The idea has been put forward by experts on the Lieutenant Governor’s (L-G) committee on the Yamuna. The team comprises Professor Vikram Soni (of National Physical Laboratory), A K Gosain (IIT-Delhi), P S Datta (Indian Agriculture Research Institute), Manu Bhatnagar (INTACH ), and Diwan Singh (Natural Heritage First).

A blueprint for the scheme is being finalised.

“The scheme proves that if used properly, the Yamuna floodplain can provide at least 1 billion cubicmetres of water, which is three-fourths of Delhi’s water needs,” Soni said.

A floodplain is the lowland adjacent to a river, lake or ocean.

Soni said L-G Tejendra Khanna has been “very open to this fairly radical plan and has invited objections to the plan from 42 experts from organisations such as the Central Ground Water Board, Central Water Commission and NEERI. Following that the working plan and blueprint is being worked out by the Technical Committee.”

The plan suggests creating barrages with embankments at the Yamuna’s entry point to Delhi — at Palla, Wazirabad — between the places, and at Okhla, the river’s exit point. Up next, it suggests creation of a 30-40-metre-deep underground bund across the river at Okhla, similar to the natural bund in Wazirabad.

At Wazirabad, the bedrock rises, almost touching the riverbed, and the bund helps store water underground and prevent it from flowing downstream underground.

Subsequently, a controlled flood needs to be created by allowing excess monsoon water to flow from one barrage to cover the embanked plain to a depth of two feet for a few days by closing the next downstream barrage during monsoon, the study suggests. Recharge wells are to be dug where sandy layer is interspersed with less pervious clayey or gravelly layers.

“This is not an alternative but the only option for Delhi’s water problems,” Soni said. “New York gets its water from the Catskills forest, some 150 kilometres away, but Delhi does not have such an option. At a conservative estimate of 250 litres per day per person, we find that Delhi’s present population of 18 million requires 1650 million cubic metres (MCM) of water per year.

“Of this about 630 MCM comes from the Yamuna, over 300 MCM is derived from other river basins, and the rest is groundwater.”

Relying only on recycled water is unrealistic, he said, for the cost per person per year comes to Rs 9,000 — almost one-third the country’s per capita income. And rainwater harvesting can provide not more than 5 per cent of the city’s annual water demand, Soni stressed.