Trace the evolution of irrigation infrastructure in the Kaveri basin from the Sangam period to the present.

The Kallanai or Grand Anicut, built by the Chola king Karikala in the 2nd century CE and recognised by the ICID as a World Heritage Irrigation Structure in 2021 [1], still diverts the Kaveri — making the basin a rare, living continuum of irrigation engineering from the Sangam age to the present.

Sangam and early historic foundations

• Kallanai: a 329-metre barrage of unhewn interlocking stone laid without cement, described as the fourth oldest dam in the world and the first in India, which turned the Kaveri towards the Thanjavur delta and originally watered about 69,000 acres [1].
• Beyond diversion, the period shows regulation technology: the ASI's Tiruchi Circle has provisionally identified a brick-and-stone inlet/water-regulation structure on the Kollidam bed at Koogur, near Lalgudi, tentatively dated to the 3rd–4th century CE — pending excavation, an indicator that sluice-type control accompanied the anicut [2].

Medieval to colonial consolidation

• Successive dynasties and later colonial engineers extended the diversion principle into a branch network, adding anicuts across the Kollidam and formalising the delta's distributary channels rather than replacing the ancient works.
• The emphasis shifted from seasonal diversion to assured supply, culminating in upstream storage at Mettur, which converted the delta into a regulated command [3].

Contemporary phase: storage, distribution and governance

• Water released from Mettur reaches the Grand Anicut, where it is apportioned among the Cauvery, Vennar, Grand Anicut Canal and Coleroon, serving a command of 4,53,046 acres in Thanjavur district alone [3]; Kallanai's own command has grown to roughly 1.32 million acres [1].
• Infrastructure is now matched by institutions — the Cauvery Water Management Authority (2018), constituted under the Inter-State River Water Disputes Act, 1956, regulates sharing across riparian states [4].

The basin's trajectory runs from stone diversion to storage, and finally to negotiated allocation. Sustaining it now demands canal modernisation, micro-irrigation and delta ecosystem protection, so that a two-millennia-old engineering inheritance advances water security under SDG-6.