The entire historical record of rainfall archives held by the Bureau of Meteorology over the region of Australia affected by tropical storms has been examined and the extreme storms have been extracted. From this database, we account for site specific effects (moisture and topography) from each of the storms, allowing us to compare storms amongst each other. This then allows us to construct a theoretical maximum precipitation in a generalised sense. By then returning the site specific information for a particular region, we can infer the probable maximum precipitation at this location.
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Now showing 1-12 of 27 2964:
M. B. Barker and D. Holroyde
A detailed study was completed for the Stage 2 works of the Grahamstown Dam augmentation to investigate various alternatives for the slope protection of the Saddle Dam and Subsidiary Dam embankments, including a standards based and a risk management approach. The standards based approach required an evaluation of the slope protection level and least cost option based on the hazard rating of the dam. Due to the sand construction of the embankments, it was possible to apply a wave erosion model SBEACH to develop an economic risk model for optimising the slope protection alternatives. The erosion model included the effects of the wind direction, reservoir level and wind speed variation during flood events, embankment profile and material parameters. The risk management approach clearly showed that significant cost savings could be achieved by using the risk management approach. Furthermore, the cost curves indicated the sections of the embankments for which present capital works would not be economically justified and for which ongoing maintenance works would be economically advantageous.
Jack Rynn, John Pix, Garry Grant and Albert Hill
Ground motions resulting from seismic activity can cause significant damage to existing dams. For this reason, monitoring of seismic activity is an important component of a dam safety management program. Similarly, the long term gathering of data on regional seismic activity provides a sound platform for structural adequacy checks of components of existing dams under seismic loading, as well as for future dam design. In this context, the South East Queensland Water Corporation Ltd (SEQWater) and its predecessors have been monitoring earthquake activity in relation to the Wivenhoe, Somerset and North Pine Dams in South East Queensland since 1977. In 1998, SEQWater upgraded the seismic instrumentation with a digital telemetered seismic surveillance system (DTSSS) six-station network to replace the original analogue seven-station network. This state-of-the-art instrumentation was supplied and installed by Nanometrics Inc., Canada through an international tendering process. This paper presents an overview of the DTSSS, results to date and future planning for an integrated strong ground motion accelerograph network.
I. R. Forster
Lyell Dam is a concrete-faced rockfill dam, located on the Coxs River, near Lithgow, NSW. The dam forms part of the Coxs River Water Supply Scheme, which supplies water to Delta Electricity’s Wallerawang and Mount Piper Power Stations. In 1994, the spillway capacity of the dam was upgraded, and the storage augmented with the addition of two 40 m long by 3.5 m high inflatable rubber dams to the spillway crest. An automatic deflation system, controlled by a programmable logic controller, was installed to provide a staged bag deflation sequence during flooding, and hence minimise the downstream impact of rubber dam operation.
Although the rubber dams and control system initially operated as designed, more recently, two uncontrolled bag deflations have occurred, which have caused flooding downstream and loss of significant storage volumes. In the first incident, a spontaneous uncontrolled deflation of the rubber dams released about 1600 ML, before the bags re-inflated automatically. An investigation revealed that the incident was most likely the result of design deficiencies in the control system. Recommendations were made for improvements to the system.
During the most recent deflation, one of the rubber dams failed by spontaneous rupture, and approximately 6000 ML of water was released from the dam. The Dam Safety Emergency Plan was activated to ensure persons at risk downstream were notified of the impending flood wave. A post- failure inspection of the ruptured bag suggested that the likely cause of failure was a manufacturing defect, which allowed air to penetrate the layers of rubber forming the bag. The rupture most likely occurred when the resulting air pocket expanded on exposure to the sun.
The paper examines the two deflation incidents in detail, and analyses the emergency response to the second incident.
Failure modes and effects analysis (FMEA) has been increasingly utilised to prioritise and investigate dam safety deficiencies. It can be used to enhance dam safety programmes. Dam Surveillance, O & M procedures, and emergency plans can all be evaluated for their effectiveness in detecting and mitigating the applicable failure modes for a dam. Experience with a workshop process to carry out this evaluation and some of the improvements that have been identified are described.
This paper describes the use of a high strength woven geotextile and preloading to stabilise the surface of a very low strength tailings pond, and the incorporation of a geosynthetic clay liner (GCL) within the final capping design to complete closure. The pond, which contains tin and copper tailings, formed the lower tailings containment area of a three-tiered tailings storage, located directly above the Wild River in North Queensland. Stabilising the lower pond (area 2,500 m2), which contained tailings of “zero strength” in the central area involved the placement of a woven geotextile over the surface, which was anchored around the perimeter. The placement of finger berms (preloading fill) on the geotextile was successful without exceeding the bearing capacity of the tailings overall. Settlements of the berms were closely monitored to allow the system to support construction plant. After the finger berms were joined, they were widened until the area was covered. A sand layer was then placed over the area followed by a GCL to form an impermeable barrier prior to the placement of clay and topsoil.