts on projects, such as through the construction of elaborate cofferdam arrangements and/or staging of works. This is particularly the case where upgrade works involve modifications to the dam’s spillway.The use of risk assessment has provided a reasonable basis for evaluating the existing and incremental risks associated with the works, such as the requirement for implementation of critical construction works during periods where floods are less likely, in order to justify the As Low As Reasonably Practicable (ALARP) position. This paper explores the ANCOLD guidelines addressing flood risk, and compares against international practice. The paper also presents a number of case studies of construction flood risk mitigation adopted for dam upgrades on some of Australia’s High and Extreme consequence dams, as well as international examples. The case studies demonstrate a range of construction approaches which enable compliance with the ANCOLD Acceptable Flood Capacity guidelines
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2017 Papers

2017 – The Hamata Tailings Dam Design and Construction at the Hidden Valley Mine in Papua New Guinea
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Mark Stephen Rynhoud, David Johns and Len Murray

The Hamata tailings storage facility at the Hidden Valley mine is being constructed in a remote, high rainfall, tropical environment in a mountainous region of Papua New Guinea. Implementation of the design hasrequired adapting the design in response to various challenges encountered on the site during the ongoing construction period, based on observations by the designers and site monitoring data which is continuously collected and compared against design assumptions. This paper describes some of the design and construction modifications which have been implemented since construction of the tailings facility started and provides a case history of some of the challenges facing designers and construction crews when mining in remote, tropical conditions.
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2018 Papers

2018 – Design Development and Construction of Cofferdam within HPP Scheme
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Nikifor Petrovic GHD, Mladen Vuckovic STRABAG

For hydropower dam projects, design and construction of the temporary works including cofferdams are very important. Improper selection, design and/or construction of temporary works may cause delay of major construction works and increase construction cost.

The authors worked on the preparation of the Engineering, procurement and construct EPC tender (based on International Federation of Consulting Engineers (FIDIC) contract-yellow book) for a 20 MW Hydro Power Plant (HPP) project in the Balkans Region. The scheme involved the design and construction of three cofferdams to enable construction of the main dam, intake and powerhouse. The basis for tendering, as a part the contract documents, was the preliminary design of the HPP scheme. The tenderers were allowed to deviate from the solutions presented in the preliminary design as long as the proposed solutions fulfilled the Employer’s Requirements.

As a part of a winning strategy, the preliminary design cofferdams were changed and modified, providing significant saving and facilitating quicker and safer construction. This paper presents the development of the design and challenges faced during construction work.
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2019 Papers

2019 – The Lessons Learned and Construction Challenges for the Leslie Harrison Dam Upgrade
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Ryan Cantrill, Peyman Andaroodi, Colin Thompson

Leslie Harrison Dam is located on Tingalpa Creek in the Redlands region, approximately 18 km southeast of Brisbane. It is classified as an extreme hazard category dam with a large population at risk only a short distance downstream.

The dam comprises a 25 m high zoned earthfill embankment, with a dry well concrete intake tower and an outlet conduit located at the base of the dam near the old river channel. The spillway has a 43 m wide concrete gravity ogee crest, with a concrete lined chute terminating in an energy dissipator structure.

Seqwater is undertaking a staged upgrade of Leslie Harrison Dam to address deficiencies identified during the Portfolio Risk Assessment (URS 2013) and Geotechnical Investigations (GHD 2016).
While the dam has met the water supply needs of the community for the past 50 years, the upgrade ensures local residents will be well served into the future. Additionally, the structure will meet the most up to date requirements of dam safety management and national industry standards.

