| Seismic safety
THE SEISMIC DESIGN OF Australian dams is described as being relatively young when compared with other countries, such as the US or Japan. As Quigley et al explain in recent research published in Environment Systems and Decisions, early dams built before the 1970s generally weren’t designed to consider seismic loading, primarily because Australia was perceived to be a tectonically stable region with lower seismic risks. However, after one of Australia’s most significant seismic events - the Meckering earthquake in 1968 which measured 6.9 on the Richter scale - and following improved global understanding of seismic hazards, from the late twentieth century onwards seismic loading was included in new dam designs, becoming more formalised with the adoption of seismic hazard assessments. Australian dams are predominantly concrete gravity, and earth fill embankment dams which are more common in rural areas and were constructed throughout the twentieth century. Many older dams have recently undergone structural upgrades to meet more stringent seismic design criteria.
Australian dams In their study Quigley et al wanted to obtain estimates
of ground surface rupture and ground motion hazards at standardised scales useful for general reference and regional comparisons of dams registered with the Australian National Committee on Large Dams. Geospatial and statistical methods were used to investigate the exposure of dams to seismic hazard from 409 faults in the Geoscience Australia Neotectonic Features Database (NFD). They identified 216 NFD fault traces within 100km of 428 ANCOLD dams. Allowing for geospatial measurement and mapping uncertainties, between 16 and 31 dams could be directly exposed to primary ground surface rupture hazard on NFD faults. Displacement modelling on these dam-proximal faults yielded displacements that exceed suggested tolerable limits for fault displacement through foundations. The authors conclude that detailed fault studies
will increase knowledge of many dam-proximal faults to better support dam hazard and risk analyses. Fault studies could include mapping of fault traces with LiDAR and other high-resolution geospatial datasets, paleoseismic trenching to establish rupture characteristics from past earthquakes, geological and geophysical studies to better characterise fault geometries and displacements, and Probabilistic Fault Displacement Hazard Assessment.
New Zealand In comparison to Australia, New Zealand is situated at
the convergence of tectonic plates and is a seismically active country which faces unique challenges, often in the form of frequent, large seismic events. Built for Waimea Water by Fulton Hogan and Taylors Contracting, the 52m high concrete faced rockfill Waimea Community Dam is the first large dam to be constructed in New Zealand for 25 years, and the first publicly funded large dam to be constructed since the Clyde Dam was finished 30 years ago. Located in the northwest part of New Zealand’s South Island, the project was completed in early 2024 with the primary purpose of providing irrigation and community water supply.
As the dam is sited on the boundary of the Australian and Pacific tectonic plates, it lies in a region of high seismicity with several regional active faults within 12km of the dam site in different directions. This meant that the project necessitated a geotechnical approach to ensure appropriate seismic performance and internal stability of the supporting embankment materials, including a comprehensive understanding of the movement of the various components of the embankment during an earthquake. While structural configuration of the upstream zone of the structure had to be able to resist earthquake effects, with an emphasis on ensuring dam safety during and after such an event. Key elements of Waimea Community Dam’s seismic design include: An erosion-resistant and flexible rockfill embankment, allowing controlled movement during earthquakes. The overarching embankment design performance requirements were the accommodation of earthquake deformations and conveyance of post-earthquake leakage which would have reduced embankment stability to an unsafe level. A reinforced concrete facing slab with appropriate slab dimensions, joint details and reinforcing. Constructable pre-cast upstream crest wall elements.
Above: Warragamba dam was completed in 1960 and is Sydney’s most important source of water. It’s one of many Australian dams that have undergone seismic upgrades in recent years
Below: Machine learning can recognise subtle changes in seismic activity
www.waterpowermagazine.com | December 2025 | 33
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