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Wark, Bob; Thomas, Louise
This paper discusses the rating curves developed for several case studies from the Pilbara and Kimberley, including the Harding Dam, Moochalabra Dam and Ophthalmia Dam. The paper will discuss the impact of underestimated rating curves on the design of infrastructure. An example has occurred at Harding Dam where the pump station was designed to be inundated at a 1:100 AEP and this is now estimated to occur at a lower AEP. The paper will also discuss methods to improve the accuracy of rating curves and the challenges associated with determining accurate rating curves.
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2014 Papers
2014 – Does Your Rating Curve Hold Water: The Consequence of Rating Curve Errors
Learn moreWark, Bob; Thomas, Louise
This paper discusses the rating curves developed for several case studies from the Pilbara and Kimberley, including the Harding Dam, Moochalabra Dam and Ophthalmia Dam. The paper will discuss the impact of underestimated rating curves on the design of infrastructure. An example has occurred at Harding Dam where the pump station was designed to be inundated at a 1:100 AEP and this is now estimated to occur at a lower AEP. The paper will also discuss methods to improve the accuracy of rating curves and the challenges associated with determining accurate rating curves.
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2014 Papers
2014 – Oaky River Dam Failure
Learn moreGeorge Samios and Steve Gough
Following an extreme flood event late on Friday 22nd February 2013, water overtopped the dam crest leading to total collapse of the dam’s right embankment and a span of the nearby intake tower access bridge as well as the cutting of power to the dam gates. The dam’s left embankment was also severely damaged. Options considered for remediation of the dam include decommissioning or reinstatement and upgrading to NSW Dams Safety Committee requirements.
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2016 Papers
2016 – Paradise Dam – An Analysis of Severe Damage to a Modern Dam
Learn moreDavid Scriven, Lawrence Fahey
Paradise Dam is located approximately 20 km north-west of Biggenden and 80 km south-west of Bundaberg on the Burnett River in Queensland. The dam was designed and constructed under an alliance agreement with construction completed in mid 2005. It is a concrete gravity structure up to 52 m high, the primary construction material being roller compacted concrete (RCC).
In January 2013 the flood of record was experienced at the dam with a depth of overflow on the primary spillway reaching 8.65 m following heavy rainfall in the catchment from ex-tropical cyclone Oswald. The peak outflow was approximately 17,000 m3/s. This equated to a 1 in 170 AEP flood event. When the flood receded it was discovered that the dam and surrounds had suffered severe damage in a number of locations including: extensive rock scour downstream of the primary dissipator and the left abutment, damage to portions of the primary dissipator apron, and the loss of most of the primary dissipator end sill.
SunWater initiated a staged remediation program to manage the dam safety risks and by November 2013 had completed the initial Phase 1 Emergency and Phase 2 Interim repairs. Phase 3 of the program was to implement a comprehensive Dam Safety Review (DSR) and a Comprehensive Risk Assessment (CRA). The DSR became arguably the largest ever undertaken by SunWater and included: extensive geotechnical investigations, large scale physical modelling, numerical scour analysis, stability analysis, and an extensive design assessment. This paper describes some of the key aspects of the DSR undertaken related to the flood damage.
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2017 Papers
2017 – Construction Flood Risk Strategies for Dam Upgrades
Learn moreColleen 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 – Tropical Cyclone Debbie – A SunWater Experience
Learn moreMichael Hughes, James Stuart
Tropical Cyclone Debbie (TC Debbie) formed in the Coral Sea on Saturday 25th March, 2017 and developed into a category 4 system that crossed the coast near Proserpine, Queensland with the eye passing very close to Peter Faust Dam. TC Debbie, later becoming Ex-TC Debbie embarked on a tour of SunWater infrastructure (See Figure 1). Of 23 referable dams managed or owned by SunWater in Queensland, only 3 had no inflows with spills resulting at twelve locations. The paper describes the varied experiences of SunWater with relation to preparation for, and operations during TC Debbie. Some key areas of interest to other dam owners include;
- Uncertainty around forecasts;
- Flash flood destruction of key hydrographic equipment;
- A review into dam operation;
- Returning a spillway construction site touse;
- A ‘direct hit’ by the eye of TC Debbie over Peter Faust Dam catchment;
- Successful prediction of Cyclone rainfall temporal patterns; and
- A record flood influenced by land use with learnings for flood risk assessments.
