Dam old

Ageing dams will pose a growing risk over the next few decades, warns an analysis from United Nations University’s Canada-based Institute for Water, Environment and Health (UNU-INWEH) – and the threat will be exacerbated by climate change.

The 20th century saw a dam-building boom that peaked in the 1960s and ’70s, with tens of thousands constructed around the globe to store and control water. Their uses vary by region, from water supply to irrigation, flood control to hydropower.

According to the UNU report released late last week, 58,700 of the world’s large dams were built between 1930 and 1970. By 2050, most of the global population will live downstream of them.

But dams don’t last forever. Most have a design life of 50–100 years, which means many are already operating at or past their estimated life expectancy.

“These aged structures incur rapidly rising maintenance needs and costs,” the report says, “while simultaneously declining their effectiveness and posing potential threats to human safety and the environment.”

According to lead author and UNU-INWEH researcher Duminda Perera, “This problem of ageing large dams today confronts a relatively small number of countries – 93% of all the world’s large dams are located in just 25 nations.”

The report found that China has 40% of the world’s total large dams; 55% are concentrated in China, India, Japan and the Republic of Korea alone. The majority of these will reach the end of their design life very soon, as will many large dams across Africa, South America and Eastern Europe.

Co-author Vladimir Smakhtin, Director of UNU-INWEH, says that he hopes this report will “attract global attention to the creeping issue of ageing water storage infrastructure and stimulate international efforts to deal with this emerging, rising water risk”.

Fewer dams are being built today, but the report notes that when planning water storage infrastructure developments, it is important to consider dam decommissioning – the removal of dams to allow rivers to return to their natural course.

Decommissioning is predicted to increase, particularly as dams become impractical to maintain or their use becomes obsolete. This phenomenon is already spreading across Europe and the USA.

But the report notes that, to date, most dams removed have been small – decommissioning large dams of more than 15 metres in height is “still in its infancy, with only a few known cases in the last decade”.

One example of a successful removal is the dismantling of the 64m tall Glines Canyon Dam in Washington State, US. The process was completed in 2014 and allowed the Elwha River to flow freely again, restoring habitat for fish and other wildlife. Though this is currently the largest dam removal in US history, it will soon lose the record to the Klamath River on the Oregon-California border, which will see four dams dismantled in the next few years – kickstarting an enormous salmon restoration attempt.

“A few case studies of ageing and decommissioned large dams illustrate the complexity and length of the process that is often necessary to orchestrate the dam removal safely,” says co-author R Allen Curry, from the University of New Brunswick, Canada.

“Even removing a small dam requires years (often decades) of continuous expert and public involvement, and lengthy regulatory reviews. With the mass ageing of dams well underway, it is important to develop a framework of protocols that will guide and accelerate the dam removal process.”

Decommissioning must weigh up the potential socio-economic impacts – both positive and negative – including those on local livelihoods, heritage, property value, recreation, and aesthetics; these vary significantly between low- and high-income countries, the report says.

Smakhtin points out that, “the rising frequency and severity of flooding and other extreme environmental events can overwhelm a dam’s design limits and accelerate a dam’s ageing process. Decisions about decommissioning, therefore, need to be taken in the context of a changing climate.” 

In Australia – the driest inhabited continent, with highly variable rainfall – water storage infrastructure is particularly crucial. Dams are used to stabilise water supply, as well as for irrigation and energy production. But perhaps they aren’t the only solution, according to Bill Peirson, water engineering expert from the UNSW Water Research Laboratory, who didn’t contribute to the report.

Breakout: Australia’s five largest built reservoirs

Dam Reservoir State Capacity Completed Age

Gordon Lake Gordon Tas. 12,450 GL 1978 43

Ord River Lake Argyle WA 10,760 GL 1971 50

Eucumbene Lake Eucumbene NSW 4,798 GL 1958 63

Dartmouth Dartmouth Reservoir Vic 4,000 GL 1979 42

Burdekin Falls Lake Dalrymple Qld 1,860 GL 1984 37

Source: Geoscience Australia

“The inspiration in Australia largely comes from Europe and the US, where you have spring snowmelt, and so the hydrology there is quite different from this drought-ridden country,” he explains. 

Instead of a steady-state hydrology, Australia is subject to 10-year “cataclysms” of floods and droughts.

“There is no doubt that regulation of river flows in Australia have enabled agriculture to happen on large scales, given our flood-drought dominated climate,” he says – scales that would not otherwise have been possible.

But dams also have negative ecological impacts on river ecosystems, and the redistribution of water they allow is highly politicised.

Plus, as droughts become longer and more severe due to climate change, dams are featuring heavily in discussions about the future of the country’s water security.

Out of 650 large dams in Australia, the UNU report notes that half of them are over 50 years old and more than 50 have been in operation for over 100 years.

The oldest and most numerous are water-supply dams, most of which are in the south of the country – though attention has recently turned to NSW northern river systems such as the Clarence, Richmond and Tweed, with the aim of bringing more water southwards. 

Peirson says that there are other options for our country’s water infrastructure – we just need to put our heads together and think about them.

“I think there is a strange reluctance to actually try and come up with solutions to the ecological problems associated with dams,” he says. “There’s actually not a lot of thinking going in the middle space about how we might actually produce outcomes for the environment, and for Australia’s water supply at the same time.”

Alternatives include pipelines taking water to inland communities and desalination plants on the coasts. These would both be highly energy-intensive, but could feasibly be run off renewables.

“It would actually be good for the inland water budget if we were letting more water go down the rivers and the human supply was coming from renewable energy derived from seawater,” Peirson says.

Related reading: Why do dams collapse?