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D Stephens, S Lang, P Hill, M Scorah
Robust estimates of the duration of flood overtopping are a key input into the dam safety risk assessment process. For embankment dams, the likelihood of erosion of the dam crest, downstream face and eventual unravelling of the embankment are heavily dependent on the duration of water flowing over the crest. Similarly, the chance of erosion of the abutments of concrete dams is strongly linked to the duration of floodwaters overtopping the dam. Previously, it has been difficult to define the annual exceedance probability (AEP) of the flood required to cause overtopping of a certain depth for a certain duration, and coarse assessments have typically been made based on critical storm durations of the dam crest flood (DCF). This approach carries significant uncertainty, particularly for structures on smaller catchments where the critical storm duration on outflow may be relatively short. In these cases, it has been difficult to confirm with any reliability that the flood required to achieve a significant duration of overtopping has an AEP close to that of the DCF. This paper describes a new algorithm that has been incorporated into the RORB hydrological model which allows for a frequency curve of flood overtopping duration to be determined within a Monte Carlo framework. The results of this analysis are presented for a case study of a quantitative risk assessment, to demonstrate how the outcomes influenced numerous aspects of the risk analysis process.
Now showing 13–24 of 47 search results:
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2017 Papers
2017 – Estimating the Duration of Flood Overtopping for Risk Assessment
Learn moreD Stephens, S Lang, P Hill, M Scorah
Robust estimates of the duration of flood overtopping are a key input into the dam safety risk assessment process. For embankment dams, the likelihood of erosion of the dam crest, downstream face and eventual unravelling of the embankment are heavily dependent on the duration of water flowing over the crest. Similarly, the chance of erosion of the abutments of concrete dams is strongly linked to the duration of floodwaters overtopping the dam. Previously, it has been difficult to define the annual exceedance probability (AEP) of the flood required to cause overtopping of a certain depth for a certain duration, and coarse assessments have typically been made based on critical storm durations of the dam crest flood (DCF). This approach carries significant uncertainty, particularly for structures on smaller catchments where the critical storm duration on outflow may be relatively short. In these cases, it has been difficult to confirm with any reliability that the flood required to achieve a significant duration of overtopping has an AEP close to that of the DCF. This paper describes a new algorithm that has been incorporated into the RORB hydrological model which allows for a frequency curve of flood overtopping duration to be determined within a Monte Carlo framework. The results of this analysis are presented for a case study of a quantitative risk assessment, to demonstrate how the outcomes influenced numerous aspects of the risk analysis process.
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2017 Papers
2017 – Factor of Safety? – Do we use it correctly?
Learn moreJiri Herza, Michael Ashley, James Thorp
The principle of minimum acceptable factors of safety has been used to assess the stability of embankment dams for decades. The commonly applied minimum acceptable factors of safety remain very similar to those recommended in the early 1970’s, despite the development of new design tools and better understanding of material behaviour. The purpose of factors of safety is to ensure reliability of the dam design and to account for uncertainties and variability of dam and foundation material parameters, uncertainties of design loads and limitations of the analysis method used. The impact of uncertainties and reliability of input values into stability analyses was recognised many decades ago, and the factor of safety was recommended depending on the loading conditions and the consequences of failure or unacceptable performance. Interestingly, the minimum recommended factors of safety used today do not take into account the potential consequences of dam failure or the uncertainties in input values, and are based on the loading conditions only. Yet, several authors have demonstrated that a higher factor of safety does not necessarily result in a lower probability of failure, as the analysis also depends on the quality of investigations, testing, design and construction. This paper summarises the history of the factor of safety principle in dam engineering, discusses the calculation of the factor of safety using commonly used analytical tools, demonstrates the impact of uncertainties using a case study and provides recommendations for potential improvements.
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2017 Papers
2017 – Great Expectations for Biopassage Innovation in Design of a Turtle Passage at Gympie Weir
Learn moreHelena Sutherland
In recent years, there has been greater expectations of waterway barriers to have more consideration of environmental factors; in particular associated with facilitating biopassage across the site.
