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Advanced rain gauge raises dry road hope

A team led by an IIT Kharagpur professor has developed a mechanism to measure rainfall in the city at 15-minute intervals, a reading that can be of help to the civic authorities in preventing or tackling waterlogging.

The updated information automatically gets uploaded on a website.

At present, readings on the amount of rainfall in the city can be obtained from either the Met office at Alipore and Dum Dum or the drainage pumping stations of the Calcutta Municipal Corporation. But none of these places provides updates at such short intervals.

So far, the team — it includes a student from Calcutta’s Heritage Institute of Technology — has installed four such devices at the Alipore and Dum Dum Met offices, and two drainage pumping stations at Ultadanga and Behala.

“Our device comprises a bucket with a sensor fitted to it that tips after every .01 inch of rain. A micro-controller attached to the sensor counts the number of tips in 15 minutes,” said Dhrubajyoti Sen, a professor of civil engineering at IIT Kharagpur and the leader of the team that came up with the device calledtipping bucket rain gauge”.

The number of tips is converted to rainfall in millimetres and the message is transmitted to a server at IIT Kharagpur, from where the data is posted on the website.

The regular updates on which area is receiving how much rainfall can help civic engineers react quickly and take timely steps to prevent waterlogging.

Recent rainfall patterns have shown that areas separated by a few kilometres had vastly varied amount of rainfall. On June 18, Alipore had received 2.4mm of rain and Belgachhia 72mm. Between last Saturday evening and 1pm on Sunday, Ultadanga had received 129mm of rain and Ballygunge only 72mm.

The civic body has the infrastructure to measure rainfall at 18 locations across the city through rain gauges installed at drainage pumping stations. But the updates are not regular, depending on how frequently engineers at the civic headquarters are asking for the information.

The Sen-led team has also installed equipment at three of the civic drainage pumping stations to measure the water level in the sumps. A sump is the drainage channel at each pumping station into which underground sewer lines merge.

“The gadget can supplement the role of the tipping bucket rain gauge in preventing waterlogging,” said Sen.

“A rise in the water level of the sump will indicate that water is accumulating in the sewer lines quicker than it is being drained out. Civic engineers can instantly start looking for the reason and take steps to fix the problem.”

Amit Roy, the chief engineer of the CMC’s drainage and sewerage department said the National Disaster Management guidelines has called for 39 rainfall measurement centres in Calcutta, or one in every 4sq km.

The city has only 20 conventional rain gauge centres — at 18 drainage pumping stations and the Met offices at Alipore and Dum Dum.

Experts said the gadgets should be set up at locations other than the ones where the civic body has its rain gauges as rainfall is often a local phenomenon.

Harish Chatterjee Street and its vicinity had received 150 mm of rainfall on June 20. The water from the area is drained out through Ballygunge drainage pumping station, where the gauge recorded only 76 mm of rain.

Engineers at the pumping station did not have the information that Harish Chatterjee Street was receiving so much rain. “Flowing at a rate of two-and-a-half-feet per second through the sewer network, it took one 1 hour and 23 minutes for the water in the Harish Chatterjee Street area to reach the pumping station. Had the engineers known about the rainfall difference, they could have pressed more pumps into operation in advance and water could have been drained out quicker,” said an official.

Each of the tipping buckets costs about Rs 60,000. Technology giant IBM had made a one-time grant of Rs 30 lakh to the team, which was spent on installing the gadgets and carrying out research. The IIT team has applied to the Union water resources ministry for funds to measure rainfall at some more locations.