A. Swindon, M. Gillon, D. Clark, P Somerville, R. Van Dissen and D. Rhoades
The 45 km long Lake Edgar Fault in south-west Tasmania passes through the right abutment of the Edgar Dam and into Lake Pedder, and within 30 km of three other large dams. In 2004 an independent seismotectonic study concluded that the fault had moved three times in the past 48–61,000 years, with the last movement around 18,000 years ago.
In order to better constrain the risk assessment for the nearby dams, the likelihood of a rupture recurrence along the fault was required. Two independent methods were investigated. The first was a comprehensive review of active faulting and deformation of stable continental region faults within Australia, and a comparison with similar faults worldwide with the well studied behaviour of the Lake Edgar Fault. The study results demonstrated the episodic nature of stable continental region fault activity, separated by much longer periods of quiescence, with a decreasing likelihood of rupture following each event within an active period. The time window of applicability of this paleoseismological study is thousands to tens of thousands of years.
The second study looked for evidence of precursory seismic activity in the vicinity of the fault which could indicate an increasing risk of rupture over the next decade or so. This method does not predict specific earthquakes, but does forecast whether the level of future earthquake activity in the short to intermediate term is relatively low, high or at an average level. Using a catalogue of seismic activity for south-eastern Australia, the study concluded that there is no evidence for precursory seismic activity in the area of the Lake Edgar Fault that would give rise to an elevated forecast rate of occurrence of moderate magnitude earthquakes either in the short to intermediate term. This precursory method has a window of applicability of a decade to perhaps several decades.
The combination of these two studies has advanced the understanding of the Lake Edgar Fault activity by both setting it in the long-term stable continental region fault context and investigating the presence of short-term behavioural activity. This has allowed the seismic hazard to be re-assessed as nearer to ambient levels than earlier postulated. This work has applicability for other fault scarps in Australia, both with regards to better defining the long-term hazard (103-105 years) posed by a fault, and potentially also giving advance (short-term 101 years) notification of increasing risk of fault rupture. Better long- and short-term hazard information allows more complete and thorough engineering decisions to be made.
Keywords: Earthquake, seismic, fault rupture, dam safety, risk assessment, Hydro Tasmania, Lake Edgar Fault.
Now showing 1-12 of 17 2971:
Bruce Walpole and Craig Scott
Monitoring and surveillance is crucial to managing the ongoing performance of dam structures.
The true value of appropriate monitoring, surveillance and review processes is only realised when
potential dam safety issues arise. TrustPower’s civil safety monitoring and surveillance program
includes nineteen hydro schemes throughout New Zealand and incorporates structures with
Potential Impact Classifications (PIC) ranging from Low to High.
TrustPower promotes a continual improvement policy on its management of safety issues and
conducts inspections on a regular basis. Routine and periodic independent inspections of the key
components within a scheme are paramount to the viability of the safety management system. The
importance and purpose of these inspections has recently been highlighted by the discovery of two
sinkholes on the face of the earth dam associated with the Cobb hydro electric power scheme.
This paper provides an example of the need for continual monitoring and surveillance, vigilance
of observations, good archiving systems and documentation. It discusses the broader issues
surrounding the subsequent response processes to potential dam safety deficiencies, and the
success (or otherwise) of investigative methods. It also highlights that an adequate dam safety
compliance system has commercial value as there is a measurable reduction in dam performance
uncertainty and hence greater efficiency in the speed at which accurate resolutions can be drawn.
Keywords: Dam safety, embankment, sinkholes, foundations, dam drainage, geophysical
Mike Marley, Greg Dryden, Geoff Eades, Edwin Brown, and Gary Huftile
Traveston Crossing Dam is proposed for construction at AMTD 207.6 km on the Mary River, about 25 km upstream of Gympie in South East Queensland. The Mary Valley at the dam site is located in a zone of complex geology resulting from formation in a tectonic accretionary wedge setting. This has been responsible for its complex geological structure, which has required a range of geological and geotechnical investigation and interpretation techniques to develop a model on which to base the dam’s preliminary design. This paper describes the tectonic history and the innovative techniques used in developing the geological model for the dam foundation.
The investigation involved aerial photograph interpretation, geological mapping; geotechnical drilling, including water pressure testing; seismic refraction profiling; downhole geophysical logging; excavation and geological mapping of large excavations; and hydrogeological investigation involving investigative drilling and pumping tests.
