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.
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.
Design floods for most dams and levees typically have an annual exceedance probability (AEP) of 1:100 (1E-2) or less frequent. In the U.S., high hazard dams are designed to pass the Probable Maximum Flood (PMF), which typically has an AEP of 1:10,000 (1E-4) or less frequent. In order to reduce epistemic uncertainties in the estimated AEP for extreme floods, such as the PMF, it is important to incorporate as much hydrologic information into the frequency analysis as reasonably possible. This paper presents a Bayesian analysis framework, originally profiled by Viglione et al. (2013), for combining at-site flood data with temporal information on historic and paleofloods, spatial information on precipitation-frequency, and causal information on the flood processes. This framework is used to evaluate the flood hazard for Lookout Point Dam, which is a high priority dam located in the Willamette River Basin, upstream of Portland, Oregon. Flood frequency results are compared with those from the Expected Moments Algorithm (EMA). Both analysis methods produce similar results for typical censored data, such as historical floods; however, unlike the Bayesian analysis framework, EMA is not capable of incorporating the causal rainfall-runoff information in a formal, probabilistic manner. Consequently, the Bayesian method considered herein provides higher confidence in the fitted flood frequency curves and resulting reservoir stage-frequency curves to be used in dam and levee safety risk assessments.
As part of the development of some dams and hydroelectric power schemes, deep infrastructure is often required which requires and understanding of the in situ stresses of the rock mass. Recent works completed in southern Australia and Europe have led to improved methodologies for conducting effective, reliable, and repeatable measurements of in situ strain and/or deformation, as well as the subsequent estimation of in situ stress.
In situ stress testing is generally an item that is specified as part of a geotechnical investigation, however it is not commonly well understood in terms of reliability, repeatability, or, in fact, what the result actually means and its implications to project design. Commonly, a handful of tests are completed, with variable results, which often generates more confusion than answers.
This paper provides a discussion of recent in situ stress testing completed for two deep Australian projects. It summarises the aim of the investigations, test selection process, laboratory testing, data review and model development. This is to illustrate how complex the estimation of in situ stress can be and some of the pitfalls that may be avoided whilst acquiring and assessing the data. It also examines several different testing methods available in the Australian and International industry and some of the analysis techniques available to dam and tunnel projects. Finally, the paper provides an update on topical developments provided at recent workshops in Europe.
Estimating the likely extent, depth and velocity of flooding should a dam fail – and planning to both prevent and respond to such a failure – are important parts of managing risk from dams and ensuring community resilience. This paper compares and contrasts current standards and practices for dambreak analyses and flood routing in New Zealand, Australia, the US, and the UK. Comparisons highlight consistent and evolving practices and consider how dambreak modelling supports robust dam safety decision making. In addition, the paper offers opinions regarding selected areas for future research, and insights into the benefits and limitations of increasing complexity in breach modelling.
Loss of life estimates in dam breach circumstances are a key determining input in establishing the appropriate risk profile for these assets. They can also be useful in identifying the most effective emergency management responses. While there are a range of approaches described in the literature for assessing loss of life for concentrated population centres, there is little specific guidance on approaches to be taken when there is only a small number of properties or where itinerant loss of life has the potential to be the dominant risk element. Itinerants are most commonly considered to be road users, although, they can alternatively be any temporary users of the floodplain. The literature on flood fatalities indicates that the largest number of deaths occurs at vehicle crossings or otherwise when individuals voluntarily enter waterways. An approach has been developed for identifying the cases where itinerant loss of life has the potential to be the dominant vector for flood fatalities. In addition, the available flood fatality literature and associated databases have been reviewed to establish the precursors to fatalities.
A simple stepped procedure is presented which allows the user to identify cases where itinerant risk to life on roads should be considered with a separate procedure and a method presented by which itinerant life loss may be identified.