Central Ground Water Board (CGWB) and State Ground Water Board in consultation with National Bank for Agriculture and Rural Development (NABARD) jointly carry out periodical estimation of ground water resources of the country to assess the changes in ground water scenario, which occur due to natural and man-made reasons. The State Level Committee headed by the Secretary, In-charge, Water Resources/Irrigation discuss and approve the state level estimation reports. The latest estimate was carried out with 2004 as the Reference Year.
Annual replenishable groundwater resources was estimated as 433 bcm; net annual ground water availability as 399 bcm; annual ground water draft as 231 bcm; and stage of ground water development as 58 %. Out of 5723 assessment units, 4078 units were categorised as ‘safe’, 550 units as ‘semi-critical’, 226 units as ‘critical’ and 839 units as ‘over exploited’. Rest of blocks have saline ground water. The next estimation has envisaged for the reference year 2007-08.
The methodology of estimation of ground water resources of the country has been periodically revised. The latest methodology was evolved by a Committee known as ‘Ground Water Resources Estimation Committee’ which was constituted drawing members from CGWB, NABARD, various academic institutes like Indian Institute of Science, Bangalore, National Institute of Hydrology, Roorkee, University of Roorkee, Centre for Water Resources, Kozhikode, and various state ground water departments. The Committee submitted its recommendation in 1997.
The methodology involves estimation of annual recharge to ground water through various sources like rainfall, canal seepage, return flow of irrigation, seepage from tanks and ponds and recharge from water conservation structures. It also estimates annual ground water draft for different uses viz. domestic and industrial irrigation. The stage of ground water development is calculated as a percentage of ground water draft to the net ground water availability. Finally, the categorisation of an assessment unit (mostly block) is done based on stage of ground water development and long-term water level trend.
Different types of database are required for Ground Water Resources estimation. Database involving geographical details like watershed boundary, canal command areas and non-command areas, slope of the landform aquifer disposition, canal morphology, morphology of tanks and ponds, water conservation structures, drainage pattern, cropping pattern, land use pattern, well census, irrigated area etc. needs to be spatially as detailed as possible. Measured data like water level, rainfall, canal discharge, water availability in tanks and ponds, base flow etc. are required to be intensified both in time and space.
Database on parameters and norms like special yield, rainfall infiltration factor, canal seepage factor, irrigation recharge factor, well discharge, crop water requirement etc. should represent different agro-climatic zones, hydrological units and soil types pavilion in the State. Strengthening of database would largely refine the ground water resource estimation and since these database are being generated and maintained by various Central and State agencies, strengthening of database would therefore, require collated efforts on the part of all concerned agencies.
No comments:
Post a Comment