This paper provides the insight of one practitioner into the process and application of Dam Safety Risk Assessment. The ANCOLD Guidelines on Risk Assessment provide a reasonably comprehensive outline of the key tasks involved in the risk assessment process. The intent of this paper is not to rehash the Guidelines but rather to discuss some of the practicalities of completing a dam safety risk assessment and highlight some key learning’s gained from a wide range of projects for a number of different owners.
The paper includes a brief overview of each component of the risk assessment process as well as some of the advantages and disadvantages of the various approaches to completing a risk assessment project.
2011 – Dam Safety Risk Assessment – A Practitioner’s Perspective
Roger Vreugdenhil, Peter Hill, Siraj Perera, Susan Ryan
All Australian water authorities have in place dam safety programs that seek to ensure the ongoing safety and serviceability of their dams along with the benefits they secure for the wider community. Many have progressed multiple dam safety upgrades over the past decade and embraced risk assessment as a helpful tool in prioritising upgrade investment.
The ANCOLD Guidelines on Risk Assessment (2003) have been applied across the country and, coupled with State regulation, have supported dam owner efforts in reducing risks below the ANCOLD “Limit of Tolerability”. However, it is generally acknowledged that in their current form, the ANCOLD guidelines provide limited guidance to dam owners for determining appropriate levels of risk reduction and timing of dam safety improvements. This has contributed to a range of guideline interpretations and inconsistency in subsequent dam safety investment decisions across Australia. Having achieved priority risk reduction, a number of owners are beginning to assess their dams against the ALARP principle, bringing dam safety investment within an owner’s portfolio into more direct competition with other important and urgent organisational investment decisions.
This paper outlines the outcomes of a recent study commissioned by the Victoria Department of Sustainability and Environment into risk reduction principles and the application of ALARP by a number of Australian and international dam owners and regulators, hazardous industry owners and regulators, and the interaction of ALARP with whole-of-organisation investment. The paper highlights the study process and significant points of interest regarding risk reduction principles and current application of ALARP and some options for refinement and clarity.
Towards increased clarity in the application of ALARP
Dan Forster, Murray Gillon
A robust and defensible dam surveillance process is considered to be the ‘front-line of defence’ in ensuring dams do not present an unacceptable risk to people, property and the environment. The concept of a ‘Quality Chain of Dam Surveillance’ describes the surveillance process as a multi-linked chain where each step in the process forms a critical link. Without rigorous attention given to quality assurance links in the chain can become tenuous or broken and thus compromise the integrity of the whole chain. Hydro Tasmania is currently re-engineering its existing surveillance process using the Quality Chain of Dam Surveillance as a basis.
This paper presents the concept of the quality chain and uses the Hydro Tasmania improvement initiative as an example application of the concept. The paper is intended to provide a fresh perspective on what is sometimes considered a stale topic and reinforces the need for a considered approach to dam surveillance.
2011 – The Quality Chain of Dam Surveillance
Rod Westmore, Andrew George& Robert Wilson
A 2007 risk assessment of Hume Dam concluded that the dam did not satisfy the ANCOLD societal risk criteria for existing dams. The Spillway Southern Junction (SSJ) and its associated failure modes was one of the main contributors to the risk profile.
Upgrade works at the SSJ involved the retro-installation of additional filter and drainage materials in the 40m high embankment immediately downstream of the tower block and central core wall by installation of more than 10,000m of secant caisson drilled columns backfilled with filter and/or drainage materials.
This paper describes the design and construction issues associated with the upgrade works, the equipment and methodologies developed to achieve the principal design objectives of coverage and connectivity of filter and drainage columns, and optimisation of compaction of the backfill materials. It also describes how these requirements were met whilst minimising adverse affects such as vertical deviation, excessive vibration, subsidence of secant filter columns during construction, and clay smearing of the perimeter of individual columns.
Hume Dam Spillway Southern Junction Filter and Drainage Works
G. Hadzilacos, ML. Ng, K. Taske, A. Small and B. Loney
Alteration of flow patterns by constructing a dam may have an irreversible impact on ecosystems depending on the timing, duration and frequency of these flows. As part of an Environmental Impact Study, carried out for a proposed mining operation in Australia that included an earth dam on a pristine ephemeral creek, an appropriate waterway management scheme was proposed that required the establishment of measurable instream flow requirements. This paper describes an environmental flow analysis (EFA) carried out to identify flow regimes that achieve the desired ecological outcomes for the affected waterways. The EFA methodology was based on the range-of-variability approach using a calibrated rainfall-runoff model to form the hydrologic basis. The study established a relationship between flow components and ecological variables based upon which the flow requirements were estimated using a simple methodology.
2011 – A case study of an initial Environmental Flows Assessment for an earth dam on a pristine stream in Cape York
The 2011 Tohoku Earthquake of magnitude 9.0 shook the east Japan and caused enormous damage. As of September 22, The Japanese National Police Agency has confirmed 15,805 deaths, and 4,040 people missing, as well as over 295,047 buildings completely or partially destroyed. About 8,700,000 homes lost power, and about 2,290,000 homes were shut down from water supply. The transportation lifelines such as highways and railways including Shinkansen (high speed train) were disrupted. The earthquake triggered extremely destructive tsunami waves of the height of 15 metres, in the east coast of the Pacific Ocean. Fukushima No.1 nuclear power plant had accidents.
2011 – Perspectives of the 2011 Tohoku Earthquake and Tsunami