Defence Colony drain cleaned, desilted in 9-month operation

To clear the massive sediment buildup that had accumulated underneath, engineers relied on what MCD described as a “cut-skip-cut” method: breaking open 19 sections on the concrete cover at intervals of roughly 40 metres.

Work on cleaning and desilting the 1.3km-long Defence Colony drain – a subsidiary channel that ultimately empties into the Barapullah drain – is finally complete after nine months, the Municipal Corporation of Delhi (MCD) and the Delhi Pollution Control Committee (DPCC) have informed the National Green Tribunal (NGT) in separate affidavits.

MCD said the entire stretch was eventually desilted using backhoe loaders, power shovels and manual cleaning teams (File photo)

The drain, covered between 2009 and 2013 as part of a beautification project to create parks on top, had become inaccessible. To clear the massive sediment buildup that had accumulated underneath, engineers relied on what MCD described as a “cut-skip-cut” method: breaking open 19 sections on the concrete cover at intervals of roughly 40 metres.

These openings allowed mechanical access to the drain bed for desilting and were later resealed using steel sheets that can be easily removed in the future, ensuring the drain remains accessible and does not trigger waterlogging during the monsoon, according to the affidavits.

In its December 10 report, MCD noted that although the Defence Colony drain is technically a stormwater drain, it has long been receiving sewage flows from Greater Kailash, Andrews Ganj and surrounding neighbourhoods. “During inspection, it was observed that the existing ventilation shafts were blocked, and accumulation of hazardous gases rendered entry unsafe. The three available access ramps were therefore inadequate for safe mechanical de-silting,” the report said.

MCD said the entire stretch was eventually desilted using backhoe loaders, power shovels and manual cleaning teams. The removed silt and debris – estimated between 22,000 and 24,000 tonnes – was transported to the Okhla landfill. After cleaning, the openings created in the concrete were secured with mild-steel sheets for future access.

“The three existing ramps, which serve as essential access points for mechanised equipment during desilting and maintenance, have also been secured with mild-steel enclosures. These ramps will remain functional for routine upkeep,” the affidavit said.

Sewage gap persists

In a parallel submission, DPCC flagged a significant gap between the sewage Delhi generates and the volume treated – about 88 million gallons per day (MGD), or 11% of the city’s total sewage load of 792 MGD. The committee said that while 28 of Delhi’s 37 sewage treatment plants (STPs) currently meet prescribed norms, nine plants continue to fall short of standards.

The NGT is hearing multiple pleas filed by residents of Nizamuddin West, Defence Colony, Shahdara and other neighbourhoods seeking urgent intervention to stop sewage from flowing into stormwater drains – a problem that has led to odour and recurring waterlogging.

In its December 10 update, DPCC said that of the 22 major drains carrying sewage to the Yamuna, 10 had been fully “trapped” and diverted to STPs, while two – the Delhi Gate drain and Sen Nursing Home drain – were partially trapped. The Najafgarh and Shahdara drains, the city’s largest, cannot be trapped due to their size, while several other drains remain untrapped.

Delhi generates around 792 MGD of sewage, equivalent to 80% of the 990 MGD of water supplied by the Delhi Jal Board. While the installed treatment capacity stands at 794 MGD, only 704 MGD is currently being utilised, the DPCC said. It added that letters have been issued to the DJB to take corrective action at non-compliant STPs.