Geology Reference
In-Depth Information
The large alluvial tract in the Sindhu-Ganga-Brahmaputra plains, extending
over a distance of 2000 kms from Punjab in the west to Assam in the East,
constitute one of the largest and most potential groundwater reservoirs in the
world. These aquifer systems are extensive, thick, hydraulically interconnected
and moderate to high yielding. To the north of this tract all along the
Himalayan foot hills, lies the linear belt of Bhabar piedmont deposits, and
the Tarai belt down slope with characteristic auto flowing conditions.
Hydrogeologically alluvial formation consists of unconsolidated sand, silt
and clay with occasional beds of gravel extending to a depth of more than
one km at some places. In a narrow belt in the north, at the foot of the
Himalayas, artesian aquifers, under free flowing conditions exist at a depth
of 50 to 100 m. Possibilities of deep confined aquifers as a potential source
of water is indicated from deep drilling carried out for oil exploration at
some places (Jones, 1987). The area is also bestowed with good rainfall and
recharge conditions. Ground water is mainly used for irrigation in addition
to domestic and other uses. Tube well irrigation is being practiced in this
area from the last more than one hundred years.
The next older formation of Cenozoic age consisting of unconsolidated to
semi-consolidated sandstone and shale occupy parts of coastal areas and also
in the northeast. Under favourable conditions these formations form artesian
aquifers as in parts of Cambay basin in the west and Neyveli in Tamilnadu
in South India.
The main volcanic suite of rocks is represented by Deccan Traps occupying
an area of more than 500,000 km
2
in the western and central parts of the
country. A number of basaltic flow units are identified of age varying from
Upper Cretaceous to Lower Eocene. Main source of groundwater is from the
weathered, fractured and vesicular horizons. At places different layers of
basalt form a multi-aquifer system. Parts of this area has semi-arid climate
due to which recharge is limited and availability of groundwater is poor.
The Gondwanas are represented by semi-consolidated sandstone, shale
and coal beds, which were deposited in the structurally controlled faulted
basins. They are fresh water deposits of age varying from Permo-
Carboniferous to Late Jurassic. They also form multi-aquifer system.
Uncontrolled mining has resulted in the flooding of mines causing great loss
of life of miners.
Most part of Peninsular India is occupied by a variety of hard and fissured
formations, including Crystalline, trappean basalt and consolidated
sedimentaries (including carbonate rocks), with patches of semi-consolidated
sediments in narrow intracratonic basins. Rugged topography and compact
and fissured nature of the rock formations combine to give rise to
discontinuous aquifers, with limited to moderate yield potentials. The near
