Madras, April 12.

The Central Groundwater Board is compiling a hydrogeological map of India to be presented at the 25th International Geological Congress in Sydney.

This map will be drawn on a scale 1:5,000,000. The Board will later produce another map on a scale 1:2,000,000 on statewide basis with suitable insets incorporating more data.

Under the international hydrological decade programme, 700 hydrograph stations have been selected to monitor seasonal water levels from different geological formations under known hydrogeological settings.

For the first time on a national scale, the Board has undertaken systematic search for locating groundwater. It has so far covered over a million sq.km. out of a total estimated area of 3.2 million sq.km.

Data collected by these stations on water level fluctuations and temperature variations covers over 60 per cent of unexplored area in the country.

Over 5,000 short term water supply investigations in drought prone areas have been completed. These are confined to small isolated pockets and resulted in setting up of new hydrogeological horizons.

The Board has undertaken special investigations for locating and investigating thermal springs, mines and coalfields to spot out inland salinity of groundwater in these areas.

Vast areas in the loose and unconsolidated and semi-consolidated sedimentary rocks have for the first time been demarcated for moderate scale development of groundwater.

Exploratory drilling has started in certain areas to ascertain the quantity available.

The results varied from 100 per cent in West Bengal to 10 per cent in Rajasthan. The Board has now extended the drilling operations to Andhra Pradesh, Bihar and Maharashtra.

Pilot projects for water balance studies in varieties of formations with uniform and diverse hydrogeological setting, like hard and compact sedimentaries and crystalline rocks with scope for applying the methodology elsewhere have been taken up, according to Board sources.