Papers
Papers are made available through the website 12 months after they are presented at the annual conference. Please add to your shopping cart to purchase and you will receive a link to download.
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A CD can be purchased containing ANCOLD Bulletins from 1961 to 2001 on the OTHER PUBLICATIONS page.
If there is a paper you require prior to 2007 that has not been uploaded please contact the secretariat [email protected]
Use the search below using keywords, year or author.
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Papers
2015 – Estimation of Seismic Hazard for Dams with a Consistent Risk Approach
Learn moreMaz Mahzari and Chi-Fai Wan
Upgrading of an existing dam often faces challenges in both static and seismic safety assessment. The use of new hydrological and seismological data and improved design methods often mean more severe loading which outdates the original design and demands expensive upgrade works. Establishing the design criteria for checking the structural adequacy of an existing dam for multiple unusual load events occurring within a relatively short time frame presents another challenge.
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A probabilistic approach is presented to rigorously address the effects of multiple load events while maintaining a consistent risk of failure for the structure. This is based on a probabilistic conditional combination where probability of each event is defined and used to develop a joint probability distribution. For instance if an earthquake occurs following a severe flood, the seismic hazard curve of the site can be used to adjust the seismic loading with shorter average recurrence interval to be used in conjunction with the pre-earthquake flood when assessing the structural adequacy of the dam. With this method of adjustment, the design can benefit from the choice of a reduced seismic design loading and hence a more cost effective design solution.
The proposed method is straightforward and can be effectively used in most engineering practices, including the design of hydraulic structures such as dams.
Keywords: Dams, Seismic Hazard, Post-earthquake, Risk analysis -
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Papers
2015 – Towards Risk-Based Surveillance Programmes – Maximising the Value of Your Monitoring Spend
Learn moreMark Arnold, Chris Topham, Phil Cummins
A central tenet of the ANCOLD Guidelines on Dam Safety Management (2003) is that the higher the consequence of failure of a dam, the more stringent the surveillance scope, frequency, and safety criteria that should be applied to that dam. This concept has generally served the industry well to date in assisting regulators and dam owners to focus on the dams that could have the highest impacts if they failed. ANCOLD 2003 does also suggest that risk may be taken into consideration, however it is the experience of the authors that for dam surveillance and monitoring programmes, the majority of owners and consultants are reluctant to stray too far from the tables provided in the Guideline. However, two owners have recently embarked on a formal process to apply a risk based approach to the specification of surveillance and monitoring for their dams. This paper outlines how sub-optimal outcomes that can arise when the guideline tables are applied exclusively, presents the process undertaken by two owners of large portfolios of high consequence dams, and demonstrates the benefits achieved when a risk based approach is used. The paper concludes that any update or rewrite of the 2003 Dam Safety Management Guidelines should promote a risk based, rather than a consequence based approach to surveillance and monitoring.
Keywords: Risk, risk-based surveillance programme, instrumentation, monitoring.
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Papers
2015 – The hydropower dam lenders’ technical advisor – roles, responsibilities and lessons learned
Learn moreAndrew Noble
This paper explores the role of the Lenders’ Technical Advisor (LTA) in identifying and mitigating risks in hydropower dam projects on behalf of the project lenders. It describes the LTA services that are required to manage the pre-financial close, construction and financing periods.
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There are differing types of risk in both large and small hydropower projects (contractual, commercial, participant, completion, country, technology, reputational, environmental and social, etc.) and these are discussed with regard to how the lenders may be exposed if the risk eventuates either during dam construction or in operation.
Whereas a large dam for water supply would in its own right be a major project, the dam(s) associated with large hydropower will likely represent less than 25% of the total project cost and with this imbalance comes competing drivers for the other components (tunnels, waterways, powerhouse, M&E equipment, transmission lines, substations, etc).
The paper discusses the typical process whereby a hydropower developer has procured a feasibility study and is working towards financial close — covering both large and small types, i.e. storage dams and run-of-river diversion weir types, and the noticeable trend for fast-tracked developments to make a single large step from feasibility study through to engineer-procure-construct (EPC) contracting. This scenario presents some challenges for the initial due diligence when assessing in the pre-financial close stage.
The paper draws on case studies from the Asia Pacific region to illustrate the key elements in hydropower project financing from the LTA’s perspective, together with the author’s recent and current experience on multiple hydropower projects across Asia and Africa in the run-of-river, storage reservoir and pumped storage type of plants. It also brings together findings from the author’s own recent papers on the subjects of hydropower feasibility studies, the roles of lenders, owners and advisors, and tailored for an ANCOLD audience where the focus is on the dams component of hydropower.
