Bronson McPherson, David Guest, Barton Maher, Ian Tanner and Amit Chanan
There is significant community interest in the potential for water supply dams to be adapted for flood mitigation, particularly for major dams located upstream of flood vulnerable populations. There may be a number of large dams which have the potential to provide significant flood mitigation benefits to Australian communities if they can be adapted for flood mitigation functionality. Other dams already provide significant flood mitigation benefits, however their limitations are not properly understood by the general public. Two major dams located near a large urban town centre prone to flooding are examined as a case study and some international cases are presented.
Flood mitigation often has a different funding source to water supply. The funding arrangements for flood mitigation dam works can be complex, considering the potential stakeholders and somewhat intangible benefits. If the community wants to use a water supply dam to provide flood mitigation then who provides the funding for the modification works?
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Luke Toombes and Rob Ayre
Many large dams are built as multi-purpose structures, providing both flood mitigation and bulk water storage, but requiring a trade-off in functionality between those purposes. In response to the Millennium Drought (2001 to 2009) closely followed by devastating floods in 2011, the State of Queensland initiated a comprehensive review of the operation of its flood mitigation dams. Part of this study involved development of an Integrated Assessment Methodology to provide an informed and unbiased assessment of the competing factors affecting dam operations. The methodology assessed the primary variables of flood damage and other impacts, future bulk water infrastructure and water security requirements in the form of a net present cost/benefit. The study concluded that modification of the dam flood release strategy to reduce flood damage during large events would come at the expense of increased frequency of minor flooding, or vice versa, with minimal net benefit. Similarly, reducing bulk water storage to increase flood mitigation would increase water supply costs by a similar magnitude to the flood damage prevented.
Paul Southcott, Tony Harman
This paper addresses structural behaviour of the Rowallan spillway walls and the learning that can be derived from this in the design of critical retaining walls in dams and how this can be applied both to remedial works and new work. The authors propose design criteria suitable for retaining walls in high hazard dams.
Behrooz Ghahreman Nejad
In recent years, dam designers have become increasingly interested in application of the geomembrane sealing systems (GSS) in design of tailings storage facilities around the world. The main reasons for this have been the deformation characteristics, environmental aspects (ie seepage minimisation), speed of construction and constructability of geomembrane liners in most climatic conditions. This paper reports the design and application of two types of geomembrane sealing system in Angas Zinc (AZ) and Sarcheshmeh Copper (SC) tailings dams. The former is a 25m high zoned earthfill embankment with an HDPE liner system, located in an environmentally sensitive site in South Australia. The latter is a 94m high zoned rockfill embankment with a PVC liner system, located in a region of high seismicity in central Iran.
The designs of the AZ and SC geomembrane sealing systems including geomembrane liner, drainage layer, anchoring, leak detection system and drains, and instrumentations are discussed in detail. The performance of the liner systems during operation is also presented.
Dennis C. Green
Current good practice for risk management as represented in ANCOLD guidelines emphasises risk reduction beyond tolerable risk levels to As Low As Reasonably Practicable (ALARP). Risk reduction reflected in key design parameters such as the spillway design flood is monitored on a quantitative basis, while the guidelines also draw attention to a number of non-quantifiable measures.
Recent work health and safety legislation in Australia does not at first appear to relate to dam safety, but it mandates elimination of risk, and, if that is not possible, then it mandates reduction of risk So Far As Is Reasonably Practicable (SFAIRP). It is tempting to believe that this is equivalent to ANCOLD’s approach to ALARP, but the devil is in the detail of the legislation. This paper argues for a change to a more systematic presentation of recording of decisions on dam safety risk management, lest the legislation expose dam owners unwittingly to liability when they thought they were following good practice. In particular, the re-focussing of ANCOLD Guidelines to align more recognisably with the new legal paradigm, including preparation and adoption of a Safety Case, is recommended.
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.