Rivers flowing into the sea are no waste
Farmer woes due to parched fields in central India and fisherfolk grappling with declining fish catches along the east coast, several hundred kilometres away, may seem very removed from each other. Yet the challenges that an altered river’s decreased functionality spark, can affect seemingly unconnected communities and livelihoods. We need to understand our rivers better before embarking on large-scale river transformations like river linking and inland water-ways which can change river systems altogether, says eco-hydrologist Jagdish Krishnaswamy, Senior Fellow at Bengaluru’s Ashoka Trust for Ecology and the Environment in an interview with The Hindu.
Complex systems yet to be understood
Riverine ecosystems are geologically, hydrologically and ecologically diverse, complexities that science is only beginning to unravel, says Krishnaswamy. The discovery of an entire fresh-water river flowing through the Bay of Bengal (parallel to the eastern coast) just two years ago is a classic case: sustained by the waters of the Ganga, Brahmaputra and Godavari, this river has tremendous 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,” says Krishnaswamy.
This also changes the false discourse that rivers draining their freshwater into the sea are a waste: a justification often used while constructing dams and reservoirs. Fresh-water, sediments and nutrients that flow into the sea help sustain mangrove, delatic and estuarine ecosystems along the coasts and support marine fisheries. Embarking on huge transformations like linking rivers (the transfer of water from one water basin to another) which could reduce the flow of rivers into oceans and seas, is as good as signing the death warrant of our estuarine and coastal ecosystems, from the Sunderbans to the mangroves of the Krishna delta or others along the west coast, adds Krishnaswamy. “We need to really rethink the value of rivers reaching the sea, economically and ecologically.”
However, science is yet to generate this information: there is a lack of interdisciplinary research to study these river systems from economic, ecological, climate and hydrological perspectives. “If we do not generate this knowledge and convey this to the society, judiciary and political representatives in the near future, we are likely to commit to large-scale transformations without having the knowledge of consequences.”
Actions and their consequences
The after-effects of some of these large scale river transformations could be like opening a can of worms. The move to make rivers navigational channels, for instance, would involve civil engineering, dredging and removal of sediments to facilitate the movement of barges. In the Ganga, this is likely to impair water quality, says Krishnaswamy.
“The sediment here has been absorbing pollutants and contaminants for a long time apart from natural toxins like arsenic. Dredging 10-15 metres of sediment from the river bottom could release these pollutants into the water; there is already some evidence of this,” he says.
Yet another fallout of this would be underwater noise, the increase in sonar waves in the water. This could interfere in the survival of India’s national aquatic animal the Gangetic dolphin, which relies solely on sonar and acoustics for activities from feeding to communication with other individuals. “There is evidence that signals from dredging and mechanisation of this river is interfering with the ability of dolphins to detect prey and communications between dolphins,” he says. “This species has been doing really well considering the natural changes, disturbances and threats it has encountered so far for millions of years– but this one might be really difficult to cope with.”
The consequences of linking rivers vary from the spread of invasive fish like piranhas (native to South American rivers) to transferring pollutants to intact river systems. “Homogenising our rivers also makes them less resilient to future climate change,” he adds.
However, this does not mean that river linking should not be attempted at all, says Krishnaswamy. “Learning from a smaller-scale project before embarking on large ones is important,” he says. We need to consider all other options before drastic transformations like river linking.
Another requirement is the availability of better climate models to predict rainfall. “The monsoon has been declining since the 1950s, but the models we use to project India’s future climate have not been able to simulate this decline in observed data. Therefore their effectiveness in predicting future climate is questionable.”
Prioritising river basins that are already regulated by dams, by preventing new ones on the last remaining free-flowing tributaries is also vital, he adds. “The cumulative impact of a series of small dams can be as devastating – or even more – than one large dam. We do know that it will have serious consequences for endemic fish diversity as well as ecosystem services and functions that these streams generate further downstream.”
A shift to less water-intensive crops would not only ease the pressure on rivers but also help in food and nutritional security too. “Prioritising crops like pulses or millets that require less water with support prices, their incorporation in the public distribution system, mid-day meal schemes, and the food industry creates an economic incentive for farmers to cultivate them,” says Krishnaswamy. This would save water that could instead flow in rivers and sustain fisheries, biodiversity and ecosystem services.
The need of the hour is a transparent platform to assess the changes occurring to our river ecosystems, he adds. “Even though India is so dependant on its monsoons and rivers, it is really remarkable or rather, unfortunate, how little we know about the flow and sediment dynamics of our river systems. Even data that does exist is largely not accessible due to disputes between state governments or India and neighbouring countries due to strategic, geopolitical issues…but we need to start now and establish river monitoring systems, sharing the data with scientists, farmers and fisherfolk and society at large to understand the short and long term dynamics of our river systems.”
First published by The Hindu