Siltation, encroachment, lack of dredging and flushing are to blame, experts tell DTE
This is the second of a 3-part ground report on the Delhi floods
Several parts of the national capital Delhi started to flood after the Yamuna river crossed its evacuation mark on July 11, 2023.
The flooding happened despite water released from Haryana’s Hathnikund barrage being less than previous flood years. A section of experts told Down To Earth (DTE) that the flooding was human-induced and completely avoidable.
“If we look into the history of Delhi floods, the last time the city witnessed such record-breaking floods was in 1978. Back then, the highest water level the Yamuna reached in Delhi was 207.49 metres,” Himanshu Thakkar, coordinator of South Asia Network on Dams, Rivers & People, told DTE.
This water level had never been breached since 1978. “At the time, water used to be released from the now-decommissioned Tajewala barrage in today’s Yamuna Nagar district (carved out of Ambala in 1989), not Hathnikund,” recalled Thakkar.
The amount of water released was 0.72 million cusecs. In 2010, when there was an extreme rainfall situation in Delhi, the release from the Hathnikund barrage was more than 0.7 million cusecs. But the surge in the Yamuna’s water level wasn’t even close to 207.4 metres.
In 2013, the amount of water released from the Hathnikund barrage into the Yamuna was more than 0.81 million cusecs. Yet, the surge in river water level didn’t approach the 1978 flood record.
In 2019, 0.83 million cusecs of water were released from the barrage into the Yamuna and the surge wasn’t even close to the record year.
“This year, it is astonishing that even though the peak release from the Hathnikund barrage into the Yamuna was a much lesser amount of 0.31 million cusecs and that too only for a span of two hours, it broke records. The water level of the Yamuna went up to 208.66 metres and crossed the surge record from 45 years ago by a considerable 1.17 metres beyond it,” Thakkar told DTE.
Thakkar said the deluge was as the result of the cumulative impact of several anthropogenic factors.
“A factor indeed could be rainfall in the catchment downstream from Hathnikund barrage up to Delhi. The rainfall was possibly higher than previous instances. But we need to specifically look at what is happening in regard to the riverbed and floodplains within Delhi,” Thakkar said.
First, he noted, the riverbed and floodplains had been encroached to a huge extent. Second, Thakkar drew attention to the obstructions caused by 30 bridges and flyovers crossing the Yamuna in Delhi, most of them completed but at least four under construction.
“All of these obstruct the flow of the river and are a key factor behind the alarming situation of the Yamuna today. Also, there has been an increase in the riverbed level due to indiscriminate sand mining and deforestation upstream as well as other factors,” Thakkar said.
All these factors increase the silt content in the river, which mostly gets deposited on the riverbed when it enters Delhi.
To make things worse, the flushing of river water downstream is taking place at such a small scale that the silt gets accumulated and the riverbed level goes up. This reduces the river’s carrying capacity, detailed Thakkar.
A number of cases of illegal farming taking place are witnessed along the course of Yamuna and that leads to encroachment of river as well.
Both Depinder Kapur, director, Water Program at the Centre for Science and Environment and water economist Gourishankar Ghosh also pointed to the Yamuna’s silting being a key factor.
Kapur said, “Sewage and solid waste are mixing with the waters of the Yamuna. According to my analysis as well as discussions with experts’ groups, the siltation could also be caused by untreated water. So, I find that plausible.”
The Yamuna, when it enters Delhi, is dry for seven-eight months. Meanwhile, wastewater from Delhi — which generates 1,000 million gallons of it per day — as well as from Haryana and Uttar Pradesh are probably also running into the Yamuna.
“The water supplied to and used by the people of Delhi is also going back and mixing with the river water the level of which is already up,” Ghosh had told DTE right before floods hit Delhi.
“A lot of wastewater contains sediments — both organic and inorganic waste — which are getting deposited on the riverbed. Sewers are either directly going into the river or because the river is flooded, the river water is coming in and pushing the sewage water back,” Kapur said.
This means the seven-eight months when the river runs dry, the sewers are emptying into it. “The water level of 208.6 metres hasn’t been seen ever in Delhi by this generation. This is the highest flood level and these factors which have triggered the situation, do compound it,” Kapur elaborated.
Thakkar agreed that the damaged drain regulator no. 12 in Delhi led to the flooding of the ITO and Supreme Court areas.
According to the experts, destruction of water bodies in the Aravalis and cloudbursts in the upper catchment of the river are also among the factors that compounded the situation and led to the deluge in Delhi.
“We are not even monitoring what is happening at various cross sections in Delhi at different points,” pointed out Thakkar.
“Among three main barrages in Delhi —Wazirabad, ITO and Okhla — the authorities were not able to open the sluice gates for ITO. This could have also contributed to the flooding in the Yamuna. To what extent, should be analysed,” he added.
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