2018 – Proposed Technique to Validate and Constrain Extreme Flood Estimates
Tim Rhodes, Hugh Nguyen-Mallen
Extreme flood analyses are routinely used as inputs to dam risk assessments, spillway adequacy assessments and spillway designs. Estimation methods applied in Australia using rainfall-runoff models in combination with a Probable Maximum Precipitation (PMP) estimate are consistent with the current best practice applied around the world. The estimation methods can, however, result in substantial variability in peak flow estimates depending upon the practitioner and the methods used to quantify model parameters. Around the world, validation procedures are commonly applied to combat this variability, but no such techniques are routinely applied in Australia. A method is proposed for application across Australia which may variously be applied to validate and constrain extreme flood estimates and also provide quick estimates.
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2018 Papers
2018 – Importance of Integrated Asset Management for Dams and Outlet Works – A Melbourne Water Perspective
Learn moreMark Callander
Melbourne Water (MW) has historically seen dam safety management as a civil discipline and has focussed on understanding and managing the civil assets at its dam sites. The recent addition of a mechanical engineering resource to the team responsible for the dam safety management has refocused attention on the mechanical and electrical (M&E) assets and provided a more holistic asset management approach to MWs large dams.
This paper discusses the process MW has developed over the past two years to improve their understanding and management of M&E assets. It centres on key process points for how MW has prioritised the development of M&E asset management programs on the basis of an autogenous ‘asset criticality’ rating system and has utilised ANCOLD comprehensive inspections to plan and implement new inspections and tests on dam M&E assets. The two case studies of Sugarloaf and Upper Yarra Reservoirs’ outlet works demonstrate the the benefits of the process to gain operational and technical knowledge of M&E assets, strategic importance to the water supply network, identifying risks therein and reallocate significant funding to address these risks as prioritised by asset criticality.
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2018 Papers
2018 – Advanced InSAR Techniques for Remote Monitoring of Dam Stability
Learn moreJessica Morgan
Regular assessment of dam stability is essential to ensure safe and reliable operation of these structures throughout their service life. In some cases, monitoring of the surrounding environment can be as important as monitoring carried out over the dam itself. Risk management programs should therefore look at the entire site and nearby terrain to ensure any and all possible geohazards which may impact dam integrity are identified and tracked over time.
InSAR is a type of remote sensing that uses radar satellite imagery to measure surface movement occurring over time, often achieving millimetric levels of precision. This approach does not require fieldwork or the installation of equipment, measurements are instead obtained from reflections of the satellite radar signal off infrastructure, rocks and bare ground. Furthermore, as the measurements are obtained from satellite images that extend over regions thousands of kilometres squared in size, they can provide information on stability over dams, surrounding reservoirs, even entire regions.
The main advantage of InSAR technology for dam monitoring is two-fold. First, in addition to monitoring the dam itself, stability of the surrounding area (including slopes around dam reservoirs) can be tracked. Second, both long- and short-term displacement trends can be captured (including historical analyses) providing a more complete picture of dam behaviour over time.Several examples of InSAR results obtained over different dam sites are presented.
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2018 Papers
2018 – Unusual Combinations of ‘Usual Conditions’- The Possibility of the Improbable!
