The developed world built numerous large dams from the 1920s to the 1970s. Today, hydropower is the world’s leading source of renewable energy, accounting for 71 percent of renewable energy in 2016.
However, this trend seems to be changing. Across Europe and North America, more dams are currently being dismantled than built.
A new study published in Proceedings of the National Academy of Sciences has given a damning analysis of the impact of large dams on the environment. Titled Sustainable hydropower in the 21st century, the study states that large dams disrupt river ecology, cause significant deforestation, decimate aquatic and terrestrial biodiversity, increase pollutant concentration by reducing water flow and release significant amounts of greenhouse gases through the decomposition of flooded forest and grasslands.
There is also a human cost to these dams. Their construction can cause widespread displacement of people and alter their livelihoods as well. Food systems, water quality and agriculture can also be negatively affected in the peripheries of large dams.
All of this has led to the decline of the hydropower sector in developed nations. Presently, hydropower now accounts for only 6 percent of US electricity. Furthermore, dams are now being removed at a rate of more than one a week on both sides of the Atlantic Ocean.
However, this does not mean that large hydropower projects have become a thing of the past. Thousands of new dams are being planned for the rivers of Asia and Africa, including the highly ecologically significant regions of the Amazon, Mekong and Congo. The study warns that the aforementioned dangers associated with large reservoirs are even more pronounced in these regions as their governments do not have the resources to control or reverse the damage caused by such megaprojects.
Traditionally, these mega dams are sold to the public as being cost efficient projects, but the study found that 90 percent of dams built since the 1930s proved to be more expensive than initially anticipated.
This revelation comes at a time when Pakistan is trying to build the Diamer-Bhasha dam, the world’s first crowd funded major water reservoir. It should also be noted that there have been reports over the years that the Diamer-Bhasha dam’s construction site is located in an unstable seismic zone.
Despite all this, the study does not call for the dismantling of all existing dams or the abandonment of all hydropower projects currently being planned. However, it does recommend that the governments of developing countries consider all the costs associated with major hydropower projects, and divert some of the resources being used towards other forms of renewable energy such as wind and solar power.