Tamil Nadu, a state blessed with 34 rivers and a formidable history of irrigation endeavours, is currently grappling with a myriad of challenges in its agricultural sector, especially due to climate change. However, amid these trials, there is a glimmer of hope emanating from new projects aimed at addressing the pressing situation.
The average annual rainfall of the state stands at 973 mm, with a total surface water potential of 865 tmcft, including 260 tmcft released from neighbouring states through inter-state agreements. Among the 17 river basins in Tamil Nadu, the Cauvery basin has been the prominent one, encompassing the four Cauvery delta districts which account for 30% of the state's rice production. Prior to colonial rule, the Cauvery Delta was hailed as one of the richest, oldest and most fertile regions of human settlement in South Asia.
The history
At the heart of Tamil Nadu's irrigation legacy stands the Kallanai dam, also known as the Grand Anicut, constructed across the Cauvery during the second century AD by Chola King Karikalan. It is considered the fourth oldest dam in the world.
Constructed primarily to divert flood waters from the Cauvery into the Kollidam through a connecting stream, the Kallanai facilitated minimal agricultural damage by channelling excess water directly to the sea. Over the centuries, the dam underwent numerous repairs and modernisations. In 1804, Captain Coldwell repaired the Grand Anicut and provided dam stones on its crest and also raised the river embankment ensuring additional water to the Cauvery. Improvements were made to the dam in the 19th century by Arthur Cotton (1803-1899), a British general and irrigation engineer.
Writing about the structure of Kallanai in 1874, Arthur Cotton said, “It was from them we learnt how to secure a foundation on loose sand of unmeasured depth. With this lesson about foundation, we built bridges, weirs, aqueducts and every kind of hydraulic work. We are thus deeply indebted to native engineers.”
Besides mastering the art of harvesting the river water, Tamils also got expertise in conserving and utilising rainwater through a system of tanks across the state. Although there is mention of tanks in Sangam literature, the Pallava kings must get the credit for creating more tanks between AD 500 and AD 900, according to historians.
During that period, there was a rapid development of tank irrigation in the northern parts of the state. Similarly, the Pandya kings contributed to tank irrigation in the southern parts of Tamil Nadu. The early Tamils designed ingenious varieties of sluices called Kumili, Madai and Madagu. They also built a vent for surplus water to flow out of the tank during flooding, which is called Kalingu (surplus weir).
Modern challenges
Though the state boasts of a rich history in irrigation endeavours, modern challenges loom large over Tamil Nadu's irrigation landscape.
Except the Tamirabharani, one of the major rivers originating in the state, all other major rivers in the state had been facing perennial water problems due to inter-state water disputes. As the major rivers like Cauvery depend on flow from upper riparian states like Karnataka, there has been uncertainty about the quantum of water released by TN which lands farmers in trouble. The Cauvery Delta is one of the water-stressed areas. Though the final award of the Cauvery Water Disputes Tribunal (CWDT) and subsequent Supreme Court order has fixed annual and monthly quantum of water to be released by Karnataka to Tamil Nadu, the upper riparian state fails to adhere to it. During the 2023-24 water year, Karnataka released only 75 tmcft against the 177.25 tmcft mandated by the Supreme Court. Though Karnataka cited a drought this year, delta farmers rued that sharing of the deficit was unfair. “Karnataka failed to release the rightful quantum water for Tamil Nadu, to be calculated based on the quantum of deficit in a drought year,” said P S Masilamani, state general secretary of Tamil Nadu Farmers Association and farmer from Tiruvarur.
“Despite the release of surplus water into the Kollidam in 2022, hundreds of farmers in that block were unable to cultivate more than a single crop that year due to lack of proper water management,” said Kollidam V Viswanathan, a farmer representative from the Kollidam block in Mayiladuthurai district. Moreover, low-lying villages in the Kollidam river mouth in the block were flooded several times during the 2022-23 water year, he added.
P Maniyarasan, coordinator of the Cauvery Rights Retrieval Committee (CRRC), said the Cauvery as a river, faces many problems now. "The deforestation in the Cauvery catchment area in the Western Ghats in Karnataka is a cause of concern," he said, adding that for laying roads and habitations, trees are felled in large numbers in the area. It may be noted that during the 2018 floods, coffee plantations on hundreds of acres in the Kodagu region, the catchment area of Cauvery, were destroyed. This also paved the way for flash floods in the Cauvery during heavy rains. Global warming also added to the woes of farmers.
“There have been drastic changes in rainfall. In delta districts there was rain deficit while southern districts were pounded by heavy rain in a short time leading to floods,” Masilamani said. To tackle the effects of global warming, it is vital to rejuvenate the catchment areas of Cauvery through afforestation efforts so that soil erosion which leads to flash floods during heavy rains would be checked, he said.
Breaches in tanks and other water bodies not maintained properly also contributed to floods in the southern districts. As 63% of the water used for agriculture in the state comes from groundwater sources, there is a need for augmenting water percolation structures, including tanks, and ponds, besides ensuring water flow in rivers which recharge, experts said.
Even in Cauvery delta districts, where surface water sources are available, farmers are increasingly becoming dependent on groundwater owing to uncertainty in getting Cauvery water in a timely manner. Widespread use of groundwater resources across the state has led to severe depletion which has been causing seawater ingress in several coastal areas. Though there have been calls to cultivate alternative crops instead of paddy in the delta area, due to reducing availability of water, cracking clay soil in most areas in these districts is not suitable for other crops, said Masilamani. "In other parts of the state whenever possible, farmers can take up crops needing less water," he added.
Hopes
The state budget this year has allocated `734 crore for the Water Resources Department to carry out works. Funds will be utilised for the construction of water recharge structures and maintenance of 55 irrigation systems, including construction of subsurface dykes, renovation of channels and new anicuts this year.
A Veerappan, retired chief engineer and general secretary of Tamil Nadu PWD Senior Engineers Association, said one of the easiest ways of tackling water scarcity in the state is to desilt tanks. “Of the total 40,000 tanks in the state, around 19,000 big tanks with an ayacut area of more than 100 acres each are with the Water Resources Department. The government has to take up desilting of at least 5,000 to 6,000 of these simultaneously”, Veerappan said.Tanks should be optimally desilted and deepened at least by one meter over and above their original depth so that water during heavy rain is sufficiently stored. “Besides, groundwater will also be recharged by the water in the tanks. It is also important to desilt inlet canals which bring rainwater into the tanks. Similarly, the surplus weirs and outlet channels should also be renovated,” Veerappan added.
(With inputs from Antony Fernando)