Ecological and social impacts of constructing dams

Introduction

Dams store water for irrigation, drinking and electricity, and they bring real economic gains. Their costs are ecological and social, and both spread far beyond the dam site, up and down the whole river valley.

Ecological impacts

• Submergence. Large areas of forest and agricultural land go under the reservoir.
• Damage to wildlife. Animal populations are dislodged, their habitat is damaged and their migration routes are cut.
• Changed rivers. A dam fragments and physically transforms the river and seriously affects riverine ecosystems.
• Waterlogged and saline land. Land around the project becomes waterlogged and saline.
• Silting. Silt, made worse by deforestation in the catchment, fills the reservoir and shortens its life.
• Floods. Dams and canals can lead to major floods in the monsoon, and drained wetlands no longer soak up high rainfall.
• Greenhouse gases. Rotting vegetation and carbon flowing in from the catchment release these gases from reservoirs.
• Earthquake risk. In certain regions a large dam can induce seismic activity.

Social impacts

• Displacement. In India, 16 to 18 million people have been displaced by dams, and 40 to 50 per cent of them were tribal people, who form only about 8 per cent of the population, taken at one billion.
• Poor resettlement. Most projects have failed to resettle those affected, and arable land is rarely found for them.
• Mental and cultural loss. Being uprooted from a place of long family roots causes emotional trauma, and tribal people find it hardest to adapt.
• Pressure on host communities. People already living at the resettlement site also suffer, and conflict over resources follows.
• Unequal costs and benefits. Poor tribal people lose their homes and fishermen their livelihood, while rich landholders downstream gain most; costs and benefits fall on different people, which is a question of fairness.
• Lost livelihoods and water conflicts. Fishing and boat travel are disrupted, and power, farming, homes and industry compete for the same water.
• Weak compliance. An Indian assessment of dams cleared in the 1980s and 1990s found that in 90 per cent of cases the authorities had not met the environmental conditions attached to clearance.

Conclusion

A dam's benefits are real, but they go largely to people far from the valley, while the river and the valley's people bear the costs. Decisions on dams must count both sides honestly, involve those affected, and ask first whether watershed work or smaller dams would serve.