Human activities altering Ganga basin: Study

Study finds rise in flood events in Alaknanda and Bhagirathi rivers

Human activities have had a disastrous impact on the Ganga river basin, ranging from severe pollution to changing its course, and are behind the landslides and floods seen in recent years, according to a new study.

The grim findings were published in Scientific Reports journal by researchers from the Indian Institute of Science (IISc) and the Indian Institute of Technology, Kanpur (IITK) and warned of a further increase in the magnitude of extreme flows and occurrence of floods in the Ganga basin.

For the study, researchers analysed the effects of past human activity on mountainous regions, focusing on Bhagirathi and Alaknanda: two major tributaries which merge at Devprayag to form the Ganga, the lifeline of half a billion Indians.

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Researchers examined data on rainfall, water discharge in the rivers and sediment load from weather stations across the Upper Ganga Basin from 1971 to 2010. They analysed the data corresponding to two periods: pre-1995 and post-1995.

What they found was a steady increase in the number of flooding events in both river basins after 1995. The change in low flows and middle-level flows in Bhagirathi can be attributed to three major dams — Maneri, Tehri, and Koteshwar — on the river, they said.

The Alaknanda basin saw a doubling of water flow from 1995 to 2005 at Joshimath weather station, while also seeing an increase in the rate of flow of water, termed extreme flow.

“We observed that the basin has a high, statistically increasing rainfall trend, unlike the Bhagirathi basin. Most of these trends were observed in the downstream region of the Alaknanda. Therefore, we have also seen an increase in the magnitude of extreme flow in these regions,” said Somil Swarnkar, a post-doctoral fellow at the IISc’s Interdisciplinary Centre for Water Research (ICWaR), and first author of the study.

After 2010, the building of dams in the Alaknanda region might have modified the water activity in addition to climatic changes, researchers suggested.

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“Due to abrupt changes in water flow, sediment depositions in the upper reaches of the Ganga have led to changes in the sediment composition downstream. The Tehri dam, for instance, blocks sediment flow from upstream and controls the volume of water that flows downstream. At the same time, dams have also been instrumental in reducing flood peaks downstream,” the researchers said.

Professor Pradeep Mujumdar of ICWaR, corresponding author of the study, said dams will "likely affect the water flow" in these regions.

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