Ryan Cantrill, Petros Armenis & Angus Cannon
Large Australian dams span a range of ages and were designed and constructed to the prevailing
standards and practices of the day. Since that time, there has been a veritable explosion in monitoring and surveillance technologies available to dam owners to assist with risk management of their portfolio. Coupled with this has been the formalization and ongoing development of regulatory frameworks across the industry.
This paper endeavours to share Sunwater’s recent experience on this topic. Specifically, the following question is considered – how best to apply modern monitoring and surveillance technologies to manage dam safety risks associated with decades old structures, all while still meeting regulatory requirements? In answering this question, the authors necessarily had to consider several inputs including – physical condition of the existing assets; analysis of existing controls and mitigation measures; risk assessment and risk profile of the assets; and operational constraints. As always, outputs invariably required the prioritization of recommendations.
While dam owners must strive to comply with a standard and accepted way of managing their portfolio, it is vital they recognize and address the unique risks that each structure presents. It therefore follows that owners must be prepared to allow the time and provide the necessary resources when formulating a monitoring and surveillance program commensurate with the dam safety risk that their respective portfolio presents
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Damien Bryan, John Sukkar, Erin Hughes, Michael Cawood
Alert triggers are a critical component of Dam Safety Emergency Management, aligning clearly defined adverse conditions with alert levels to initiate an appropriate emergency response. Early detection of these conditions allows for potential mitigation measures to be undertaken, early engagement of key stakeholders such as emergency agencies, and where necessary, the warning or evacuation of affected downstream communities. The Dam Safety Alert Trigger Framework provides WaterNSW with a consistent, repeatable, and defensible methodology for the determination of appropriate dam safety alert triggers. The framework was developed through the engagement of consultants, emergency and regulatory agencies (NSW SES & DSNSW), and several Australian large dam owners.
The determination of appropriate Dam Safety Alert Triggers is a challenge faced by all dam owners. Through the development and implementation of the Alert Trigger Framework, WaterNSW has achieved the ability to define defensible alert triggers through a consistent and repeatable methodology. This has resulted in an improved dam safety emergency response posture for WaterNSW, key emergency services partner the NSW SES, and greater protection for affected downstream communities. Concepts, processes and methodology covered in this paper could be used by other dam owners in addressing their own dam safety alert trigger challenges.
Yuqi Tan, Behrooz Ghahreman-Nejad, Keith Seddon
Inadequate geotechnical investigation and hence undetected issues within the dam foundation have been responsible for many dam failures in the past. Fissured clay in the foundation poses a significant risk to the stability of the dam if it is not adequately detected and characterised. This paper presents a framework to evaluate the strength characteristics of fissured clay and its effect on the stability and performance of an embankment dam. The strength of fissured clay can be characterised from conventional triaxial test result based on the dip angle of the fissure plane. A design chart for the strength of the fissure has been developed based on the dip angle. The stability assessment for a tailings dam indicated that the dip angle of the fissure has significant impact on the overall stability of the embankment when the angle of the fissure aligns with the angle of the critical failure plane. Both fissure strength and fissure angle should be carefully evaluated for a site where fissured clay is observed.
Ryan Singh, Jiri Herza, James Thorp, Michael Ashley
Performance-based risk-informed decision making is an underlying principle of the Global Industry
Standard on Tailings Management (GISTM). While owners make significant efforts to align with this
principle, commonly used risk assessment and management practices in the mining industry have largely been based on the HSE principles, which consider more frequent, lower consequence incidents.
As a result, the existing risk assessment frameworks do not provide the owners with a comprehensive understanding of the risk profiles of their tailings storage facilities (TSFs). Without the understanding of a facility’s risk profile, the owners cannot appreciate how changes to their facility, processes and operational activities may impact the risk profile. A large step-change in thinking is therefore required in risk assessment practices for the owner to align their TSF management with GISTM requirements.
Beyond risk assessments, the mining industry has other valuable concepts to manage the safety of their tailings management practices, such as Critical Controls, however, commonly used risk assessment and management practices do not incorporate these concepts.
This paper explores commonly used risk assessment practices and the concepts of Critical Controls. It proposes how these concepts can be linked, with Critical Controls being embedded in the risk assessment process. The outcomes of linking these concepts result in an estimation of the effectiveness of the Critical Controls and how they can be improved to demonstrably reduce the risk presented by a TSF. A case study has been included to demonstrate the benefits of linking risk assessment with Critical Controls and how owners can readily identify deficiencies and efficiently manage the risk profiles of their facilities.
Hench Wang, Edward Funnell, Albert Shen, Matt Scorah, Peter Hill
The use of simulation models to assess dam failure consequences has progressively advanced in Australia over the past few years. For example, it is now common for HEC-LifeSim to be used to estimate potential loss of life from the failure of large dams with large populations at risk downstream. Since its introduction to Australia, numerous presentations and papers have been provided by USACE and industry professionals that highlight the benefits of using HEC-LifeSim Version 1.0.1 for a range of different case studies.
This paper identifies some of the new features in the latest version of HEC-LifeSim that can improve the robustness and defensibility of the potential loss of life estimates for dambreak consequence assessments. The techniques that have been used to overcome these challenges are also discussed using some case studies.
The first case study demonstrates the sensitivity of the model performance and potential loss of life to changes in version and number of iterations used to simulate the life loss. This is done by comparing the differences in simulation run time and life loss between the previous and new versions of HEC-LifeSim for an example model. The second case study presents an example application of both versions of HEC-LifeSim to compare the results between one version and the other for a different dam and the final case study illustrates an improved method for interrogating the available outputs from HEC-LifeSim to provide the user with more information that otherwise could not be obtained from the default outputs.
Jarrad Coffey and John Plunkett
As tailings standards continue to evolve, a greater focus is being placed on the monitoring of tailings storage facilities (TSFs). While this is a positive development for TSF safety into the future, it is only one component of the work required to implement Performance Based Risk Informed (PBRI) management. There is also a significant human element that can be aided by reducing the time spent of personnel sourcing/aggregating data and instead focussing on decision making. It is discussed in this paper how a more holistic approach to monitoring via a dashboard that displays all management data relevant to a portfolio of TSFs can be applied in parallel to risk assessment to work towards the goal of PBRI. The dashboard also facilitates review and governance activities, which are central to the Global Industry Standard on Tailings Management. An example of the dashboard utilised at Rio Tinto Iron Ore is presented to provide an example of such a system and its benefits.