This term comes from the Tamil 'anai kattu' meaning dam building. It is a small to a medium-sized dam meant to serve as a reservoir. At a height of 20 feet or so, it spans across the length of the river and is meant for village usage in case of a small river and for irrigation channels in case of a large river such as Kaveri.
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Eri
A tank in Tamil Nadu is called an eri and its maintenance is the responsibility of the community.