This paper discusses the current regulatory requirements and guidelines, which address to varying degrees the need for recovery controls and the engagement of Owners with Impacted Communities (ICs) within a Dam Safety Emergency Response Plan. The planning and application of appropriate recovery controls, which are applicable from the moment of failure, help to build resilience and reduce the ultimate consequence of TSF failure. The application of such controls, developed with close engagement with impacted communities has a strong precedent, being recommended as a result of the International Council on Mining and Metals (ICMM) review of good practice for emergency preparedness (Emery, 2005).
This paper presents a simple method to assess various recovery controls, with risk minimisation as its basis, and the use of existing risk assessment techniques such as bow-tie diagrams or the inclusion of recovery controls to other qualitative assessment methods. This will be illustrated through application to some relevant historical TSF failures.
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Satellite remote sensing data can be used to monitor environmental processes and inform disaster risk reduction and hazard early warning. This paper describes the analysis of satellite remote sensing images to investigate the partial wall collapse of a tailings dam at the Cadia gold-copper mine in Australia that occurred on 9th March 2018. Our case study uses freely available remote sensing imagery acquired by the Copernicus Sentinel-1 (radar) and Sentinel-2 (multispectral) satellite constellations to monitor land surface changes in the Cadia mine area before and after the collapse. In this paper we discuss the benefits of utilising both radar and multispectral remote sensing imagery in a holistic approach to remote sensing, which could be used for continuous, near-real time monitoring of risk-related infrastructure such as dams without the need for in-situ measurement equipment.
We applied the Interferometric Synthetic Aperture Radar (InSAR) technique to measure surface displacements and interferometric coherence maps from a stack of Sentinel-1 radar images acquired between 2nd December 2015 and 25th June 2018 at regular 12 day intervals. The time series of surface displacements show a significant increase in the rate of movement of the dam wall in the area that eventually breached in the two months prior to the collapse. This change in movement behaviour was not observed at parts of the dam wall that remained intact. This analysis demonstrates the potential for InSAR monitoring to identify issues in advance of infrastructure failure, which could allow risk mitigation strategies to be implemented by the mine operator. We used interferometric coherence data to observe changes in the dam wall and surrounding areas before and after the collapse. A drop in coherence occurred in the breached section of dam wall, indicating the surface change caused by the collapse. Coherence for unaffected parts of the dam wall remained stable. Sentinel-2 multispectral imagery acquired between 2nd July 2017 and 24th June 2018 show the timing, extent and effects of the collapse as well as the rate of tailings movement.
International emergency agencies such as the Federal Emergency Management Authority (FEMA) in the U.S. highlight a lack of public awareness of hazards relating to dams (FEMA, 2012). This is an issue faced by emergency management agencies around the world, including in Australia and New Zealand. Without hazard awareness, communities who live downstream of large dams are potentially more vulnerable to possible risks, and are likely to be less resilient when hazards arise. One way to address this knowledge gap is risk communication or the meaningful and purposeful exchange of information about risk among relevant parties (Covello, von Winterfeldt, & Slovic, 1984).
This study adopted a mental models approach (see Lazrus et al., 2016) to identify community members’ knowledge of dam failure by comparing their views with those of experts. Data were collected via depth interviews with dam safety experts (n=5) from across Australia, and community members (n=26) living downstream of dams in South East Queensland in Australia. Participants were asked to discuss knowledge about dam failure and to evaluate a dam safety message taken from a U.S. dam authority that was verbally read to them. Interviews were transcribed and analysed to identify the gaps between expert and community member knowledge.
Analysis showed some convergence on general dam operations but, less comprehensive community understanding of the causes of dam failure and dam safety management. Response to the U.S. dam safety message was mixed, with some participants believing it delivered the message appropriately, and others feeling it overstated risk or that its intended use was primarily to protect dam operators. Notably, these varied responses were often related to participants’ level of knowledge of dams. Combined, the findings highlight an opportunity to close the gap in knowledge. These findings will inform the strategies and materials for the South East Queensland bulk water authority Seqwater in engaging with communities downstream of their 26 dams. The research will guide the approach in conveying knowledge with an appropriate tone to support ongoing community engagement activities and increase resilience.
