David Stephens, Kristen Sih, Peter Hill, Rory Nathan, David Dole
The spring and summer of 2010-11 were characterised by severe flooding affecting much of Victoria. In a number of cases, communities downstream of large dams developed to supply water for irrigation and critical human and stock needs were significantly impacted. Following the floods, the Victorian Government commissioned the Victorian Floods Review (VFR) to consider the total warning and response to these floods. Whilst dam operations were not specifically included in the terms of reference, overwhelming community interest lead to the VFR commissioning a high level review of the way a number of key dams were operated during the floods. This review identified some of the inherent tensions in the legislative framework for water harvesting, storage and dam safety in Victoria. These tensions were often matched by the conflicting expectations of the public living immediately downstream of the dams versus those dependent on the water resource stored in the dams. The final report of the VFR was handed down in December 2011 and contained a number of recommendations specifically for dam owners. These recommendations are reviewed and discussed in light of both the legal and public relations ramifications for owners and operators of large water supply dams. An overview is also given of the operational constraints to downstream flood mitigation facing many dam owners. Such constraints are typically imposed by the type of dam (i.e. fixed crest), relatively small storage and outlet capacities when compared to flood volumes and limitations on the reliability of forecast rainfall information. Some possible ways of overcoming these constraints are identified and discussed.
Keywords: Flood, mitigation, Victorian Floods Review
P C Styles, A L Garrard
The Victorian town of Nathalia was surrounded by flood water during the March 2012 floods in Northern Victoria.
Nathalia is protected by earthen levees of various sizes and age. Portable aluminium levees were installed during the March 2012 flood event, generally in areas where a permanent levee would restrict access to a park and views. The flood level came within 200mm of the crest of many of the levees and remained at a high level for nearly 2 weeks.
The paper describes the emergency management issues and procedures which relied on engineering advice to provide targeted and relevant remedial works on the levee system as potential problems arose. Engineers worked alongside the SES, CFA, Victoria Police, ADF and other volunteers to monitor, repair and reinforce the levee system on a 24 hour basis. The engineering support continued over a period of approximately 2 weeks, from the time the flood waters commenced rising until they had receded sufficiently for the orders for evacuation of the town to be rescinded.
Keywords: Nathalia, floods, levees, emergency management
Andrew Barclay, Greg Kotze
The Enlarged Cotter Dam (ECD) is under construction on the Cotter River, 18km west of Canberra. The new dam comprises an 85m high roller compacted concrete gravity dam, located 120m downstream of an existing 31m high concrete dam. This paper describes the geological structures that prevail at the site and their significance with respect to design and construction considerations.
Geological mapping has confirmed that the abutment slopes are characterised by zones of prominent rock outcrop and thin mantles of colluvial soil that form overall slope angles of 45 degrees. The Cotter River valley in the ECD area has been eroded through a geological sequence of Early to Late Silurian age, comprised predominantly of porphyritic rhyolite and lapilli tuffs of the Walker Volcanics.
Geotechnical investigations for the ECD were extensive and comprehensive. The results obtained have enabled the compilation of a detailed geological model of the dam site. Particular attention was paid to defining, characterising and kinematically analysing prominent geological structures, including intersecting sheared or crushed seams and zones that traverse the dam footprint.
Prominent geological structures that were encountered during the abutment excavation had significant design and construction implications for:
Abutment stripping and foundation preparations;
Rock slope stabilisation;
The foundation of the intake tower that comprises a 66m high concrete structure; and
The foundations for 1 x 56m high and 2 x 78m high tower cranes that required positioning on the steep abutment slopes during construction.
This paper highlights the importance of understanding the geological origin, nature and distribution of rockmass defects within a complex rock foundation. Site specific construction requirements and engineering design solutions used to successfully negotiate adverse geological structures are described.
Keywords: Dam, Roller Compacted Concrete, Geological Structures, Abutment, Foundation.
Robert Wark, R.N.M. Nixon
Sediment inflows to Lake Argyle, the reservoir formed by the construction of the Ord River Dam, were seen as a significant threat to the Ord Irrigation Project when the scheme was being developed through the 1960s. Sediment monitoring was built into the operation of Lake Argyle when the Ord River Dam was completed in 1971. The paper describes the strategies that have been in place to assess sediment loads and monitor sediment build up in the reservoir.
Spectacular reduction in sediment flows has been achieved through developing a comprehensive catchment management program. The program commenced in the early 1960s and was adapted and modified as progress was made. The paper describes the steps taken to identify the areas of the catchment at risk, the measures implemented and the current status of the catchment.
A key feature of the catchment management program has been the willingness to critically review progress and adapt the program. A variety of sediment tracing techniques have been used to help confirm the sources of sediment in the catchment, and the paper describes these, and the broad range of results and how they have helped direct the work on catchment management.
Keywords: Sediment, monitoring, catchment management, Lake Argyle, Ord River
Dr Andy Hughes
This paper will outline changes currently being implemented to the UK legislation via the Flood & Water Management Act 2010. This legislation has driven a change towards a risk based approach.
Significant consultation with the profession and owners has provided an interesting insight to the different and disparate views of owners, engineers and the public.
The guidance documents associated with the Act associated with floods and risk management are currently being rewritten and will be completed by the time of the conference in Perth and so progress with reformatting of those documents will be reported upon.
Keywords: Legislation, guidance, consultation
Penelope Shaw, Brian Walford, Daniel Yates
The Bowen Basin is one of Australia’s economic mining powerhouses. Key to the mining of coal is the efficient management of the available water resources. For many years drought has meant that coal mines have had to manage operations with low quantities of water. For a new mine, this involved sophisticated hydrologic modelling as part of staying in business. In recent years a turnaround in weather conditions and changes to discharge permissions have meant that mines have too much saline water!
The paper describes how one mine augmented its small system of storages with a new dam and pumping system to meet regulatory requirements. Although not a large dam, the challenges confronted are shown to be similar to those involved in the delivery of much larger projects, all related to the power of water.
Keywords: Design storage allowance, water management, challenges, environmental protection, mining dams, automated pumping systems, spillway upgrading.