Graeme Maher, Richard Herweynen, Martin Mallen-Cooper and Stuart Marshall
Increasing awareness of the environmental impact of dams means that fish passage is emerging as a critical issue for both existing and new dams in Australia.
The fish passage and outlet works for Wyaralong Dam, a new dam currently under construction, required accommodation of large ranges of head and tailwater levels. The solution that has been adopted, a bi‐directional fishlift using a single hopper with trapping for downstream fish movement occurring within the intake tower, is a world first. The solution required the innovative integration of a number of existing technologies to create a system which is necessarily complex, yet reliable and effective.
The paper incorporates discussion of the critical design constraints, the biology of fish passage, the process adopted to reach the concept solution and a description of the final design including its integration with the outlet works. A number of design issues and their solution are discussed in detail, particularly those associated with dealing with the complexity of the design constraints and how the components of the solution were integrated into a seamless design.
The paper will be of use to those involved in the process of providing fish passage on both existing and new structures that obstruct river flow.
A Bi-Directional Fishlift – An Innovative Solution for Fish Passage
Now showing 1-12 of 41 2974:
Jim Walker, Sergio Vallesi, Neil Sutherland, Peter Amos, Tim Mills
The Tekapo Canal is a 26km long hydropower canal owned by Meridian Energy Ltd in New Zealand. Completed in 1976, the canal is 40m wide, 7m deep and has a capacity of 120m3/s. The canal was constructed from compacted local glacial soils with a compacted silt lining sourced from till deposits.
During 2007 and 2008 the canal showed signs of leakage where it crossed over a twin barrel culvert structure. In October 2008 a diver inspection identified depressions and sinkholes on the invert of the canal above the culvert. Approximately 6m3 of silty gravel lining material had settled. Testing showed direct and rapid connections between lining defects and seepage outflows at the culvert outlet headwall. Subsequent ground penetrating radar survey confirmed the presence of voids above the culvert barrels. Diver placed filling of the defects with granular materials was immediately implemented, and a series of remedial actions over the next four months were required to arrest deterioration and enable the canal to remain operational.
The paper describes the initial response to this situation and the immediate measures taken to prevent failure. It also describes the medium term and ongoing measures implemented to maintain the safety of the canal while permanent remediation requirements are assessed. The lessons learned from this event, and their impacts on Meridian’s Dam Safety Assurance Programme (DSAP) are also discussed.
Immediate response measures included ongoing filling of lining defects with filter gravel, intensive land based and diver surveillance of the canal, planning and resourcing for emergency contingency actions in the event that a risk of breach developed. Medium term measures included arresting leakage by placing a low permeability blanket of silty gravel over the damaged area using a concrete pump, and constructing external buttresses capable of safely withstanding large discharges should deterioration of the canal structure occur.
These short and medium term remedial measures were completed with the canal full and in operation and continue to perform well 20 months later. Continuing risk mitigation measures include enhanced surveillance and monitoring (land based and using divers), localised treatment of defects, as well as ongoing monitoring and review of the Dam Safety management regime and sustained Emergency Management preparedness.
Hamish Smith, Graeme Maher
In order to achieve environmental sustainability it has become standard engineering practice to include a fishway on all new or refurbished large dams in Australia.
As regulators expand their understanding of fishways, project approval conditions associated with these complex engineering structures are changing. Regulators now increasingly wish to participate in the development and selection of the final fishway to be adopted.
This paper describes the process developed and implemented at Queensland’s most recent dam under construction, the Wyaralong Dam, to ensure that the views and opinions of regulators and stakeholders were sought and considered during the fishway selection and design process.
With no written guidelines available on “how to select and design a suitable fishway”, all associated parties entered into the process without a full knowledge of how it would unfold and what the final outcome would be.
This paper demonstrates that in an increasingly regulated environment it is possible to have regulators, proponents and stakeholders work cooperatively together to achieve a result that provides for sustainable development and is acceptable to all parties.
This paper will provide a model that could be adopted for the development of new fishways or the refurbishment of existing fishways on large dams in Australasia.
Changing Regulatory Environment – Large Dams and Fishways
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.
Richard Herweynen, Robert Montalvo, John Ager
The choice of materials used in the construction of a dam is one of the most critical decisions in the design process. Our natural behaviour as engineers is to adopt materials which have proven performance, and which conform to Australian or international standards, which sometimes causes us to overlook the specific conditions and demands of the project at hand. In an environment where the majority of concrete produced is for structural purposes, the properties of these concretes is often vastly different to those desired for mass concrete structures such as dams and spillways.
The big question at Wyaralong Dam was could onsite aggregate be used in the Roller Compacted Concrete (RCC)? The Wyaralong Dam is located in the Gatton Sandstone (early Jurassic), predominantly feldspathic to lithic‐feldspathic sandstones with a clay matrix. Early analyses and tests suggested that the Gatton Sandstone was not suitable for RCC aggregate due to a 68% wet/dry strength reduction, high water absorption (5.2 – 7.5%) and petrographic interpretation that clay content was mainly swelling clay, leading to durability concerns.
Due to significant community, safety and cost issues with importing aggregate, Wyaralong Dam Alliance (WDA), during the development of the RCC mix design for Wyaralong Dam, chose to pursue the use of onsite quarried sandstone aggregate instead of importing aggregate. Additional petrographic and XRD analyses and extensive durability tests were undertaken on cores of sandstone and RCC samples, including wet‐dry cycles, soak tests in ethylene glycol, soaks in sodium hydroxide, and heating and cooling cycles. These tests indicated that, if swelling clays are present, they do not impact the durability behavior of the RCC aggregate.
The substantial effort put into testing the sandstone aggregate has paid off for WDA. Not only have the results indicated that the RCC mix performs remarkably well in terms of durability, but the very low modulus of elasticity of the mix has provided exceptional performance in terms of thermal loading; with all the related benefits in reduced restrictions to placement schedule and cooling requirements. Onsite sandstone was not only proven to be a feasible option, it has been demonstrated that it is the best option for the project. Details of the study are provided in this paper.
Keywords: Roller Compacted Concrete (RCC), Sandstone, Aggregate, Clay, Mix, Durability
Keirnan Fowler, Peter Hill, Phillip Jordan, Rory Nathan, Kristen Sih
Although there are considerable uncertainties in the science of climate change, there is a growing recognition of the importance of the issue. Incorporation of climate change impacts is now required in policy guidance from several government authorities and it is prudent risk management to consider the effects of climate change in planning for water resource infrastructure, including assessment and design of dam upgrades. This paper describes the potential impact of climate change on extreme flood estimates and provides a case study for Dartmouth Dam in south-eastern Australia. Three inputs to flood estimation were considered according to the projected impact of climate change; namely design rainfalls, modelled losses and initial reservoir level. The relative influence of each of these factors is explored. Rainfall and losses had a similar (and opposite) influence on results and for this dam the reservoir level prior to the flood event had the largest influence on results. This case study demonstrates that the insights of climate modellers and hydrologists need to be integrated in order to provide defensible estimates of the impact of climate change in flood hydrology studies. Credible projections of changes in design rainfall intensities are required for the full range of exceedance probabilities across Australia.
Application of Available Climate Science to Assess the Impact of Climate Change on Spillway Adequacy