DamsAging Dams Pose Growing Threat

Published 25 January 2021

By 2050, most people on Earth will live downstream of tens of thousands of large dams built in the twentieth century, many of them already operating at or beyond their design life. Increasingly expensive to maintain, experts foresee a trend to decommissioning dams.

By 2050, most people on Earth will live downstream of tens of thousands of large dams built in the tentieth century, many of them already operating at or beyond their design life, according to a UN University analysis.

The report, Ageing Water Infrastructure: An Emerging Global Risk,” by UNU’s Canadian-based Institute for Water, Environment and Health, says most of the 58,700 large dams worldwide were constructed between 1930 and 1970 with a design life of 50 to 100 years, adding that at 50 years, a large concrete dam “would most probably begin to express signs of aging.”

Aging signs include increasing cases of dam failures, progressively increasing costs of dam repair and maintenance, increasing reservoir sedimentation, and loss of a dam’s functionality and effectiveness, “strongly interconnected” manifestations, the paper says.

The report says dams that are well designed, constructed and maintained can “easily” reach 100 years of service but predicts an increase in “decommissioning” — a phenomenon gaining pace in the USA and Europe — as economic and practical limitations prevent ageing dams from being upgraded or if their original use is now obsolete.

Worldwide, the huge volume of water stored behind large dams is estimated at 7,000 to 8,300 cubic kilometers — enough to cover about 80 percent of Canada’s landmass under a meter of water.

The report provides an overview of dam ageing by world region and primary function — water supply, irrigation, flood control, hydropower, and recreation.

It also details the increasing risk of older dams, the rising maintenance expense, the declining functionality due to sedimentation, the benefits of restoring or redesigning natural environments, and the societal impacts — pro and con — that need to be weighed by policy makers deciding what to do. Notably, “the nature of these impacts varies significantly between low- and high-income countries.”

The analysis also includes dam decommissioning or ageing case studies from the USA, France, Canada, India, Japan, and Zambia & Zimbabwe.
Climate Change Will Accelerate the Dam Ageing Process
“This report aims to attract global attention to the creeping issue of ageing water storage infrastructure and stimulate international efforts to deal with this emerging, rising water risk,” says co-author Vladimir Smakhtin, Director of UNU-INWEH.