Small hydropower project graveyard for fish: Study

Small hydropower projects, long viewed as environment-friendly alternatives to large dams, themselves appear to threaten the diversity and populations of native freshwater fish, a study on river tributaries in the Western Ghats has suggested.

By G.S. Mudur
  • Published 3.06.18
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The Mahseer. Picture credit: Asghar Nawab / WWF-India

New Delhi: Small hydropower projects, long viewed as environment-friendly alternatives to large dams, themselves appear to threaten the diversity and populations of native freshwater fish, a study on river tributaries in the Western Ghats has suggested.

The study by scientists in multiple institutions in Bangalore has foundsignificantly lower levels of fish species diversity and richness in segments of two tributaries of Karnataka's Netravathi river with small hydropower project dams compared to an undammed tributary.

"Small hydropower projects lower the catch-per-siteof native freshwater fish adapted to free-flowing water and allow species adapted to stagnant or pond-like waters to proliferate," said Shishir Rao, a river ecologist and study team member with the Wildlife Conservation Society, India.

Rao and his colleagues examined fish species diversity along three tributaries with similar rainfall conditions, stream behaviour and terrain - two of which had small hydropower dams. The dams were found to influence stream geometry, water chemistry and fish.

They observed that the catch-per-sitenumbers for several endemic fish, native to the waters, including an iconic fish called the Mahseer, were lower in the tributaries with the small hydropower dams than in the tributary without the dam.

The Malabar baril is another example of a native species affected by small hydropower projects.

"The alterations in water flow induced by the small hydropower projects appear to impact the diversity of native fish," said Rao.

The study's findings were published on Wednesday in the journal Aquatic Conservation: Marine and Freshwater Ecosystems.

Even a small dam, Rao said, depletes the flow of water immediately ahead of the reservoir while the canal used to divert and release water to operate turbines leads to periodic torrent-like flow conditions downstream.

The study is among the first to assess impacts of small hydropower projects in the forested regions of the Western Ghats on fish diversity.

"Since small hydropower projects divert water for long distances, they leave stretches of the river almost completely devoid of water flow in the dry season," said Suman Jumani, the lead author of the study with the Foundation for Ecological Research Advocacy and Learning.

"The water in these stretches had lower oxygen levels and higher water temperature - such habitat alterations strongly affected freshwater fish assemblages," she said.

Environmental scientists point out that India has over 1,266 small hydropower projects, most of them along tributaries of rivers along the Western Ghats and in the Himalayan region.

They say proponents have identified more than 6,400 more sites for small hydropower projects.

Small hydropower projects have been promoted as more friendly to the environment compared to large dams and giant reservoirs that lead to the submersion of vast tracts of land, often displacing local communities there and changing local ecosystems.

But, Jumani said, small hydropower projects are defined not based on their ecological footprints but rather on their installed capacity - dams that produce up to 25MW of power.

India had a cumulative capacity of about 4,400MW from small hydropower projects in December 2017 with the most projects in Arunachal Pradesh, Himachal Pradesh, Karnataka and Uttarakhand.

But the Union ministry for new and renewable energy, tasked with developing small hydropower projects, estimates that the power generation potential from such projects is about 20,000 MW.

The WCS researchers say given the ambitious targets for the future, there is need for changes in small hydropower project operations and policies to enable conservation of river fish diversity.

"Many are likely to be located in the ecologically fragile regions such as the Himalayas and the Northeast," said Rao.

"There is need for regular monitoring of the impacts of small hydropower projects to understand how they are affecting local river ecosystems."