The Bureau of Meteorology (the Bureau) is revising the current Intensity-Frequency-Duration (IFD) design rainfall estimates which are an essential component in the design of infrastructure. The current IFDs were developed by over 20 years ago using data from the Bureau’s network of rain gauges and adopting techniques for the statistical analysis of the data that were considered appropriate at the time.
The IFD Revision Project, which will provide revised IFD estimates in November 2012, uses a greatly expanded rainfall database in addition to adopting more statistically rigorous methods that are most appropriate to Australian rainfall data. The revised IFD estimates will be provided for durations from 1 minute to 7 days and Annual Exceedance Probabilities (AEPs) from 50% to 1%. The revised IFD information will be blended with the CRCFORGE estimates developed by each state to enable a smooth rainfall frequency curve to be derived from 50% AEP to 0.05% AEP.
Keywords: Design rainfall, Intensity-Frequency-Duration, IFD .
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Now showing 1-12 of 40 2976:
David Stephens, Kristen Sih, Peter Hill, Rory Nathan, David Dole
The spring and summer of 2010-11 were characterised by severe flooding affecting much of Victoria. In a number of cases, communities downstream of large dams developed to supply water for irrigation and critical human and stock needs were significantly impacted. Following the floods, the Victorian Government commissioned the Victorian Floods Review (VFR) to consider the total warning and response to these floods. Whilst dam operations were not specifically included in the terms of reference, overwhelming community interest lead to the VFR commissioning a high level review of the way a number of key dams were operated during the floods. This review identified some of the inherent tensions in the legislative framework for water harvesting, storage and dam safety in Victoria. These tensions were often matched by the conflicting expectations of the public living immediately downstream of the dams versus those dependent on the water resource stored in the dams. The final report of the VFR was handed down in December 2011 and contained a number of recommendations specifically for dam owners. These recommendations are reviewed and discussed in light of both the legal and public relations ramifications for owners and operators of large water supply dams. An overview is also given of the operational constraints to downstream flood mitigation facing many dam owners. Such constraints are typically imposed by the type of dam (i.e. fixed crest), relatively small storage and outlet capacities when compared to flood volumes and limitations on the reliability of forecast rainfall information. Some possible ways of overcoming these constraints are identified and discussed.
Keywords: Flood, mitigation, Victorian Floods Review
Shane McGrath, Andrew Reynolds, Garry Fyfe, Chris Kelly, Steven Fox
Goulburn-Murray Water is a rural water corporation located in Northern Victoria. It has responsibility for 12 State dams and is also the constructing authority for the Murray Darling Basin Authority’s Victorian assets.
Over the past 15 years G-MW has been engaged in a dam improvement program across its portfolio. To date 14 individual projects have been undertaken at 11 dams. The total expenditure is $125 million.
Starting from a base level of data at its inception in 1997, the program has encompassed all facets required for a dam improvement program. From early prioritisation to set the investigation program, through design reviews and risk assessments to develop the upgrading program and subsequent implementation. Some elements of the program were at the leading edge of practice at the time and a range of experiences along the way were character building as dam safety investment challenged other corporate priorities.
This paper sets out the lessons learned in developing the methodology and implementing the program of works, particularly relating to corporate adoption of the program, organisational capability, investigations, risk assessments, design and implementation.
Richard R. Davidson, Nate Snorteland , Doug Boyer, John France
The US Army Corps of Engineers (USACE) has embarked upon a monumental journey in applying risk-informed decision making in the management of the safety of the 650 major dams for which it is responsible. This process has shifted safety criteria from fully deterministic to a probabilistic basis. There has also been a shift from de-centralized district-based decision-making to centralized management of resources through the new Risk Management Center (RMC) and the Senior Oversight Group (SOG), a group of senior engineers and managers from across the USACE organization. The risk process began about five years ago with a portfolio prioritisation using screening-level risk assessments of the entire dam inventory, culminating in Dam Safety Action Classifications (DSAC) for each of the dams. Based on this risk prioritisation, Issue Evaluation Studies (IES) were initiated for the highest risk DSAC I and II dams, with each study including detailed failure mode and risk analyses for each dam. Because the Corps was relatively new to dam safety risk analyses, and their dam design history was one of following codified manuals of practice, various risk tools were prepared to provide guidance when assessing the risk of potential static, seismic and flood failure modes, as well as life loss and economic consequences of dam failure. Although these tools provided useful guidance to a relative large population of inexperienced risk estimators, many of these early risk assessments were flawed; they provided unrealistically high estimates of failure probabilities and the tools did not help estimators understand or explain each failure mode. To assist the RMC in bringing more defensible risk estimates to the table and improve consistency of the evaluations, the Quality Control and Consistency (QCC) review process was initiated about two years ago. The QCC process provides high level review of IES activities, including detailed reviews of risk analyses, by a small group of experienced dam safety risk estimators. Not only has this brought risk estimates into a more reasonable range, it has provided valuable training for risk estimators, and important checks and balances on the risk-informed decision making process for moving dam safety upgrade projects forward. The justification for a number of very expensive projects has been challenged and, in some cases, re-prioritised, and other projects have risen to the prominence they deserve.
Penelope Shaw, Brian Walford, Daniel Yates
The Bowen Basin is one of Australia’s economic mining powerhouses. Key to the mining of coal is the efficient management of the available water resources. For many years drought has meant that coal mines have had to manage operations with low quantities of water. For a new mine, this involved sophisticated hydrologic modelling as part of staying in business. In recent years a turnaround in weather conditions and changes to discharge permissions have meant that mines have too much saline water!
The paper describes how one mine augmented its small system of storages with a new dam and pumping system to meet regulatory requirements. Although not a large dam, the challenges confronted are shown to be similar to those involved in the delivery of much larger projects, all related to the power of water.
Keywords: Design storage allowance, water management, challenges, environmental protection, mining dams, automated pumping systems, spillway upgrading.
Sofia Vargas, Robert Wark
Logue Brook Dam, 130 km south east of Perth, was completed in 1963 and comprises a 49 m high main embankment with a crest length of approximately 335 m and the reservoir impounds 24.59 GL of storage. The outlet works comprise an inlet tower, an outlet pipe (DN 1100 mm) and a valve house. Water from the dam is released through a clam shell valve and there is a sluice valve upstream of the clam shell which acts as a scour isolation valve.
Previously Logue Brook Dam supplied water into the Harvey irrigation system by releasing water down the river which was then drawn off downstream and pumped into the piped network. The scheme planning had identified that constructing a pipeline from the dam outlet to connect directly into the piped irrigation system would eliminate the need for pumping as the system could then be gravity fed directly from the dam.
The outlet works upgrade comprised the refurbishment of the Inlet Tower, refurbishment of the Valve House, installation of new valves, environmental release and magnetic flow meters, electrical, communications, SCADA, instrumentation and security upgrades.
This paper describes the diving inspection and above water inspections of the inlet tower, refurbishment of the existing installation, challenges of the design, adopted solutions, connection to the Harvey Water pipeline and construction issues. The project represents an interesting case history of improving dam safety standards to current ANCOLD guidelines to provide a modern and safe facility.
Keywords: Outlet works, diving, OH &S Issues, safety, deterioration