Construction of the Stage 1 upgrade commenced in June 2018 and involved the removal and replacement of liquefiable material in the foundation, modernisation and extension of the outlet works, addition of a new downstream filter buttress to the embankment, and lastly, the installation of both active and passive anchors within the spillway ogee and lower chute floor.
As with any major project, the works involved a number of challenges that had to be addressed. This paper provides an insight into the key challenges encountered and how these were overcome by the design and construction teams using practical engineered solutions. The intent is to provide the reader with an account of the “lessons learned” during the construction phase, along with recommendations for future dam upgrades.
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2021 Papers

2021 – Don’t risk it to get the biscuit – Managing construction risk at Ewen
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Zara Bostock, Helena Sutherland

Ewen Maddock Dam is located approximately 12.0 km west of Caloundra, in the Sunshine Coast area of Southern Queensland. The dam is a homogeneous earthfill embankment dam 10.5 m high and 724 m long. The dam was originally built between 1973 and 1976 and later upgraded in 1982 to raise the ogee spillway crest by 2.44 m to the current Full Supply Level (FSL) of 25.38 m AHD.

Seqwater is undertaking a staged upgrade of Ewen Maddock Dam to address deficiencies identified during the Acceptable Flood Capacity (AFC) Review (GHD, 2010). The consequence category assigned to Ewen Maddock Dam is ‘Extreme’ with a downstream Population at Risk greater than 1000.

Stage 1 construction was completed in 2012 to manage the seepage underneath the dam to reduce the risk of piping and improve embankment stability. Stage 2A involved retrofitting a filter in the existing embankment and raising the dam 1.61 m to 30.11 m AHD using a reinforced concrete parapet wall. Stage 2B involves spillway upgrade works and was split from 2A due to approval constraints.

Stage 2A construction was completed in April 2021, navigating various project and dam safety challenges. This paper presents some practical ways dam safety and risk was managed on the ground from the perspective of both the designer and owner.
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2013 Papers

2013 – Challenges and lessons learnt from high-risk dam construction projects
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Matthew Sentry and Darren Loidl

To triple Yass’ water storage capacity, Yass Valley Council was required to increase the height of their existing concrete weir by 3.0 m. The 100 m wide weir was originally constructed back in the 1920’s. Upgrade works to the weir included raising the height of the existing concrete weir by 3.0 m with reinforced concrete; install 33 number 27 strand post-tensioned ground anchors vertically into the crest; construct a new outlet structure; upgrade existing mechanical pipe works; and replace the existing pedestrian bridge with a concrete bridge capable of vehicle traffic.
The key project constraints during construction were to maintain constant water to the town’s water treatment plant and maintain minimum 70% reservoir storage.
The original weir had no auxiliary means of flow diversion and the construction constraints meant that the water storage could only be reduced by 1.0 m from the existing crest during construction, resulting in the construction work being carried out in an active water course with minimal means of flow diversion. These key project constraints meant that there was a high risk of flooding during construction work.
Geotechnical Engineering was engaged by Yass Valley Council to carry out the required upgrade work at Yass Dam. Prior to construction work commencing, risk workshops with client and designers clarified the flood risks during construction. To minimise the impact of flood events during construction, Geotech implemented several flood mitigation measures which were controlled by a detailed construction flood management plan. These control measures included construction of two temporary diversion slots cut into the existing concrete weir capable of supporting a 1 in 2 year rain event whilst allowing construction work to continue; re-design of concrete works to minimise the volume of concrete which was to be cut from the existing wall’s downstream face; detailed construction sequencing to minimise impact to existing and new wall during construction work; and the early installation and stressing of anchors.
Although a detailed construction flood management plan was developed and implemented, the Yass Dam site was impacted by 13 floods during the 20 month construction period. Several floods recorded water levels between 1.5 m and 1.9 m above the existing crest, resulting in work ceasing for weeks if not months at a time. As a result of the consistent flooding, Geotech was able to develop stronger and more resilient methods to be able to effectively work within an active watercourse on dam structures where minimal flow diversions are available. This paper presents the unique techniques implemented through the Yass Dam Upgrade project and discusses the effectiveness of these techniques and lessons learnt through the 13 flood events experienced.
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2013 Papers

2013 – Managing the risk of under-designed spillway training walls: an owner’s guide
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Chris Topham, Eoin Nicholson and David Tanner

