J.H.Green, C.Beesley, C.The, S.Podgerand, A.Frost
The ability to estimate design rainfalls for probabilities rarer than 100 years or 1% Annual Exceedance Probability (AEP) is an essential part of dam hydrology. The earliest means of estimating rare events consisted of a pragmatic curve fitting procedure between the 50 and 100 year design rainfalls and the Probable Maximum Precipitation. In the 1990s a more rigorous method of estimating design rainfalls as rare as 2000 years was developed – the Cooperative Research Centre – FOcussed Rainfall Growth Estimation (CRC-FORGE) method. CRC-FORGE estimates were derived for Victoria in 1997 followed progressively by each of the other states. Over the subsequent two decades CRC-FORGE estimates were an integral part of the risk assessment of large dams – being used to determine the AEP of the Dam Crest Flood.
The Bureau of Meteorology will soon release new rare design rainfall estimates for probabilities to 2000 years. The new rare design rainfalls are a significant improvement on the CRC-FORGE estimates as they have been derived using up to date data; contemporary analytical techniques and a method that is consistent across Australia.
However, there are differences between the CRC-FORGE estimates and the new rare design rainfalls. These differences do not constitute a systematic change to the CRC-FORGE estimates but rather vary with location; duration and probability. The results of a detailed comparison between the CRC-FORGE estimates and the new rare design rainfalls are presented together will an assessment of the possible impacts on previous estimates of the AEP of the Dam Crest Flood.
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The National Seismic Hazard Assessment 2018 (NSHA 18) project intends to revise the existing seismic hazard map (AS1170.4 2007) for Australia. Geoscience Australia (GA) are leading the project along with a consortium of seismologists, geologists and earthquake engineers.
The NSHA 18, due to be released in 2018 is of great importance to dam owners and operators. The project intends to incorporate a comprehensive approach to seismic hazard, particularly in modelling uncertainty and variability.
The Global Earthquake Model (GEM) is an international consortium of scientists, engineers and policy makers. One of the primary aims of GEM is to provide a uniform set of tools for analysis in seismic hazard and risk. GEM was established to provide a framework for global standards in comparing risk analysis, awareness and actions in an effort to increase resilience to vulnerable communities.
The NSHA 18 will use the GEM framework in order to meet its own objectives for the new upcoming hazard map. The Seismology Research Centre will contribute to the NSHA 18 in three areas. Firstly, to produce a unified earthquake catalogue where GA will homogenise magnitudes to a uniform scale. Secondly, to produce a number of applicable alternate seismotectonic models, and thirdly, through the contribution of ground motion data collected over the last forty years within Australia.
There is a significant body of knowledge in relation to assessing the impacts of earthquakes on earth and rock fill dams which has led to a number of widely recognised and accepted methodologies for the calculation of potential deformations from an earthquake event. However, limited research has been conducted into the assessment of blasting impacts on earth structures. This has led to an adoption of earthquake analysis methods in the assessment of blasting impacts on earth structures without adequate consideration to the difference between the stresses and displacements imposed on an embankment as a result of a blast as opposed to an earthquake. Adopting earthquake analysis techniques may result in conservative vibration limits being imposed when undertaking blasting near embankment dams which may have negative financial impacts.
This paper explores the risks associated with blasting adjacent to earth fill dams and details the difference between stresses and displacements imposed on an embankment by a blast versus an earthquake.
This paper also discusses previously adopted approaches to assessing potential impacts associated with blasting and the limitations associated with adopting a pseudo-static and simplified permanent deformation analysis for blasts modelled as equivalent earthquakes. Finally, the paper proposes an alternate risk based analysis approach.
Sean Ladiges, Robert Wark, Richard Rodd
The use of permanent, load-monitorable post-tensioned, anchors for dam projects has been in place for approximately 35 years in Australia. Since then, over 30 large Australian dams have been strengthened using this technology, including the world record for anchor length (142 m – Canning Dam, WA) and size (91×15.7 mm strands – Wellington Dam, WA and Catugunya Dam, TAS).
In order to achieve the design life of 100 years expected of these anchors, an ongoing program of monitoring, testing and maintenance is required, to identify and rectify the initiation of corrosion or loss of pre-stress. Guidance for maintenance and testing regime for post-tensioned anchors in dams is provided in the ANCOLD Guidelines on Dam Safety Management (2003). The various conditions which may affect the performance of the anchor with time, such as anchor type, ground condition and loading fluctuations are not covered in the Guideline.
This paper reviews the implementation and results of anchor monitoring programs by Australian dam owners. The first part of this paper provides a summary of the testing and monitoring programs currently being implemented. The second part of the paper reviews the aggregated anchor load test results from a number of Australian dam owners, and identifies trends in anchor response over time following installation.
The paper aims to assess whether the recommended anchor testing regime proposed in ANCOLD (2003) is appropriate and cost effective, using evidence from recent load test data which has become available following the writing of the guideline. The lessons learnt from anchor maintenance programs will also be discussed.
Assoc. Prof. Shu-Qing Yang
Next to air, freshwater has been always considered as a key resource, central for economic development and human’s basic needs. Currently the total population is about 7 billion, and by 2050, global population is projected to be 9 billion. An additional 10 more Nile Rivers are needed, and the water demand is increasing steadily and significantly. The dams industry has successfully solved the water deficit problems in many places for most of the time, but more and more countries and regions are gradually resorting to other emerging technologies like desalination, wastewater recycling and rainwater tanks etc. as they believe that a dam is the 20th century technology and has too many significant negative impacts. However, available data show that the global water consumption is only 5~6% of annual runoff, e.g., Australia’s water use is about 20km3, but the runoff lost to the sea is up to 440km3. A coastal reservoir is a freshwater reservoir inside seawater, aimed at the development of freshwater from the sea without desalination. The 1st generation of coastal reservoir has emerged in China, Singapore, Hong Kong and Korea successfully, but generally its water quality is not as good as that in inland dams. The 2nd generation of coastal reservoirs has been developed and its water quality is at least comparable with the water in existing reservoirs like Warragamba dam. The application of coastal reservoirs in Australia is discussed and the feasibility is investigated. The preliminary designs of coastal reservoirs in SE Queensland, Sydney, Melbourne, Adelaide and Perth show that the coastal reservoir is a feasible and effective technology for Australia’s water crisis.
Ryan Singh, Bob Wark
For existing dams built before modern theories and understanding of soil mechanics were fully developed, it was often the case that comprehensive investigations into the properties of the embankment and foundation material were not carried out. With more stringent dam safety requirements and engineering criteria, and a better understanding of soil mechanics, it is necessary to undertake embankment and foundation investigations on such dams, with the view to gain a better understanding of the embankment and foundation conditions.
This paper details the method used for a risk-based assessment of a dam’s stability against slope failure for steady-state seepage conditions, based on a probabilistic assessment of differing interpretations of the material properties for the foundation. To achieve this, several separate interpretations of material strength models were developed for a foundation, using various subsets of available tri-axial data. The mean strengths of these models were used to assess the stability, and to account for the variation in strength properties of each model, the sampling distribution of the mean was used to assess the likelihood of failure.
Finally, an event-tree type risk analysis was used to calculate a value for the probability of slope failure.
A case study has been presented using this method.