2006 – Emergency Action Planning for SunWater Dams
A. Khan
SunWater manages its portfolio of 29 major dams through 6 business centres each responsible for the Dam Safety Program for the dams under its management control.
The effectiveness of responses during an emergency depends on the amount of planning and training performed. Management must show its support for dam safety programs and the importance of emergency planning.
If management is not interested in community protection and in minimising property loss, little can be done to promote dam safety. It is therefore management’s responsibility to see that a program is instituted and that it is frequently reviewed and updated.
The input and support of all communities must be obtained to ensure an effective program. The emergency response plan should be developed locally and should be comprehensive enough to deal with all types of emergencies specific to that site.
SunWater is a responsible dam owner and has recently upgraded all its emergency action plans in consultation with emergency services of Queensland. This paper details the basic steps to handle emergencies of water infrastructure. These emergencies include inflow floods, rapid drawdown, earthquake, sunny day failure, changes in reservoir water quality and terrorist attacks including hoax.
This paper is intended to assist small dam owners that do not have dam safety programs in place. It is not intended as an all inclusive safety program but rather a provision of guidelines for planning for emergencies.
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Papers 2006
2006 – PMP ESTIMATES – ARE WE KIDDING OURSELVES?
Learn moreJanice H. Green and Jeanette Meighen
The Probable Maximum Precipitation (PMP) is defined as ‘the theoretical greatest depth of
precipitation that is physically possible over a particular catchment’. The PMP depths provided by
the Bureau of Meteorology are described as ‘operational estimates of the PMP’ as they represent the best estimate of the PMP depth that can be made, based on the relatively small number of large events that have been observed and our limited knowledge of the causative mechanisms of extreme rainfalls.Nevertheless, the magnitudes of the PMP depths provided by the Bureau are often met with scepticism concerning their accuracy when compared to large rainfall events which have been observed within catchments and which are, typically, only 20% to 25% of the PMP estimates. The recent increases in the PMP depths, resulting from the revision of the Generalised Tropical Storm Method (GTSMR), have served only to entrench this cynicism.
However, analyses of the magnitudes of the storms in the databases adopted for deriving PMP depths show that these observed storms constituted up to 76% of the corresponding GTSMR PMP depths and up to 80% of the Generalised Southeast Australia Method PMPs for the storm location. Further, comparisons of the PMP depths to large storms observed in similar climatic regions around the world indicate that the PMPs are not outliers.
The results of these analyses are presented for a range of catchment locations and sizes and storm durations and demonstrate that the PMP estimates provided by the Bureau of Meteorology are reasonable and are not unduly large.
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Papers 2006
2006 – Performance of New Orleans’ Hurricane Protection System: The Good, The Bad, and The Ugly
Learn moreG. L. Sills, N. D. Vroman, J. B. Dunbar, R. E. Wahl
In August 2005, Hurricane Katrina made landfall just east of New Orleans and inflicted widespread damage on the Hurricane Protection System (HPS) for southeast Louisiana. Subsequent flooding was a major catastrophe for the region and the Nation.
The response to this disaster by the U.S. Army Corps of Engineers included forming an Interagency
Performance Evaluation Taskforce (IPET) to study the response of the system and, among many lines of inquiry, to identify causes of failure of levees and floodwalls.Beginning in September 2005, the IPET gathered geotechnical forensic data from failed portions of levees and floodwalls. Major clues discovered at the 17th Street break, including clay wedges dividing a formerly continuous layer of peat, led to an explanation of the failures. Field data from the failure sites were interpreted within the regional geologic setting of the New Orleans area to identify geologic and geotechnical factors that contributed to the catastrophe. The data gathered provided a method that resulted in the “IPET Strength Model.” This strength was used in analyses of the I-walls and levees using limit equilibrium stability analyses, physical modeling using a powerful centrifuge, and finite-element analyses.
The results of all three types of studies revealed a consistent mode of failure that included deformation of the I-walls and foundation instability. The IPET also studied non-failed I-walls at Orleans and Michoud Canals, to identify geotechnical, structural, and geologic distinctions between failed and non-failed reaches.
