Concrete rings and recharge wells
The monsoon is about to set in and it is time to act, advises our water expert S. Vishwanath
Finally the much awaited monsoon will arrive on the coast of Kerala on June 1 or perhaps a day earlier. One section of the Bangalore populace is eagerly waiting to receive the promised rain and turn it into an asset. These people will ensure that our groundwater banks are filled and good for utilisation throughout the year or at least a good part. And there are the pre-cast concrete ring makers.
They are part of the city's informal sector and a vacant plot of land is all they need for business. They are ubiquitous especially in the suburbs of the city and they work with steel moulds and concrete.
They cast rings of various dimensions ranging from two-and-a-half to four-and-a-half ft. in diameter. You place an order and the rings should be ready in a fortnight at the most. Business is brisk, especially with the coming of the bye-law which makes rainwater harvesting compulsory.
The prices of the concrete rings are in the following range in different parts of the city:
Ring with a diameter of two-and-a-half ft. costs Rs. 300-325. The height is 18 inches. If the diameter is three ft. the rate is Rs. 350-375, height being 18 inches. Another half ft. increase in height will cost Rs. 400-425, height being the same. A four ft. ring will cost Rs. 450, height being 13 inches. If you add half-a-ft., the rate is Rs. 450, height being 13 inches.
Pre-cast concrete rings with concrete cover are cast in informal yards. These rings are transported to site using small vehicles such as tempos and the price is actually the landed cost of the rings. The well diggers then use these rings to make ‘leaky' wells or recharge wells as they are called here.
These wells, according to the bye-laws, have to be a minimum of 10 ft. in depth. Generally it is recommended that they be about 20 ft. in depth. About 14 rings should be used. Rainwater from rooftops and paved areas can then be led into the recharge wells. Rainwater from storm-water drains also can be led into these wells. A precaution is to make sure that there is no polluted water such as sewage that can go in.
After a preliminary filtering to keep leaves and other organic matter out, the rains are recharged here. Recharge rates can vary from 1,000 litres per hour to even as high as 6,000 litres per hour. A slug test, whereby water from a tanker is filled into these wells and the time taken for the water to empty noted, will tell the exact rate of recharge.
Depending on this parameter and the catchment area they serve, sufficient number of recharge wells can be designed.
Recharge wells play an important part in topping up the groundwater table of Bangalore. Every borewell in the city should have one. Every house and apartment in the city too can have one except in areas where the water table is very high.
If the conditions permit, the recharge well can also be used as discharge wells and the groundwater can be used in summer time. The concrete ring manufactures are environmental heroes working on livelihoods which provide water to people of the city and mitigate floods.
These are the true water warriors.
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