Notes on Percolation tanks
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The downward movement of the water through the soil due to force of gravity is termed as Percolation. The percolation water goes deep into the soil until it meets the free water table. On the one hand, due to rapid percolation, there is practically no danger of soil suffering from bed drainage, but on the other hand, there is a possibility of the dissolved plant nutrients like calcium and magnesium being carried deep into lower layers and depositing beyond the reach of the roots of common field crops. In sandy or open textured soils there is a rapid loss of water through percolation. The flow of water due to gravity is very marked when the soil is in a saturated condition, and generally the direction of such flow is downward, although a little lateral flow also takes place. The larger pores i.e., the macro-pores serve as the main channels for this gravitational flow.
Percolation losses: When rainfall is high and water holding capacity of soil is less, the losses due to percolation are very great. Such losses are very rapid particularly when the soils are sandy and porous e.g., in case of lateritic soil in Konkan region, the soil is quite workable within a few hours even after a heavy rainfall. Besides rapid percolation of water there is also a heavy loss of plant nutrients viz., Ca, Mg, S, K, etc., resulting in soil becoming acidic.
Percolation tanks are the structures for recharging ground water. These are generally constructed across streams and bigger gullies in order to impound a part of the run-off water. This water, in due course, finds its way into subsoil and recharges the found water. This leads to better recuperation of wells in the downstream areas. Such ponds have become popular in many a place. In Maharashtra there is legislation to cover percolation tanks. The water is not used for surface irrigation. In Tamil Nadu, where there is over-exploitation of ground water, farmers are now volunteering to spare land for percolation tanks.
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