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Occurrence of ground water -
Role of Geology - Hydrogeological set up
Occurrence and movement of ground water is controlled by the geology of the
area. In contrast to the common three types of rocks, i.e. metamorphic,
igneous and sedimentary, hydrogeologists prefer to classify geological
formations as consolidated, semi-consolidated and unconsoli-dated formations.
Consolidated rocks are metamorphic, igneous and hard sedimentaries rocks
and groundwater occurs in joints, fractures, and weathered residuum. This
formation does not hold large quantities of water and are not good aquifers.
Semi-consolidated formations are sedimentary rocks like sandstone, shale,
limestones etc. Sandstone can yield moderate quantity of water, while Karstic
limestones can be good aquifers. Unconsolidated formations, mostly of recent
origin, are good repository of groundwater and form the major aquifers.
Geological history like migration of river beds in space and time has formed
buried channels and are good locations for tapping aquifers. Other important
deposits are fluvial deposits in plain lands, inter montane valley deposits.
Deposits at the foothills of the Himalayas are known as 'bhabar' deposits.
Geological or hydrogeological and topographical set up influences the
accumulation of groundwater deposits. While in hills, major part of rainfall passes
away as run-off, in the plains and intermontane' valley deposits, groundwater
occurs in plenty. In hard rock areas, the outcrop area is not good locales of
groundwater reserve, while weathered rocks can hold copious amount of
water. Weathered granite, weathered vesicular lava, laterites have good water
holding capacities. In short, unless you know the geological set up of the area,
you cannot plan to explore the area for groundwater development.
OCCURRENCE OF GROUNDWATER IN INDIA
Groundwater in India occurs depending upon the hydrological set up.
Hydrologically the country can be divided into the following three important zones:-
1)
Bhabar and Piedmont in the foot hills of the Himalayas.
2)
Indo-Gangetic Alluvial plains which is the main repository of
groundwater.
3)
The Peninsular shield area which is occupied mainly by the hard rocks.
