Approximately one-third of the irrigated area of Tamil Nadu
is watered by eris (tanks). Eris have played several
important roles in maintaining ecological harmony as flood-control
systems, preventing soil erosion and wastage of runoff during
periods of heavy rainfall, and recharging the groundwater in
the surrounding areas. The presence of eris provided
an appropriate micro-climate for the local areas. Without eris,
paddy cultivation would have been impossible.
Till the British arrived, local communities maintained eris.
Historical data from Chengalpattu district, for instance, indicates
that in the 18th century about 4-5 per cent of the gross produce
of each village was allocated to maintain eris and other
irrigation structures. Assignments of revenue-free lands, called
manyams, were made to support village functionaries who undertook
to maintain and manage eris. These allocations ensured
eri upkeep through regular desilting and maintenance of sluices,
inlets and irrigation channels.
The early British rule saw disastrous experiments with the land
tenure system in quest for larger land revenues. The enormous
expropriation of village resources by the state led to the disintegration
of the traditional society, its economy and polity. Allocations
for maintenance of eris could no longer be supported by the
village communities, and these extraordinary water harvesting
systems began to decline.
The tanks, in south Travancore, though numerous, were in most
cases oornis containing just enough water to cultivate the few
acres of land dependent on them. The irregular topography of
the region and the absence of large open spaces facilitated
the construction of only small tanks unlike large ones seen
in the flat districts of the then Madras Presidency, now Tamil