The scope of the Gympie Weir Detailed Design Project included facilitating biopassage to as many aquatic species as possible,including the protected Mary River Turtle,while maintaining the required gauging accuracy and public amenities.Very rarely has a turtle been observed successfully traversing a fishway, as the designed velocity and depth criteria required to optimise fish passage is unsuitable for turtle passage. Thus for Gympie Weir,a leading-edge innovative solution was designed.
The design incorporates a low flow trapezoidal fishway chute, high flow rock ramp and turtle ramp. The turtle passage is the first of its kind and includes a curved concrete ramp with a variety of textures, two resting pools with protective niches, and limited vertical drop heights. Construction of the weir is intended for the near future and ongoing monitoring will be critical to assessing and improving performance, as well as contributing to the scientific knowledge base for future designs.
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2017 Papers
2017 – Haldon Dam Remediation: A Case Study of Earthquake Damage and Restoration
Learn moreJohn Harris, James Robinson, Ron Fleming
Haldon Dam Remediation: A Case Study of Earthquake Damage and RestorationJohn Harris, James Robinson, Ron FlemingAECOM New Zealand LimitedAECOM New Zealand Limited, Fleming Project Services Limited Haldon Dam is a 15m high zoned earth-fill embankment irrigation dam, located approximately 10 km south-west of Seddon, in the Awatere Valley, New Zealand. The crest and upstream shoulder of the embankment suffered serious damage during the 2013 Cook Strait earthquakes, and the Regulator enforced emergency lowering of the reservoir by 5.5m to reduce the risk of flooding to Seddon Township from a potential dam failure. AECOM was engaged by the owner to carry out a forensic analysis of the damaged dam and subsequently the design of the 2-Stage remedial works. The remedial works addressed the existing dam deficiencies and earthquake damage in order to restore the dam to full operational capacity and gain code compliance certification. Key features oft he approach included holding a design workshop with the owner prior to undertaking detailed design, careful rationalisation of the upstream shoulder to optimise the competing interests of strength and permeability, contractor and regulator involvement in the design and construction process, and balancing risk and constructability with the chimney filter retrofit. This paper presents a description of, and approach to, remedial works solution undertaken to remediate a substandard and earthquake-damaged dam to fully operational status in an area of high seismicity. Applying this approach, the objective of achieving a robust, safe, economical design that was acceptable to the regulators and the owner was achieved.
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2017 Papers
2017 – Hardfill Dams and Geomembrane Facings
Learn moreAlberto Scuero, Giovanna Lilliu, Marco Scarella, Gabriella Vaschetti
Hardfill dams present technical and cost advantages. Placement is like in embankment dams, thus construction is fast. The typical trapezoidal shape makes possible use of local aggregates and low cement content. Despite the low strength material, these dams can be built on weak foundation, and resist earthquake and overtopping. However, being the material semi-pervious, they require an impervious facing. Until 2014 this was typically made with conventional concrete slabs with waterstops, or grout enriched hardfill. Concrete facings require heavy and costly equipment, long construction time, are expensive, frequently require maintenance.Construction of the facing can have a big impact on the overall construction costs of the dam. Replacing the concrete facing with a geomembrane lining is a cost-effective solution. This paper describes two hardfill dams’ projects with an exposed geomembrane as upstream liner: Filiatrinos (Greece, 2015), 55.6 m high,and Ambarau(Democratic Republic of the Congo, 2017), 19.30 m high.
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2017 Papers
2017 – Have Physical Hydraulic Models Had Their Day?
