Ways to control breeding of mosquitoes in Chennai
The Hindu
‘Mosquitoes are engineering problem; malaria, dengue are medical problem’
As the Corporation’s City Health Officer in Chennai from 2006 to 2014, I was in charge of handling mosquito control activities in the city. At that time, the major complaint of the members of the public was the mosquito menace — the issue came up repeatedly in the Corporation Council, grievance meetings and via petitions to the civic body.
It is common knowledge that 50% of mosquitoes breed in rivers and canals, another 40% in stormwater drains and about 10% breed in individual houses. These mosquitoes that breed in domestic settings are responsible for causing malaria and dengue, and therefore, control requires people’s participation to be successful. At that point in time, it was very difficult and hence we wanted to make it people’s movement in order to get it to work.
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Among the perennial sources of mosquito breeding in the city are the waterways like Cooum, and Adayar rivers, and canals like Buckingham, Otteri Nallah, and Virugambakkam Canal, all running for about 247 kilometres. The other source is the stormwater drains flowing under the streets of Chennai City for nearly 2,100 kms, and side drains for about 412 kms. They are the water sources that allow the breeding of what we call nuisance mosquitoes throughout the year based on the amount of water stagnation. These are culex mosquitoes, and they do not cause malaria or dengue but sometimes filariasis.
The stormwater drains in the city have over have about 3 lakh illegal connections of sewers either intentionally damaged by people, or accidental breakage during the construction of stormwater drains. The non-flowing sewer water stagnates throughout the year.
My engineer friends would always be annoyed at me during the Commissioners’ review on Saturdays when I used to list out the length of SWD having stagnation — and thus homes for breeding mosquitoes. The stormwater drains which are supposed to be dry during summer were 60% filled with sewage. They are constructed only for floods in rain not for sewers. They have no interconnections to drain out of the city as they were not scientifically designed for this purpose. Moreover like Mumbai, Chennai is located equal to or lower than sea level, hence drainage is difficult.
The solution for this could be like in Japan we need to install deep charging bores or wells in many parts of the city which will not only reduce flooding but raise the ground level water. They could also fill the temple tanks and lakes in and around the city providing connecting pipelines from the places of heavy water stagnations.
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