Rainwater harvesting may be taken up during the period of the north-east monsoon too when the coastal region receives about 15 % of its annual rainfall, suggested an expert in marine geology.
North-east monsoon brings rain normally till the end of November; but this time it may get extended till December 15 as the south-west monsoon ended just before November, said Hejmady Gangadhar Bhat, professor in Marine Geology with Mangalore University.
Though it does not rain continuously as it does during the south-west monsoon, north-east monsoon brings rain enough for storage as well as groundwater recharge. One centimetre of rain for a day on a 1,000 sq ft surface could yield up to 2,500 litres of water that could be stored safely, Prof. Bhat said. If the entire annual average rainfall of 3,500 mm on 1,000 sq ft surface in the coastal region could yield over 3.24 lakh litres of water; but one may not be able to store the entire quantity.
However, rainwater could not directly be stored in tanks. One has to use filtering method to remove colour, micro organisms, insects, among others. The normal method of channelising rainwater through crushed stones, sand and netlon filters would remove impurities in the water and then, it could either be stored in tanks or used to recharge open wells or borewells, Prof. Bhat suggested.
He noted that rainwater harvesting is one of the cheapest methods of water collection and groundwater recharge. Rainwater harvesting for groundwater recharge would help improve the groundwater level in the locality. On the other hand, rainwater stored in tanks could be utilised during dry days. The method not only helps preserve natural resources but also reduces supply costs of piped water.
While a water tank measuring one metre by one metre could hold 1,000 litres of water, one could easily store not less than 10,000 litres of rainwater in an average size tank. This stored water could suffice for 10 days for a family of four members. One could get tanks constructed depending upon one’s requirement.
Farmers too could store rainwater during the north-east monsoon utilising the available space from 50,000 litres to one lakh litres. Besides storing rainwater in ponds in their fields, they could resort to constructing temporary bunds (katta) across streams adjoining their fields to conserve water and recharge groundwater.
Prof. Bhat suggested that everyone should resort to rainwater harvesting given the grim situation of severe shortage of fresh water.