Learn moreBronson McPherson, Scott Marshall1, Clément Monteil, Eric Lesleighter
This paper explores whether physical modelling has had its day in modern engineering or whether there is still a place for it. Physical hydraulic modelling is used as a tool for analysing hydraulic behaviour for a wide range of applications including; dams, channels,rivers,coastal etc. With advances in computer technology and power, the last few decades have seen the rise in numerical modelling, e.g. Computational Fluid Dynamics (CFD), often as an adjunct to physical modelling and sometimes as a replacement. A number of physical modelling case studies have been explored to identify the value provided by physical modelling.
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2017 Papers
2017 – Impact of Detailed Consequence Assessment on Leslie Harrison Dam Upgrade Works
Learn morePeyman Andaroodi, Barton Maher
Seqwater is a statutory authority of the Government of Queensland that provides bulk water storage, transport and treatment, water grid management and planning, catchment management and flood mitigation services to the South East Queensland region of Australia. Seqwater also provides irrigation services to about 1,200 rural customers in the region that are not connected to the grid and provides recreation facilities. Seqwater owns and operates 26 referable dams regulated under Queensland dam safety legislation.
Leslie Harrison Dam is an Extreme Hazard category dam located in the Redland Bay area of Brisbane.A significant portion of Population at Risk is located within a short distance downstream of the dam, reducing the available warning time in the event of a dam safety issue and impacting on the estimated loss of life used to assess risk. Following the Portfolio Risk Assessment undertaken by Seqwater in 2013, a series of detailed investigations were undertaken to confirm the assessed risk and the scope and urgency of the upgrade works.
Before a final decision on the scope and timing of the dam upgrade is made, Seqwater has completed a detailed review of the downstream consequences. This review was intended to update the Population at Risk(PAR) and Potential Loss of Life(PLL) estimates using the latest estimation methods for a range of scenarios. Three life loss estimation methods were used including empirical and dynamic simulation models and the results were compared.
This paper discusses the updated consequences assessment and the impact on the assessed risks, for Leslie Harrison Dam for both the current dam and the proposed upgrade scenarios using the revised Potential Loss of Life estimates.
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2017 Papers
2017 – Lessons Learned and the impacts of Cyclones Debbie and Marcia on Queensland’s Emergency Planning and Guidelines
Learn morePeter Allen and Mark Rhimes
Recent tropical cyclones have had significant impacts on coastal Queensland and produced significant inflows into a large number of major dams with the triggering of a number of Emergency Action Plans for downstream release hazards. While there were several floods of record, there were no significant dam safety incidents. The dams seemed to have been blamed for a lot of this flooding even though they provided significant flood mitigation. This paper will cover the emergency responses to these events, the public perceptions and the associated third party reviews of these events. Community expectations and the ability to undertake post flood event assessments of dam operations is also driving such investigations.This paper will also discuss the consequential updates being made to Queensland Emergency Action Planning Guidelines to encourage effective engagement with local emergency planners and other stakeholders in the development of these guidelines.
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2017 Papers
2017 – Nagmati Dam – A Project of Environmental and Cultural Significance
Learn moreRichard Herweynen, Suraj Neupane, Paul Southcott and Ashish B. Khanal
Kathmandu, the capital city of Nepal, is home to more than five million people. Three major rivers including the Bagmati run through the city of Kathmandu, providing the environmental and cultural lifelines for the civilisation and local people. High population growth in Kathmandu over the past 30years has put a serious environmental strain on the Bagmati River. Water is drawn from the Bagmati River for drinking, farming, industries and construction. Due to the lack of capacity in the current sewerage systems, untreated sewage is entering the river system, along with high quantities of rubbish. Although a holy river, the Bagmati River is highly degraded, with reduced flows, high pollution, and a fresh water ecosystem that is now destroyed.To revive the Bagmati River, the Government of Nepal with funding from the Asian Development Bank (ADB), is undertaking the Bagmati River Basin Improvement Project (BRBIP). One of the sub-projects is the construction of a dam on the Nagmati River to store water during the monsoon period for environmental release during dry season.Since November 2015, Entura have been involved in the investigation and detailed design of the Nagmati Dam. Through a simple storage model, it was determined that 8.2Mm 3 of live storage was required to meet the environmental flow objectives. To achieve this storage a 95m high dam was required at the Nagmati site, with a concrete faced rockfill dam (CFRD) determined to be the best option.This paper will present the development of this unique project, highlighting how a number of the challenges were addressed, leading to a sustainable project.
