The Kolkata Municipal Corporation (KMC) will lay underground drainage lines along 12.87km of roads in a part of Behala that till now has open drains.

The main underground sewer lines in this part of Behala — Ward 122 — have been laid already, but sewer lines connecting the homes to the main sewer network will be laid now.

Ward 122 covers parts like Sodpur, Kazipara and Sukanta Pally in Behala and also parts of Haridevpur.

The mayoral council of the civic body on Wednesday gave its nod for the ₹20.45-crore project to lay the lines following which the sewerage and drainage department of the KMC will invite bids to carry out the work.

“We will float the tender to invite bids for the work. We are expecting that the laying of underground lines will start after Durga Puja. It will take about one year to complete,” said a senior official of the KMC.

Large stretches of Behala still lack an underground drainage network. The rainwater as well as sewage discharged from homes and other buildings flow through these open (surface) drains. These are public health hazards, said a KMC official.

“Most of these drains were built based on the need at that time. There was no comprehensive planning,” said another official.

Lack of cleaning and the habit of people throwing waste into open drains often end up clogging them.

During heavy rains, the drains often overflow and there are risks that pedestrians may fall into a surface drain on a waterlogged street.

“The main sewer lines under the wider roads were laid over the last three or four years. But the main lines have to be connected to the homes. The work to lay the intermediate lines between the main sewer lines and the home will be taken up now,” said another official.

The work will require digging of narrow lanes and bylanes.

The main sewer lines were laid as part of the Kolkata Environmental Improvement Investment Programme, a project funded by the Asian Development Bank. The project aims to create underground drainage infrastructure in parts of Calcutta that lacks underground drainage.

The KMC is the executing agency of the project.

Besides the underground sewer lines, the project will include the construction of 1,210 manholes and 2,420 gully pits or catch pits, which are outlets through which rainwater accumulating on the road goes into the underground network.