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2018 Papers
2018 – Performance of U.S. Federal Flood Protection Systems from 2010 through 2017
Learn moreNathan J. Snorteland, P.E., David A. Margo, P.E.
The U.S. Army Corps of Engineers (USACE) is responsible for flood risk management across the United States. USACE has more than 710 dams and is responsible for more than 24,000 kilometres of levees. Since 2008, USACE projects have prevented more than AU$1.2 Trillion (in 2017 dollars) in damages from flooding. Although some of this came as a result of dozens of smaller floods, much of that protection came during three events within the last five years. From 2010 through 2017, the U.S. has had three major inland floods and two coastal events where federal flood protection exists: in 2010 on the Cumberland River, in 2011 on the Missouri, Ohio, White, and Mississippi Rivers, in 2015 on several rivers in Texas and Oklahoma, and in 2017 along the Gulf Coast of the U.S. and its territories in the Caribbean. For many of these locations, these events produced record rainfall and the flood of record. USACE operated many large facilities on these systems and those systems overall performed as expected. However, USACE also experienced some operational issues, did a substantial amount of flood fighting, had several incidents, and several failures. This paper will describe the flooding experienced in those events, the operations of the flood protection systems, the performance overall, and some of the lessons learned.
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2019 Papers
2019 – Design of Rockfill Embankments for Overtopping During Construction
Learn moreMeysam Safavian, Bob Wark, Damian Nott
The paper evaluates the stability of the reinforced rockfill at the downstream side of Waimea Dam, a new CFRD dam that is currently under construction in New Zealand. The reinforced rockfill is part of the overall diversion strategy for the dam during construction and has been designed to allow for safe overtopping to a depth of 2.9m, which corresponds to the 1 in 1,000 AEP flood.
Design of reinforced rockfill for overtopping allows for the safe passage of floods that exceed the capacity of the primary diversion works. This may be required for dam safety during construction, as is the requirement for Waimea Dam. It also serves to protect the works whist the dam is being built.The focus of the paper is the stability assessment of the reinforced rockfill to prevent seepage induced instability during overtopping. As seepage forces have a considerable effect on the stability of the dam, a finite element seepage analysis was undertaken to estimate the seepage forces throughout the embankment, which was used in the design of the reinforcement system.
Details of the design process, including the seepage and stability analysis for a range of configurations are outlined, and recommendations for the design of similar future projects are provided.
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2013 Papers
2013 – Challenges and lessons learnt from high-risk dam construction projects
Learn moreMatthew 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.
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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 – Cotter Dam – recovering from major floods during construction
Learn morePeter Buchanan, Damian Nott, Martin Weir and John Dymke
The Bulk Water Alliance (BWA) consisting of ACTEW and ACTEW-AGL, GHD, and John
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Holland/Abigroup, was formed to deliver the Enlarged Cotter Dam project in Canberra,
ACT. This project consisted of the construction of an 87 m high RCC dam and two
saddle dams, 15 m and 20 m high, to provide additional capacity to the ACT‘s water
supply system. The project is scheduled to be completed in September 2013.
During construction, the dam site was subject to three significant flood events which
affected the construction program. The March 2012 flood, the largest of the three, also
indirectly caused the formation of longitudinal cracks at the top surface of the RCC, when
the dam had reached about 45 m in height.
This paper first looks at the consequence of the flooding on both the design and
construction of the dam; in particular the modification of the diversion strategy and the
impacts on the final dam arrangement. The risk mitigation strategies put in place,
including the construction of a significantly larger diversion conduit through the partially
completed dam, are also discussed. The paper then focusses on the formation of
longitudinal cracks in the dam; the cause of cracking, analysis of the likely extent of
cracking, and the treatment of the cracks to minimise the risk of any significant long-term
impacts on the safety of the dam.
