Rick W. Schultz P.E.
The Corps of Engineers Risk Management Center is undergoing a nationwide assessment of its navigation and flood control projects. Development of the methodology and tools used to determine probability of failure of mechanical and electrical systems for dams is being presented in this document. Development of the Weibull formulas for specific use in dam will be addressed along with use of fault tree analysis to determine system reliability.
Keywords: Dormant-Weibull Formula, Fault Tree, Characteristic Life of Components, Beta Shape Parameters, Inspection intervals.
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Now showing 1-12 of 41 2974:
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.
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.
An essential criterion for any new dam project in Australia is to provide for passage of fish past the structure in both the upstream and downstream direction. In recent projects with a relatively high barrier this has been provided by mechanised systems such as locks, lifts or a combination of both.
A nature-like fishway provides for passage of fish past a barrier by applying some of the features of natural streams. The concept has been increasingly applied to fishway designs in North America and Europe. A nature-like fishway will provide variable flow depths, velocities and turbulence across its width and along its length and is constructed using natural materials to simulate the natural stream characteristics. The variable flow conditions coupled with the use of natural materials inherently result in different channel substrates that support the passage of a large range and size of fish species as well as other aquatic species. Where fish habitat has been depleted, a nature-like fishway can also supplement and enhance aquatic habitat.
The performance of nature-like fishways can be difficult to quantify due the very nature of the system. However, qualitative assessments in North America are indicating that a wide range of species are using such fishways and that fish species that were previously extirpated from rivers are again migrating.
The nature-like fishway concept has been applied to in-stream structures up to four metres high in the eastern states of Australia. However, the substantial progress made with this design in North America and Europe has not as yet been applied in this country.
This paper analyses the advantages and disadvantages of nature-like fishways over mechanised systems, such as locks and lifts, and makes an assessment of the suitability of the concept to dams in Australia with relatively high walls.
Kristen Sih, Peter Hill, Susan Ryan, Siraj Perera
Although ANCOLD provides guidance on good dam safety practices, in Australia it is the State and Territory Governments’ role to protect the public from dam safety incidents and in many cases these jurisdictions have legally binding regulations in place that dam owners must adhere to. This paper presents a comparative analysis of the dam safety regulations currently in place for Australian states, as well as selected international jurisdictions. The limit of applicability of the regulations, number of dams regulated, content of the regulations and powers and responsibilities of the regulator are all compared. It was found that there is a large range within each of these categories with regulatory approaches varying from light-handed and objective based, to highly prescriptive. The extent to which risk management principles are used in the regulations for each jurisdiction has also been investigated. It was found that in jurisdictions where higher hazard category dams account for a higher proportion of dams being regulated, risk analysis is included in the regulations. Finally, the ANCOLD societal risk criteria and ALARP considerations have been compared and contrasted with those from international jurisdictions and other hazardous industries.
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.