David Scriven, Errol Beitz, Aaron Elphinstone
The Bowen River Weir is located at AMTD 94.4 km on the Bowen River, some 25 km south of Collinsville in North Queensland. The weir is part of the Bowen/Broken Rivers Water Supply Scheme and it provides a pumping pool for pipelines serving two nearby coal mining developments and a power station, and also acts as a regulator for riparian water users downstream until it meets the Burdekin River.
The weir was constructed in 1982 and incorporated a fishway towards the southern (left) bank, the design of which was based on the old “pool and weir” fish ladder type layout, typical of that era, with 48 separate cells containing partial vertical slots and baffles. This design has since been found to be ineffective for Australian native fish. In addition it was often out of service due to cells becoming filled with river sediment and debris. For these reasons it was decommissioned and made safe in late 2008 on the condition that a new fishway be constructed.
In late 2008 agreement was reached with Fisheries Queensland to install a “fish lock” type fishway at the site. This type of fishway has in recent years proved to be reliable and effective (eg. successful fish locks at Neville Hewitt and Claude Wharton Weirs). The preliminary and then final design was undertaken by SunWater (Infrastructure Development) between September 2008 and March 2009. The construction was undertaken by SunWater direct management, commencing in July 2009 and completed in late 2010.
Bowen River Weir Fishway – Design and Construction
Ben Greentree, David Bamforth, Matthew O’Rourke and James Willey
A series of relatively small floods occurring between end of construction in 1978 and late 1980s caused extensive and dramatic rock erosion to the very steep unlined section of the Googong Dam spillway. Following a review of hydraulic performance at larger floods, the spillway’s future erosion potential was evaluated and it became clear that extensive remedial work was required. A detailed design was developed comprising the retro-fitting of a full concrete-lined chute, the raising and extension of the spillway chute walls, strengthening of the upstream training walls and excavation of a large plunge pool. The Googong Dam has an ANCOLD hazard rating of ‘extreme’ because of its location upstream of Queanbeyan and Canberra.
In early 2008, the Bulk Water Alliance (BWA), comprising ACTEW Corporation Ltd, (in cooperation with ActewAGL) (the Owner), GHD Pty Ltd (the Designer) and Abigroup Contractors Pty Ltd in joint venture with John Holland Pty Ltd (the Constructors) was formed to deliver a package of water security projects for the ACT, one of which is the Googong Dam Spillway Upgrade.
After preparation of a construction methodology and target outturn cost (TOC), the project was approved by the Actew Board and construction commenced in February 2009. Completion is due in late 2010. A number of significant geotechnical, structural and logistical challenges were encountered during construction, resulting in major changes to the construction methodology necessitating design changes. The changes were incorporated within the original TOC, without instigating scope change contractual claims and while still maintaining spillway functionality in line with Owner operational requirements.
This paper presents delivery phase challenges that necessitated construction methodology and design changes to achieve best for project outcomes; how these challenges were overcome through genuine innovation reliant on a collaborative effort by all the Alliance partners; and how the contractual framework of the Alliance was essential for the change management process to be successful.
Steven Slarke, Martin Mallen-Cooper, Andrew Evans, John Prentice
As part of the Murray-Darling Basin Authority ‘Sea to Hume Dam’ program to restore fish passage along the River Murray, an innovative Denil fishway is being retrofitted into Mildura Weir (Lock 11). Due for completion in the latter half of 2010, the fishway will allow the upstream and downstream passage of medium and large sized fish past Mildura Weir, which has a difference in water levels of 3.5 metres.
Constructed on the sloped concrete apron at the left abutment of the Dethridge weir, the Mildura Weir Denil fishway design is innovative in the River Murray. The Denil fishway is essentially separate from the existing weir, and its superstructure can be fully removed from the river during floods. The fishway can also be progressively removed during periods of rising floodwaters, maintaining operation during periods when fish migrate in particularly large numbers. The fishway represents a cost effective design, reflecting the decision to maintain the current weir structure for a further forty years, but still providing passage to a broad range of fish sizes and species. Innovative fish monitoring and carp separation facilities will be provided, shared with the other River Murray fishways. But, unique to the River Murray, viewing windows are provided to allow the public to observe fish negotiating the fishway, and to enable a better understanding of fish movement.
