Richard R. Davidson, Nate Snorteland , Doug Boyer, John France
The US Army Corps of Engineers (USACE) has embarked upon a monumental journey in applying risk-informed decision making in the management of the safety of the 650 major dams for which it is responsible. This process has shifted safety criteria from fully deterministic to a probabilistic basis. There has also been a shift from de-centralized district-based decision-making to centralized management of resources through the new Risk Management Center (RMC) and the Senior Oversight Group (SOG), a group of senior engineers and managers from across the USACE organization. The risk process began about five years ago with a portfolio prioritisation using screening-level risk assessments of the entire dam inventory, culminating in Dam Safety Action Classifications (DSAC) for each of the dams. Based on this risk prioritisation, Issue Evaluation Studies (IES) were initiated for the highest risk DSAC I and II dams, with each study including detailed failure mode and risk analyses for each dam. Because the Corps was relatively new to dam safety risk analyses, and their dam design history was one of following codified manuals of practice, various risk tools were prepared to provide guidance when assessing the risk of potential static, seismic and flood failure modes, as well as life loss and economic consequences of dam failure. Although these tools provided useful guidance to a relative large population of inexperienced risk estimators, many of these early risk assessments were flawed; they provided unrealistically high estimates of failure probabilities and the tools did not help estimators understand or explain each failure mode. To assist the RMC in bringing more defensible risk estimates to the table and improve consistency of the evaluations, the Quality Control and Consistency (QCC) review process was initiated about two years ago. The QCC process provides high level review of IES activities, including detailed reviews of risk analyses, by a small group of experienced dam safety risk estimators. Not only has this brought risk estimates into a more reasonable range, it has provided valuable training for risk estimators, and important checks and balances on the risk-informed decision making process for moving dam safety upgrade projects forward. The justification for a number of very expensive projects has been challenged and, in some cases, re-prioritised, and other projects have risen to the prominence they deserve.
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Shane McGrath, Andrew Reynolds, Garry Fyfe, Chris Kelly, Steven Fox
Goulburn-Murray Water is a rural water corporation located in Northern Victoria. It has responsibility for 12 State dams and is also the constructing authority for the Murray Darling Basin Authority’s Victorian assets.
Over the past 15 years G-MW has been engaged in a dam improvement program across its portfolio. To date 14 individual projects have been undertaken at 11 dams. The total expenditure is $125 million.
Starting from a base level of data at its inception in 1997, the program has encompassed all facets required for a dam improvement program. From early prioritisation to set the investigation program, through design reviews and risk assessments to develop the upgrading program and subsequent implementation. Some elements of the program were at the leading edge of practice at the time and a range of experiences along the way were character building as dam safety investment challenged other corporate priorities.
This paper sets out the lessons learned in developing the methodology and implementing the program of works, particularly relating to corporate adoption of the program, organisational capability, investigations, risk assessments, design and implementation.
In recent years the option to decommission water supply dams has had renewed focus due to a number of drivers. These include the increased costs of upgrading aging infrastructure against their provided value, climate change reducing the effectiveness of some dams as a reliable water source, greater value placed on environmental outcomes and changing demands for the water including power in case of Hydropower dams. In addition the recent construction of large coastal desalination plants as an alternate water source for large urban areas, particularly in Australia, has reduced the need for some dam assets.
In response to this changing dynamic in the Industry, ICOLD formed a technical committee in 2007 to prepare a bulletin on dam decommissioning for use by those considering the option of decommissioning a dam. The purpose of the bulletin or guideline was not as a design manual but to provide industry with information and guidance to better understand the key drivers of decommissioning and the issues around decommissioning. It is probably a fair summation of the practice to date, that issues associated with decommissioning of major dams have not always been well understood prior to this option being selected. This has on occasion resulted in dramatic increases in the cost of decommissioning, extended timelines and not least, strong community and other stakeholder resistance. Hence the ICOLD decision to prepare a bulletin. The Author of this paper was a part of this committee and has also been involved with a number of dam decommissionings and assisting regulators in developing their own guidelines.
In this paper the key findings from development of the ICOLD bulletin will be presented including illustration of various key issues via case studies from this region and internationally. In particular, the true cost of decommissioning. The final draft of bulletin is currently under review.
Keywords: Decommissioning, ICOLD, community, stakeholder, water supply, hydropower, cost.
Robert Kingsland, Jamie Anderson, Andrew Russell, David Brooke
This paper presents the methods, observations and results from a programme of No-Erosion Filter (NEF) testing for the evaluation of a manufactured filter aggregate product that did not conform to normally accepted D15F grading limits. Base materials tested include both dispersive and non-dispersive soils. The results are compared against published no-erosion, excessive erosion and continuing erosion thresholds. The paper comments on the validity of the adopted thresholds and the effectiveness of the NEF test as a filter evaluation method.
Keywords: dam, filter, test, no-erosion
Simon Lang, Peter Hill, Wayne Graham
The empirical method developed by Graham (1999) is the most widely used in Australia to estimate potential loss of life from dam failure. It is likely to remain that way while spatially based dynamic simulation models are not publicly available (e.g. LIFESim, HEC-FIA and LSM). When the Graham (1999) approach was first developed the prevalence of spatial data and the speed of computers was much less. In addition, most people did not have mobile phones, social media was in its infancy, and automatic emergency alert telephone systems were 10 years from being used in Australia. Graham (1999) was intended to be applied to populations at risk (PAR) lumped into a discrete number of reaches. The selection of fatality rates for the PAR in each reach was based on average flood severity and dam failure warning times. Today, there is typically much more spatially distributed data available to those doing dam failure consequence assessments. Often a property database is available that identifies the location of each individual building where PAR may be, along with estimates of flood depths and velocities at those buildings. News of severe flooding is likely to be circulated by Facebook, Twitter and e-mail, in conjunction with official warnings provided by emergency agencies through radio and television and emergency alert telephone systems.
This raises the question of how Graham (1999) is best applied in today’s digital age. This paper explores some of the issues, including the estimation of dam failure warning time, using Graham (1999) to estimate loss of life in individual buildings and the suitability of Graham (1999) for estimating loss of life for very large PAR.
Keywords: loss of life, dam safety, risk analysis.
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.