Even small dams have severe impact on river ecology


Mains Paper 3: Environment | Conservation, environmental pollution and degradation, environmental impact assessment

From UPSC perspective, the following things are important:

Prelims level: Nethravati River, Various zones of a Dam

Mains level: Need for EIA of small dams and hydropower project


Study conducted on Nethravati River, K’taka

  1. We often assume that small dams cause less environmental problems than large ones due to low submergence area.
  2. A study on small hydropower projects in India proves that they cause as severe ecological impacts as big dams, including altering fish communities and changing river flows.
  3. Such projects receive financial subsidies — even carbon credits — for being ‘greener’.
  4. To see how green such small dams really are, scientists from organisations including Bengaluru’s Foundation for Ecological Research, Advocacy and Learning (FERAL) compared almost 50 kilometers of river tributaries of the Netravathi river in the Western Ghats of Karnataka.
  5. They studied three zones in detail: above the dam (upstream), in the area between the dam’s wall and the powerhouse, sometimes completely devoid of water (‘de-watered’) and below the powerhouse (downstream).

Outcomes of the Study

  1. Water flow in the dammed sections reduced the stream’s depth and width;
  2. Water in these stretches was also warmer due to low depth
  3. These rivers had lower dissolved oxygen levels
  4. These changes were most evident in the ‘de-watered’ zones and worsened in the dry seasons.

Habitat quality is worst hit

  1. This decrease in habitat quantity and quality showed in fish diversity too.
  2. The team found that un-dammed stretches recorded a higher diversity of fish species, including endemics (species seen only in the Western Ghats).
  3. The upstream and downstream stretches get disconnected and this impedes the river.

Need for EIA

  1. Such small hydro-projects cropping up on rivers in the Ghats is a serious worry especially because they do not require environmental impact assessments.
  2. It is not a question of small versus big dams; Small dams are not necessarily bad if there are proper regulations in place.
  3. Regulations could include limiting the number of dams in a river basin or maintaining a minimum distance between dams on the same river stretch.
Disasters and Disaster Management – Sendai Framework, Floods, Cyclones, etc.
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