2021 – Flood Modelling of Cooma Water Storage Tank Failure
Meizhiwen Zheng, Nimal Gamage
This study used MIKE 21 to replicate the Cooma tank failure by varying modelling input parameters. This study explores the mechanism by which flood water can damage buildings and investigated different damage category assessment method to predict building damages.
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2021 Papers
2021 – Some considerations when using deformation monitoring to manage the static liquefaction risks of TSFs
Learn moreDavid Reid, Andy Fourie, Riccardo Fanni, Cristina Vulpe, Alexandra Halliday
Recent failures of a number of tailings storage facilities (TSFs) has highlighted the need for better
governance and operational management of these structures. One means to improve their safety is clearly better and more focussed monitoring. Significant efforts are underway in this area, with a number of technologies being deployed. In particular, the monitoring of deformations through a variety of means (direct, satellite inferred) is increasingly being applied. While deformation monitoring to warn against failure has a long history in geotechnical engineering, some aspects of the rapid triggering and resulting flow of some TSFs may not be amenable to deformation monitoring, in the sense that actionable warning of an impending failure is not assured.To examine this issue, a series of numerical models of an idealised TSF are carried out. This idealised TSF is brought to failure by means of a rising phreatic surface – often referred to as the constant shear drained (CSD) stress path. Deformations of the outer slope and crest of the numerical model – i.e. those that could be monitored for a real TSF – are tracked and analyses for the models carried out. It is seen that under CSD loading distinct deformation patterns indicative of impending failure are not always clear. Rather, minimal deformations and indeed swelling of the crest is seen leading to failure. The importance of recognising the minimal pre-failure deformation patterns that may manifest with a rising phreatic surface is noted.
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2021 Papers
2021 – A tale of two sites, siting optimal fish passage location at Ewen Maddock Dam
Learn moreLindsay Millard, David T Roberts, Steven Cox, Andrew Berghuis, Anna Hams
Addressing historical impacts of waterway barriers on regional fisheries values is a major focus for fisheries regulators when assessing proposed water infrastructure projects such as dam safety improvements. To inform prudent investment decisions, it is essential to quantitatively determine the feasibility and benefits of various fish passage options to mitigate barrier effects. In Queensland, the regulatory frameworks require consideration of multiple options to achieve mitigation with the overarching goal to support and restore regional fish productivity. Addressing multiple objectives on large water infrastructure projects can be challenging, particularly for existing assets requiring retrofit solutions. There is a need to balance the requirements for dam safety, water supply reliability, while also mitigating the loss of fish habitat access upstream of barriers. Finding optimal fish passage solutions requires consideration of multiple options and using objective approaches that can weigh up the many aspects. The best solution may not always be the most obvious. Here we describe an approach that addresses multiple objectives through a novel off-site solution that provides increased benefit to the impacted fish community. Seqwater, Queensland,
The approach involved weighing up various fish passage options, informed by stochastic hydrologic
modelling to produce a range of probabilistic scenarios. 120 years of modelled water levels and discharges from the study site and the broader catchment, enabled an evaluation of the benefits and dis-benefits of different options in relation to dam safety, water supply reliability and fish migration opportunities. Inputs to the assessment process included fish habitat availability and migratory needs, capital and operational feasibility considerations. Numerous modelling scenarios were produced to assess a range of possible solutions, both on and off-site, to provide an objective weighting of the relative strengths of each scenario.In this instance, while an onsite option could be feasibly engineered, it would be costly and given the
hydrology of the system, would operate so infrequently as to provide limited opportunities for fish passage and minimal regional fisheries productivity benefits. The optimal solution found was to provide fish passage on a higher order stream within the same catchment area that has impacted fish migration and access to upstream habitats for the same fish community. This option improves fish habitat access to a larger proportion of the catchment and over a wide range of flow conditions, thus providing greater regional fisheries productivity outcomes.Our method demonstrated an objective approach to balancing multiple project objectives for dam
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improvements. The use of hydrologic modelling combined with fish migration and habitat information, found an optimal solution for regional fisheries productivity goals, while also balancing the dam safety and water supply reliability goals. -
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2021 Papers
2021 – Don’t risk it to get the biscuit – Managing construction risk at Ewen
Learn moreZara Bostock, Helena Sutherland
Ewen Maddock Dam is located approximately 12.0 km west of Caloundra, in the Sunshine Coast area of Southern Queensland. The dam is a homogeneous earthfill embankment dam 10.5 m high and 724 m long. The dam was originally built between 1973 and 1976 and later upgraded in 1982 to raise the ogee spillway crest by 2.44 m to the current Full Supply Level (FSL) of 25.38 m AHD.
Seqwater is undertaking a staged upgrade of Ewen Maddock Dam to address deficiencies identified during the Acceptable Flood Capacity (AFC) Review (GHD, 2010). The consequence category assigned to Ewen Maddock Dam is ‘Extreme’ with a downstream Population at Risk greater than 1000.
Stage 1 construction was completed in 2012 to manage the seepage underneath the dam to reduce the risk of piping and improve embankment stability. Stage 2A involved retrofitting a filter in the existing embankment and raising the dam 1.61 m to 30.11 m AHD using a reinforced concrete parapet wall. Stage 2B involves spillway upgrade works and was split from 2A due to approval constraints.
Stage 2A construction was completed in April 2021, navigating various project and dam safety challenges. This paper presents some practical ways dam safety and risk was managed on the ground from the perspective of both the designer and owner.
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2021 Papers
2021 – Lessons learnt from the application of HEC-LifeSim 2.0 to multiple dams across Australia
Learn moreHench 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.
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2021 Papers
2021 – Importance of adequate characterisation of fissured clay in dam foundations, a case study
Learn moreYuqi 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.
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