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
Ted Montoya, David Hughes, Orville Werner
The existing Hinze Dam was raised beginning in 2007 to increase water storage capacity, improve its ability to regulate floods, and raise the level of structural safety as compared to the current dam. As part of the 15 m raise of Hinze Dam, the existing 33 m high spillway structure was raised using mass concrete. This new composite structure was constructed as a downstream raise, placing mass concrete on the downstream and top of the existing spillway. The designers of the composite spillway structure developed a finite-element model to consider the early expansion and subsequent slow contraction of the new concrete against the existing concrete. The temperature rise of the new section of mass concrete had to be monitored and controlled to reduce the tensile strains along its interface with the existing spillway, and differential temperatures had to be limited to avoid cracking of the new mass section. Low-heat cement for a conventional mass concrete mix was not readily available so a mix was developed using local materials.
Typical mass concrete dams are monolithic structures constructed with lowheat cement. The Hinze Dam spillway design was predicated on the use of materials readily available. The paper presents the assumptions, methods, and criteria that were used in developing the mass concrete mix. It also presents the means and methods for tracking temperature gain during construction of the raised spillway, and how temperature was influenced by placement temperature, construction sequencing, and seasonal conditions. Lastly, the paper will compare the actual performance of the mix with the design analysis, laboratory testing, and finite element studies that were performed during the design.
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.
Justin Howes, Peter Amos
For many years Mighty River Power has operated an intensive Dam Safety Assurance Programme with respect to our nine large hydro assets, a unique run of river cascade system built between 1927 and 1972. From 2001 to 2007 the Arapuni Foundation Enhancement Project was a high profile activity, but there has also been much dam safety analysis and minor mitigation work that could be classified as “Business As Usual Dam Safety Activity” – this paper seeks to give a high level overview of the work carried out from 2000 to 2010. Items covered include; an overview of the hydraulic structures, their hydrological and geological setting, and the current dam safety regime. Examples of typical issues identified by the Programme are given on a structure by structure basis along the river. Seismic, Flooding, Emergency Planning, Documentation, Monitoring, Control, Electrical and Mechanical type issues are covered.
Peter A Ballantine, Christopher V Seddon
Massingir Dam, constructed in the late 1970’s on the Olifants River in Mozambique, is a 48 m high zoned earthfill dam. Due to various safety concerns, the dam was operated at a reduced full supply level of 110 masl, compared to the design full supply level of 125 masl. Between 2004 and 2006 remedial works were undertaken, including the construction of a berm on the downstream face of the dam, grouting and drainage of the foundations and installation of the spillway crest gates. From December 2005 the storage level of the dam was allowed to increase.
On 22 May 2008, with the reservoir storage level at 122.43 masl and the gates on the outlet conduits closed, the reinforced concrete conduits failed at the downstream end, releasing an estimated 1,000 m3 /s of water into the Olifants River.
A 2-D finite element analysis was undertaken in order to establish the safe load bearing capacity of the as-constructed conduits. On the basis of the analysis, it was concluded that the original design did not take proper account of the pressure that would develop within the thick concrete sections of the conduit. In view of assumptions regarding the load paths, the reinforcement was not placed in the most appropriate positions.
This paper describes the events leading up to the failure of the conduit, presents the findings of the investigation into the failure and makes recommendations on the basis of the findings.
Karen Riddette, David Ho
Recent dam safety reviews of a number of Australian dams have identified that the arms of raised radial gates may be partially submerged by extreme flows which exceed the original design flood for the dam. Various design solutions have been proposed to secure and strengthen the radial gates, however an important concern is the potential for flow-induced vibration. Under extreme flood conditions, flows near the gate arms will be high-velocity, free-surface, with a steep angle of attack on the arm beams. Traditional hand calculations for computing vibrations are of limited applicability in this situation, and there is little published data available for this combination of flow conditions and arm geometry. A detailed study using CFD modelling of the potential for vibration around radial gate arms was carried out for Wyangala Dam. This paper presents the results of the validation and reveals some interesting flow patterns and vortex shedding behaviour.
Assessment of flow-induced vibration in radial gates during extreme flood