Dams, despite their gains, are hardly ever free from controversy. They throw the ecology of their surroundings off—migrating fish species can’t reach breeding grounds and often die out, setting off a chain of consequences for the food-chain; damming impacts local flora dependent on an uninterrupted supply; and contrary to the purpose of improving access to water through storage, dams often bring down river capacity by as much as 25% because of silting.
Hence, dam removal has been gaining ground in developed nations—the US alone has retired and brought down over 1,200 man-made barriers to the flow of the river in the last couple of decades while in France, Sweden, Spain, Finland and the United Kingdom, over the past 20-25 years, at least 5,000 small dams, weirs and culverts have been removed, reports Nature. Recently, Spain has started dismantling is Yecla de Yeltes dam, the largest in the European Union to be decommissioned—this has been hailed as a milestone for river restoration. Studies show that the effects of dam removal have been beneficial for the ambient ecology.
India, the third largest dam-building nation in the world after China and the US, has more than 5,000 large dams. To prevent ecological degradation, should it do what the West is doing? That’s a hard question to answer. Some scientists call for more research into the adverse effects of dam removal, since it could dislodge toxic sediment and also help invasive species spread.
Also, while ecological considerations must be factored in while evaluating dam proposals, it helps to keep in mind that there are more sustainable alternatives that can serve the some of the purposes that dams serve. Japan relies on sub-surface dams to store river water underground, rather than pooling it in reservoirs. This is far more sustainable since it cuts evaporation losses while not altering the river’s flow.