To save us from flooding

With the Monsoon not far away, what are the beneficial drainage actions that have to be taken to avert recurrence of last year’s floods or even what happened during recent rains?
At the Macro-Level:

1. Instal more reservoirs. Our reservoir capacity today is woefully inadequate. So, more than a year’s supply to the city of rainwater (with just 100 parts salt in a million parts (ppm) ) wastefully flows into the sea every year! We then instal costly desalination plants (with 60% efficiency!) to remove 35,000 ppm of salt from sea water!

Poondi was the last reservoir built (in 1943) and that was when Chennai’s population was 10 lakh. Today, it is 50 lakh. Plans to provide a new reservoir have been announced recently but it will be years before that comes into being.

2. Existing reservoirs have never been desilted and so hold much less water than what they were built for. Desilt them on an emergency basis when they become dry again and also clear, on an emergency basis, the blocked channels draining rainwater into the existing water bodies. Remove the encroachments thereon.

2. Well before the Monsoon, desilt the stormwater drains (SWD) thoroughly, and not in the desultory, limited manner just a few weeks before the rains come. Remove the excavated material promptly. Clear the mud on the drains abutting the pavements and the clogged inlet points

3. Divert rainwater from the SWDs into large dug wells covered with heavy duty R.C.C. covers in school and college play-grounds, parks and other open spaces such as the Gandhi Mandap area. The wells should reach a depth where the soil is reasonably sandy and not in the present meaningless mechanical manner: e.g. 10-ft pits provided under fly-overs, as in the Vani Mahal area, and where the soil is clayey till 18ft!

5. Provide holes on the medians at intermittent distances on roads with SWDs only on one side for rainwater to flow from the other side on its own and by vehicular movement.

6. Enforce the 2003 Rules for terrace rainwater harvesting (RWH) strictly. Government buildings and colonies are, incidentally among the worst non-compliants!

7. Provide recharge wells (covered with perforated heavy-duty lids) at the lowest point in row house streets.
At the Citizens’ Level:

1. Revive the traditional dug well and divert terrace rainwater into them directly without any filters and into sumps to get potable water and/or water for all non-potable use in the dry days. Ensure that the terrace is swept once in May and once in September. This writer has introduced this system in more than 150 apartment complexes in Chennai in the last two decades with very good benefit. The traditional dug wells need to be actively revived as they generally yield good quality water and are sustained by charging them with rainwater. This system is economic, needs minimum maintenance and is relevant even in the rocky areas in South Chennai where they yield excellent water for a good part of the year. Rainwater improves well water quality, dilutes iron salts present in micro-quantities in several areas enabling its direct use. Borewells too can be charged with rainwater but it is not as economic or efficient as charging dug wells.

2. The open spaces around most buildings have much more area than the terrace but all rainwater falling on them flows wastefully on to the road through the gate(s). All this can be trapped by installing shallow cemented trenches between the gate columns, covered with perforated RCC slabs and connected either to dug wells or recharge wells (i.e. pits reaching a reasonably sandy layer). This water travels through the soil and sustains the dug well. Dug wells can be safely located even inside the stilts portions of the building and covered with heavy-duty RCC lids.

Beneficial drainage as detailed above will not only avoid inundation of the city and destruction experienced during the last year but will provide much more water for citizens’ use.

isragade@yahoo.com

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