SCI-TECH & AGRI

Knowing our rivers better before changing them

Science is yet to understand the complexity of riverine ecosystems which are geologically, hydrologically and ecologically diverse, says Jagdish Krishnaswamy, eco-hydrologist at Bengaluru's Ashoka Trust for Ecology and the Environment. He said this in connection with the need to understand our rivers better before embarking on large-scale river transformations like river linking and inland waterways.

The recent discovery of an entire freshwater river flowing through the Bay of Bengal (parallel to the eastern coast) is a classic case. Sustained by the waters of the Ganga, Brahmaputra and Godavari, this river has great consequences for biodiversity, ecosystem services and fisheries. “Some scientists’ work suggests this could even affect the salt balance between the Arabian Sea and Bay of Bengal, possibly impacting climate regulation,” he says.

This also changes the false discourse (used while constructing dams) that rivers draining their freshwater into the sea are a waste. Freshwater, sediments and nutrients that flow into the sea help sustain mangrove, delatic and estuarine ecosystems, supporting marine fisheries. Embarking on huge transformations like linking rivers which reduces the flow of rivers into oceans and seas could affect ecosystems and livelihoods, says Dr. Krishnaswamy.

The lack of interdisciplinary research to study these river systems from economic, ecological, climate and hydrological perspectives could also force us to commit to large-scale transformations without having the knowledge of their consequences, he adds.

The after-effects of some of the large-scale river transformations could create more problems. Making rivers navigational channels, for instance, would involve dredging.In rivers like the Ganga, where sediment has been absorbing pollutants for a long time, there is already evidence that dredging causes the release of toxins including arsenic, says Dr. Krishnaswamy.

Underwater noise (sonar waves due to use of machinery) can interfere with the survival of India’s national aquatic animal — the Gangetic dolphin — which relies solely on sonar and acoustics for survival. “This species has been doing really well considering the natural changes, and disturbances it has encountered for millions of years, but this one might be really difficult to cope with,” he says.

The consequences of linking rivers vary from the spread of invasive fish like piranhas to transferring pollutants to intact river systems. “Homogenising our rivers also makes them less resilient to future climate change,” he adds.

We need to consider all other options before drastically transforming our rivers, he adds. “Learning from a smaller-scale project before embarking on large-river linking schemes is important,” he says. Other vital steps include preventing new dams on the last remaining free-flowing tributaries, as well as a shift to less water-intensive crops that will not only ease the pressure on rivers but also help in food and nutritional security.

The need of the hour is a transparent platform to assess the changes occurring in our river ecosystems. “Even though India is so dependant on its monsoons and rivers, it is really unfortunate, how little we know about the flow and sediment dynamics of our river systems,” he says. “Even data that does exist is largely not accessible due to disputes between States or countries. We need to start now and establish river monitoring systems, sharing data [with all stakeholders] to understand the short- and long-term dynamics of our river systems.”