Why does Bangalore flood when it rains?

Why does Bangalore flood when it rains?
Deccan Herald

There is an urgent need for implementing an effective rain water harvesting in our roads, says George Kuruvila.

I wonder whether the rains are a blessing or a nuisance to the “Silicon Valley of India”? Even after a short spell of rain, Bangalore’s streets get flooded. A couple of months ago, while driving during a brief, but heavy downpour, I found my car along with many others, in flooded water! We were caught in a traffic jam on the recently built Ring Road, connecting Indiranagar’s 100 feet road to Koramangala.
The flood water reached up to the middle of the car wheels, seeping into our car floor and soaking the carpet in the car. If this type of flooding is true on this newly developed Ring Road, after just about 20 to 30 minutes of heavy and medium spells of rain downpour, then what is the condition of other city roads? Why are these roads flooding?

To investigate, I decided to walk along the prime, central areas of Bangalore (i.e. M. G. Road, Brigade Road, Cubbon Road, part of Queens Road and Commercial Street) to survey what causes storm (rain) water flooding on our roads, even after short spells of rain. Ordinarily, a street cross section is designed to be raised in the middle and sloping towards the sides, so that rain water flows out to the sides, and is then connected to rain (storm) water drains.

What I observed, shocked me! For example, on the main stretch of M G Road, from Brigade Road to St. Mark’s Road (a stretch of about 650 meters), there exists only one rain water outlet on each side of the road! As part of very basic level city planning, city engineers should have planned for presence of one rain water outlet say about 15 meters length of the road i.e. there should have been at least 43 rain water outlets on each side of this main stretch of M G Road (total of 86 on both sides).

Imagine, one (1) rain water outlet (as existing) trying to do the work of 43! Talk about water overloading at these outlets! The load and flow of water will mostly just bypass this one outlet. At the Kumble Circle intersection, there is not a single (i.e. zero) rain water outlet! Little wonder, there is flooding on such roads!! Examination of other roads, confirmed to me that this is a typical example of the careless state of lack of effective rain water outlets on many of Bangalore’s roads. With storm water drains already provided on the sides of these roads, why did not the city authorities / engineers provide adequate storm water outlets to drain the rain water to these drains?

The above examination reveals that eight (8) of the above twelve (12) road stretches in the most prime area of Bangalore Central Business District (CBD), have absolutely no rain water outlets. Two road stretches have between 2 per cent to 3 per cent of the required rain water outlets, which is negligible. The maximum rain water outlets provided are on two road stretches which amount to just 10 per cent to 16 per cent of the required number.

The examination of the street intersections (junctions, which are the critical areas of traffic movement) in this prime area of Bangalore CBD, show that three (3) out of eight (8) important traffic junctions have absolutely no storm water outlets, the others have one or two (in one corner side; how about drainage from the other three sides?). It should also be noted that the few existing storm water outlets have no garbage / silt traps, hence are often clogged with garbage, or even bricks and rock. Little wonder, we have water flooding on the streets of Bangalore.
Note that prime Commercial Street (approximately 421 meters long) and Brigade Road (approx. 330 meters long) do not have a single rain water outlet. My tailor on Commercial Street, who has an ancestral property there, informed me that up to a few decades ago, rain water outlets existed on the sides of this major commercial corridor, but these were subsequently covered up by the city when widening the road. They could still have provided rain water outlets at the ground / street level, but they chose to overlook the consequent problem. This seems to be the story of Bangalore’s roads, from its small streets to its arterial corridors … In spite of storm water drain infrastructure existing below or adjoining the pedestrian sidewalks / roads, there seem to be no connections from the roads to these drains. In fact, I noted that many of the newly paved pedestrian sidewalks have no storm water outlets, hence no connection to the drains underneath. What good is it to spend crores of rupees on laying storm water drains on the side of the roads, or under sidewalks, when in most cases as shown, the connections to these drains have been left out?

Let us examine the consequences of rain water flooding on our streets:
Street Erosion: Water logging on the roof of a house or on the streets has great erosive damage potential and must be avoided for easier and economical maintenance. Water seepage / erosion on the street leads to capsizing of the weaker sections of the road, leading to potholes and cracks. With proper drainage, we can avoid flooding and hence damage to our streets.

*Potholes on our roads cause accidents and automobile damage.
*Water flooding in low lying areas (due to improper drainage) cause tremendous damage to property and lives (through drowning, disease etc.).
*Water is an essential precious commodity and should not be wasted. For the last few years, as at present, when water shortage is being felt in the city and the country, it is sad to see the city authorities wasting the water from approximately 30 per cent of the city’s land area (i.e. its paved street area). When rain water harvesting is being recommended for every building, shouldn’t the city set an example of harvesting water from its streets? There are some good means of harvesting water from our streets, but space and subject limitation does not permit me to discuss these here.

Besides providing adequate number of storm water outlets, here are some pointers to allow for efficient storm water drainage:
*Provide garbage and silt traps at mouth of storm water outlets. These could be metal grates which would stop plastic bags, paper and silt from choking our storm water drains.
*Storm water outlets should preferably be round, rather than rectangular in shape (As observed, the existing rectangular outlets of 1" to 3" height often get blocked with dirt / garbage).
*Where sidewalk curbs are too low, storm water outlets should be provided at the street / ground level with adequate garbage / silt traps.