India is immeasurably dependant on groundwater. Its need for human existence cannot be overemphasized, as water constitutes an important source of drinking and irrigation water in both urban and rural India. Industries too are heavily abstracting groundwater for their use. As it is an integral part of the hydrological or water cycle, its availability depends on a good monsoon and recharge conditions.
Formation of groundwater in a region is controlled by several factors including topography, terrain slope, lithology, rainfall pattern and surface water bodies etc. Mapping of the resource involves the investigation of hydro-geological setting, aquifer and its characterisation.
These investigations are usually done by
- airborne electromagnetic survey (AEM),
- surface investigation methods (time domain or frequency domain electromagnetic survey, GPR’s, proton magnetic resonance survey or electrical resistivity imaging technique, etc.) and,
- through sub-surface investigation (borehole geophysical loggings, chemical and isotopic tracer techniques etc).
State geology maps and accompanying description of lithologies of tube-well logs can also be integrated to prepare 2D and 3D hydro-lithology and aquifer permeability maps across the country.
Adopting a similar approach, Central Ground Water Board (CGWB) is integrating information on hydrology, geomorphology, geology, hydrogeology and hydro-chemical data to prepare aquifer and vulnerability maps of India at 1:50,000 scale for quantity and quality of groundwater under the National Aquifer Mapping and Management (NAQUIM) programme. The programme is integrating data over 3171158 square km area.
In its first analysis, the Board has demarcated the Indian groundwater system into 14 principal aquifers and 42 major aquifers (Fig. 1). The percentage-wise distribution of these 14 principal aquifer systems are
- alluvium (29.82),
- ·basalt (16.15),
- ·banded gneissic complex (15.09),
- ·sandstone (8.21), shale (7.11),
- gneiss (5.01),
- schist (4.44),
- granite (3.18),
- charnokite (2.41),
- limestone (1.98),
- quartzite (1.48),
- laterite (1.29),
- khondlite (1.04),
- intrusives (0.63), and
- unclassified aquifers (2.16).
The detailed map would help in systematic aquifer-wise planning of groundwater development programme is presented below.