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2017 Papers
2017 – Observations from Five Australian Applications of HEC-LifeSim to Estimate Potential Loss of Life from Dam Failure
Learn moreChriselyn Kavanagh, Simon Lang, Andrew Northfield, Peter Hill
The U.S. Army Corps of Engineers have recently releasedHEC-LifeSim1.0, a dynamic simulation model for estimating life loss from severe flooding (Fields, 2016). In contrast to the empirical models that are often used to estimate life loss from dam failure, HEC-LifeSim explicitly models the warning and mobilisation of the population at risk, and predicts the spatial distribution of fatalities across the structures and transport networks expected to be inundated. This capability provides additional insights to dam owners that can be used to better understand and reduce the life safety risks posed by large dams. In this paper, we demonstrate the use of HEC-LifeSim to model the potential loss of life from failure of five large Australian dams. Particular attention is paid to how the predicted life loss varies with warning time, in a manner that depends on human response and the transport network’s capacity for mass evacuations, and the modelled severity of flooding. We also examine how the HEC-LifeSim estimates of life loss compare with those from the empirical Reclamation Consequence Estimating Methodology (RCEM).
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2017 Papers
2017 – Operation and Implementation of a Web-based Dam Monitoring Platform
Learn moreStefan Hoppe, Vicent J. Espert-Canet
Monitoring data has to be transformed into useful knowledge to provide owners and operators with valuable information about the safety status of their dams. This information should be up-to-date and easily accessible for all technicians and engineers involved inthe safety program,and directly linked to operation and emergency preparedness procedures.This article describes the main functions of a web-based software for the acquisition, processing,and evaluation of monitoring data. It runs on conventional internet browsers,and does not require the installation of any additional software. It provides appropriate tools for monitoring the safety status of dams and analysing dam behaviour.This article uses a case study to outline the experience gained from implementing and operating the software for 8 years to control more than 50 Spanish public dams owned by a river basin authority. The implementation involved completely revisingthe installed monitoring systems and recompiling all available information. This was used as a basis for an updated,goal-oriented definition of necessary variables, configuration of charts, SCADA views and threshold values. A key aspect of the software ́s successful implementation was the theoretical and practical training of all stakeholders.As a result of the software ́s implementation, the dam owner was able to use the data from their monitoring system more efficiently. The development of safety reviews and dam safety status evaluations were also considerably improved.
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2017 Papers
2017 – Public Safety Around Dams: Best Practices for Barrier & Signage Placement at Water Control Dams & Hydroelectric Powerplants
Learn morePaul S. Meeks
In June 2008 a young girl kayaking at a hydroelectric control dam owned by Alcan in Quebec Canada, tragically drowned when she was swept through the open spillgates. The public safety boat barrier, installed the year before, failed to prevent this accident. In June 2015, Stephen Hembree took his daughter and 7 of her friends out for a pontoon boat ride on Lake Linganore to celebrate her 16th birthday. A short time later, Mr. Hembree was dead while his daughter and her friends were be rescued by helicopter as they clung to boulders in the spillway. Contrast these incidents to one in March 2017, when the public safety boat barrier installed by Alliant Energy at Kilbourn Dam was credited with preventing the loss of life after a woman fell into the river above the dam. What went wrong in the first 2 instances and what can we learn from the third incident? What steps can dam owners take to prevent accidents like these from happening?
The first two incidents represent preventable loss of life at a dam while the third incident proves how a proactive approach to public safety results in reduced liability for dam owners and lower loss of life. In the Alcan instance, the public safety barrier installed to prevent this very scenario was instead installed in a location that doomed the girl even before she set her kayak in the water. The second instance demonstrates how a dam owners lack of risk awareness coupled with a boat owners carelessness resulted in a fatality.
