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 for dams
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
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 (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.
Navigating major life changes
Over my career, I’ve been fascinated to watch the rapid uptake of wind and solar power and the rising demand for long-duration energy storage. It’s an exciting time for the hydropower sector as market dynamics shift and create new opportunities for hydropower asset owners – such as reassessing their asset portfolio and operating regimes to provide fast-response ‘peaking’ when wind and solar are inadequate to meet energy demand.
Right now, Entura is supporting Hydro Tasmania as it embarks on increasing the flexibility and capacity of the Tarraleah Power Station, one of Tasmania’s oldest. A feasibility study demonstrated that redeveloping Tarraleah could deliver more renewable energy, more capacity and more flexibility to support Tasmania’s future energy vision. The redevelopment will double the station’s capacity and a new pressurised water conveyance system will transform the scheme’s current baseload and inflexible operation into flexible, instantaneous dispatchability with full access to the energy in storage in Lake King William (formed by the Clark Dam, a 67m-high, gravity-arch dam, constructed
in 1965).
In the last few years, I’ve also been delighted to witness the reemergence of pumped hydro in Australia. It’s another ‘new life’ opportunity for existing dams – which, when the topography is right, may form one of the paired reservoirs. We’ve explored the feasibility of this opportunity for Tasmania, ultimately identifying a preferred scheme incorporating the existing Lake Cethana (created by a 110m-high concrete-faced rockfill dam constructed in 1971).
Expert care
If a dam is well designed and maintained so that it can remain structurally safe, it can usually continue to operate long beyond an 80–100-year design life, remaining resilient in the face of nature’s challenges, such as floods and earthquakes, and the inevitable processes of aging. At Entura and Hydro Tasmania, we feel an enormous sense of responsibility and pride when we work on Hydro Tasmania’s dams, which were built over more than a century and have been fundamental to shaping our state’s economy and delivering the lifestyles our communities now enjoy. Under the expert care and custodianship of experienced dam engineers – examining, diagnosing and treating these dams throughout their long lives – we can maximise the value of these important assets so that future generations will continue to enjoy all the benefits they can offer, whatever their age.
