The south-west monsoon for the year 2014 officially ended on September 30. Overall the monsoon has been a mixed bag with many areas of India having a deficit but some areas having a surplus. In the city of Bangalore we were confronted with heavy rains in September; on one particular day it rained more than 120 mm in a short span of a few hours, causing flooding. This will be the pattern in cities, floods at certain times and shortage of piped water at the same time.
As cities get paved, creating hard impenetrable surfaces, the ability of rainwater to percolate into the soil and thence to the aquifer reduces to almost zero. Surface run-off increases dramatically and can go up by a factor of 9. The garbage-choked drains have to cope with a high intensity of rainfall and substantially increased run-off, not to mention buildings in valleys and low lying areas, causing urban floods. At the root of this phenomenon is lack of planning, and building in the wrong places. Not respecting drainage lines and flood plains exacerbates the situation. What can be done about it?
One remedy is to design and plan for every urban micro-watershed by reducing run-off and increasing infiltration into the soil and aquifers. A recharge well is a good way of doing this.
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What is a recharge well? Usually a precast concrete ring lined structure, typically a metre or 1.5 metres in diameter and going to a depth of 3 to 8 metres, a recharge well takes water run-off from rooftops, paved areas and roads, filters it and sends it underground to increase the water table. Unlike a conventional well which taps into the aquifer, the recharge well sends water into the aquifer. By changing the flow of rainwater into the ground it is possible to mitigate the impact of floods.
A well-designed recharge well, depending on the soil profile of a place, can send a million litres of water annually into the ground. By coordinating a given catchment area, the coefficient of runoff and the infiltration rate at a place, appropriate recharge wells can be made and the numbers required can be arrived at. They can be linked to the stormwater drains present and placed within the drains itself.
Layouts, apartments and institutions have found that they become zero storm-water discharge zones and have had the added benefit of increased water availability in their borewells and open wells.
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It is time that we use the recharge well as an important tool in the sustainable management of water in our cities and in preventing or mitigating floods. October is one of the rainiest months in the city of Bangalore and it would be best that October rains are directed into our wells. The time is now.