The canal that turned southern Thanjavur's parched land into fertile farms

TIRUCHY: Despite Thanjavur being revered as the major rice contributor (popularly known as the rice bowl of Tamil Nadu) among the Cauvery Delta districts, a major portion of the district once had rain-fed cultivation and the people dropped agricultural activities due to water scarcity.

However, things changed after the realisation of the 90-year-old contour of the Grand Anicut Canal (GA Canal). The canal was engineered for the Thanjavur irrigation which transformed the face of southern Thanjavur and made the region fertile.

The northern Thanjavur has been considered the most fertile land due to the abundance of the River Cauvery and Vennaru. But the southern Thanjavur had rain-fed cultivation and was mostly parched till the GA canal came into existence in 1936. The rest is history.

While the farmers were longing for rains for their irrigation, the need for an irrigation canal was felt by the then rulers who planned for a contour canal that would transform the parched land into fertile land.

According to the historical records, the GA canal otherwise called Puthu Aru, created during British rule, has been serving as a source for irrigation to the ayacut at around 2.56 lakh acres in Budalur, Orathanadu, Pattukottai, Peravurani areas in Thanjavur district and some parts of Pudukottai district.

This man-made canal in Tamil Nadu was constructed as part of the Cauvery-Mettur project. British Engineer Colonel WM Ellis, who is also the architect of Mettur Dam, designed this canal at the request of CP Ramaswami Iyer, the then Diwan of Travancore.

Work on the canal system was started in 1926 and completed by 1934. This contour canal carries only the designed discharges with all the local drainages excluded through cross drainage structures.

There are several fairly large and important drainage courses crossing the canal that also serve as natural drainages for the Ayacut.

The canal takes off from the Grand Anicut head on the right side of the Cauvery immediately above the right flank of the Vennar Regulator.

The head sluice of the canal which also carries a road over it consists of six vents, each 30 feet wide fitted with radial shutters, and operated by electrical motors. The canal is designed with a full supply discharge of 3,500 cusecs of water initially.

However, to flush and fill up tanks when supplies are available, the canal is designed to provide for a maximum supply of 4,100 cusecs, or 600 cusecs over the full supply discharge so that the branch canals are also recharged.

The canal passes through Thanjavur town for a distance of six kilometres at a depth of 26 feet to keep the waterway protected with revetment.

The full supply level of the canal is kept below ground level as far as possible. The canal in this reach is taken with a reduced bed width of 80 feet. Full supply depth of 10 feet is suitably adjusted increasing the slope of the canal with transitions.

The Grand Anicut Canal system supplements the storage in as many as 694 system tanks. They are located, both in Thanjavur and Pudukkottai districts. Thanjavur has as many as 524, and Pudukkottai has 170 such system tanks recharged by the GA canal.

Interestingly, the system tanks have an ayacut of as much as 81,944 acres. These tanks are getting filled only during the northeast monsoon period. Nearly one-third of the tank storage is fed by GA Canal and two third is getting filled up from their catchment rainfall.

“This was initially planned for Pudukkottai but the then Pudukkottai Samasthanam refused it and so it was CP Ramaswami Iyer, the then Diwan of Travancore who initiated steps for supporting Thanjavur cultivation,” says Mani Maran, Historical Researcher of Saraswati Mahal, Thanjavur.

Mani Maran said that there was a stony terrain for around 20 km from Buthalur to the Big Temple, so the British engineer brought specially designed machines to drill the ground to make the canal.

“Records say that an amount of Rs 4.50 crore was spent for the canal construction during the period,” Mani Maran said.

Though the canal was designed for purely irrigation purposes, the natural drains were not disturbed and it was carefully designed to avoid sewage and stormwater into the canal for which siphan tunnels, super passages and aqueducts were constructed. To maintain the flow of water, as many as 505 sluices were established all along the passage of the canal, he said.

While the rivers normally flow down the slopes, this irrigation canal can flow onto a slope as well as a raised land.

“For instance, this canal flows 30 feet deep near the Big Temple and 30 feet raised land at Vattikadu in Orathanadu. Interestingly, the water reaches the tail-end and never mixes with the sea. Hence this construction is considered a marvel,” Mani Maran said.

“The GA canal has played a vital role in the lives of farmers in Thanjavur as it helped in transforming them from mere agricultural labourers into full-time farmers and thus improving their economic conditions,” he added.

Less flow of water in GA canal irks ryots

Farmers dependent on the GA canal for irrigation have often complained that the officials refuse to release adequate water into the canal and hence it fails to reach the tail-end region. They are forced to stage several protests for the release of water for irrigation to save their standing crops.

“All is well that the canal was meant for irrigating the rain-fed regions of Thanjavur and Pudukkottai but we rarely witness the full flow of water in the GA Canal. It results in withering away of our standing crops very frequently,” charges Kannan, Tamil Nadu Vivasyigal Sangam, Thanjavur secretary.

He said that there is a regulation that at least 10 per cent of water storage in the Grand Anicut should be released into the GA Canal for tail-end irrigation. But the officials fail to release adequate water and so the crops cultivated in the tail-end regions wilt away due to water shortage.

“While water from Mettur was released, it reached Tiruvarur and Nagapattinam and supported the farmers for irrigation. But the water fails to reach Boothalur and Pattukkottai unions in Thanjavur district. This is due to the lethargic attitude of the officials, the situation in the region becomes very pathetic and we need to stage a series of protests to ensure the release of water into GA canal,” Kannan said.

He appealed to the Water Resource Department to make the regulation of the release of 10 per cent of storage from Grand Anicut permanent so that the farmers could initiate cultivation accordingly.