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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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.
In 2015, a study was undertaken where recommendations were made to provide protection to the exposed rock in the unlined channel of the spillway at Burdekin Falls Dam. The protection included a matrix of anchor bars which extended the full 504 m width of the spillway and 25 m in the downstream direction. Over 1,200 anchors were proposed comprising 36 mm diameter bar extending up to 15 m into the foundation.
A value engineering study was undertaken in 2017 where a review of the rock scour potential was undertaken. The study was based on a methodology developed by Pells (2016) as part of a research grant funded under an Australian Research Council (ARC) Linkage Project which was jointly financed by the Federal Government of Australia, various state government bodies and engineering consultancies involved in dam design, operations and management.
This paper describes the approach taken as part of the value engineering study, the methods used in the assessment and the benefits of both innovative thinking and challenging the more traditional approach of rock scour assessment, the outcome of which resulted in a $11 m plus saving to the owner of the asset.
Installing a suite of appropriate instruments such as piezometers, settlement plates, extensometers, and inclinometers etc., in strategic locations to monitor the performance of an embankment built on soft soils is vital when there are major design uncertainties; the monitoring data can also be used to calibrate the design parameters. Questionable readings of pore water pressure (PWP) have been reported in various case studies involving the development of dams, embankment foundations and reclamation work in Australia and in South East Asia, especially in low-lying acid sulphate soil (ASS) floodplains. Despite having vertical drains (PVDs), excess pore water pressure readings from Vibrating Wire Piezometers (VWPs) do not always dissipate as fast as expected, especially after a certain period of time, typically a year. This paper describes the biological and geo-chemical factors affecting reliability of Vibrating Wire (VW) piezometers, filter-tip clogging, smearing of soil adjoining the filter, gas generation, chemical alteration or corrosion of the filter, as well as electro-osmotic effects and cavitation. To that end, several VW piezometers installed in ASS terrain were extracted after being in place for 1.5 years and the soil surrounding the tips was tested for iron related and sulphate reducing bacteria. It is found that sulphate reducing bacteria has medium to high aggressivity whereas iron related bacteria has very high aggressivity with the bacteria count exceeding 20,000. VWPs with ceramic/stainless steel filter tips installed in acidic ground with organic contents exceeding say 4-5% have shown impeded dissipation of excess pore water pressure after a year or so. Accordingly, it appears that this issue is likely in other types of piezometers fitted with such ceramic or stainless filters when installed in ASS soils. Further Scanning Electron Microscopy (SEM) analysis of the piezometer filter is also ongoing at the University of Wollongong (UOW) laboratory to determine how ionic precipitation causes a VW piezometer to clog. In addition, several samples were collected from Victorian Dams and are being tested in University of Wollongong (UOW) laboratory to quantify the clogging effect in Dam practice when installed in ASS terrain.
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.
Investigations into the core material of earth fill dams are undertaken reluctantly due to the potential to cause damage to the embankment. Where investigations are required, Cone Penetration Testing (CPT) is increasingly used to assist with the geotechnical assessment of dam embankments. The risk of hydraulic fracture within embankment core material is well known and procedures are typically adopted to minimise the risk of hydraulic fracture during remediation of the holes. Backfilling is typically done in stages allowing for an initial set of the cement/bentonite grout mixture prior to subsequent lifts.
While the risk of hydraulic fracture is well understood, the lesser known risk of pneumatic fracture is a possibility where certain conditions exist. This paper discusses CPT investigations at Fairbairn Dam, operated by Sunwater in Central Queensland, and the challenges faced in undertaking the remediation of the CPT holes. The potential for pneumatic fracture of the embankment core was highlighted during the investigations and details of alternative techniques adopted for reinstatement of the holes are presented. Recommendations are made to appropriately manage the risk of pneumatic fracture when undertaking CPT’s through embankment core.