Keywords: Lenders’ Technical Advisor, Dams, Hydropower. -
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Papers
2015 – What influences dam safety outcomes: a state-wide perspective
Learn moreMakeena Kiugu, Siraj Perera
Dam owners are influenced by drivers such as ensuring economic efficiency, achieving industry good practice, and meeting regulatory or due diligence obligations when making decisions on how to manage their dams. While these drivers can be inter-related, the decisions finally made by dam owners are reflected in planned and completed dam safety activities.
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In Victoria, dam owners update the regulator on the status of their dam safety management programs every year. Victorian dam safety regulation is underpinned by risk management principles. Benchmarking of dam safety management practices is also promoted within the industry. The information provided to the regulator includes risk levels of dams, scheduled upgrades and associated cost estimates, interim risk reduction measures, and details of surveillance, emergency management and operation and maintenance programs. A considerable amount of information has been collected over the past few years allowing trends in dam safety management activities to be examined at a State-wide level.
This paper will consider how dam safety management decisions, and the drivers behind those decisions, are reflected in the dam safety practices of Victorian dam owners. Trends in dam safety activities will be observed and linkages made to prevailing industry-wide challenges.
Dam owners are increasingly being required to address a wider range of issues in an environment of limited resources. Ensuring due diligence and improving emergency preparedness are some current challenges facing dam owners. This paper also examines how these emerging drivers may influence dam safety activities into the future.
Keywords: Dam safety management -
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Papers
2015 – A critical assessment of liquefaction triggering sensitivity to design magnitude for Australian dams
Learn moreT. I. Mote, M.L. So, N. Vitharana, and M. Taylor
This paper explores the sensitivity of selection of earthquake design magnitude to liquefaction triggering in Australia for ground motions typically used for dams. The low seismicity of Australia creates a situation where liquefaction triggering is marginal at design hazard levels and this low level of seismic hazard makes the liquefaction trigger analysis very sensitive to the derivation of the seismic inputs. A methodology is presented that couples the probability of liquefaction triggering with the distribution of earthquake contribution to the hazard from the magnitude-distance deaggregation. The results show that for the “typical” soil profile and input ground motions approximately equivalent to the maximum design earthquake for Australia, the probability of liquefaction triggering varies significantly with the design magnitude selected. Using the maximum credible earthquake or mean magnitude may provide significantly different liquefaction triggering implications. Combining the probability of liquefaction triggering with the contribution of varying magnitudes to calculate liquefaction probability is a useful method to understanding the sensitivity of liquefaction to design magnitude.
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Keywords: Liquefaction Assessment, Design Magnitude, Probability of Liquefaction, Magnitude-distance deaggregation, Australia -
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Papers
2015 – Towards consistency in potential loss of life estimates: Testing the new Reclamation Consequence Estimating Methodology
Learn moreChriselyn Meneses, Simon Lang, Peter Hill, Mark Arnold
Risk is the product of likelihood and consequences. Much effort is put into the risk assessment process for large dams to ensure there is a consistent approach to estimating failure likelihoods across an owner’s portfolio. For example, the use of common peer review teams and methods like the ‘piping toolbox’ allow the risk assessment team to apply repeatable logic and processes when estimating failure likelihoods. However, the methods for estimating life safety consequences are often not applied consistently. This inconsistency leads to estimates of potential loss of life (PLL) that vary between dams in unexpected ways, because results from the most commonly applied method (Graham, 1999) are sensitive to threshold changes in flood severity and dam failure warning time.
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The recently released Reclamation Consequence Estimating Methodology (RCEM) is intended to supersede Graham (1999). RCEM varies fatality rates continuously with DV, and is therefore less sensitive to changes in flood severity. In this paper, estimates of PLL from RCEM are compared with results from Graham (1999) for five dams. Results from the latest US Army Corps of Engineers model for estimating the consequences of dam failure (HEC-FIA 3.0) are also compared with RCEM and Graham (1999) for one dam. Comment is then made about the important considerations for applying RCEM consistently across a portfolio of dams.