Vertical gates and their operating plant are an essential part of dam safety at many dam sites. Apportioning appropriate levels of resilience during the design phase requires a thorough understanding of a gate system as a whole, not only of a single component in isolation.
This paper offers a designer’s perspective on modern engineering design features, materials and practices which can improve gate resilience during onerous operating conditions. This is of particular relevance to gates that are seldom used. Design aspects relating to the capability and limitations of the gate, hoist type, power supply arrangement and control system equipment to work together as a complete system are paramount design considerations in ensuring overall system resilience.
A discussion of the role and duty a hydraulic gate has in a dam safety context is presented. Supporting commentary is offered on appropriate levels of reliability, redundancy and diversity, including a comparison of different gate, bearing and hoist types. The authors draw on their own experience regarding gate design, fabrication and operation from completed and ongoing projects both locally and internationally.
The geographical location of New Zealand to the south west of the ‘Pacific Ring of Fire’ and in the ‘Roaring Forties’ of the Pacific Ocean exposes national infrastructure networks across the country to a range of natural hazards. Despite this, studies of built environment resilience to natural hazards in New Zealand, have historically focused on the robustness of individual physical assets, with less emphasis on the performance of infrastructure networks at a national level. This is particularly true for the stopbank (levee) network. Until recently, stopbanks have often been considered at regional scales and to varying degrees depending on what information has been catalogued, and the level of interest / requirements and local expertise available at the time.
We present the findings of a preliminary national level natural hazard exposure assessment of New Zealand’s stopbank network by adopting the newly developed New Zealand Inventory of Stopbanks (NZIS). Geospatial seismic hazard data from recent modelling is used as a case study to demonstrate how understanding the exposure of stopbanks in NZIS can inform multi-hazard risk and resilience assessments. Four seismic and co- seismic hazard metrics are considered in our stopbank network exposure assessment: surface rupture (through proximity to known active faults), the strength of ground shaking (i.e. probabilistic estimates of peak ground accelerations and velocities), and liquefaction and landslide susceptibility.
With over 20% of current catalogued NZIS stopbank length and a relatively high seismic hazard exposure (active fault proximity and liquefaction susceptibility) in Southland, the likelihood of stopbank failure or breaching due to seismic activity appears to be relatively high in this region of New Zealand. Large sections of the stopbank network in other regions including Manawatu-Wanganui, Wellington and Hawkes Bay are also particularly exposed to large seismic hazards in our preliminary assessment. However, further work is required to more appropriately understand stopbank attributes including design and safety considerations.
The Waimea Community Dam will be the largest multipurpose concrete face rockfill dam (CFRD) to be constructed in New Zealand. This 53 m high CFRD will impound a reservoir of 13 Mm3 and is essential to securing the future water needs of the community and environment of the Waimea Plains and wider Tasman/Nelson region.
The design of this unique large dam in the New Zealand context was a long-term collaboration of local dam design expertise and international experience that took the ‘historic precedent based design approach’ for CFRD’s and supplemented this with modern embankment design techniques for the highly seismic environment at the dam site. Design of this High Potential Impact Category dam presented a range of technical challenges for the designers and wider project team, which required new and innovative design solutions and approaches.
The dam features a number of unique arrangements in the New Zealand context including:
The project had its origins in the early 2000’s. Detailed design commenced in 2010, and was externally peer reviewed. The detailed design stage was undertaken in an Early Contractor Involvement (ECI) process which was completed in February 2019.
This paper covers the important seismic design aspects for this large dam, including understanding and designing for the potential range of displacements and embankment deformations to inform the crest parapet wall and diversion culvert designs, and understand how differing rockfill properties might affect the dam performance. Quantifying the range of potential dam performance enabled a more resilient dam design.