How barrages and concrete turned the Yamuna into a shadow of its 1799 self

A string of barrages and embankments built over nearly 150 years has fundamentally reshaped the Yamuna as it flows through Delhi, according to a new study by geologists from Delhi University and the Indian Institute of Science Education and Research (IISER), Bhopal. The researchers trace the transformation back to the British-era Tajewala and Okhla barrages built in the 1870s, followed by the Wazirabad, ITO and Hathnikund barrages built in subsequent decades.

The cumulative effect, the study found, has been dramatic. The river’s average width in Delhi has shrunk by nearly 68%, from around 658 metres in 1799 to about 210 metres today, while its estimated discharge has dropped by 89%, from close to 30,000 cubic metres per second to around 3,900 cubic metres per second since the late 18th century. The findings were published in the Journal of Geological Society of India.

Professor Vimal Singh of Delhi University’s geology department, one of the study’s authors, said the barrages and canals upstream have diverted water away from the river, leaving little flow downstream. He linked this directly to how the city has treated the Yamuna’s floodplain over time: with the river now flooding for only around 15 days to a month each year, the rest of the floodplain came to be seen as unused land. ‘People started seeing this as vacant land and started encroaching upon it,’ Singh said, noting the same pattern of encroachment and embankment-building has occurred with rivers ‘all over the world.’

To reach their conclusions, the researchers reconstructed 200 years of change along the 50-km Delhi stretch of the river using historical maps from 1799, old topographic surveys, satellite imagery and river-width analysis. They found that roughly a third of Delhi’s floodplains have become disconnected from the river over the past century because of embankments and urban development, while river islands and channel bars shrank from about 20 square kilometres in 1985 to around 4 square kilometres by 2020.

The study also connects the shrinking river channel to recent flood behaviour. During the 2023 floods, Delhi recorded its highest-ever water level despite a lower peak discharge than the devastating 1978 flood, which the authors attribute to embankments and floodplain encroachment forcing water to stay confined within a narrower corridor instead of spreading laterally.

Besides Singh, the study’s authors include professors Sampat Kumar Tandon and Tanya of Delhi University’s geology department and Kumar Gaurav of IISER Bhopal, who caution that the historical maps used carry some uncertainty and that the estimates should be treated as reconstructions rather than precise measurements.

Image credit: Wikimedia Commons/by Goutam1962