Great Tamil Kings promoteed the constructions of a network of wells, ponds, lakes and rivers. The famous king Mathurantaka Cholan constructued largest artificial lake. But very few folk know of the auotmatic desluicing system which was installed in most of the lakes in olden times.
A large stone box was placed at the bottom of lakes and irrigation canals lead the lake water through the stone box. The stone box was created with two kind of holes. The one at the top of the stone box had the larger hole and was covered by a stone sphere. Two or three smaller holes were made at the bottom surface of the stone box to lead sluice at the bottom of the lake into the stone box.
The stone ball covering the top surface was removed periodically to allow lake water to gush into the stone box. The gushing water lowered the pressure within the stone, The lower pressure pushes the sluice at a higher pressure at the bottom of the lake, up the smaller holes at the bottom of the stone box. Craftmen who created the stone box aimed to achieve a 4:1 ratio of fresh water to muddy water through the stone box. Metal/bamboo/stone pipes carried this rich mix of soil and water from the stone box to the fields from the lake.
Most of the older lakes have disappeared today. Shrubs surround strange looking stone contraptions which were once cherished for their practical use.
குமிழித் தூம்பு மதகு - the tamil name for the mechanism to described above