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Groundwater Structures :
Design of groundwater structure will require knowledge of the geology of the
area. Following are the different types of groundwater structures :
A.
Hard Rock / Consolidated rocks :
a) Dug wells
b) Dug-cum-borewells
c) Bore wells
a)
Dug wells or open wells :
Dug wells are excavated as pits or holes to reach the water table for extraction
of ground water. These are the most ancient methods of drawal of groundwater
and are recorded in all ancient civilization. Dug wells are mostly circular and
varies in diameter from 1 meters to 10 meters Depth also ranges from a few
meters to as much 100 meters depending upon the hydrogeological condition.
Depth of the well should be decided in such a manner so that at least 0.8 meters
water column exists during summer months to enable the foot valve of the pump
to operate in case of mechanized lifting devices. There are records of
rectangular shaped dug wells also, but circular design is preferred for
stability. For the ease of construction for deep dugwells, telescopic diameter
are also constructed.
In the hard rocks, the weathered zone is curbed by masonary or concrete rings.
The hard rocks portion may remain naked. The masonary or concrete rings
must have weep holes for ease of entry of water from the side.
b)
Dug-cum-bore wells :
In many areas a borewell is drilled at the bottom of a dug well to increase the
well yield. Groundwater in the fractured zone percolates through inclined
fracture planes and create a confining layer and when the drilled hole at the
bottom of the dugwell touches this layer, water will rush in to the bottom of the
dugwell thus increasing the well yield.
