Delhi’s Yamuna has lost 68% of its width in 200 years, new study finds

A river that once spread across nearly 658 metres through Delhi in 1799 now measures roughly 210 metres, according to a new study by geology researchers at Delhi University and the Indian Institute of Science Education and Research (IISER), Bhopal. The research, published in the Journal of Geological Society of India, found that the Yamuna’s average width in the capital has shrunk by close to 68% over 200 years, while its estimated discharge has fallen by 89% since the late 18th century.

To arrive at these numbers, the researchers reconstructed changes along the 50-km Delhi stretch of the river using historical maps dating back to 1799, old topographic surveys, satellite imagery and river-width analysis. The estimated discharge, they found, declined from close to 30,000 cubic metres per second to around 3,900 cubic metres per second over the same period.

The study attributes the change to a string of engineering interventions rather than any shift in climate. It traces the pattern back to the British-era Tajewala and Okhla barrages built in the 1870s, followed later by the Wazirabad, ITO and Hathnikund barrages. Professor Vimal Singh of Delhi University’s geology department, one of the study’s authors, said ‘water gets diverted and the river itself has little water downstream because of the barrages and canals upstream.’

Singh explained that as Delhi’s population grew, the city needed room to expand, and land that only floods for around 15 days to a month each year began to be viewed as vacant rather than part of the river’s natural floodplain. ‘People started seeing this as vacant land and started encroaching upon it,’ he said, adding that embankments built in response have compounded the effect. ‘This is happening all over the world,’ he said.

The researchers also found that about a third of Delhi’s floodplains have become disconnected from the river over the last century because of embankments and urban development, while the area of river islands and channel bars fell from roughly 20 square kilometres in 1985 to about 4 square kilometres by 2020. They noted that Delhi’s population has grown from around 250,000 in the early 19th century to about 21.5 million today, even as the river’s discharge has moved in the opposite direction.

Alongside Singh, the study was authored by professors Sampat Kumar Tandon and Tanya from Delhi University’s department of geology, and Kumar Gaurav of IISER Bhopal. The team cautioned that historical maps vary in accuracy and that some early surveys were prepared for tourism rather than scientific use, meaning their estimates should be read as reconstructions rather than exact measurements.

Image credit: Wikimedia Commons/by Goutam1962