On 1 July 2017, the Water Supply (Safety and Reliability) Act 2008 (Qld) was amended to improve the way referable dam owners manage dam safety and integration of dam safety with disaster management. While each dam and emergency event differs, and each state has different dam safety and disaster management legislation, it is important that communication strategies are effectively delivered to empower dam owners and emergency practitioners to improve warning capability for affected communities. The paper provides an overview of the intent of the amended legislation, key concepts, what makes an effective emergency action plan and a performance analysis of the emergency action planning regulatory program. Lessons learnt from the analysis are provided.
Yarrawonga and Torrumbarry Weirs; located on the Murray River bordering Victoria and New South
Wales, are operated by Goulburn Murray Water on behalf of the Murray Darling Basin Authority.
The electrical and control systems that operate both structures were nearing 20 years of age, resulting in risk associated with equipment nearing the end of its useful working life and hardware obsolescence, driving this upgrade program. These control systems are critical in the monitoring and management of river levels and flows that extensively affect Victorian and New South Wales irrigation supplies and recreational users on the Murray River and Lake Mulwala.
Considerable effort was required to update and develop the control philosophy before proceeding to the design phase of the projects. The requirement to work on these brownfield sites, while maintaining operational ability and minimising dam safety and water delivery risks, resulted in a significant implementation and commissioning process. During the course of these works, the opportunity was also taken to enhance and update remote monitoring capability.
The lessons learnt on these projects are being incorporated into current Electrical and Control System Upgrade projects at Cairn Curran Reservoir and Dartmouth Dam.
Ulu Jelai project is a recently completed 372MW hydroelectric peak – power project located in the Cameron Highlands of Malaysia. A combination of power generating and reservoir operating conditions together with the site topography, existing road infrastructure, geology and hydrogeological conditions pose a significant risk to the viability of the project during operation. As a result, significant reservoir rim stability treatments were designed and constructed along a 3.5km section of the right abutment of t he Susu Reservoir to reduce the risk of instability to acceptable levels. This paper describes the methods of investigations, stability assessment and design aspects of the reservoir rim stability treatments that were constructed.
Trustpower is a New Zealand based hydro generator and retailer. It started off as a business that only owned a few schemes and then during a period of rapid expansion between 1998 and 2002 acquired the bulk of its current schemes. Now it owns and operates 25 hydro schemes across New Zealand ranging from 150kW to 80MW output.
This paper examines how Trustpower’s Dam Safety Management System (DSMS) has evolved over time, taking account of developments in the business environment, proposed regulatory changes, improvements in the NZSOLD guidelines and evolution in international dam safety practice.
The Kumara-Dillmans-Duffers Hydro Electric Power Scheme (HEPS) and in particular its Kapitea Reservoir (high Potential Impact Category) will be used as an example to highlight how the DSMS evolved over this period.
The paper describes the development of UK guidance on reservoir drawdown capacity. The guidance provides for a consistent thought process to be used in determining the recommended capacity. A basic recommended standard is proposed for embankment dams which varies with the consequences of failure of a dam. The drawdown rate for the highest consequence dams is 5% dam height/day with an upper limit of 1m/day. Engineering judgement is used to vary this standard allowing for ‘other considerations’ including the vulnerability to rapid dam failure, surveillance and precedent practice. A different approach is proposed for concrete/masonry dam, which considers the prime purpose of drawdown being to lower the reservoir in a reasonable timeframe to permit repairs rather than rapid lowering to avert failure. The UK approach is compared with that used in Australia and suggestions made for where its use may be appropriate.
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.