Paul Southcott,Suraj Neupane and David Krushka
TasWater owns and operates the water supply in Queenstown on the west coast of Tasmania. Anew water treatment plant was constructed downstream from one of the seven small dams that made up the original supply system, making the remaining six dams redundant.Two of these dams hada very high annual probability of failure and unacceptable societal life and financial risk due to their poor condition.Both dams required urgent attention (upgrade) to retain them as a lasting asset and legacy for the community or decommissioning to create a new ecological legacy.Roaring Meg Dam (6m high with a 9ML capacity) was constructed on Roaring Meg Creek around 1963. The Cutten Street Dam No 3 (10m high with a 2.4ML capacity) was constructed on Reservoir Creek around 1902to supply water to a growing mining community and had been in use since then. From a heritage perspective, the dam had some value as a timber crib and rockfill dam and its historical context as a key factor in the development of the town.There is limited guidance in the ANCOLD (2003) Dam Safety Management Guidelines on decommissioning and a process had to be developed in cooperation with the Regulator in this relatively new area of dam engineering. Detailed design of the decommissioning including diversion work during decommissioning, channel design to align with the original creek to help restore its ecological function and rehabilitation work on the exposed reservoir soils to stabilise them were undertaken. Aboriginal and historic heritage studies, flora & fauna studies and fluvio-geomorphological study at the dam sites were also undertaken to ensure that the decommissioning work did not interfere with the heritage, threatened species and riparian processes. The community were consulted to ensure acceptance of the changes to their town. Dam safety emergency management plans for the decommissioning of these dams was were also prepared. A significant issue in the decommissioning work was frequent and high rainfall due to the location of these dams on the west coast of Tasmania. The entire dam removal work had to be planned within the window of dry weather or very little rainfall. This paper presents the process, activities and lessons learned in successfully decommissioning these dams,to eliminate the unacceptably high risks posed by these dams and to restore the normal riparian processes.The general approach adopted for this project has applicability for other damsandis proposed as a starting point for an ANCOLD practice note in this area
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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.
Bronson McPherson, Scott Marshall1, Clément Monteil, Eric Lesleighter
This paper explores whether physical modelling has had its day in modern engineering or whether there is still a place for it. Physical hydraulic modelling is used as a tool for analysing hydraulic behaviour for a wide range of applications including; dams, channels,rivers,coastal etc. With advances in computer technology and power, the last few decades have seen the rise in numerical modelling, e.g. Computational Fluid Dynamics (CFD), often as an adjunct to physical modelling and sometimes as a replacement. A number of physical modelling case studies have been explored to identify the value provided by physical modelling.
Monique Eggenhuizen, Peter Buchanan, Reena Ram, Tusitha Karunaratne
The Department of Environment, Land, Water and Planning (DELWP) has a regulatory role for the safety of dams under the Water Act 1989 (Act) and is the control agency for dam related emergencies. Local Government in Victoria is divided up between 79 LocalGovernment Authorities (LGAs), each responsible for administering local infrastructure and community services such as roads, drainage, parks etc. Current records indicate that 42 of the 79 LGAs own or manage up to 435 dams and retarding basins.Many of these assets, which include a mix of old water supply dams, ornamental lakes and retarding basins, have been accumulated by LGAs over many years as a result of asset transfers and conversions, land development projects, flood mitigation programs and opportunistic acquisitions by the transfer of land. DELWP engaged GHD to assist and provide advice to the LGAs to significantly improve and update knowledge on LGA dams and retarding basins. The objective of this project is to ascertain where the State’s LGA dams and retarding basins are located, what risks they might pose to communities and infrastructure, what to consider during emergency management planning and response, and to provide owners with the essential management tools and procedures to effectively manage these assets, if these are not in place already.The outcome of this project was to support LGAs to improve management of their dams and retarding basins. It aimed to do this by assisting LGAs with the development of basic dam safety programs that will enable LGAs to more effectively manage their portfolios of dams and retarding basins in terms of ongoing maintenance, dam surveillance and emergency planning and response, and demonstrate due care.This project had a number of key challenges. These included the requirement to process and assess a large number of sites within a small timeframe whilst achieving good value for money,without compromising DELWP’s objectives. A number of efficient methods were adopted during this project particularly during the initial data gathering process, identifying those dams which needed to be inspected based on embankment heights, reservoir capacity and consequences, rapid preliminary assessment of consequences, the development of effective templates for the site inspections, and a method of applying qualitative risk assessments, applicable to the majority of the dams, allowing a consistent assessment of the status of each dam and damsafety documentation.The methods discussed(although developed specifically for the Victorian LGA dams portfolio)provide a sound basis for a screening tool to assess a large number of smaller dams in an efficient manner and quickly identify higher consequence category dams requiring attention. This method could easily be modified and adapted to be applied to similar portfolios of dams.
Alberto Scuero, Gabriella Vaschetti, John Cowland
Waterproofing geomembranes have been used for new construction and rehabilitation of dams since 1959. Research for underwater rehabilitation with geomembranes started at the beginning of the 1990s. The first installation was made in 1997 at Lost Creek arch dam in USA, where a SIBELON PVC geomembrane system was installed partly underwater, to restore watertightness to the upstream face. Techniques for underwater cracks/joints repair, and for staged repair, were developed and first adopted in 2002 and 2010 respectively. The paper presents through some significant case histories the range of underwater applications available today. The paper also presents a new underwater technology, the Sibelonmat®mattress, that allows water-tightening canals without reducing water flow.The Sibelonmat®can be used in embankment dams, to waterproof the upstream. face or as upstream blanket
Lesa Delaere, Dr Natalie Clark, Dr Shayan Maleki
Waterway barriers, such as dams and weirs, have the potential to impact aquatic fauna species through the restriction of fauna movement and direct injury and mortality of individuals. Without suitably designed aquatic fauna passages and features to minimise injury and mortality, these barriers may adversely affect the viability of local and regional populations, through disruption to critical behaviours (e.g. breeding, dispersal).
The Lower Fitzroy River Infrastructure Project comprises of two weirs on the Fitzroy River in central Queensland. Two threatened turtle species, the Fitzroy River turtle and the white-throated snapping turtle, and a range of fish species needed consideration of species-specific requirements and development of targeted design solutions.
This paper discusses the ecological needs of these species as well as features incorporated into the design to reduce the impact of the weirs. The design incorporated modular fishlocks, gate, spillway and stilling basin features, an innovative turtle passage, special considerations for outlets and operational aspects. The design was further subject to complexity due to the variation in river flows, zero flow to approximately 9,000m3/sat bank full, and needed to account for a wide range of operational scenarios with respect to the species impacts.The paper also includes a discussion on computational fluid dynamics modelling (CFD) which was used to validate the design of fish passage structures.