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.
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The ANCOLD (2003) Guidelines on Risk Assessment contain criteria regarding the tolerable level of individual risk from dam failure. Maslin et al. (2012) describe an approach to estimating individual risk from dam failure, using exposure factors, warning and evacuation factors, and fatality factors. These factors vary according to the people at risk, the anticipated warning time, the flood severity and the shelter people are likely to be in. Maslin et al. (2012) provide step-by-step instructions, which means their approach can be applied in a consistent manner from dam to dam. However, the recommended fatality factors are based on Graham (1999) and DHS (2011) definitions of high, medium and low severity flooding which have been superseded by the Reclamation Consequence Estimating Methodology (RCEM). Therefore, in this paper modifications to the Maslin et al. (2012) approach are proposed, so that estimates of individual risk from dam failure are consistent with RCEM-based estimates of societal risk. The paper then concludes with two predictions about how the assessment and use of individual risk in Australian dam safety management may change in future.
Flood inundation consequence and emergency evacuation assessment using advanced numerical modelling tools such as HEC-LifeSim is progressively emerging as accepted best practice, due in part to the growing ease in obtaining the necessary datasets and hydraulic numerical modelling results and the increasing computational power readily available to perform analyses. In turn, these tools are being applied to assess dam failure consequence and the effectiveness of emergency response procedures.
An essential resource is an approved Emergency Action Plan (EAP, also known as a Dam Safety Emergency Plan), which describes how dam owners and disaster management groups notify and warn persons at risk of harm during an emergency event. There have been progressive improvements in the effectiveness of EAPs through a series of reviews and lessons learnt from emergency events, legislative and regulatory amendments and general improvements in communications, monitoring, alerts and public awareness. Effectiveness is measured through feedback from training exercises and expert reviews, however a more quantitative measure is not presently available. This limitation can challenge decision makers who need to balance costs associated with emergency preparedness with anticipated reductions in life safety risks.
The paper explores the feasibility of providing a quantitative assessment of the effectiveness of an EAP using advanced consequence modelling (HEC-LifeSim). Using consequence models for two dams in Queensland, EAP effectiveness is assessed for a range of emergency response measures. The accuracy and reliability of the model parameters applied to each simulation and their impact upon the reliability of predictions of potential loss of life (PLL) are analysed and discussed. The feasibility of the approach is discussed and recommendations to be considered for future applications made.
Auckland Council (Council) is developing a dam safety management system with an overall objective to protect people, property, infrastructure, and the environment, from the harmful effects of a dam failure.
Council has responsibilities as an owner and operator of approximately 600 stormwater ponds and wetlands, many associated with dams. Council also has wider responsibilities for safety in the Auckland region, which may be affected by dams owned by others and even by inadvertent dams, such as road or rail embankments across streams that have the unintended but potential function of diverting, storing or holding back water. Three categories of dams have been distinguished, associated with Council’s different types of responsibility. Each category of dam is managed differently in the dam safety management system.
Given the large number of structures, which are not always obviously dams, a key activity has been the initial identification of dams across the Auckland region. Prioritisation has also been a necessary tool to direct resources and programme. Once dams have been identified, the consequences and risk of dam failure have been assessed, and commensurate measures have been established to manage those risks. There is limited guidance for some of these activities, and new procedures and tools have been developed.
This paper describes the process and the challenges encountered, for consideration by other councils when developing their own systems, and for consideration by the wider dams’ community.
The importance of building and maintaining safe, resilient tailings dams has become increasingly apparent with the rise in catastrophic failures in recent years. According to the World Mine Tailings Failures (WMTF) data base, 11 major failures have occurred over the past decade, often with devastating impacts to nearby communities in terms of loss of life and impact to the environment. With the occurrence of these types of events only expected to increase in coming years, there has been a corresponding increase in global calls to action to develop monitoring systems to better predict and wherever possible, prevent these failures from occurring.
With up to an estimated 20,000 tailings dams around the world, the development and implementation of a worldwide monitoring protocol is a daunting task, particularly as many of these structures are remote and difficult to access. This is where a technology like InSAR can make an immediate impact. InSAR is a remote sensing technique that uses radar satellite imagery to measure ground movement with up to millimetric precision. Radar systems are active, meaning they collect information from reflections of the radar signal off the ground and therefore do not require the installation of any equipment. As satellite images cover areas that extend thousands of square kilometres, they can provide information not only on the stability of dams, but also entire regions. Global archives already exist due to the Sentinel constellation of satellites, which provide coverage since 2014 over most parts of the world.
In an ideal world, tailings dams are safe and constructed to provide permanent containment of mining by- products. However, experience has shown that they can fail, often with dire consequences, especially if these failures occur without warning. The development of an internationally accepted standard for tailings dam monitoring is imperative to ensure the safety and resiliency of these structures is continuously tracked. This paper explores the role InSAR can play in the development of a global protocol for tailings dam monitoring.
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.