New dams pose increased risk of failure. Scientists call for investment

As many as 23 of the world’s large dams could fail by 2035, according to a study published in the journal Nature Water. According to the researchers, structures built in recent years in poor countries are particularly vulnerable to failure. What can be done to prevent disasters?

Historical analysis of dam failures

In September 2023, Libya’s Cyrenaica region experienced record rainfall – 414 mm in 24 hours. As a result, the Wadi Darnah River overtopped its banks and led to the breaking of two dams in the city of Derna. Nearly 6,000 people were killed, 876 buildings were completely destroyed and 3,100 damaged. According to the Dutch-British team, which took charge of a global analysis of past dam failures, preventing disasters of this scale should be a priority today. The latter were defined as uncontrolled water discharge or structural damage.

Researchers from the Deltares Institute of Technology, the IHE Delft Institute for Water Education and Imperial College London used the International Commission on Large Dams (ICOLD) database of 62,000 structures worldwide. Data on failures that occurred from 1900 to 2024 were subjected to statistical multi-parameter analysis to determine the likelihood of similar disasters in the future. It turned out that the age of the structure, climatic conditions and the wealth of the country were factors determining the level of risk.

Improving dam safety in the late 20th century.

In many countries, new dams began to be built intensively in the middle of the last century. Unfortunately, this construction boom brought a series of failures, including the infamous Vajont dam disaster in Italy, which cost the lives of nearly 2,000 people. However, advances in technology and tighter safety standards have led to a gradual reduction in failures – by an average of 30 percent each decade.

The causes of accidents and damage were largely dependent on the type of structure. Earthen dams were found to be 2.31 times more prone to failure than concrete dams, with internal erosion and overtopping failures proving to be their main weaknesses. Thanks to engineering advances in the second half of the 20th century, many design flaws have been eliminated, and the risk of overtopping has decreased markedly for earth dams and almost disappeared for concrete dams.

New dams are the least secure, a reversal of a trend in the 21st century.

Contemporary dam failures observed in 2014 in Vietnam and 2018 in Laos, among others, have renewed international discussion of the safety of hydroelectric structures. The analysis shows that dams erected in the last decade are particularly at risk today. However, lack of technological knowledge is no longer considered a major cause of accidents. The two- to threefold increase in the frequency of overflows over the past two decades appears to be primarily related to the increase in flood risk.

The highest risk of dam failure has been found in the first five years after completion. The critical moment happens to be the first filling, during which hidden defects usually manifest themselves. After five years, the risk stabilizes and only increases after half a century, with the degradation of materials and mechanical wear and tear of moving parts. The latter fact is important because, according to ICOLD data, 53 percent of large dams are more than 50 years old, 16 percent are more than 70 years old, and 7 percent were built more than a century ago.

The higher the dam, the greater the risk

One of the key parameters considered in the Dutch-British team’s analysis was also the height of the structure. As expected, it turned out that the higher the dam, the more likely it was to fail. A 30-meter-high dam is subject to a 10 percent lower risk of failure than a 45-meter-high dam and a 20 percent lower risk than a 60-meter-high structure. Interestingly, above 100 meters, the risk seems to stabilize and even decrease, which may be due to the technical sophistication of huge structures.

The study’s authors note that this trend is very important, as the height of a dam translates into an increased scale of serious consequences in the event of a failure. Not only are large dams more susceptible to damage, but a disaster on them is associated with a greater threat to the population and infrastructure.

Regional differences in the safety of large dams

The risk of dam failure is clearly correlated with GDP calculated according to purchasing power parity in each country. This, of course, correlates with the potential for government authorities to invest in the construction, inspection and monitoring of hydrotechnical structures. Smaller financial resources in a region usually translate into a higher number of fatalities in the event of a disaster.

The likelihood of dam failure is particularly high in countries with lower GDP ppp, located in tropical and monsoon regions. The increasing intensity of heavy rains and flooding make structural safety monitoring and maintenance work crucial. In poor regions, investments in this area must be made at the expense of other public spending, often leading to neglect.

The fact that new dams fail so often can be explained in part by the climate change hypothesis. The conditions faced by new constructions are significantly different from those of decades ago, which does not everywhere go hand in hand with a change in safety standards. This regularity can be seen most clearly precisely in tropical and monsoon regions, while in temperate and dry climate countries with higher GDP levels, the number of failures seems to be decreasing.

Climate change is increasing the level of moisture in the air over the Indian Ocean, contributing to an intensification of the monsoon season. The authors of the analysis cite a 2020 study that says a 1°C increase in temperature translates into a 5-7 percent increase in rainfall intensity. When you add the risks associated with melting mountain glaciers in Asia and increasing the volume of glacial lakes, the need to reevaluate the risks for any large dam becomes obvious.

Forecasts for the future

It is clear from the analysis that the highest risk of failure is subject to:

• Earthen dams 10-80 m high built in the last 10 years in countries with low GDP;
• All earthen dams erected between 1900 and 1940;
• Concrete dams with a height of 50-150 m, built in the last 5-10 years;
• large earth dams erected in the last two decades in countries with low GDP.

After transferring historical trends to modern realities, it was shown that 4.4 percent of large dams are subject to a risk of failure greater than the normative threshold of 1/10000. Projections for 2023-2035 predict that 23 facilities will suffer actual physical damage, not including new dams built in the next decade. On a more optimistic note, 85 percent of the world’s large dams are twice as safe as current regulations require.

The conclusions of the study are clear – observation of changing hydrological conditions and meticulous monitoring of the technical condition of structures is the only way to prevent further disasters. The study’s authors emphasize the importance of dams to water, food and energy security in the regions, calling for the allocation of funds toward increasing the lifespan of structures while taking into account the challenges of climate change.