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Coimbatore is a city with average annual rainfall between 600-700mm. But the water scenario of the city has been oscillating widely. The city used to witness heavy water logging and flooding on roads and open spaces, after each monsoon rains. This created lot of traffic chaos and the same traumatized the normal life of commuters at many locations within the city. But, the same city also became a water-starved one with the failure of two consecutive monsoons in 2002 and 2003.
Studies revealed that more than 70% of the rain water is getting wasted as run off water, which if saved, can quench the thirst of the city. In 2004, Siruthuli made a geo-hydrological study which brought to light that 600 RWHS is required to harvest the rainwater falling on the 105.60 Sq.Km area of Coimbatore city. Hence SIRUTHULI decided to tackle the problem by constructing rainwater harvesting structures in roads and open spaces.
What is a Rain Water Harvesting Structure (RWHS)?
A RWHS is a physical structure getting constructed below ground level. This structure filters runoff water and recharges the clean water into the ground through a drilled borewell. Due to hard rock strata of Coimbatore region, Siruthuli planned to construct RWHS consisting of a recharge borewell, recharge pit and filter materials like sand, blue metals etc. thus ensuring aquifer recharge. The intake capacity of the bore well depends upon the number of crack zones getting encountered during the vertical drill. Constructing rain water harvesting structure around such bore well pits is an innovative initiative to harness the storm-water marooning on low-lying areas and to recharge the same as groundwater.
After identifying locations, borewells are drilled up to 250-400 feet. Towards the top of borewell, for a length of 40 feet, a casing pipe is inserted, of which, top 20 feet is perforated. Typically, the civil structure is nothing but a brick wall of two meter length, one meter width and two meter depth, constructed around the borewell. This brick wall conceals filter chamber and filter media. In filter chamber, filter materials like 3 feet Soling, 2.5 feet 40mm metal and 2.5 feet pebbles are filled in layers to ensure filtration of dirty particles. Typically, as it rains, water enters into filter media first and thereafter water percolates into the ground through the borewell.
Rectangular structures are constructed for roadside rain water harvesting and circular structures for open spaces. Roadside structures are covered with concrete slabs having few holes so that heavy duty vehicles can move.
| Sketch of Rectangular RWHS | Sketch of Circular RWHS | |
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Siruthuli thought of accomplishing this project in three different phases.
This novel project is sure to prevent run-off water from being washed away and to utilise it to recharge the underground water table.