As the water level of the Yamuna in Delhi breached the all-time record of 207.49 metres set 45 years ago, experts attributed the situation to the encroachment of floodplains, extreme rainfall in a short duration, and the accumulation of silt, which elevated the riverbed.
At 1 pm, the river swelled to 207.55 metres, surpassing the previous record set in 1978, and causing further inundation of areas near the floodplains.
Thousands of people have been shifted to safer areas as water gushed into their homes and markets near the river.
In view of the grave situation, the Delhi Police imposed prohibitory measures under CrPC section 144 in flood-prone areas of the city, preventing unlawful assembly of four or more people and public movement in groups.
A senior official at the Central Water Commission (CWC) said, "We noticed that the water released from the Hathnikund Barrage took less time to reach Delhi compared to previous years. The main reason could be encroachment and siltation. Earlier, the water would have had more space to flow. Now, it passes through a constricted cross-section." The water from the barrage at Yamunanagar in Haryana, around 180 kilometres from the national capital, takes around two to three days to reach Delhi.
Manu Bhatnagar, Principal Director of the Natural Heritage Division at the Indian National Trust for Art and Cultural Heritage (INTACH), identified extreme rainfall in a short duration as the primary reason for the raging Yamuna in Delhi.
"The same amount of water falling over a longer period of time would not lead to such a situation, as it allows time for the water to pass through. Even a lesser amount of precipitation can result in a higher level downstream if it falls in a shorter period of time," he explained.
Country representative of the International Union for Conservation of Nature (IUCN), Yashveer Bhatnagar, attributed the record water level in the Yamuna to intense rainfall in the entire upper catchment area. He said, "Encroachment of the floodplains may have an incremental effect." Bhim Singh Rawat, associate coordinator of the South Asia Network on Dams, Rivers, People (SANDRP), said a major reason for the unprecedented rise in the Yamuna's water level is the riverbed's elevation due to significant silt accumulation.
"More than 20 bridges within the 22-km river stretch from Wazirabad to Okhla obstruct the flow, leading to the deposition of silt in the riverbed and the formation of numerous mid-stream sandbars," he told PTI.
The locations of these sandbars include beneath the Signature Bridge, between the ITO barrage and Yamunabank, between ISBT Kashmiri Gate and ORB (Old Railway Bridge), and between ORB and Geeta Colony Bridge.
In 1978, the river reached a height of 207.49 metres in September after becoming saturated in the monsoon season and it coincided with a flow rate exceeding 7 lakh cusecs from the Tajewala Barrage, Rawat said.
The maximum flow rate this time was 3.59 lakh cusec on Tuesday.
Major floods in Delhi occurred in 1924, 1977, 1978, 1995, 2010 and 2013.
Analysis of flood data from 1963 to 2010 indicates an increasing trend for floods occurring in September, and a decreasing trend in July, according to research.
An official of the Delhi Irrigation and Flood Control Department explained that the sharp rise in water level was due to continuous rainfall in the upper catchment areas and saturated soil from heavy precipitation in Delhi and nearby regions over the weekend.
People living in low-lying areas have been shifted to safer places at higher altitudes, the department said.
It said 45 boats have been deployed for awareness, evacuation and rescue work and NGOs have been roped in to provide relief to the evacuated people.
"The Old Railway Bridge has been closed for traffic. All gates of the Okhla Barrage have been opened to release excess water and prevent prolonged high water levels," the department said.
Delhi Chief Minister Arvind Kejriwal urged the Centre to intervene to ensure that levels of the Yamuna don't rise further.
In a letter to Union Home Minister Amit Shah, he requested that "if possible the water from Hathnikund Barrage in Haryana be released in limited speed" and pointed out that Delhi is set to host the G-20 Summit meeting in a few weeks.
"The news of flooding in the capital of the country will not send a good message to the world. Together we will have to save the people of Delhi from this situation," Kejriwal said.
The swelling of the Yamuna river led to waterlogging in the Delhi Transport Corporation headquarters area near ITO. Its employees waded through the waterlogged entrance to get into the office on Wednesday.
In northeast Delhi's Gandhi Mendu and Usmanpur villages, flood water has risen to over four feet, local MLA Ajay Mahawar said, adding that the residents have already been moved to safety.
According to the CWC, the flow rate at the Hathnikund Barrage increased to 3,59,760 cusecs at 11 am on Tuesday, the highest in the last three days. It oscillated between 1 lakh cusec and 3 lakh cusec on Wednesday.
Normally, the flow rate at the barrage is 352 cusecs, but heavy rainfall in the catchment areas increases the discharge. One cusec is equivalent to 28.32 litres per second.
The India Meteorological Department predicted heavy rain in Uttarakhand and Uttar Pradesh over the next two days, raising concerns about a further rise in the water level in rivers.
Jammu and Kashmir, Himachal Pradesh, Punjab and Haryana recorded "heavy to extremely heavy" rains over three days from Saturday. This resulted in overflowing rivers, creeks and drains that have massively damaged infrastructure and disrupted essential services.
Delhi witnessed its highest rainfall (153 mm) in a single day in July since 1982 in the 24-hour period ending at 8:30 am on Sunday. The city received an additional 107 mm of rain in the subsequent 24 hours, exacerbating the situation. The heavy rain transformed roads into gushing streams, parks into watery labyrinths and marketplaces into submerged realms.
The Yamuna river system's catchment covers parts of Uttar Pradesh, Uttarakhand, Himachal Pradesh, Haryana, Rajasthan, Madhya Pradesh and Delhi.
The low-lying areas near the river in Delhi, inhabited by around 41,000 people, are considered prone to flooding. Encroachments on the river floodplain have occurred over the years, despite the land belonging to the Delhi Development Authority, the revenue department and private individuals.
The Yamuna breached the danger mark twice in September last year, with the water level reaching 206.38 metres.
In 2019, the river witnessed a peak flow rate of 8.28 lakh cusecs on August 18-19 and the water level rose to 206.6 metres. In 2013, it reached a level of 207.32 metres.
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