A Vulcan 3-D computerised geological model was constructed using borehole data, seismic refraction interpretation and downhole geophysics interpretation. The geological model has been used in the development of the preliminary design and confirms that the foundations are suitable for the proposed structure.
Keywords: Dam Foundation; Geophysics; Investigation Tectonics; Geological Strength Index Kinetic Analysis
Paul Hurst, Tom Ewing, Steven Fox and Bob Wark
For an ogee-shaped spillway crest, it is well recognised that sub-atmospheric pressures will develop on the lower-nappe profile for operating heads greater than design head. This effect is useful in providing an increase in efficiency of the spillway discharge for small increases in operating head. However, there is limited data on the formation of sub-atmospheric crest pressures for high-head operation above 1.3 times greater than the design head
This paper reports on modelling work done by GHD and the Water Corporation for the Wellington Dam Remedial Works Project in Western Australia where the current design flood has increased to more than twice the original design head. Two-dimensional physical scale modelling and 3-D Computational Fluid Dynamics (CFD) modelling of the existing Wellington Dam spillway profile was carried out to determine the discharge coefficient and uplift force generated by the formation of sub-atmospheric crest pressures under high-head operation.
The paper compares the results of the physical scale model and the CFD model and earlier published data by Cassidy (1970) and concludes that there exists a good correlation between the three data sets.
Keywords: Ogee, sub-atmospheric, crest pressures, Wellington Dam
Dörte Jakob, Robert Smalley, Jeanette Meighen, Brian Taylor and Karin Xuereb
Probable Maximum Precipitation (PMP) is one of the required inputs for estimating the PMP design flood. In estimating the PMP, currently no allowance is made for long-term climatic trends. A 2-year project funded jointly by the Australian Greenhouse Office and the Queensland Department for Natural Resources and Water, and with in-kind contributions by the Bureau of Meteorology began in May 2006. This study aims to assess how climate change might affect estimates of PMP. Preliminary results from this work will be presented.
Changes in factors used in PMP estimation, such as storm type and depth-duration-area curves, were assessed using a storm database covering the period 1893 to 2001 (Beesley et al. 2004). Based on the last 50 years, there is little evidence to support the notion that tropical cyclones (connected to major rainfall events) are penetrating further south or have become more frequent. A recent event that led to widespread flooding (Gold Coast, June 2005) was found to have very high storm efficiency. Changes in observed and projected moisture availability were assessed on the basis of a high-quality dataset of surface dewpoint temperatures and climate model output.
It is assumed that PMP received by a catchment is not uniformly distributed over a catchment but rather follows a typical spatial pattern. A pilot study to revise design rainfall estimates is currently under way at the Bureau of Meteorology. The methods developed in the pilot study were used to assess whether the spatial distribution of design rainfall estimates might be changing under a changing climate.
Keywords: Probable Maximum Precipitation, climate change, moisture availability, storm efficiency
Mike Phillips and Karen Riddette
The use of Computational Fluid Dynamics (CFD) models in the dams industry has increased significantly in recent years and conversely the use of physical hydraulic models has decreased. Typical design approaches for an upgrade of similar magnitude to the Hinze Dam Stage 3 project would have allowed for considerable time to develop a preliminary spillway design before hydraulic modelling was introduced, potentially requiring only one type of model. So is there a need for both types of models?
Because of the complex hydraulics associated with the spillway required for the Hinze Dam Stage 3 raise and accelerated schedule, the utilisation of CFD and 1:50 Froude Scale physical hydraulic models was necessary. Both models were constructed independent of each other. Both models complemented each others strengths and weaknesses, and each provided critical information at the following different stages of design:
• Spillway selection and conceptual design stage – the CFD model results were highly valuable in steering the selection of spillway type and configuration, particularly with visual representations of the ranges of flow for each spillway option.
• Preliminary design – in a one week period, 90 to 95% of the final spillway layout was resolved with interactive modifications of the physical hydraulic model.
• Detailed design – both the physical hydraulic model and the CFD model were utilised to determine water pressures, velocities and water surfaces and evaluate cavitation potential as input to detailed design.
In the case of the Hinze Dam Stage 3 project, it was highly advantageous to utilise a CFD and physical hydraulic model to achieve the design outcomes at each phase of the design. The dual-model study approach also provided advantages for project management of the design and stakeholder involvements.
Keywords: Computational fluid dynamics, CFD, physical hydraulic model, spillway, hydraulics