Michael Hughes, James Stuart
Tropical Cyclone Debbie (TC Debbie) formed in the Coral Sea on Saturday 25th March, 2017 and developed into a category 4 system that crossed the coast near Proserpine, Queensland with the eye passing very close to Peter Faust Dam. TC Debbie, later becoming Ex-TC Debbie embarked on a tour of SunWater infrastructure (See Figure 1). Of 23 referable dams managed or owned by SunWater in Queensland, only 3 had no inflows with spills resulting at twelve locations. The paper describes the varied experiences of SunWater with relation to preparation for, and operations during TC Debbie. Some key areas of interest to other dam owners include;
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There is increased pressure from stakeholders for projects to include evaluation of emerging broader development issues within the environmental assessment process. These emerging issues are not well documented or understood and at the forefront of untested preliminary government policy positions.
Agencies expect proponents to invest in evaluating these matters outside of typical assessment practices. Requests are made late in the evaluation and approval process.Assessmen involves matters not directly related to the project or within the proponent’s control and occurs late in the project development cycle.
The Lower Fitzroy River Infrastructure Project (LFRIP) was identified through the Central Queensland Regional Water Supply Study in 2006, as a solution to secure future water supplies for the Rockhampton, Capricorn Coast and Gladstone regions. The Gladstone Area Water Board and SunWater Limited, as proponents, propose to raise the existing Eden Bann Weir and construct a new weir at Rookwood on the Fitzroy River in Central Queensland.
The LFRIP environmental impact statement (EIS) was approved, subject to conditions, by the Queensland Coordinator-General in December 2016 and the Commonwealth Minister for the Environment and Energy in February 2017. Achieving conditions that will realise positive environmental outcomes while simultaneously achieving project objectives, particularly with regard to timeframes and costs, was not without its challenges.
The EIS was developed in accordance with the requirements of the State Development Public Works Organisation Act 1971 (Qld) and the Commonwealth’s Environment Protection and Biodiversity Conservation Act 1999, including an extensive stakeholder consultation programme. These regulatory requirements are well understood and applied to projects as normal accepted practice. They ensured that potential project impacts and benefits were identified, that appropriate levels of effort were applied to investigations to establish baseline conditions and that risks to and impacts on environmental (including social and cultural) matters were adequately mitigated and managed.
The environment is not static. Emerging issues and perceptions results in regulation and policy changes in response to political and social drivers. During the development of the EIS both new legislation and new policies were imposed on the project.New legislation resulted in additional assessment around matters previously considered mitigated and managed (fish passage). New legislation introduced new matters for assessment (connectivity). Collaboration and engagement with stakeholders were key to understanding the applicability of these elements to the project and for developing an approach to address the legislative requirements late in the project’s development and assessment process.
In Queensland,policy is emerging to mitigate and manage impacts of development on the Great Barrier Reef World Heritage Area’s universal values. The EIS was required to address the direct project impacts on water quality and the impacts arising because of the LFRIP (facilitated development). Water secured by the LFRIP is for urban, industrial and agricultural purposes. Urban and industrial developments are well regulated and subject to specific environmental approvals processes. Use of water for agricultural purposes, intensive irrigated agriculture in particular,is less regulated. Policies developed are reactive and require individual projects to address these impacts.In the absence of regulatory guidelines for assessment of consequential impacts, the project adopted a collaborative approach. The proponents established a working group, including State and Commonwealth technical agencies. This allowed for robust and scientifically defendable methodologies to be developed and agreed upfront. Streamlining the approach by including key decision makers assisted in managing expectations and focused the assessment on realistic and achievable outcomes relative to the project. The result was defendable outcomes allowing timely decision making and avoided rework as much as possible.
This paper describes developments in environmental assessment relating to new and augmented weirs.
