Lindsay 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
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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Yuqi 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.
Jarrad Coffey and John Plunkett
As tailings standards continue to evolve, a greater focus is being placed on the monitoring of tailings storage facilities (TSFs). While this is a positive development for TSF safety into the future, it is only one component of the work required to implement Performance Based Risk Informed (PBRI) management. There is also a significant human element that can be aided by reducing the time spent of personnel sourcing/aggregating data and instead focussing on decision making. It is discussed in this paper how a more holistic approach to monitoring via a dashboard that displays all management data relevant to a portfolio of TSFs can be applied in parallel to risk assessment to work towards the goal of PBRI. The dashboard also facilitates review and governance activities, which are central to the Global Industry Standard on Tailings Management. An example of the dashboard utilised at Rio Tinto Iron Ore is presented to provide an example of such a system and its benefits.
Chris Nielsen, Ron Guppy, Gary Hargraves, Robert Fowden
Dam safety upgrade projects of major dams typically involve a large capital investment. It is important that expenditure decisions are based on sound criteria, both technical and non-technical. Independent peer review of technical matters plays a key role in meeting design, construction and safety objectives within practical financial constraints and assuring robust, resilient and reliable project outcomes.
An independent technical review is recommended for all dam projects.
The Queensland dam safety regulator has developed guidelines associated with technical review for dam safety projects that considers scope and limitations, expertise and governance. The guidelines are informed by literature, recent projects, a commission of inquiry, internal and external review and industry feedback. The guidelines are being implemented across major dam safety upgrade business cases through preparation of terms of reference by the Queensland Government’s business planning and implementation entities, who maintain the responsibility of providing assurance to state government projects, as well as the state’s major dam owners.
The terms of reference, supported by the underlying principles in the guidelines, provide a platform for consistent and appropriate application of technical assurance to dam projects in Queensland. Among other matters, governance is highlighted as a critical factor for success as well as clarity of the roles, responsibilities and reporting lines of all parties. The application of both guidelines and terms of reference to recent projects is discussed.
Sonel Reynolds, Alex Gower, Bob Wark
During the outlet works upgrade in 2017 it was found that the valve pit and stilling basin at Mundaring Weir were not founded on rock. Based on these observations and the arrangement of the spillway and outlet works, it was considered that during significant spillway overflow events, a high velocity jet could displace the stilling basin slabs, erode the underlying material, and progress to failure of the outlet pipe and valve pit. A comprehensive risk assessment was conducted to estimate the likelihood of stilling basin slab uplift, erosion of the underlying material, and failure of the outlet works. A geotechnical investigation was undertaken comprising drilling nine boreholes and a program of geophysical downhole logging. Computational Fluid Dynamic (CFD) modelling was used to determine the pressure fluctuations and turbulence intensity over the spillway slab which could lead to uplift. The erodibility of the rock mass material below the stilling basin slabs was assessed using the outcomes of the geotechnical investigations and CFD output, with analyses based on the Kirsten Index and eGSI. A net benefit analysis was conducted to assess whether preventative remedial works were justified. Through this process it was demonstrated that the business risk was low and risk reduction measures were not justified.
Regulatory risk for large civil engineering projects such as dams and hydropower schemes can be larger than the engineering risks. The seriousness of project regulatory risks is rarely acknowledged publicly and almost never dealt with contractually. The recent adoption by the World Bank of the FIDIC/ITA Emerald Book contractual framework introduces geotechnical baseline reports as a contractual mechanism for managing ground risk in World Bank hydro projects. Regulatory risks created by government agencies and utilities due to changing project requirements can likewise be managed by adopting the concept of geotechnical baselines to regulatory impositions as a baseline report.
Government agencies changing regulatory burdens mid project can fairly be held accountable for the
burdens of those changes by establishing regulatory baselines at the earliest stages of a project. By
contractually embedding regulatory risk baselines, governments and their agencies can adjust their
payments to reflect the changed cost in delivering an agreed project caused by regulatory changes. In this way the compensation for delivering a project more closely aligns with its value and cost. A regulatory baseline report in reducing project exposure due to regulatory change driven costs is a new tool in more efficient and competitive project delivery.
A transparent mechanism for costing regulatory change risk and apportioning it in accordance with pre agreed mechanisms, is an innovation of great use to the dam and hydropower sector.