Learn moreDND Hartford
The notion of probability and its various interpretations brings numerous opportunities for errors and misunderstandings. This is particularly true of contemporary risk analysis for dams that mostly consider geotechnical, hydraulic, and structural capacities subjected to extreme loads considered as independent evets. In these analyses subjective “degree of belief” probability has a major role, both in the modelling of the risk in the system by means of event trees based on inductive reasoning and in the assignment of probabilities to events in the event tree. There are numerous situations where physically possible conditions are eliminated from consideration in a risk analysis on the basis of probabilities that are judged to be too low to be of relevance. This is despite the fact that the assignment of a probability to a condition means that the occurrence of the event or condition is inevitable sometime, with the added complication that the time of occurrence is unknown and unknowable. Although there is no relationship between a remote probability and the possibility (or credibility) of the occurrence of the event in the event tree, it is quite common for physically feasible conditions to be either eliminated or their importance discounted on the basis of low probability in a risk assessment of a dam. Twenty five years ago, this elimination process might have been referred to as “judicious pruning of the event tree”. In more modern parlance, the elimination process is based on consideration of whether or not the condition or sequence of events is clearly so remote a possibility as to be non-credible or not reasonable to postulate. In contrast to the consideration of extreme loads vs. structural or geotechnical capacities, experience has shown that many dam failures and perhaps the majority of dam incidents do not result from extreme geophysical loads, but rather from operational factors. These incidents and failures occur because an unusual combination of reasonably common events occurs, and that unusual combination of events has a bad outcome. For example, a moderately high reservoir inflow occurs, but nowhere near extreme; the sensor and SCADA system fail to provide early warning for some unanticipated reason; one or more spillway gates are unavailable due to maintenance, or an operator makes an error, or there is no operator on site and it takes a long time for one to arrive; and the pool was uncommonly high at the time. This chain of reasonable events, none by itself particularly dangerous, can in combination lead to an incident or even a failure. This leads to the unnerving conclusions that; our estimates of risk made in terms of best available practice using the best available estimates will be underestimates of the actual risk, and the extent to which we underestimate the risk is unknowable. This paper examines why these improbable events occur and what can be done to prevent them. Some implications with respect to the endeavour of risk evaluation are also considered.
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2018 Papers
2018 – ANCOLD Proceedings of Technical Groups 1 Dam Safety Decision Making
Learn moreJane Branson,, Kelly Maslin, Samantha Watt, Chriselyn Kavanaghah
Since publication in 2003, the ANCOLD Guidelines for Risk Assessment have reached broad acceptance and use in Australia. In practice, dam owners use the principles of risk assessment to drive business investment decisions. As the guidelines undergo revision, it is timely to assess whether our practices need to evolve to more holistically consider all types of consequences, rather than our current focus on loss of life, in decision-making. This paper aims to prompt dam owners and consultants alike to re-assess our focus on loss of life in risk assessment decision-making, and whether we should more meaningfully consider alternative or broader indicators.
An industry survey was undertaken which found that large dam owners are generally happy with the current system of dam safety decision making. However, the survey responses did identify difficulties in relation to justifying investment below the limit of tolerability that are subject to ALARP principles. In a small number of cases, dam owners found it difficult to justify investment when life safety was not important.
Building on the industry survey and subsequent discussions with practitioners, this paper discusses how the current approach to risk based decision making may result in sub optimal decision making. Further it is discussed how there is an important role that economics should play in providing a universally accepted framework for assessing trade-offs and providing consistent evidence to support decision making.
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2018 Papers
2018 – The Challenges of Increasing Public Use and Expectations around Dams
Learn moreMartina Cusack
Across Australia, recreation usage around dams is growing rapidly. There is also increasing public expectation around the facilities provided and the activities that can be undertaken.
While dams create many benefits, they also have inherent risks associated with them. The risks associated with public access include public and staff safety, water quality, pollution, environmental degradation, bushfires, water availability, dam & power generation operations, and financial.
In 2016 the Victorian government released “Water for Victoria”, a strategy for managing increasingly valued water resources and a growing population. This strategy recognises the importance of recreational enjoyment of waterways and commits water corporations to continuing to maintain infrastructure and facilities to support recreational objectives at their water storages. Water for Victoria also commits water corporations to consider recreational user objectives in the way water storage and supply is managed. However, this must be within legislative requirements to meet the needs of water entitlement holders and with awareness of the realities of dry conditions and climate change.For the last 10 years, Goulburn Murray Water has been progressively rolling out Land & on Water Management Plans and setting up Land & on Water Implementation Committees. These committees provide a forum for liaison with local government, other statutory authorities, as well as interested environmental, heritage, indigenous, commercial and recreation groups. The groups aim to understand the concerns and requirements of all parties, take appropriate action, which may involve educating communities where some of their desired actions are not achievable.
While this approach has been successful, the growth in social media and the emergence of groups outside of the Land & on Water process has meant that consultation has had to be extended to include self-identifying, special interest groups. This has involved the development of separate groups at Dartmouth and Lake Eppalock to educate and work through the issue at hand, developing appropriate actions, which are accepted and implemented by all parties.This paper will review the Goulburn Murray Water Land & on Water process, and consider two cases studies, namely the “Save Lake Eppalock” community driven campaign and the provision of fishing access on Dartmouth regulating pondage.
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