Delhi govt plans check dams on major drains to trap pollutants

The Delhi government is working on creating low-cost check dams in at least 20 “strategic locations” on major drains to reduce the pollutant load being released into the Yamuna by 70-80%, senior officials said.

While two such check dams have already been installed -- on the supplementary drain near Rithala and Rohini sewage treatment plant and on the Shahdara drain -- on a pilot basis, officials said the project will be expanded to the rest of the locations once its tested during the monsoon when water level in the drains rise.

A senior official privy to the developments explained that the idea behind installing these check dams or weirs is to increase the travel time of drain water so as to allow solid pollutants, primarily sewage from nearby unauthorised colonies, to settle down before the water is released into the river. Officials said it will also strengthen the biological treatment process.

“The primary idea behind constructing these weirs is to increase the time taken for the drain water to reach the river. For instance, if it took eight hours for the drain water to reach the river earlier, now we will increase it to 24 hours, by blocking the flow of the drains at these strategic locations. What we are achieving by this is that, first, when a wall is created, the solid pollutants settle down before the water overflows from the weirs, and second, the time for microbial treatment or the natural treatment process of drain water increases,” the official explained.

He said that these weirs will act as checkpoints, beyond which untreated wastewater will not move forward.

Delhi Jal Board (DJB) data shows that the Capital generates around 720 million gallons of wastewater per day, of which around 525 million gallons is treated by sewage treatment plants. While there are five major drains — at Najafgarh, Shahdara, Barapullah, Delhi Gate and Mori Gate -- carrying wastewater to the Yamuna, the 20 check dams will be installed only on the drains at Najafgarh, its supplementary channel and the one at Shahdara. Curiously, apart from local polluting sources, the Najafgarh and Shahdara drains also gets waste from Uttar Pradesh and Haryana.

Government estimates show that with these check dams, the pollutant load entering the Yamuna from these drains will drop by nearly 70-80%.

Officials explained that these weirs are based on “in-house designs”, each of which cost the government ₹4-5 lakhs. Going by this figure, the construction of around 20 weirs, which is the government target, will be completed with a budget of under ₹1 crore.

“The cubes used for the weirs have all been constructed and assembled on site. We have also taken into consideration that in case of emergency, when Delhi receives extremely heavy rainfall, these cubes can be lifted and kept aside. However, the design of the weirs has taken into consideration the fact that during monsoon, water level will rise and can easily overflow,” the official explained.

Bhim Singh Rawat, from South Asian Network on Dams, Rivers and People, said that bioremediation is a known method to clean water bodies, but it’s success depends on how polluted the water body is. “For instance, the Najafgarh drain is highly polluted and carries discharge from industries and household. The check dams may not have a visible effect but it is a promising start,” he said.