Finally the paper will discuss lessons learned from constructing the Enlarged Cotter Dam
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2012 Papers
2012 – The Victorian Floods Review: a hydrologist’s perspective for dam owners
Learn moreDavid Stephens, Kristen Sih, Peter Hill, Rory Nathan, David Dole
The spring and summer of 2010-11 were characterised by severe flooding affecting much of Victoria. In a number of cases, communities downstream of large dams developed to supply water for irrigation and critical human and stock needs were significantly impacted. Following the floods, the Victorian Government commissioned the Victorian Floods Review (VFR) to consider the total warning and response to these floods. Whilst dam operations were not specifically included in the terms of reference, overwhelming community interest lead to the VFR commissioning a high level review of the way a number of key dams were operated during the floods. This review identified some of the inherent tensions in the legislative framework for water harvesting, storage and dam safety in Victoria. These tensions were often matched by the conflicting expectations of the public living immediately downstream of the dams versus those dependent on the water resource stored in the dams. The final report of the VFR was handed down in December 2011 and contained a number of recommendations specifically for dam owners. These recommendations are reviewed and discussed in light of both the legal and public relations ramifications for owners and operators of large water supply dams. An overview is also given of the operational constraints to downstream flood mitigation facing many dam owners. Such constraints are typically imposed by the type of dam (i.e. fixed crest), relatively small storage and outlet capacities when compared to flood volumes and limitations on the reliability of forecast rainfall information. Some possible ways of overcoming these constraints are identified and discussed.
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Keywords: Flood, mitigation, Victorian Floods Review -
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2011 Papers
2011 – January 2011 Brisbane River Floods and Examination by Media of the Dam Operations
Learn moreMichel Raymond
The large flood inundating areas of Brisbane and Ipswich along the lower Brisbane River below Wivenhoe Dam in January 2011 was extensively reported by the media. An independent Commission of Inquiry was formed soon after the flood with broad terms of reference including matters related to dam operations. Prior to the Inquiry hearings and findings, reporting in the media continued and made strong allegations of blame of the flood on dam operations. The media relied on limited expertise but the articles were portrayed and subsequently re-produced by other media outlets as ‘expert’ analyses. The author’s interpretation is that media claims were misleading and damaging to the public confidence in the role of dams for flood mitigation, and this damage occurred before official Inquiry findings were available.
A brief summary is presented of now publicly available credible reports on the flood event, and a summary is also presented of the key matters and allegations reported in the media related to the dam operations. An analysis and commentary of media reporting on the flood operations of the Wivenhoe Dam is presented in the context of time and people with reference to information and expertise available to the media, and media conduct in relation to fair public interest and professional practice.
Matters of importance for objective and informed knowledge of key technical matters in relation to operation of dams, dam safety, and the inevitable extremes of nature and floods are discussed. The paper then examines the roles and possible limitations of dams engineering professionals in relation to media reporting of such matters.
This paper solely focuses on matters of media examination of the floods and dam operations, and generally does not comment on technical matters that are in the terms of reference of the Commission of Inquiry.
2011 – January 2011 Brisbane River Floods and Examination by Media of the Dam Operations
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2011 Papers
2011 – ACHIEVING CONSISTENCY IN DERIVATION OF THE PROBABLE MAXIMUM FLOOD
Learn moreR.J. Nathan, P.I. Hill, and P.E. Weinmann
The current definition of the Probable Maximum Flood (PMF) is open to subjective interpretation, and this lack of objectivity can lead to inconsistencies in the application of risk-based and standards-based criteria. This paper summarises the different approaches used to estimate the PMF, and highlights how these reflect differences in the availability of design information and local tradition and experience. A number of approaches are available that can aid the objective definition of the PMF. These approaches attempt to define the “reasonableness” of the manner in which the various flood producing factors are combined by reference to the relative shift in the annual exceedance probability of the event. The implications of the different approaches to deriving the PMF are summarised for a number of dams from across Australia. Guidance on deriving the PMF is provided in the paper with a view to seeking feedback from industry and consideration for inclusion in relevant guidelines.
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