Geology Reference
In-Depth Information
surface weathered mantle forms the all important groundwater reservoir, and
the source for circulation of groundwater through the underlying fracture
systems. In the hard rock terrain, deep weathered pediments, low-lying valleys
and abandoned river channels generally contain adequate thickness of porous
material, to sustain groundwater development under favourable
hydrometeorological conditions. Generally, the potential water saturated
fracture systems occur down to 100 m depth, and in cases yield even up to
30 litres per second (Ips). The friable semi consolidated sandstones also
form moderate yielding aquifers, and auto flowing zones in these formations
are not uncommon. Shallow large diameter dug-wells and small diameter
bore-well s are the main source of water supply for domestic and irrigation
purposes. The yield characteristic of wells varies widely. Over exploitation
of groundwater has caused considerable lowering of water table. Recent
studies have indicated the presence of potential aquifers at deeper levels due
to the presence of deep-seated fractures along lineaments. These lineament
zones are found to be highly productive for construction of bore-well s
(Singhal and Gupta, 1999).
Consolidated sedimentary formations viz., sandstone, shale and limestone
of Pre-Cambrian age occur as isolated basins in different parts of the country.
The permeability of the rocks is usually poor. Limestone is usually massive
and lack in the development of secondary porosity due to the lack of solution
activity except in some parts of western and Peninsular India.
The coastal and deltaic tracts in the country form a narrow linear strip
around the peninsula. The eastern coastal and deltaic tract and the estuarine
areas of Gujarat are receptacles of thick alluvial sediments. Though highly
productive aquifers occur in these tracts, salinity hazards impose quality
constraints for groundwater development. In this terrain, groundwater
withdrawal requires to be regulated so as not to exceed annual recharge and
not to disturb hydro-chemical balance leading to seawater ingress.
The high relief areas of the northern and northeastern regions occupied by
the Himalayan ranges, the hilly tracts of Rajasthan and peninsular regions
with steep topographic slope, and characteristic geological set-up offer high
run-off and little scope for rainwater infiltration. The groundwater potential
in these terrains are limited to intermontane valleys. Distribution of
hydrogeological units in India is given in Table 3.