Keywords: potential loss of life, dam safety, risk analysis -
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Papers
2015 – Boondooma Dam, flood damage, 3D physical hydraulic modelling, comprehensive scour assessment
Learn moreDeryk Forster
Since their development, rock mass classification systems have used and manipulated various populations of geomechanical data to allow a rock mass to be divided into different domains or engineering ‘masses’ with the aim of assisting in the geotechnical design of underground openings, excavations, foundations and ground support systems.
Each of these methods consider different characteristics to generate a material classification; including rock strength, joint weathering, defect spacing, in-situ stress and groundwater. However, none of these systems cater for classification of the rock mass based on whole rock weathering, whole rock strength and incipient defect spacing along a borehole.
This new classification system, the Rock Condition Number (RCN), has been developed to reduce the human factor of variability in interpretation when collecting data to classify the rock mass, as other methods, such as Rock Quality Designation (RQD), are prone to significant variability based on the experience of the person logging the core. RQD provides an indication of rock quality over the length of the cored interval, which varies depending on the drilling equipment and ground conditions. This value may typically be calculated over an interval of 1.0, 1.5 or 3.0 metres. The RQD system does not allow for the rapid identification of thin, though important features in the subsurface.
Using data captured electronically in the field, the RCN calculates an instantaneous classification of the rock mass at any point along the borehole, highlighting variations within the rock mass by assessing a combination of characteristics, allowing rapid identification of potential hazardous zones within the rock mass. This allows for significant improvements in efficiency during the assessment and design process/es. Resolution is greatly improved over RQD, with thin, though important, zones of weak material highlighted using this new process.Comparison between existing classifications and the RCN using real field data indicates the RCN provides greater resolution when identifying deficient zones within the rock mass.
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Keywords: Rock mass characterisation, RQD, Rock Condition Number, rock quality, dam foundations. -
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Papers
2015 – Advancements made in the 3D modelling of unlined spillway chutes and applications of comprehensive scour model
Learn morePeyman Bozorgmehr, Sarah McComber, David Harrigan, Erik F R Bollaert
Boondooma Dam is a concrete-faced rockfill dam with an unlined, uncontrolled spillway chute. The Acceptable Flood Capacity of Boondooma Dam is 1:60,000 AEP (equal to the Dam Crest Flood (DCF) and has a maximum inflow of 14,330 m3/s.
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Significant rainfall events during 2010/11 and 2013 subjected the spillway to moderate discharges over the crest which caused significant scour to the spillway chute.
Following these events, a 3D physical hydraulic model was constructed at a 1:80 scale to investigate repair options. Originally the spillway chute was modelled using a mobile bed set up which showed that that future scour could occur. However, the model could not determine the rate and characteristics of this damage.
In order to determine how future scour may occur, the 3D model was modified using laser survey mapping of the spillway chute after each flood event. Using milled aluminium and concrete capping the model was able to accurately portray the damage profile sustained by the spillway in the 2010/11 and 2013 flood events.
Transient pressure, static pressure, water elevation, velocity and jet measurements of the model were used in a Comprehensive Scour Model to help inform how damage to the chute may progress in future flood events.
Keywords: Boondooma Dam, flood damage, 3D physical hydraulic modelling, comprehensive scour assessment -
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Papers
2015 – Physical and computational scour modelling system analysis- Case study for Paradise Dam, Queensland
Learn moreBronson L McPherson, Eric J Lesleighter, David C Scriven, Erik F R Bollaert
A number of medium to major floods in Queensland caused substantial scour around spillway structures. This included the Paradise Dam primary spillway which experienced significant scour of the rock body below the spillway during flooding in January 2013. The occurrence has led to a series of evaluations of the geology, and the prevailing hydraulics behaviour as part of a process to determine the scour mechanism, and to determine the response of the spillway and areas downstream to future floods of larger magnitude. Part of the process has been to utilise a large-scale physical model to obtain transient data which together with the detailed geologic assessment would be incorporated into the comprehensive scour modelling procedures developed by Dr Erik Bollaert, AquaVision Engineering, Switzerland.
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The paper will describe the design and construction of the physical model with special features to obtain pressure transients from more than 60 transducers, and velocity transients in more than 40 locations using Acoustic Doppler Velocimeter (ADV) instrumentation. The features of the rock scour will be discussed and the geology of the area below the spillway apron will be described. The range of discharges, and the model’s results including the pressure and velocity characteristics will be described in detail to illustrate the violent nature of the turbulence in the energy dissipation zone. The paper will go on to describe the computational scour modelling procedures of calibration and application, demonstrating a “system” approach to spillway scour analysis for plunge pools and similar situations with energy dissipation on natural materials.
