In recent years, there has been greater expectations of waterway barriers to have more consideration of environmental factors; in particular associated with facilitating biopassage across the site.
The scope of the Gympie Weir Detailed Design Project included facilitating biopassage to as many aquatic species as possible,including the protected Mary River Turtle,while maintaining the required gauging accuracy and public amenities.Very rarely has a turtle been observed successfully traversing a fishway, as the designed velocity and depth criteria required to optimise fish passage is unsuitable for turtle passage. Thus for Gympie Weir,a leading-edge innovative solution was designed.
The design incorporates a low flow trapezoidal fishway chute, high flow rock ramp and turtle ramp. The turtle passage is the first of its kind and includes a curved concrete ramp with a variety of textures, two resting pools with protective niches, and limited vertical drop heights. Construction of the weir is intended for the near future and ongoing monitoring will be critical to assessing and improving performance, as well as contributing to the scientific knowledge base for future designs.
Monique de Moel, Mark Arnold, Gamini Adikari
Monbulk Saddle Dam, built in 1929, is one of two saddle dams located at the southern end of Silvan Reservoir, near the township of Monbulk, Victoria. The saddle dam is a 5.3m high earthfill embankment with a 230mm wide, centrally located, concrete core wall. The reservoir retained is located in the valley of Stonyford Creek, and impounds approximately 40,500 ML of water at FSL.
Excessive seepage at the right abutment of Monbulk Saddle Dam has been an issue since the early 1970’s. The reservoir has been operating with a level restriction since then to reduce the seepage flows. However; this restriction limits the operational flexibility of the storage. Early investigations concluded that the most likely mechanism for these excessive seepage flows was a defect in the concrete core wall.
Melbourne Water Corporation, (the owner and the operator of the reservoir), undertook a risk assessment for Silvan Reservoir as part of a review of its dams asset portfolio. Based on the information then available, the risk assessment was undertaken using the criteria and guidelines developed by ANCOLD. The result was that the piping risks associated with the seepage from the west abutment at Monbulk Saddle Dam was unacceptable. The risk assessment Panel also cast doubt on the likelihood of the seepage being caused by a defect in the concrete core wall. Melbourne Water therefore engaged SMEC Australia to investigate the likely causes and mechanisms for this seepage and to develop suitable remedial measures for the dam.
The investigations have included a desktop review of historical information, test pit investigations, Sonic borehole drilling, dynamic cone penetration tests, an infrared thermal imaging investigation and an electromagnetic groundwater seepage flow mapping investigation.
These investigations have shown that the most likely cause of the seepage is the presence of permeable foundation layers located beneath and around the existing core wall as the core wall does not extend over the full length of the embankment and becomes shallower towards the abutments.
To satisfy the ALARP principle; risk reduction remedial works Concept Designs are being developed and reviewed.
2011 – Investigating the Piping Risk Associated with Seepage at Monbulk Saddle Dam of Silvan Reservoir, Victoria
Susan Ryanand Siraj Perera
This paper describes the benefits of the statewide risk reporting framework used in dam safety regulation in Victoria and its ongoing development. Key to this approach is a web-hosted reporting system and benchmarking process, established by the Department of Sustainability and Environment in collaboration with the Victorian water industry. This is the first time that such an approach has been used in Australia for publicly owned dams.
Sector-wide reporting on dam safety is central to the objective-based approach used by the Department in the governance and regulation of the water industry. Water corporations submit detailed annual reports on dam safety status. This incorporates ‘self assessment’ against performance criteria based on ANCOLD risk and dam safety management guidelines. These are collated to produce a statewide report of industry-wide results on the progress of dam safety management programs. This benchmarking process is providing a driver for on-going improvement and proving to be an effective tool for regulation of publicly owned dams.
The reporting framework has significantly advanced the understanding of dam safety risk across the water sector, with outputs easily understood by both dam safety practitioners and decision makers. It has improved monitoring and trend analysis of risk management practices, and is informing policy development on demonstration of the ALARP principle and decision-making about appropriate long-term dam safety levels.
Rod Westmore, Andrew George& Robert Wilson
A 2007 risk assessment of Hume Dam concluded that the dam did not satisfy the ANCOLD societal risk criteria for existing dams. The Spillway Southern Junction (SSJ) and its associated failure modes was one of the main contributors to the risk profile.
Upgrade works at the SSJ involved the retro-installation of additional filter and drainage materials in the 40m high embankment immediately downstream of the tower block and central core wall by installation of more than 10,000m of secant caisson drilled columns backfilled with filter and/or drainage materials.
This paper describes the design and construction issues associated with the upgrade works, the equipment and methodologies developed to achieve the principal design objectives of coverage and connectivity of filter and drainage columns, and optimisation of compaction of the backfill materials. It also describes how these requirements were met whilst minimising adverse affects such as vertical deviation, excessive vibration, subsidence of secant filter columns during construction, and clay smearing of the perimeter of individual columns.
Hume Dam Spillway Southern Junction Filter and Drainage Works
Simon Lang, Chriselyn Meneses, Peter Hill, Kristen Sih
In Australia to date, the empirical method developed by Graham (1999) is the most widely applied approach for estimating loss of life from dambreak flooding. However, as the move to risk-based approaches of dam safety management has gathered momentum internationally, increasingly sophisticated techniques for estimating loss of life have emerged. One of these models is the United States Army Corps of Engineers (USACE) HEC-FIA model. HEC-FIA models the influence of flooding, structure characteristics, and warning and evacuation assumptions on loss of life in a spatially distributed manner. In contrast to Graham (1999), HEC-FIA also allows the user to model the loss of life for both dambreak and natural flooding.
This paper presents the results from the first Australian application of HEC-FIA to two dams in southeast Australia. The application of empirical methods developed by Graham (2004) and Reiter (2001) is also discussed.