Mark Pearse, Peter Hill
Risk assessments for large dams and the design of upgrades are often dependent on estimates of peak inflows and outflows well beyond those observed in the historic record. The flood frequencies are therefore simulated using rainfall-runoff models and design rainfalls. The recent update of Australian Rainfall and Runoff (ARR) has revised the design rainfalls used to model floods that are of interest to dam owners. This will change the best estimate of flood frequencies for some dams. However, for most dams the impact of revised design rainfalls on flood frequencies is small compared to other factors that can change (independent of dam upgrades). These include model re-calibrations to larger floods, changes to operating procedures that affect the drawdown distribution and improvements in how the joint probabilities of flood causing factors are simulated. In this paper, we look at how the design flood frequencies for some of Australia’s large dams have changed, the reasons for this and then identify five key questions for dam owners to ask to aid assessment of whether the hydrology for a dam should be reviewed
Although the total tailings dam failure frequency peaked in 1960s through 1980s, the failure rate of significant tailings dams has not dropped. The significant tailings dam failures the mining industry experienced in the recent history include: Merriespruit, South Africa, 1994; Los Frails, Spain, 1998; Kolontár, Hungry, 2010; Mount Polley, Canada, 2014; and Samarco, Brazil, 2015. The dam failures may be due to inadequate design, poor construction and inappropriate operations.This paper discusses the lessons learned and some recommendations and good practices to reduce the tailings dam failure risks. It addresses existing issues and provides some recommendations in risk based design, water management-integrity of facilities and water balance modelling, loading rates, tailings farming, adequate governance and roles and responsibilities of designers and nominated engineer.
Mojtaba E. Kan, Hossein A. Taiebat and Mahdi Taiebat
In design of new embankment dams or evaluation of the performance of existing earthfill and rockfill dams, the Newmark-type Simplified Methods are widely used to estimate the earthquake-induced displacements. These methods are simple, inexpensive, and substantially less time consuming as compared to the complicated stress–deformation approaches. They are especially recommended by technical guidelines to be used as a screening tool, to identify embankments with marginal factor of safety. The methods would serve as a reliable screening tool had they always resulted in conservative estimates of settlements. However, a number of studies in the last 15 years show the contrary. This paper provides a critical review of the fundamental theory behind the simplified Newmark-type methods. Cases in which the results of the simplified methods are reportedly non conservative are further investigated and possible reasons are discussed, that may be taken into account in future design and investigations of Australian dams. The reliability of the simplified methods is examined based on the existing thresholds proposed in the literature and accounting for the embankment geometry and type, and for the seismic activity characterization. A recently proposed practical framework is further elaborated to demonstrate its effectiveness in the study of seismic behaviour of embankment dams. In particular, the case study of Zipingpu concrete faced rockfill dam in China is discussed where all widely used simplified procedures failed to predict the order of deformations experienced by the Dam under a recent strong earthquake event.
Zerui Lu, Behrooz Ghahreman-Nejad, Mahdi M. Disfani
Particle characterisation like size distribution and shape can greatly affect the mechanical behaviour of granular materials, and is closely related to the economics for engineering projects. For rockfill material in embankment dam construction, the particle size distribution (PSD) is fundamental to the design, quality control and numerical modelling. Traditionally, particle size distribution for engineering materials is obtained through physical sieving. However, with rockfill material, the size varies significantly and can range from gravels (+2mm) to cobbles (+60mm) and boulders (+200mm) with the maximum size usually limited to 1m, which makes the conventional sieving process considerably difficult to conduct as well as being time-consuming. Meanwhile, the advanced technology in computer image processing has created many possibilities in characterising particles within digital photographs, and therefore can be utilised as an effective alternative to the conventional sieve analysis. This method has been in use mainly in the mining industry over the past two decades to assist with rock fragmentation and process monitoring and control. Notwithstanding, the use of this technique in the dam industry for quality control of rockfill material has been rare. Thus, an innovative approach is proposed in this paper to estimate the PSD curves for rockfill material using image analysis along with the latest developments in aerial photography. The results of PSD analysis using the image processing software Split Desktop are presented and compared with the results from sieve analyses for verification. Recommendations are made to improve the process and increase the accuracy of the outcome. It is demonstrated that the proposed method has a reasonable accuracy and is a viable option for quality control in construction of rockfill structures such as rockfill embankment dams.