Shao Kwan Ng
Asset management aims to ensure that assets, such as dams, are sustainable. In order to achieve this, management decisions need to be defensible and the long-term impacts of short-term decisions need to be clearly demonstrated, such that an asset operates and is maintained in an appropriate fashion and in a satisfactory condition. Expert rule systems are becoming widely recognised as powerful and elegant tools suitable for engineering and management decision-making. They are powerful, transparent and flexible tools that mimic how people make decisions, and hence provide a natural way of thinking for decision-making. This paper reviews the current usage of expert systems in asset management, and illustrates the potential of these tools, in conjunction with the available (ANCOLD) guidelines, to assist dam owners in decision-making, such as in condition evaluation and dam hazard assessment applications.
Keywords: Decision-making, expert rule systems.
Tony Harman, Richard Herweynen, Malay Ghosh
Following a number of years of investigation into the condition of the existing 1960’s post tensioned anchors at Catagunya Dam Hydro Tasmania embarked on an options study to determine the best method to restore the dam stability to acceptable limits for the long term. The required solution was intended to not only resolve the issue of anchor deterioration but also to increase the flood capacity of the dam.
Based on preliminary design work a concrete buttress solution was recommended and approved for detailed design. The preliminary design utilised a simplified, 2-dimensional, rigid body model, including crack analysis. As part of the detailed design a finite element model was developed to refine the preliminary design. However, this model did not support the simplified analysis and further non-linear finite element analysis demonstrated that the proposed passive buttress design solution was not technically feasible. The options were reconsidered and the adopted solution was to replace the original anchors with new modern anchors with a high level of corrosion protection.
The new anchors adopted are the largest post tensioned anchor loading currently used for a dam in the world. This along with the existing post-tensioned anchors and the tight geometry of the dam, which has a central spillway with a cantilevered ogee crest, provided significant challenges with the design of this dam upgrade. Some of the key design challenges included:
– Appropriate level of modeling and analysis to be able to make sound design decisions. (Hydraulic modeling and FEA).
– Congestion due to the tight geometry of the original design.
– Anchor head block detail to ensure the loads would be adequately secured and dispersed into the dam body
– Crest cantilever support to ensure that structural integrity was retained during construction and later in service. Innovative installation of carbon fibre reinforcement was used.
– Strain compatibility. It was important to ensure the structural contribution of new and old working together and that the consequences of application of new large stresses was manageable.
– Existing anchor degradation. The design needed to ensure that stability compliance was achieved for complete to zero effectiveness over time.
– Maintaining operability of dam and power station during construction.
– Achieving an effective long term maintainable solution.
This paper will present the risk associated with committing to a solution too early and the design challenges and the solutions finally developed, providing the dam industry with a valuable reference for future similar projects.
Analysis and Design Challenges Associated with the Catagunya Dam Restoration Project
Cat McConkey, Zarmina Nasir, Rachel Caoil
The Enlarged Cotter Dam (ECD) is the first major project to be assessed and approved under the new planning regime in the Australian Capital Territory (ACT). ACTEW chose the ECD as its highest priority option in securing Canberra’s water supply for the future because of its relative economic benefit to the community, reliability of water supply, technical feasibility and comparatively low environmental impact.
The planning and construction of large dams has been reduced from a typical 10 plus years to four years in the ACT and surrounds for the ECD. Australian and International Dam design and construction has significantly developed from a time when dam approvals focused on engineering, economics and constructability to now include regulatory planning processes that seek to reconcile environmental, social and economic impacts.
This paper explores and contrasts the experience of securing approvals for the ECD in 2009 to past experiences of dam planning approvals and consultation processes.