Recharging the aquifer – Leaky wells.May 28, 2011
Finally the much awaited monsoon will arrive on the coast of Kerala on June 1st or perhaps a day earlier. One section of the Bangalore populace is eagerly contributing to receive the promised rains and turn it into an asset. They will ensure that our groundwater banks are filled and good for utilisation throughout the year or at least a good part. These 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 the rings of various dimensions ranging from 21/2 feet in diameter to 4 ½ feet 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 price of the concrete rings are in the following range in different parts of the city
Diameter ( feet ) Cost (Rs) Height (inches )
2 ½ 300 -325 18
3 350 – 375 18
3 ½ 400 -425 18
4 450 13
4 ½ 500 13
Pre-cast concrete rings. These 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 feet in depth. Generally it is recommended that they be about 20 feet 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 1000 litres per hour to even as high as 6000 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 bore-well 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.