Keywords: Spillways, flood hydraulics, hydraulic modelling, rock scour, transients, numerical analysis, energy dissipation. -
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Papers
2015 – Erosion of unlined spillways in rock – does a ‘scour threshold’ exist?
Learn moreSteven E Pells, Philip J N Pells, William L. Peirson; Kurt Douglas and Robin Fell
The method of Annandale (1995) is widely used by Australian practitioners for the assessment of erosion in unlined spillways. This method is based on comparison to various case studies, where the geology at each site is characterised using the Kirsten index (a rock mass index previously developed to assess the rippability of rock), and the hydraulic conditions are characterised using the unit stream power dissipation. In this paper, the historical development of this comparative design technique is traced and is critically reviewed against the original geotechnical and hydraulic data, and against a new, independent, dataset gained from unlined spillways in fractured rock in Australia, South Africa and the USA. It is shown that, while erosion can be usefully correlated against rock-mass indices and hydraulic indices, this ‘comparative’ design technique has been promoted beyond its reach – the data do not support the inference of an erosion ‘threshold’ as presented by Annandale (1995). It is argued that this type of analysis should be used only as an initial ‘first indication of erosion potential’, as originally proposed by van Schalkwyk (1994b).
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Keywords: scour; erosion; spillways. -
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Papers
2015 – The Challenges Dam Owners Face When Considering Engineering Repairs in a Commercial Climate
Learn moreSarah McComber, Peyman Bozorgmehr
Boondooma Dam is a concrete-faced rockfill dam with an unlined, uncontrolled spillway chute. Construction was scheduled for completion in 1983; however a spill event occurred during the last stage.of construction Following this spill event an Erosion Control Structure (ECS) was built across the spillway chute to help mitigate any future scouring.
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The spillway performed as expected during minor spill events in the 1990s and early 2000s. During the significant rainfall event of 2010/11, significant scour occurred to the spillway chute and downstream of the ECS, as a result of the spillway operation.
Following the 2010/11 flood, emergency repairs were made and long term repair solutions were investigated. However, during Tropical Cyclone Oswald in January 2013, the dam experienced the flood of record, and further scour occurred in the spillway chute.
The long term repair solution was reviewed in light of the 2013 damage. A solution is required that would satisfy the engineering problem and prevent further damage, while satisfying the commercial considerations faced by dam owners, insurers, customers and downstream stakeholders.
Keywords: Boondooma Dam, flood damage, scour damage, commercial engineering solutions. -
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Papers
2015 – Design of the overbank spillway for St Georges Dam
Learn moreMonique Eggenhuizen, Eric Lesleighter, Gamini Adikari
St Georges Dam is located on Creswick Creek approximately 2km southeast of the township of Creswick and 135km northwest of Melbourne. The reservoir, located within the Creswick Regional Park and originally constructed to supply water for the Creswick quartz crushing plant in the 1890s, has since been established as a popular recreational storage and is the responsibility of Parks Victoria. The dam is approximately 16m high and located across a relatively steep gully. The embankment consists of earthfill with an upstream face of rock beaching and a grass covered downstream face. The primary and secondary spillways are cut into the right and left abutments respectively.
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At the completion of a detailed design review, St Georges Dam was assessed to be within the top three of Parks Victoria’s dams portfolio in regards to Public Safety Risks. The detailed design review assessed that the risk position for the dam plotted within the unacceptable region of the ANCOLD Guidelines for the static, earthquake and flood failure modes. As such, upgrade measures were considered to be required. In 2010 and 2011, a number of significant flood events emphasised the importance of upgrade works at this dam, particularly in regards to upgrading the spillway capacity, and consequently Parks Victoria assigned these works a high priority.
SMEC was engaged to design the upgrade works for the dam. A number of arrangements to increase the spillway capacity of the dam were considered, with the most cost effective option being assessed to be a secondary spillway over the dam embankment in the form of a rock chute.
This paper describes the decision making process associated with the option selection and the methodology for designing the overbank spillway which utilised the findings in ‘Riprap Design for Overtopping Flows (Abt & Johnson, 1991), and US Army Corps of Engineers, Waterways Experiment Station, publications of standard riprap gradations and computer program CHANLPRO.
Keywords: Embankment Dams, Spillway, Rock Chute, Erosion Protection