Drains will be ineffective if encroachments stay: Experts

CHENNAI: Even as intense rains are predicted for Chennai in the coming days, the inundation of certain city areas in the first two spells of the northeast monsoon despite the civic body undertaking large-scale construction of storm water drains leaves many questions unanswered. Experts, whom DT Next spoke to, state that while the rapid increase in urbanisation and encroachment of water bodies are the prime reasons for flooding the new drains may not help prevent inundation unless the illegal encroachments are evicted.

“There are many faults in the urban planning system, leading to buildings deviating from plans and violating the rules. In a 2,400 sqft plot, only 60 per cent should be constructed. The remaining must be vacant, which would help prevent water stagnation and help infiltration. Now, it has been completely exploited with a rapid increase in urbanisation,” said S Thirunavukarasu, retired PWD assistant executive engineer.

Many areas still experience water stagnation during rains because of the constructions on the natural drainage. Even the channels are not proper and are mostly encroached on. Earlier, 2,000 cubic feet outflowed from Porur lake. Now, due to urbanisation, over 4,000 cubic feet of water are discharged. There is no surplus course to flow into the river stream.

“The government hesitates to evict houses and commercial establishments due to rehabilitation issues. Unless the court intervenes, the departments concerned will take it slowly in a phased manner,” added Thirunavukarasu.

During the recent intense spell, north Chennai was badly impacted. This is because over 19 water bodies and 20 insignificant lakes have disappeared from there. Several water bodies were filled up over 50 years ago due to rapid urbanisation in the northern part, such as Dr Ambedkar Arts College that encroaches on Vyasarpadi lake, stated the retired officer.

Experts said rapid urbanisation is the major reason for the water bodies to disappear and it would take more than 10 years to revive. Also, the effectiveness of storm water drains (SWDs) constructed in the city can be gauged only after five years.

“As far as Chennai is concerned, there are different topographical regions. Even that doesn’t favour the faster draining into the nearby channels. However, the damage has been done in many places and it would take a lot of time to rectify it. We cannot see the results in a short duration,” said Darwin Annadurai, an activist.

“We have started the work now, and the impact will be shown in the next 5-10 years. Even in suburban Chennai, there is a lot of diversion in channels,” he added.

For example, in a lake, only one outlet is focused on, but there are three-four outlets which remain unnoticed. So, it will spread out in all the outlets instead of one single channel. It can prevent the overflow of storm water drains.