Tim Logan, Angus Swindon, Chris Topham
Edgar Dam is a 17m high saddle dam forming part of the Gordon River Power Development (GRPD) in south west Tasmania; the smallest of three dams, which created the current Lake Pedder. It is essentially a homogeneous embankment, designed and built between 1970 and 1972. It is assigned a “High A” Hazard Category. An unusual feature of the dam design is a reinforced concrete facing on the upstream face, crest and the upper portion of the downstream face provided primarily as protection against wave overtopping.The upstream facing is bedded on drainage material encapsulating a longitudinal drain 1.6m above the level of the bottom of the concrete. This drain is connected to four transverse drains (100 mm diameter PVC) which run through the body of the dam and discharge through the concrete slab on the downstream face. The screening level risk assessment for Edgar Dam identified piping through the embankment as the predominant failure mode, particularly related to the transverse drains and the uncertainty surrounding the competency of the backfill around the pipes. To address this, the condition of drain backfill has been assessed using geophysical logging, supplemented by an internal video inspection. The information has allowed a more detailed risk assessment to be performed and potential mitigation measures to be assessed.
Keywords: Risk Management, Dam safety, Conduits, Geophysical Logging.
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Amanda Barrett, Mike Marley, Tariq Rahiman
The site of the Wyaralong Dam, west of Beaudesert, Queensland, has been investigated in progressive stages since 1991. The first stage of the investigation was a siting study and the second in 2006 was designed to gather sufficient geotechnical information to develop a preliminary design and provide input into the environmental approval process. The third stage of the investigation was designed to gather further information to allow the detailed design of the dam to commence. This iterative investigation approach has ensured confidence in the site geology and geotechnical model.
The site investigations have included diamond drilling, piezo-cone penetration testing, geophysics techniques, hydraulic conductivity testing, groundwater pumping tests, costean excavation, geological mapping and accompanying laboratory test programs. Investigations have been targeted to assess the foundation conditions for the proposed engineering structure and have been refined to the needs of the dam design as it has developed.
With sufficient data, a 3-dimensional geotechnical model has been developed using the computer modelling program Vulcan, to assess the position and influence of a number of key geological features observed in the site investigation. Assessment of engineering properties based on in situ and laboratory testing were then extrapolated across the site through application of the geotechnical model.
Keywords: Wyaralong Dam, geotechnical investigation, geology, 3-D Vulcan model, foundation.
A. Tahershamsi , H. Bayat , J. Mahboubi , M. Geranmehr
Rockfill dams with inbuilt spillways are capable of passing surplus discharge by through-flow and overtopping and exhibits many advantages including reduced diversion costs, smaller terminal structures, etc. Further clarification of discharge coefficient (Cd) for this type of spillways is required for engineering purposes due to the complicated nature of turbulent flow through coarse porous media and boundary conditions. An experimental program was conducted to determine effects of uniformity coefficient (Cu), curvature coefficient (Cc), void ratio(e) and a dimensionless grain diameter defined by (d50⁄d100) on the discharge coefficient (Cd) . Observations indicated a significant reduction of discharge coefficient by increasing Cu and decreasing e and d50⁄d100. However, probable effects of (Cc) on (Cd), were not significant in these investigations.
Keywords: Internal spillway, discharge coefficient, uniformity coefficient, curvature coefficient
M. Amghar, A. Watt, C. Thorstensen
The future effects of climate change on water resources in the southeast Queensland and other parts of Australia will depend on trends in both climatic and non-climatic factors. Evaluating these impacts is challenging because water availability, quality and streamflow are sensitive to changes in temperature and precipitation. Other important factors include increased demand for water caused by population growth, changes in the economy, development of new technologies, changes in catchment characteristics and water management decisions. In Southeast Queensland, concern for climate change has increased in recent years with research on global climate change applied to part of Southeast Queensland and it has become apparent that the region’s climate has changed in recent times. Studies have shown that Southeast Queensland’s climate has been variable over history and in the present, is experiencing continuing sea level rise, and may experience
significant climate warming. The potential effects of climate change on coastal erosion, water availability, flood control, and general water management issues have been raised and widely discussed from a variety of perspectives.
This paper presents results of an integrated economic-engineering resource assessment optimisation model of Seqwater’s water supply system illustrating the value of optimisation modelling for providing an integrated approach needed to manage a complex multipurpose water system. Overall, the approach has its own limitations, but provides useful insights on the potential for operating the current or proposed infrastructure for different future conditions.
Keywords: Brisbane Water supply, Moreton, water resource plan, optimisation, environmental flows.
Giovanni De Cataldo
The ANCOLD Guidelines on Dam Safety Management August 2003 were formulated to ensure that dam owners adopt a responsible approach towards the safe operation and maintenance of their dams.
Is it possible to safely, responsibly and acceptably work outside the regulatory Guidelines/Requirements?
The challenge for dam owners now and into the future in meeting stringent standards, is to cost effectively manage their assets within available financial constraints whilst minimising risks and maintaining acceptable levels of safety.
With the continuing drought and suppressed storage levels in most dams, the risk to downstream communities and to the environment from dam failure is significantly reduced.
Based on various studies, investigations, internal workshops and external “Expert Panel” reviews, this paper puts forward a case for a sound and responsible risk-based approach to routine visual and surveillance monitoring frequencies at varying storage levels for “Sunny Day” conditions and compares it against traditional ANCOLD standards which are based solely on consequences.
Keywords: State Water Corporation, ANCOLD guidelines, risk-based approach, dam safety, regulator.
Martina Reichstetter and Dr Mohand Amghar
The future effects of climate change on water resources in southeast Queensland and other parts of Australia will depend on trends in both climatic and non-climatic factors. Evaluating these impacts is challenging because water availability, quality and streamflow are sensitive to changes in temperature and precipitation. Other important factors include increased demand for water caused by population growth, changes in the economy, development of new technologies, changes in catchment characteristics and water management decisions.
This paper provides an overview of how climate change may affect water yields and water availability in the Tinana Creek catchment. The Tinana Creek water supply is located in the south-eastern costal area of Queensland and covers an area of 783 km2. The catchment experiences a sub-tropical climate with warm to hot summers and mild dry winters. Climate variation and change are expected to impact the upper Tinana Creek water supplies and the planning of potential future water supply options. The Maryborough City’s water supply is currently supplied solely by Teddington Weir to domestic and industrial users. In this paper, climate change impacts on the water yields were investigated by assigning climate change, derived from SimCLIM, onto the input data used in the Sacramento rainfall-runoff model and Integrated Quantity and Quality Model (IQQM). Eighteen different climate change scenarios were undertaken, using three different Global Climate Models (GCM) (CSIRO MK2, HadCM3 and CGCM2), three different emission scenarios (A1FI, B2 and A1B) at two different time steps (2030 and 2050). This paper presents results with current and future climate scenarios of water availability in the study area.
Keywords: Teddington Water supply, IQQM, water resource plan, climate change, SimCLIM, Maryborough.