Performance of the HPS during Hurricane Katrina offered many lessons to be learned. These lessons learned include: the lack of resiliency in the HPS; the need for risk-based planning and design approach; the need for the examination of system-wide functionality; and knowledge, technology, and expertise deficiencies in the HPS arena. In addition, understanding of the failure mechanisms and related causes of the levee and floodwall breaches provides a new direction for future designs of hurricane protection systems.
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Papers 2006
2006 – Corporate Governance For Dam Safety
Learn moreS. Frazer
Ensuring compliance with the Regulator’s requirements is a cornerstone consideration for any water corporation in planning its risk minimisation strategies against dam failure. With the increased focus on due diligence and corporate governance however, there are emerging themes that are of equal importance for a water corporation in planning protections against its core risks to dam safety. These considerations include:
- documenting and implementing plans and strategies to ensure corporate compliance with the Regulator’s requirements and updating these in line with legislative and policy changes;
- Documenting and implementing the corporation’s defences to the common law duty of care for public liability, including keeping up to date with the latest case law development locally and internationally in interpreting implications in respect of damage to property and injury and loss of life in relation to dam failure.
- Adopting behaviours and practices that bear out a compliance culture – is the current dam safety assessment and training “best practice” and is this enough to defend a claim? What is reasonable in economic and practical terms to ensure defensibility?
- ensuring the Board, Executive and other Officers are informed of operational decisions and incidents and their advice is implemented;
- arranging and maintaining appropriate insurances if available for public liability and property damage, as well as protections for directors and officers, both past and current.
- Developing and implementing a policy for disclosure, document management and retention that will support investigation for legal proceedings purposes; including providing privilege for relevant legal advices
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Papers 2006
2006 – Justification for an Operating Restriction in Spain Incorporating ANCOLD Guidelines on Risk Assessment
Learn moreManuel G. de Membrillera, Ignacio Escuder, David Bowles, Eduardo Triana, Luis Altarejos
The work herein presented is an application of the risk assessment process to retroactively estimate the justification of an operating restriction implemented on a Spanish Dam. Since the risk approach is not yet an established practice in Spain, the main objective of this case study is to show, the utility that risk assessment can have as a decision support tool for decisions on dam safety risk reduction investments.
An operating restriction has been imposed at this dam since its first impoundment. All studies, analysis and documents related to the safety of the dam and reservoir have been completed, as required by the Technical Regulation on Dam and Reservoir Safety (Spanish legislation, 1996). In addition, the structural corrective actions recommended in these evaluations are being implemented, so it is expected that the operating restriction can be removed in the near future.
In this context, the problem that has been formulated and solved comprises an evaluation, after more than 30 years since construction, of the operating restriction justification in terms of risk mitigation. In order to achieve the objective of the work, ANCOLD guidelines on Risk Assessment (2003) have been followed in addition to tolerable risk guidelines from several other countries and organizations.
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Papers 2006
2006 – The Ability of Monitoring to Detect Internal Erosion and Slope Instability in Embankment Dams
Learn moreRobin Fell
Internal erosion and piping within embankment dams may initiate in cracks caused by differential settlement or desiccation, in cracks caused by hydraulic fracture and in very poorly compacted layers of soil. It generally cannot occur unless one of these defects is present because backwards erosion, the other mechanism for internal erosion, will not occur in embankments under normal gradients and will not occur in cohesive soils unless gradients are exceptionally high.
As a result it is very unlikely that it will be possible to detect initiation of erosion with piezometers, and the most likely successful method is seepage observation and monitoring. However the time from the first detection of increased seepage to breach of the dam may be very short-a matter of hours in some situations.
Thoughtfully positioned and read piezometers are more likely to be successful in identifying the critical gradients which may lead to the onset of backwards erosion in cohesionless soils in the foundation of dams.
Piezometers are more useful in establishing the pore pressures for use in analysis of stability, but in most cases where stability is marginal undrained strength analysis is required and the pore pressures and effective strengths alone are not sufficient to assess stability. In a number of cases differential settlements, and acceleration of settlements have proven valuable in detecting the on-set of instability and the conditions in which internal erosion and piping to initiate. Once these conditions are recognised more detailed survey monitoring and borehole inclinometers can be valuable in better defining the geometry of instability.
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