RAIN PAIN

RAIN PAIN
In a series beginning today, TOI takes a look at what ails our storm water drains and what needs to be done on a priority basis
Prathima Nandakumar | TNN

Bangalore: After every shower, a satellite image of the country’s IT capital would have shown up land masses with clear water passages, what with its 228-km network of natural drains carrying rainwater. This would have rejuvenated the 400-odd lakes across the city. But this was decades ago.
Today, the Garden City is synonymous with frequent flooding of roads and layouts, property and people being washed away after a downpour and scarcity of water to even maintain its green image. The natural drains have turned into blackish and stinking streams of sullage water, garbage, plastic and human waste. And mind you, these drains were designed primarily to carry rain water.
To tide over the crisis, the Bruhat Bangalore Mahanagara Palike (BBMP) launched the Rs 425-crore storm water drain remodelling project in 2006. But the slow pace of the project is drawing flak from the chief minister to the common man.
With monsoon around the corner, the BBMP claims that one-third of the project is completed. “We are desilting all four valleys and secondary drains, strengthening the retaining walls and building retaining walls. Through a survey, we have identified at least 110 vulnerable points that need a new bridge or culvert. We have remodelled 35 out of 110 bridges and culverts by elevating them above the road surface. They now have a single vent instead of multiple piers that obstruct free flow of water,” explained Harsh Gupta, joint commissioner (works), BBMP.
However, BBMP officials and contractors are sore over the many hurdles. The natural drains, which once acted as catchment areas carrying rainwater to recharge the lakes, are now sounding the death knell for the lakes. Reason? They’ve been reduced to open sewers. Thanks to rampant encroachment along the drain bed, increasing urbanisation leading to paving of surfaces with concrete and asphalt, flushing in of sewage into rainwater, which are a sure-shot recipe for a disaster, warn experts. “Mindless dumping of waste has clogged the network of tertiary, secondary and primary storm water drains. The tertiary drains are roadside drains (shoulder drains) that drain out water from the road and layouts and take it to a secondary drain of the area. This, in turn, is linked to primary drains or the valleys. The entire network has been distorted due to failure in checking encroachments,” explained a BBMP engineer.
No doubt, encroachments have grown to monstrous proportions and have assumed different forms. People occupy lake beds, erect houses and shops on the retaining walls of the SWDs, and build highrises without adequate setback area. This puts a lot of pressure on the drain bed and also narrows the drain width.
The absence of any law to earmark buffer zone along the drains is another bane, say officials. Unlike lakes and beaches, natural drains have no buffer zone. So, identifying extent of encroachment becomes laborious.
Encroachment along the drain bed has made difficult the movement of earth-moving and desilting equipment. “As the width of the drain is not uniform along its course, we are unable to use monolith concrete plates for the walls and the floor, though it would have been both stronger and cost-effective,” explained an engineer.
Bifurcation project
Another major hurdle has been the BWSSB’s sewers that run parallel and sometimes within the storm water drain. This results in breaching and contamination of rainwater and thus lakes. There is an urgent need to replace the sewer lines running along the valleys, which is about 83 km. The bifurcation project has become mandatory as the KMC Act insists that sewers have to be separate from SWD. A sum of Rs 40 crore has been allocated for the project.
Where it stands Four valleys Koramangala,Challaghatta
Hebbal, Vrishabhavati Started on May 2006 Design STUP Consultants Deadline December 2007 Estimated cost Rs 425 crore Total distance 228 km No. of packages 15
How it helps
Desilt all four valleys and secondary drains Strengthen retaining walls Build new retaining walls Remodel 110 culverts and bridges over open drains Consultants to maintain drains for five years after completion (including defective liability period of two years)