It is hard to think of a better symbol of mankind’s mastery over nature than dams and barrages, which hold back the power of water. More than 50,000 dams over a height of 50 feet (15 meters) have been built across rivers of the world, causing unprecedented changes to the planet’s hydrology.
The benefits of dams are well known. They are a relatively “clean” source of electricity that can adapt to demand. They also enable irrigation, allowing a considerable rise in crop yields: the 20% of irrigated crops worldwide represent 40% of production. The majority of the world’s dams are used for agricultural rather than hydroelectric purposes.
But dams also have a darker side, as has been demonstrated by an international group of experts—the World Commission on Dams. The issue was examined from three major perspectives. From an economic point of view, the planned costs of dam development, which are almost always supported by taxpayers, are regularly underestimated. At the same time, the economic benefits are frequently overestimated, particularly in developmental terms. On a social level, dam-building projects, especially in the countries of the South, are rarely profitable to all. Rural farmers are often forced off the land and into overcrowded cities. From an ecological perspective, finally, the trapping of sediment by dams has had destructive consequences for the deltas of almost all the world’s major rivers, causing them to deepen, and increasing erosion. Many wetland areas with rich biodiversity have been flooded, water quality has been affected and fish migration disturbed. In tropical zones, dams can also lead to an increase in methane, which adds to global warming.
As a result, a more reponsible attitude to dam construction is taking hold. The desire to tame nature is now being replaced by a wish to “collaborate” with it. An era of smaller-scale dams, based on more thorough studies of environmental impact, may come to supersede the day of the all-powerful civil engineer.