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Sitharam Gurumurthi

A UNIQUE feature about the Vaigai — which passes through Madurai, Sivaganga and Ramanathapuram (popularly known as Ramnad) districts in Tamil Nadu — is that unlike other rivers it does not flow directly into the sea.

The river originates in the Varushanadu hills of the Western Ghats in Madurai and meanders for about 330 km before emptying into the Bay of Bengal. About 110 channels branch off from the river, and feed nearly 300 tanks.

In the drought-prone districts of Madurai, Theni, Sivaganga,Virudhunagar, Ramnad and Tirunelveli such tanks are popularly known as kanmais. Ramnad Peria Kanmai (or Ramnad Big Tank) is one of the major tanks located at the tail end of the Vaigai and receives floodwaters directly from the river through the open off-take near the falling shutter anicut.

The Ramnad Big Tank, which is one of the largest kanmais in the district, and was created around 1700. In 1940, the regulators and the falling shutter anicut were provided.

The tank's capacity before forming the foreshore bund was 543 mcft and the depth was six-and-a-half feet.

The ayacut of the tank is now 3962.45 acres. There are three bunds: The main bund, the foreshore bund and the parallel bund.

There are also eight sluices. The falling shutter anicut lets out surplus floodwaters at the confluence of the river and the supply channel of Ramnad Big Tank. The depth of storage at the full tank level (FTL) is 2.27 metre.

The free catchment area and the combined catchment area of the tank are 8.24 and 14.34 square miles respectively. The tank's water spread area is 14.5 sq km.

The total flood discharge through surplus arrangements at the FTL and the MWL are 6,476 c/s and 11,969 c/s respectively. The capacity of the tank is now shown as 618 mcft. There is an interesting story behind raising the capacity of the tank from 543 mcft to 618 mcft.

In March 1984, Madurai and Ramanathapuram districts witnessed heavy and unseasonal rains, and the district administration and Public Works Department maximised their efforts to fill the Ramnad Big tank to its full capacity.

Even though the full capacity of the tank was shown as 618 mcft, it was not possible to store water beyond 543 mcft owing to the existence of three villages — Chittoor, Vannivayal and Sakkarakottai — within the water spread area of the Ramnad Big Tank.

Later, it came to light that the tank's original capacity had been fixed at 543 mcft after taking into account the existence of the three villages.

When the State faced a severe drought in the mid-1970s, substantial Central assistance was made available to create tangible assets in addition to such traditional drought relief works as deepening of wells, desilting of irrigation tanks and formation of roads. A sum of Rs 35 lakh was spent towards the formation of a foreshore bund for a length of 4.25 km.

As a result, the height of the storage was raised from 6.5 feet to 7.5 feet.

With this, the authorities believed that the capacity of the tank had been raised from 543 mcft to 618 mcft, without realising that there was no way that water could be stored beyond the 543 mcft mark.

Till March 1984, the question of filling the tank to its full capacity did not arise, and after it did, the authorities realised that Rs 35 lakh had gone down the drain.

(The author was the Collector of the composite Ramanathapuram district during 1983-85. The views are personal.)

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