Using the incidents above, this presentation, modeled after the Canadian Dam Associations Guidelines for Public Safety Around Dams, will educate owners and operators how to identify “dangerous” zones above and below dams. We will consider the effects of surface water velocity of individual survivability and barrier effectiveness. Flow-3D models will be shown to illustrate the effect of barrier alignment and velocity to increase an individual’s ability to “self-rescue”. Lastly, we will integrate within the presentation practical guidelines for the use of signage, sign size, lettering height and message consistency. The presentation will conclude by examining lessons learned in the Alcan incident and presenting how a proper public safety barrier and signage plan would be implemented.
More people have died from accidents around dams than have died from dam failures. The Canadian Dam Association published its guidelines in 2011 and the result has seen a significant reduction in fatalities and injuries as a result of recreating around Canadian Dams. The United States Society on Dams (USSD), the Association of State Dam Safety Officials (ASDSO) and the Federal Energy Regulatory Commission (FERC) all have embarked on efforts, modeled in large part around the CDA Guidelines to bring Public Safety out of the dam safety toolbox so Public Safety is viewed as a separate managed system. This is being conducted in an effort to educate and alert dam owners, operators and recreational users to hazards and risks in and around dams.
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2017 Papers
2017 – Ridge Park Dam: An Innovative Design for an Urban Setting
Learn moreLisa J Neumann, Rod Westmore
In Australia construction of a new dam on a greenfield site is relatively uncommon and construction of a new dam on a brownfield site is even more unusual.This paper presents an innovative design solution to address the challenges associated with such a project.Ridge Park Dam is a new flood retarding dam located in a suburban recreation park, less than 10km south east of Adelaide, South Australia.The dam was constructed in 2014/15 and was designed to limit the peak flows in the creek downstream of the park under the 1 in 100 ARI event and to impound water as a component of the infrastructure required for the Managed Aquifer Recharge (MAR) scheme located in Ridge Park.The expectations of both the client and community and the technical issues encountered in the early stages of the project resulted in some unique design criteria. At the outset the client and community expectation was that the dam would improve the overall amenity of the park without impacting the existing vegetation or functionality of the park, including public access and safety.Identifying a dam type to suit the client and community expectations and address the technical issues was not straightforward.Typical dams types such as embankment dams, mass concrete gravity or concrete buttress structures, were found to be not suitable.A less typical, innovative solution was sought.The outcome was to construct a dam comprising a concrete core wall supported by rock filled gabion baskets.
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2017 Papers
2017 – Seismic Performance of Existing and New Embankment Dams: The Myth of the Reliability of Simplified Newmark-type Methods
Learn moreMojtaba E. Kan, Hossein A. Taiebat and Mahdi Taiebat
In design of new embankment dams or evaluation of the performance of existing earthfill and rockfill dams, the Newmark-type Simplified Methods are widely used to estimate the earthquake-induced displacements. These methods are simple, inexpensive, and substantially less time consuming as compared to the complicated stress–deformation approaches. They are especially recommended by technical guidelines to be used as a screening tool, to identify embankments with marginal factor of safety. The methods would serve as a reliable screening tool had they always resulted in conservative estimates of settlements. However, a number of studies in the last 15 years show the contrary. This paper provides a critical review of the fundamental theory behind the simplified Newmark-type methods. Cases in which the results of the simplified methods are reportedly non conservative are further investigated and possible reasons are discussed, that may be taken into account in future design and investigations of Australian dams. The reliability of the simplified methods is examined based on the existing thresholds proposed in the literature and accounting for the embankment geometry and type, and for the seismic activity characterization. A recently proposed practical framework is further elaborated to demonstrate its effectiveness in the study of seismic behaviour of embankment dams. In particular, the case study of Zipingpu concrete faced rockfill dam in China is discussed where all widely used simplified procedures failed to predict the order of deformations experienced by the Dam under a recent strong earthquake event.
