BBD Bag: The data obtained from the two-day survey of Laldighi, which completed on Saturday, will be used in designing the southern diaphragm wall of East-West Metro's New Mahakaran station.

Private infrastructure firm Afcons, which is building the station and the twin tunnels of the Metro between Howrah Maidan and Esplanade, conducted the survey.

A six-member team surveyed the BBD Bag water body for 12 hours over two days. "The lake has been found to be 170m in length and 135m in breadth. It is 6m deep in the middle, while the depth of the shallowest part is 1.5m," an Afcons official said.

"We have provided the findings of the survey to the designers. Based on the data, they will finalise the design for the southern diaphragm wall of New Mahakaran station," said Virinder Kaul, project manager, Calcutta, Afcons.

"Work on building the wall is likely to start in February. We are expecting to complete the station by early 2020."

A boat was used to measure the depth of the water at various points.

A calibrated steel chain tied to a concrete block was thrown into the water from the boat. The block was pulled up by the chain after it hit the bed of the lake. The surveyors on the boat calculated the depth of the water at that point from the markings on the chain.

Another surveyor, standing on the banks with a machine called Total Station, was guiding the boat across the lake.