Refurbishment | Long lives and new tricks
Richard Herweynen is Entura’s Technical Director for Water in Australia. Here he gives an insight into how we can maximise the value of dams so future generations will continue to enjoy all the benefits they can offer, whatever their age
DAMS, LIKE ALL OF US, go through several life stages. Some dams have harder lives. Some age more quickly. Some need extra attention, and some are more robust. Of course, at some point, it may be necessary to undertake work on an older dam to bring it in line with modern standards, futureproof it for evolving conditions, or to enable it to fulfil changing roles and meet new priorities.
Regular health checks
Above: Binney Dam – retrofitting a downstream filter and weighting berm to this homogeneous earthfill dam
During a dam’s operational phase, it is important that comprehensive dam safety reviews (DSRs) occur every 20 years, or whenever there has been a major event or a change in standards or guidelines. The intent of a DSR is to determine the current condition of the dam and its safety against current practice, considering potential failure modes. If good historical documentation isn’t available, the DSR may require additional investigations and analysis to be undertaken.
Major surgery
Below: Catagunya Dam – replacing old pre-stress anchors with large, double-corrosion protection, monitorable anchors
If the DSR identifies deficiencies, a risk framework can be used to justify and guide necessary upgrades. However, dam upgrades may also be driven by the opportunity to increase value, such as by raising the height of the dam to store more water for hydropower generation or water supply. They can also be driven by changing design standards, changes to legislation, greater understanding about extreme hazards, or, more recently, climate change modelling demonstrating potential changes in weather patterns and their impacts on rainfall and runoff.
Long, healthy lives Hydro Tasmania provides an instructive example of
managing the lives of many dams of different ages and types. The portfolio, spread across the small island state of Tasmania, includes 45 ICOLD large dams
Major upgrades Dam
Catagunya
Dee, Binney & Lake Echo
Cethana, Paloona & Murchison
Rowallan Mossy Marsh Devils Gate
(including 5 of the 10 largest in Australia) and over 150 smaller dams and weirs. Most of these dams were constructed between the 1940s and the 1980s – so they’ve needed careful attention over the decades to keep them safely serving the Tasmanian community. In my 35 years with Hydro Tasmania and Entura (formerly Hydro Tasmania Consulting), I’ve witnessed the evolution of Hydro Tasmania’s world-class dam safety programme, which uses a holistic, risk-based framework to manage dam safety risks. Naturally, when managing such a large portfolio of dams, the demand on resources, both capital and human, can be significant – so a process of ‘triage’ is critical, to ensure the highest risks in the dam portfolio are addressed first. Our portfolio risk assessment (PRA) process allows us to prioritise our resources and activities to achieve this. The PRA is routinely updated as individual dam safety reviews are undertaken – and it underpins priorities for dam safety upgrades. Hydro Tasmania has undertaken a number of major upgrades to dams within its portfolio, some of which are described in the table below. Undertaking some investigations and/or assessments as a portfolio-wide initiative can be cost-effective and can immediately increase the understanding of specific risks across the portfolio. As part of Hydro Tasmania’s PRA process, specific portfolio-wide initiatives have included assessing the performance of downstream spillway aprons, understanding the reliability of spillway gates, and determining the piping risk for smaller earthfill embankment dams. And, of course, Hydro Tasmania continues to consider the impacts of climate change across its dam and hydropower portfolio. As with medical science, the information we have about dams and the methods we can apply to analyse them is always evolving. New information, analysis and knowledge continually improve our understanding of risk.
Failure mode
Flood instability & overtopping
Piping Flood overtopping
Spillway wall instability; piping; flood overtopping
Flood overtopping Flood overtopping
Description
Anchoring of pre-stressed concrete gravity dam; abutment apron for flood overtopping protection
Rockfill filter buttress Crest wall and spillway upgrade
Staged upgrade incl. outlet works upgrade, spillway wall strengthening, and embankment crest reconstruction
Crest wall, spillway upgrade and erosion protection Crest wall and thrust block stabilisation
28 | April 2025 |
www.waterpowermagazine.com
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