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2017 Papers
2017 – Seqwater Dam Improvement Program – Assessment, Prioritisation, Justification and Implementation of Dam Upgrades
Learn moreBarton Maher and Michael Peel
The Queensland Bulk Water Supply Authority (Seqwater) manages up to $12 billion of bulk water supply infrastructure and the natural catchments of the region’s water supply sources to ensure a reliable, quality water supply for more than 3million consumers across the region. Seqwater was formed on 1 January 2013 through a merger of three State-owned water businesses, the SEQ Water Grid Manager, LinkWater and the former Seqwater. Seqwater delivers a safe, secure and reliable water supply to South East Queensland, as well as providing essential flood mitigation services and managing catchment health. Seqwater also provides water for irrigation to about 1,200 farmers and offers community recreation facilities enjoyed by more than 2.5 million people each year.Seqwater owns and operates 26 referable dams which fall under the dam safety regulation in Queensland, 51 weirs, and two bore fields across the region. Twelve key dams across the region supply as much as 90% of South East Queensland’s drinking water.In 2011, Seqwater engaged a consultant team of URS (now AECOM) and SKM (now Jacobs) to undertake a portfolio risk assessment of the 26 referable dams and Mount Crosby Weir. At the completion of the project in December 2013 there were 12 dams with life safety risks assessed as being above the ANCOLD and DEWS Limit of Tolerability. A $6.2 million investigation was approved in 2014 to commence planning for the recommended dam safety upgrades and reduce uncertainties in the risk assessment.This program of work was completed in late 2016. The estimated costs of the identified dam safety upgrades exceed $900 million.Confronted with such a large capital program, Seqwater has instigated a number of key actions including:-benchmarking capital investment and rates of risk reduction achieved by other dam owners through a dam owners group-developing a dam safety investment policy to provide a clear guidance on the framework for prioritising and scheduling upgrades-undertaking targeted investigations to reduce uncertainty in the risk assessments including the use of detailed consequence assessment-preparing a prioritised schedule of planned upgrades to gain endorsement from Government and the Dam Safety Regulator. This paper presents the outcomes of the Portfolio Risk Assessment and key changes to the initial risk assessment following further studies. The basis for the dam safety investment policy is presented and the proposed prioritisation tools.The impacts of the risk assessment provisions in the most recent revision of Queensland Acceptable Flood Capacity Guidelines for Water Dams are also discussed. In particular,the application of the economic criteria for determining the minimum upgrade required by the Queensland Dam Safety Regulator and its relevance to other dam owners.
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2017 Papers
2017 – Sheet Piles: Driving a Solution to Piping Risk
Learn moreTom Ridgway, Chris Topham, Aaron Brimfield
A significant number of dams across Australia are of earthen construction and may be susceptible to internal erosion of their earth core, also known as piping. In January of 2016, during an annual inspection of the Tarraleah No 1 Pond Levee it was found that the embankment was experiencing significant seepage at the toe. Further investigations found actively developing piping holes through the embankment. To better understand the condition of the dam, HydroTasmania’s remote monitoring trailer was deployed to provide telemetered seepage data to further understand the developing issue. It was found that the leakage was increasing dramatically, and carrying suspended core material, resulting in the need for prompt resolution to protect the embankment from further loss of material. A sheet piling wall was installed in the centre of the embankment to cut off the flow of water through the embankment. After the installation of the sheet piling wall, post works monitoring showed the seepage through the embankment reduced to virtually zero, only peaking in rainfall events. This paper outlines the investigation and management of the incident, and the mitigation measures put in place from the time of identification including the use of a sheet piling wall to mitigate a developing piping failure. The paper will conclude with the outcomes of the work and how a similar solution could be utilised for other dam owners in a piping event.
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