S. Suter, G. Singh, and M. Britton
Today, many organisations rely on hydrodynamic modelling to assess the consequences of dam break failure on downstream populations and infrastructure. The availability of finite volume shock-capturing schemes and flexible mesh schematisations in widely used software platforms imply that dam break modelling projects will be carried out differently in the future: Finite volume based platforms allow widespread application of shock-capturing methods and flexible mesh platforms can represent features in the study area more realistically and are more flexible thanks to varying mesh resolutions. Furthermore, the recent adoption of Graphics Processing Unit (GPU) technology in mainstream scientific and engineering computing will also significantly decrease computation times at relatively low cost.
This paper examines the application of finite volume, flexible mesh and GPU technologies to dam break modelling. One-dimensional (1D) modelling results are compared to those from two-dimensional (2D) finite difference and finite volume approaches. The results demonstrate that there are differences between modelling approaches and that the computational speeds of 2D simulations can be significantly reduced by the use of GPU processors.
Leonard Wiliem, Rob Keogh, and David Thomas
Progressive rope creep on the steel ropes which hold 14 counterweights in tension on the seven spillway gates was monitored regularly. The 2011 annual inspection identified that the creep had taken the lower guide wheels of the suspended counterweights beyond the extent of the wheel guides.
A programed project to extend the guides was delayed due to Workplace Health and Safety concerns on confined access and working under a suspended load. A study was commissioned to deliver a safe method of extending the guides. Because regular testing and two flood events had proved the gates were functioning well, the risk of failure in gate operation during flood event was considered low and a lower priority was assigned to rectification work.
Callide Dam is a SunWater owned dam located in Central Queensland. It has a similar spillway gate mechanism as Coolmunda Dam. The only difference is that Callide Dam gates work in pairs with one counterweight attached to each gate.
In January 2013 due to heavy rainfall caused by the ex-cyclone Oswald, Callide Dam experienced a flood event which triggered a gate operation. During the draining phase, the gates operated abnormally sustaining damage to the structure and to the automatic gate opening mechanism. SunWater undertook investigations to identify the cause of the abnormal operation and found that the primary cause of the gate abnormal operation was due to jamming of the suspended counterweight on the end of the guides. This was due to cable stretched over 26 years of service to the extent that the lower wheel assembly was beyond the guide rails at the time of the flood event.
The event at Callide Dam was a wake up call for SunWater to re-evaluate the risk assessment for Coolmunda Dam. This re-evaluation recommended to assign the highest priority on the rectification of the wire rope creep issue on the radial gate as the risk of failure in gate operation during flood event was high.
This paper discusses the actions in re-evaluating the risks at SunWater’s Coolmunda Dam and the measures taken to quickly undertake remedial action on both dams and the challenges involved with each.
William Ziegler and Heather Middleton
This paper presents the collation of over 20 years of data on vertical and horizontal movements around Cataract Dam in the Southern Coalfield of New South Wales, reporting subsidence that continues 25 years after extraction in the area ceased. The occurrence of increased vertical movement over old goaf areas as the result of extraction in the same seam at greater than 1km distance has been observed. Together with a change in the behaviour of measured head of water 6 years after extraction ceased in the area. These points raise the question, how long should subsidence monitoring continue after extraction has ceased in areas of important infrastructure?
Wark, Bob; Thomas, Louise
This paper discusses the rating curves developed for several case studies from the Pilbara and Kimberley, including the Harding Dam, Moochalabra Dam and Ophthalmia Dam. The paper will discuss the impact of underestimated rating curves on the design of infrastructure. An example has occurred at Harding Dam where the pump station was designed to be inundated at a 1:100 AEP and this is now estimated to occur at a lower AEP. The paper will also discuss methods to improve the accuracy of rating curves and the challenges associated with determining accurate rating curves.
This paper outlines lessons learned from 8 years of regular operations and testing of 111 gates at 22 sites. It points out that the implementation challenges involved are not only technological in nature, but also encompass human factor and organizational issues. This is perhaps understandable since the initiative is part of the cultural shift to sustain gate reliability long-term.
An increase in gate testing frequency has led to the identification of more performance anomalies, ranging from deficiencies to operational failures. This finding may not be unique to a single dam owner. It leads to the following question to the general dam owner community: Are we testing our gates enough?
Janice Green, Cathy Beesley, Cynthia The, Catherine Jolly
Design rainfall estimates are essential inputs to the design of infrastructure such as gutters, roofs, culverts, stormwater drains, flood mitigation levees and retarding basins. They are also integral to large dam spillway adequacy assessments undertaken to determine the flood magnitude that existing dams can safely withstand.
The previous design rainfall estimates for probabilities from the 1 year Average Recurrence Interval (ARI) to the 100 year ARI were derived by the Bureau of Meteorology (the Bureau) in the early 1980s using a database comprising primarily of Bureau raingauges and techniques for statistical data analysis that were considered appropriate at the time. More recently, estimates of rare design rainfall estimates for probabilities from 100 year ARI to 2000 year ARI have been derived for each state, with the exception of the Northern Territory, using the CRC-FORGE method.
As part of the revision of the 1987 edition of Australian Rainfall and Runoff: A Guide to Flood Estimation being undertaken by Engineers Australia, the Bureau conducted a five year project to revise the design rainfall estimates for probabilities from 1 year ARI to 100 year ARI. The new design rainfall estimates are based on a greatly expanded database which incorporates data collected by organisations across Australia. These data have been analysed using contemporary statistical methods that are appropriate for Australian rainfall data. These new Intensity-Duration-Frequency (IFD) design rainfalls were released in July 2013.
Over the next 18 months, the Bureau will be deriving design rainfall estimates for probabilities more frequent than 1 year ARI and revising the existing estimates of the CRC-FORGE rare design rainfalls. The estimates for more frequent design rainfalls will replace the current ad hoc estimates that have been derived by organisations in the absence of other estimates. The revised rare design rainfall estimates will replace the current estimates that were derived on a state by state basis and which, for most states, are now in need of revision as a result of the release of the new IFDs.