Rob Ayre, Terry Malone
Abstract: Fairbairn Dam with a storage capacity of 1,301,100 ML is the second largest dam in Queensland in terms of water supply capacity. The dam forms the head works of the Nogoa – Mackenzie Water Supply Scheme operated by SunWater in Central Queensland. Completed in 1972, it consists of a zoned earth-fill embankment 49 m high and 823 m in length. The dam has an un-gated ogee spillway crest that is 4.2 m high and 165 m long, with an original design capacity of 15,600 m3/s.
In January 2008, Central Queensland experienced significant flood producing rains which were generated from low pressure systems associated with monsoonal activity across northern Australia. Rainfall totals over the 16,000 km2 catchment area of Fairbairn Dam varied in depth from around 200 mm to nearly 700 mm during a five day period to 20 January 2008. This resulted in the largest outflow from the dam since its construction and the first spill event from the dam since April 1990. While the dam had a significant mitigating impact, there was still major flooding of the township of Emerald, some 19 kilometres downstream.
This paper describes the performance of the dam during the event. Details of the data collected during and after the event, including assessments of spillway performance, dam safety surveillance and the implementation of the Emergency Action Plan will be presented. In particular, the paper focuses on the flood response concerning downstream communities and the resultant flood effects on Emerald and major infrastructure located in the downstream flood plain. It highlights the need for dam owners to have the capability of forecasting inflows and outflows to their structures and how this information contributes to the overall flood response system.
Keywords: dam safety, spillway, flooding, Fairbairn Dam, Emerald, SunWater, Queensland.
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Gregg A Scott
Abstract: The Bureau of Reclamation has been performing quantitative risk analysis as the primary dam safety decision making tool for well over a decade. This paper summarizes some of the key concepts and basic methodology currently used in the dam safety risk analysis process at Reclamation.
Keywords: dam safety, risk analysis, reliability analysis, event trees, subjective probability.
Jerome Argue, Steven Slarke, Douglas Rudd
Abstract: The North Para River Flood Control Dam is an integral part of the works proposed to manage flood risk in the Gawler River, north of Adelaide. Undertaken by the Gawler River Floodplain Management Authority (GRFMA), an authority representing the six local Councils in the area, the flood storage is located on the North Para River, about 10 kms north of Gawler. Roller Compacted Concrete (RCC) was selected for the construction material, based on an assessment of the geotechnical and geological site conditions, together with advantages of reduced cost, time and structure required to pass design flood events. With an overall project cost of $16.1 million, the dam was constructed on time and well within pre-tender budget estimates.
Keywords: flood mitigation, roller compacted concrete, North Para River, construction.
Karen Riddette, David Ho, Mike Phillips
Abstract: Stepped spillways have seen a resurgence in popularity in recent years as new research has better described flow conditions and quantified the energy dissipation capacity of this type of spillway.
While carrying out hydraulic modelling for the Hinze Dam Stage 3 upgrade project using Computational Fluid Dynamics (CFD) analysis, extensive numerical testing and validation of the CFD model for the proposed 0.8H:1V stepped spillway design was undertaken. It was found that for the expected Probable Maximum Flood (PMF) discharge, the high flow depth would result in a non-aerated, non-uniform flow, typically seen in the developing flow region just beyond the spillway crest, occurring over the entire length of the stepped spillway. To date, only limited laboratory studies have been published concerning energy losses in this particular flow regime.
This paper examines the ability of CFD modelling to compute energy dissipation and air entrainment effects in stepped spillways under extreme flow conditions. Where possible, the computed results were validated against limited published data. Some new data obtained by the CFD model is presented for energy loss in the developing flow region that has not been established before.
Keywords: stepped spillway, CFD, energy loss, developing flow.
Elizabeth Gardiner, Len Murray, David Gladwin
Abstract: The Mining Association of Canada has worked over the past 12 years to improve the management of tailings facilities. This effort began out of a realization that tailings present a major business risk to the mining industry, and that a series of major tailings failures around the world in the 1990’s were fundamentally indicative of need for improved care and management practices by tailings dam and facility owners and operators. MAC established and continues to sponsor the Tailings Working Group, which has assisted in development and publication of a three-volume set of guides to improve tailings management:
•“A Guide to the Management of Tailings Facilities”, initially published in 1998, updated edition published in 2008;
•“Developing an Operation, Maintenance and Surveillance Manual for Tailings and Water Management Facilities”, published in 2003; and
•“A Guide to Audit and Assessment of Tailings Facility Management”, published in 2008.
The three guides provide a strong message that the key to safe and environmentally responsible management of tailings is consistent application of sound engineering capability within an effective management framework.
The documents are almost directly applicable to all forms of dams and are widely used for water dams. Also, because the documents are available in Spanish and French they have found wide use in International projects.
A brief comparison with published ANCOLD guidelines is provided.
Keywords: Management of tailings facilities and water dams, Operation, Maintenance and Surveillance, Auditing, risk, safety, guides
Erik Bollaert, Nicola Bretz
Abstract: Gebidem Dam is a 122 m high double curvature arch dam situated in the canton of Wallis, Switzerland. The dam reservoir collects glacier water of the longest glacier in Europe, i.e. the Aletsch glacier (25 km length). The water is very rich in sediment. This results in huge amounts of fine sediments depositing into the reservoir. The 55 m3/s turbined by the Bitsch power station contain between 10 and 13 kg of sand, or an average of almost 40 tons per hour.
Hence, a yearly flushing is organized allowing to release about 400’000 m3 of solid material from the bottom outlets of the dam towards downstream. Moreover, the crest spillway of the dam is frequently used during summer months to release water from the reservoir, resulting in high-velocity jets impacting the downstream plunge pool. The latter consists of a series of flat concrete plates tied together by means of steel anchors and supported by a layer of underlying mass concrete.
Intensive jet impact on this concrete apron within the last 40 years has led to severe damage and, as such, replacement of the apron becomes necessary. The present paper describes the methodology applied for design of a new concrete apron. Especially the interaction between the hydrodynamic pressures exerted by overtopping jets and the steel anchorage necessary to prevent uplift of the new concrete apron is pointed out.
Keywords: scour, concrete apron design, anchorage