A number of Australian dams have spillways with reinforced concrete training walls designed in the 1950/60s to the standards of the day, but which could be considered under-designed according to modern criteria. Such walls commonly retain significant depths of earth and rockfill embankment materials, where structural failure of the wall could seriously compromise the safety of the dam. This paper presents the journey to mitigate the risk of such training walls, drawing primarily on experience in managing structurally deficient spillway training walls for a High Consequence Category dam in northern Tasmania. Reflections from each step of the risk management process are presented, including how the portfolio risk assessment contributed to a focus on the dam as a whole, and how that led to more detailed analysis and evaluation of the training wall risk. The use of instrumentation and enhanced surveillance for risk monitoring is discussed, including how real-time deformation data ultimately led to installation of temporary wall bracing works and enhanced contingency planning. The long-term risk treatment for the walls is presented, comprising a $6m structural upgrade to the training walls completed in 2013. The paper concludes with the learnings from the risk management journey and highlights the range of interventions available to owners with similar spillway training walls.
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2013 Papers

2013 – Cotter Dam construction challenges and innovations
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B. Perrin and J. Vida

The Cotter Dam project represents the most significant infrastructure project in the Australian Capital Territory (ACT) since Parliament House in 1988. Enlarging the Cotter Dam has increased the Cotter reservoir capacity from 3 GL to 78 GL, representing a 35% increase of ACTEW Corporation’s total reservoir capacity for the ACT region and providing water security to facilitate future population growth.
At 87 m high, Cotter Dam is the tallest Roller Compacted Concrete (RCC) dam in Australia. Construction began in October 2009, with excavation of the dam foundation commencing in March 2010. With typically 05H:1V slopes up to 115 m high, excavation posed a number of challenges. RCC placement commenced in August 2011 and continued until December 2012.
Innovation and continuous improvement were crucial to the success of the project. From development of specialised mechanical tools for the abutment excavation, to use of precast, to mechanical paving of the downstream RCC steps, construction practice on Cotter Dam established a number of new benchmarks for RCC dam construction.
This paper will describe the construction innovations used to overcome the challenges associated with construction during foundation preparation and RCC placement for the Cotter Dam Project.
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2012 Papers

2012 – Enlarged Cotter Dam Diversion Gate Design – The Challenge and the Test
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Frank Nitzsche

This paper highlights the importance of hydraulic diversion control structures during construction of large dams and the value of allocating sufficient resources during project planning and implementation.
The design of the diversion gate for construction of the Enlarged Cotter Dam presented various challenges, including operation for up to 38m head for discharge into a 3m diameter conduit and the need to serve as an upstream concrete form during eventual diversion closure.
The short duration of operation allowed acceptance of increased level of operational risk and a higher level of design uncertainty. The design used generally accepted gate design methods, but no hydraulic modelling. The hydrodynamic forces were estimated using published data. After installation, a 1 in 100 AEP flood event resulted in the gate being subjected to 90% of its design head while operating in conditions close to the maximum design down-pull force. Attempts to raise the gate succeeded only after increasing the hydraulic pressure above the design value.
Keywords: Guard gate design, outlet works, dam, construction.

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2012 Papers

2012 – Innovation in the Design and Construction of the Enlarged Cotter Dam
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Martin Weir

