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condition or under unconfined condition and ground water occurring under the
pressure of impermeable layer is said to be occurring under 'confined
condition'. For example groundwater in Kolkata is occurring under confined
condition while groundwater in Nadia District, West Bengal occurs under water
table condition. The zone of aeration, or the suspended zone (vedose water) is
very important for agriculture. This zone is commonly divided into three zones,
i.e. soil water zone, intermediate zone and the capillary zone. In certain cases,
due to addition of excess water in the saturated zone, water-table may rise upto
the roots of the plants in the soil water zone, affecting the productivity. Such
situations are not uncommon in the command of major irrigation projects like
Sarda Sahyak Canal Command in U.P., Indira Gandhi Nahar Yojana in Rajasthan
etc. This phenomenon is known as water-logging.
Fig. 6.1 : Divisions of subsurface water
(After Todd, 1995)
Figure 6.1 explains the vertical movement of water in a soil or permeable
stratum . When water fall on the surface a small part is first absorbed in the top
thin layer so as to replenish the soil moisture deficiency. This process of vertical
movement in the soil zone is known as infiltration. Amount of water absorbed in
