Dam owners manage many complex activities to maintain and operate their dams safely and resiliently. Identifying, and continually improving, the key elements of an effective dam safety program and associated practices can be challenging but are essential to support resilient dams and resilient communities; using the Dam Safety Maturity Matrices (DSMM) is an efficient and thorough way to do this. A maturity matrix is a tool to evaluate how well-developed and effective a process or program is. The matrices were developed within CEATI’s Dam Safety Interest Group (DSIG) for owners to assess the effectiveness of their dam safety program against industry practice, and to assist with identifying improvement initiatives.
This paper will present the matrices and demonstrate how they are used to evaluate the effectiveness (or maturity) of a dam safety program. It will also highlight the benefits associated with using the matrices as an assessment tool, including the identification of improvements that can be made to a dam safety program, and the prioritization of efforts across multiple facets of a dam safety program.
User case studies from dam owners in both New Zealand and overseas will be presented to elaborate on the tool and the process.
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Following the failure of Paloona Dam’s intake trashrack during the 2016 floods in northern Tasmania, a replacement trashrack and support structure was designed, manufactured and installed (by diver) within five months. This was a remarkable feat and hailed as a success at the time.
The euphoria, however, was short lived. A routine dive inspection in January 2018 revealed cracked
trashrack bars on one of the panels and this was after less than twelve months’ operation. This prompted a rigorous investigation where it was determined that the bars suffered fatigue due to flow induced vibration. Indeed it is possible that the bars cracked within a few weeks of returning to service.
The science of flow induced vibration is relatively mature, having been extensively researched over several decades. Its application to trashracks is well documented. However, this experience has shown that the common design approach overly simplifies the fluid-structure interaction. For Paloona, the result was a trashrack design which has proven to be inadequate, not having the resilience required for a dam outlet works component.
This paper revisits flow induced vibration theory as it pertains to trashracks, outlines the findings of vibration testing at Paloona, and suggests a design approach which will avoid similar issues. It is hoped that similar failures can be prevented and the design life expected of trashracks achieved.
Recent tailings dam failures have led to worldwide alarm that we are still getting an average of two
significant tailings dam incidents a year. This is despite the efforts of various industry organisations aroundthe world to raise the standards of tailings dam management. Clearly, a significant number of mining dams are not re silient enough to ensure the required level of safety for sustainable mining operations in a modern world in which there is increasing concern for the environment. This paper updates ANCOLD with international developments in attempting to address shortcomings in the mining industry that is allowing these failures to continue to occur.
In Australia, ANCOLD have released an addendum to the 2012 ANCOLD Guidelines on Tailings Dams, Planning, Design, Construction, Operation and Closure, to coincide with the new ANCOLD Guidelines for Design of Dams and Appurtenant Structures for Earthquake. This addendum also addresses issues of governance of tailings dams and provides additional guidance on the serious issue of static-liquefaction, a critical factor in recent failures.
On the international scene, ICOLD is progressing a Tailings Dam Safety Bulletin that is hoped will set
minimum standards for Tailings Dams for all member countries. In addition, the International Council of Mining and Metallurgy (ICMM) similarly wants to establish an international standard. It is likely that these international bodies will cooperate to ensure a consistent set of guidelines and that countries will accept and implement these.
This paper updates the ANCOLD position regarding guidelines and describes the state of various
international guidelines following the June ICOLD meeting in Ottawa.
Computational Fluid Dynamics (CFD) is the science of predicting momentum, mass and heat transport, and can aid in design and safety issues for dam resilience in modern settings. Applications of CFD have historically been in the aerospace, automotive and chemical process industries with limited application in the hydraulic engineering field; possibly due to the associated computational intensity that is typically required. However, over the past two decades the cost of computing power has decreased substantially while the processing speed has increased exponentially. These developments have now made the application of CFD in the commercial environment feasible. CFD is particularly valuable in complex flow situations where the outputs required cannot be provided by a traditional hydraulic assessment approach and where there are stakeholder drivers such as service life, insurance cover and safety implications of infrastructure. The need for CFD when these drivers and complex flow situations arise, are demonstrated by means of a case study.
In the case study, CFD was used to investigate the flow patterns and the predicted performance of the outlet pipework from Massingir Dam in Mozambique. Three flow scenarios with appropriate pressure and flow boundary conditions were analysed for the outlet pipework, which included bifurcations for power generation from the main discharge conduits. Specific concerns addressed were, firstly, the possible excessive negative pressure in the region of the offtake for power generation and the potential for cavitation effects and, secondly, unacceptable velocity gradients in the power offtake pipework. Results showed that although some negative pressures were possible in one flow scenario, mitigation measures based on the CFD outputs could be considered and designed before construction.
The implementation of CFD in the above case study displays how risk in design can be reduced to ensure safety issues are addressed effectively.
Prior to filling the Clyde Dam reservoir in 1992-93 large scale stabilisation works were undertaken on several pre-existing landslides along the reservoir margins. Monitoring and visual observations indicate that the landslides are behaving satisfactorily and have confirmed that the stability improvements undertaken have successfully offset the negative effects of the reservoir on the landslides.
This paper presents selected records detailing more than 25 years of landslide behaviour that demonstrate the effectiveness of the stabilisation works. Monitoring has been able to detect increasing water levels, drainage flow changes and, in some cases, deformation following periods of high rainfall.
However, the highly satisfactory performance of the landslides experienced to date does not allow complacency and although the surveillance monitoring has been progressively scaled back to a more focussed strategy, ongoing assessment and reviews will be required. The paper also briefly discusses the current challenges associated with changing personnel and aging instrumentation.
Identification of people impacted by a hypothetical dam-break flood is required to understand the potential hazard a dam poses to downstream communities. The New Zealand Dam Safety Guidelines and the Australian Consequence Categories for Dams define these people collectively as the “Population at Risk” (PAR) and recommend that evaluation of PAR should include both permanent and temporary populations. However, there is limited guidance on specific methods to determine these populations. This paper provides an outline of an evidence-based, repeatable method to determine the PAR (both permanent and temporary) within a dam-break flood inundation zone. The method is intended to provide guidance for people tasked with estimating PAR in accordance with the New Zealand Dam Safety Guidelines. The methodology provides a current practice framework for users to apply and estimate the PAR in a clear and defendable manner.