Peter Hill and Rory Nathan
The ANCOLD Acceptable Flood Capacity (AFC) guidelines were published in 2000 and provide guidance on the selection of design flood capacities for dams and specifically a deterministic fallback provision for spillway capacities. Since the guideline was published, there has been a continual evolution in dam safety management practices and related guidelines, including the 2003 ANCOLD guidelines on risk assessment and the current revision of Australian Rainfall and Runoff by Engineers Australia. This paper describes the scope of the current AFC guidelines and perceived opportunities for refinement. A survey of users was used to test and identify issues and gauge the need for the guideline to be updated. A number of topics were identified that would benefit from clarification or further guidance. These topics include consistency with other ANCOLD guidelines, clarity on the selection of the AFC, definition of the dam crest flood, freeboard and application to gated structures.
Neil Jacka, Christopher Dann, Jeremy Eldridge
The Tekapo Canal Remediation Works were undertaken to extend the life of the canal and enhance its seismic and environmental resilience. The deterioration of the canal lining in specific reaches has been the consequence of internal erosion of the lining under operating conditions.
The remedial works comprised installation of a supplementary geomembrane liner over selected sections of the canal, reconstruction of a culvert where the embankment had suffered piping, installation of filters in the Maryburn Fill, strengthening of the bridges across the canal and replacement of irrigation off-takes.
This paper presents a summary of key issues resolved during the design of the remediation works, in particularly the design of the geomembrane ballast system, the cofferdams and the management of side slope stability during drawdown for the works. A number of construction trials were carried out to confirm design assumptions and test construction techniques. The trials were a significant factor in the successful completion of the first season of work ahead of programme.
Keywords: Canal, Lining, Geomembrane, Cofferdam, Design, Seismic resilience
J.P. Giroud, Neil Jacka, Christopher Dann and Jeremy Eldridge
The remediation of a large hydropower canal included the lining of selected reaches of the canal with a geomembrane to extend the life of the canal and enhance seismic resilience. This paper presents a summary of innovative analyses performed to select and design the geomembrane liner system. Two mechanisms that induce tensile stress and strain in the geomembrane following the development of cracks in the supporting subgrade resulting in the deflection of the geomembrane over the cracks under the applied water pressure were analysed. The analysis uses the concept of ‘co-energy’, a geomembrane property that evaluates its ability to withstand stresses and strains together. A range of ballast configurations undertaken to assess the tension, strain and deflection of the geomembrane while evaluating the resistance to hydrodynamic forces and other loads were analysed. Stability analyses showed that geosynthetic reinforcement of the ballast over the upper canal slopes was required.
Keywords: Canal, Lining, Geomembrane, Design, Seismic resilience.
As the Panama Canal is upgraded to accommodate larger vessels, hydrological and ecological elements of the project are being closely monitored, along with the effects of the increased usage that is projected to accompany the upgrade when it opens to traffic in 2015. Each of the 14,000 ships that annually pass through the Panama Canal requires 200 ML of fresh water – drawn from Gatun Lake and other Chagres River reservoirs – to navigate through the locks. The reliability of a sustainable water supply is thus vital to the canal’s operation and, by extension, to the world’s economy.
Hydrologic, hydraulic, and sedimentation studies are providing baseline data for comparison with projected operational scenarios. Several projects are currently being undertaken to restore and protect the widely recognised and highly valued biodiversity within Gatun Lake’s catchment area. Efforts to promote biodiversity conservation during the construction and operation of the expansion project are being coordinated with the concurrent efforts of a variety of academic, scientific, and private institutions, including the Smithsonian Tropical Research Institute, which is located on the largest island in Gatun Lake.
This paper examines the implications of growth and expansion on Gatun Dam and Lake. Current studies are assessing the impacts of deforestation on sedimentation and temporal flow distribution into Gatun Lake. Methodologies and results are presented for the USAID-funded Panama Canal Watershed Biodiversity Conservation Project, an undertaking that engages public and private sector partners in an effort to improve the management and conservation of critical areas through the implementation of sustainable practices and engagement of local stakeholders.
Iain Lonie, Malcolm Barker and Colin Thompson
Consideration of flood mitigation benefits, water supply, irrigation and recreational usage played an instrumental role in developing the proposed upgrade for Maroon Dam to meet dam safety and flood capacity requirements. Maroon Dam is a 47.4 m high zoned earthfill dam completed in 1974. The dam is a multi-purpose reservoir which is now owned and operated by Seqwater and plays an important role in the local community. Key drivers for the proposed upgrade design included embankment stability, foundation concerns, piping, spillway capacity and erosion of the embankment toe.
Six options were reduced to three through a high level screening exercise. A more detailed assessment of the remaining options was undertaken using a Multi Criteria Analysis and a detailed risk assessment. Consideration of the competing uses of the reservoir was critical in the development and assessment of the preferred option. This paper will present the details of the analytical methods used as input for the Multi Criteria Analysis and the detailed risk assessment for the final proposed design option that will meet the requirements of dam safety and flood capacity without impacting on water supply, irrigation and recreational usage.
Chris Topham, Eoin Nicholson and David Tanner
A number of Australian dams have spillways with reinforced concrete training walls designed in the 1950/60s to the standards of the day, but which could be considered under-designed according to modern criteria. Such walls commonly retain significant depths of earth and rockfill embankment materials, where structural failure of the wall could seriously compromise the safety of the dam. This paper presents the journey to mitigate the risk of such training walls, drawing primarily on experience in managing structurally deficient spillway training walls for a High Consequence Category dam in northern Tasmania. Reflections from each step of the risk management process are presented, including how the portfolio risk assessment contributed to a focus on the dam as a whole, and how that led to more detailed analysis and evaluation of the training wall risk. The use of instrumentation and enhanced surveillance for risk monitoring is discussed, including how real-time deformation data ultimately led to installation of temporary wall bracing works and enhanced contingency planning. The long-term risk treatment for the walls is presented, comprising a $6m structural upgrade to the training walls completed in 2013. The paper concludes with the learnings from the risk management journey and highlights the range of interventions available to owners with similar spillway training walls.