Rainwater Harvesting and its importance

-- by Sekar Raghavan, sekar1479@yahoo.co.in

You may wonder as to the need for one more article on RWH, when it has been discussed in Seminars, Conferences and Workshops and also written about in several newspapers and magazines, for close to three decades! In spite of all that, a large majority of us living inurban areas have not understood RWH correctly, unlike our fellow humans living in rural areas.

Rainwater Harvesting

Freshwater is found and available in rivers, lakes, ponds, irrigation tanks etc. as well as below the soil as groundwater. All this must have come predominantly from rain which should be understood as the primary source. Melting of ice from snowy mountains during summer is the only other primary source. This process of rainwater becoming river water, lake and pond water and groundwater, which are the secondary sources, has come to be known as Rainwater Harvesting (RWH).

RWH can happen with or without human intervention. For example, there is hardly any human intervention in rainwater flowing in rivers. In villages, there would be natural depressions known as ‘kuttais’ in Tamil. Rainwater will get collected in them once again without human intervention. Rainwater will also percolate into the soil naturally and remain there as groundwater.This can be seen in villages due to availability of unpaved areas and also in coastal cities with sandy beaches. In addition, rainwater also gets harvested due to human intervention in dug out ponds and lakes in rural areas and due to artificial recharge in urban areas.

The text book definition of RWH is collecting rainwater when and where it falls for use during non-monsoon months. RWH is not an alternative, not a new technology, nor an option but the only way to sustain both our surface and subsoil water sources. It is relevant everywhere – Rural, Urban and Peri urban areas, at both macro and micro levels viz. in public as well as in private spaces.

Indians were one of the world leaders in harvesting rainwater. There is archaeological evidence to show that Indians had harvested rainwater as early as 3000 BC. (more than 5000 years back). Indians knew that food security could be achieved by harvesting wheat and other grains and water security by harvesting rain. Almost every part of India had its traditional harvesting systems. The state of Rajasthan had the best system since they wanted to harvest every drop of the meagre rainfall that they receive every year.

The four states of South India, namely Andhra Pradesh, Karnataka, Tamil Nadu and Telangana had a wonderful system of harvesting rain in surface water bodies, which were identical in design, having different names. In A.P and Telangana they were known as ‘Cheruvus’, in Karnataka ‘Keres’ and in Tamil Nadu ‘Eris’. They were also popularly known as irrigation tanks, a name coined by the Britishers. There are still 1,50,000 such irrigation tanks in these four states put together, but most of them are in a state of disrepair.

Among these irrigation tanks, there are two types – the system and non – system tanks. System tanks are both rain fed as well as river fed. This means that rainwater flowing in rivers is diverted and collected in these tanks located on both sides of the river and it also receives natural rain fall. Veeranam eri, which is one of the sources of fresh water for Chennai, is a good example of a system tank. Rainwater flowing in river Kaveri is diverted into this tank and harvested. In the non-system tanks, there is no river and collects only the rain falling in the catchment areas.

Red hills (Puzhal eri), Sholavaram, Chembarambakkam and the recently annexed Kannankottai thervoy kandigai, which are also sources of fresh water for Chennai are examples of traditional irrigation tanks.

Another unique feature of these irrigation tanks is that most of them are interconnected forming a chain of tanks. What does this mean? If one irrigation tank gets filled up with rainwater, it will overflow only from one or two specific points, called Overflow Weirs in English and Kalangal in Tamil. This will flow through channels and fill up another such tank in the neighbouring village and so on and so forth. Thus, wastage of rainwater flowing into the sea is minimised.

Water from these tanks will be used only for irrigation and not for domestic use.There were other surface waterbodies, called Ooranies, which would be used for domestic (potable and non-potable) purposes.

Why is RWH important?

Firstly, however much it rains, without RWH there will be no water and without water, there will be no life. The key word in water management is RWH.

Secondly all of India in general (except Rajasthan) and Tamil Nadu and Chennai in particular get enough rain. Why not harvest it and become water sufficient? We are not rain-starved and therefore should not be water-starved.Thirdly, it rains only for a few days in a year and unless we harvest that rain, we will run out of water for the rest of the year.

It is recorded that even as far behind as the 12th century, King Parakrama Bahu who ruled Sri Lanka (1153 – 1186) said “not even a drop of rain water that comes from rain must flow into the ocean without being useful to man”. Ironically, in coastal cities like Chennai, what is not harvested, flows (or is made to flow!) into the sea and gets wasted.

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