The Enlarged Cotter Dam project was selected as a key component in securing the future water supply for Canberra and the ACT region. The RCC gravity dam, when completed, will stand 84m high and will be the largest of its kind in Australia.
The dam was designed, and is currently being constructed, under the Alliance contract model. The collaboration this model brings between the owner and the design and construction teams facilitated a drive in innovation from the design through to the construction stages of the project. The focus of this paper is on some of the key innovative aspects of the project, for consideration on future RCC and dam projects.
Investigation was made into the placement of RCC in 400mm layers, compared to the industry adopted standard of placement in 300mm thick layers. Whilst full scale trials demonstrated that placement in 400mm thick layers was not detrimental to the quality of the RCC, the benefits in terms of increased production were never fully realised due to adverse weather and the geometry of the dam placement area. Some issues were also encountered with regards to the compaction of the GERCC on the dam faces. The results do however suggest that the method warrants consideration on future RCC projects.
The construction of the dam’s secondary spillway included a waterstop installation in a constrained RCC placement zone. By developing an arrangement that could hold the waterstop in place and induce the movement joint in the correct location, this arrangement simplified what could have been a complicated procedure in an already time consuming placement area.
The start of RCC placement was at risk of further delay on account of the extensive mass concrete pours required to level the dam foundation. A conventionally vibrated concrete mix, made from the existing site won RCC materials, was designed so that it could be produced from the RCC batch plant. This method of concrete production, combined with an efficient means of delivering the concrete to the pour area, accelerated the placement process and reduced the cost of construction.
Keywords: RCC, dam, construction.
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2008 Papers

2008 – Design and construction of a flood mitigation dam on the North Para River, using high-paste RCC
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Jerome Argue, Steven Slarke, Douglas Rudd

Abstract: The North Para River Flood Control Dam is an integral part of the works proposed to manage flood risk in the Gawler River, north of Adelaide. Undertaken by the Gawler River Floodplain Management Authority (GRFMA), an authority representing the six local Councils in the area, the flood storage is located on the North Para River, about 10 kms north of Gawler. Roller Compacted Concrete (RCC) was selected for the construction material, based on an assessment of the geotechnical and geological site conditions, together with advantages of reduced cost, time and structure required to pass design flood events. With an overall project cost of $16.1 million, the dam was constructed on time and well within pre-tender budget estimates.

Keywords: flood mitigation, roller compacted concrete, North Para River, construction.
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2009 Papers

2009 – Lessons learnt on design, manufacture and placement of filter materials
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Jonathon Reid, Chris Kelly, Bob Wark

One of the most important aspects in the construction of an embankment dam is to be confident that the filter materials placed meet the design intent. The design methodology for filters is now well documented.

However, all too often during construction the filter material, as placed, does not comply with the specified requirements and all parties are faced with costly decisions and delays to the works to determine correction measures and whether the work completed meets the design intent. This paper shares the knowledge gained over a number of projects the authors’ have been involved in and the methods used to improve the properties of the placed filters taking into account some of the practicalities of having these materials produced and placed in a commercial environment

Keywords: filters, specifications, manufacturing, construction, quality assurance.
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2009 Papers

2009 – Design and Construction of Tallowa Dam Environmental Flow Release and Fish Passage Works
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Peter Cordi, Paul Fuller

Tallowa Dam was completed in 1977 at the junction of the Shoalhaven and Kangaroo Rivers in the southern highlands of NSW to provide a pumping pool for water supply transfers to Sydney. These transfers were made only during drought periods, at which time limited and fixed environmental flow releases from a low level outlet were made to the downstream Shoalhaven River. After extensive consultation with the local community the Government decided in 2006 to commence transfers earlier in the drought cycle, and release variable amounts of surface water to improve river health during transfer periods. In addition, Tallowa Dam was identified as having a significant impact on fish passage, as many species migrate to the estuary during their life cycle, and approximately 75% of the viable fish habitat was upstream of the dam. This project involved the design and construction of works to be retrofitted to the dam to address both issues. A surface water release slide gate in the spillway, a low friction coating on the spillway, and a downstream weir were constructed to release environmental flows and allow safe downstream fish passage. A new fish attraction flow outlet was drilled through the dam wall, and a fish attraction chamber and a travelling bucket fish lift was installed for upstream fish passage.

Keywords: environmental flows, fish passage, Shoalhaven River, construction.
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Search Results: “” — Page 1

Nikifor Petrovic GHD, Mladen Vuckovic STRABAG

Ryan Cantrill, Peyman Andaroodi, Colin Thompson