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Pudukottai district is one of the 30 districts of Tamil Nadu with a total geographical area of 4663.29 sq. km. The total population as per 1991 census is 1,32,7148, which is only 2.37% of the state population. Out of the total geographical area, nearly 35% is the net area sown during 1997-98. Surface water is the major source of irrigation for about 82% of the net area irrigated. Vellar, Agniar, Ambuliyar, Karaiyur, Kundar and Pambar rivers drain the district. The district receives rainfall from both southwest (38%) and northeast (44%) monsoons. The district is underlain by geological formations ranging in age from Archaean to Recent. Hornblende biotite gneiss, granite gneiss traversed by quartz veins and pegmatites occur in the western part of the district. Cretaceous sediments and Tertiaries occur in the eastern part of the district, while the Recent alluvial deposits are seen along the major drainage courses and in coastal tract of the district. Numerous lineaments have been identified from LANDSAT imagery, the most prominent ones of which are those oriented in NE–SW. The thickness of weathering ranges from less than a metre to about 12 m. The important aquifers in the district are categorised into (i) fissured, fractured and weathered crystalline rocks and (ii) porous formations comprising Cretaceous, Tertiary and Quaternary sediments. Ground water occurs under phreatic to semi-confined conditions in fissured formations and productive fractures have been encountered down to a depth of 100 m bgl in the crystalline rocks. Ground water occurs in porous formations under water table and confined conditions. CGWB has established network hydrograph stations in Pudukottai district to monitor the behaviour of water table and changes in the ground water quality of the shallow aquifers. In addition to this, CGWB has constructed 11 purpose built observation wells under World Bank Aided Hydrology Project for monitoring purpose (Hard rock 9 nos. and sedimentary area 2 nos.). Pre-monsoon water levels (May 1997) are in the range of 5 to 10 m bgl, where as post-monsoon (January 1998) levels are in the range of 2-5 m bgl in the major part of the district. Analysis of water level fluctuation between May 1997 and January 1998 indicated a rise in water levels through out the district, mostly in the range of 0.20 – 5 m bgl. Long term water level fluctuation have been analysed for the period of 1989-98 (post-monsoon) which has indicated a rise in water levels in the range of 2 – 4 m in the major part of the district. Central Ground Water Board has constructed 15 exploratory wells, 7 observation wells and 5 piezometers in the eastern part of the sedimentary tract of the district. Exploration has revealed the occurrence of potential aquifers down to a depth of 450 m bgl. The thickness of granular zones in the boreholes drilled down to the basement varies between 34 to 370 m. The cumulative thickness of the aquifers within 100 m bgl ranged from 6 to 39.5 m, where as it is between 21 m in the west and north to more than 250 m in the east and southeast in the depth range between 100 and 450 m bgl. Seven wells turned out to be flowing wells and the piezometric head ranged from 2.47 to 13.47 m agl with free discharges ranging between 12 and 33 lps. The discharges of the exploratory wells tested, ranged from 7.5 to 67 lps for a draw down ranging between 4.11 and 23.45 m. The quality of ground water in the fissured formation in general, is potable and suitable for domestic and irrigation uses. In the porous formations, the quality of ground water is generally good and fit for both domestic and irrigation purposes except in the area south of Vellar river covering part of Arantangi and major part of Avudaiyarkoil taluks. Preliminary evaluation of resources based on GEC 1984 norms has indicated that the district has a considerable potential which has to be tapped in the all the blocks. The balance of groundwater resources available in the district is of the order of 76,034 ha m/year. In view of very low ground water development in all the blocks, shallow ground water levels and lack of major industries causing no ground water pollution, the district is not highly vulnerable to perils of over-exploitation, water logging or ground water pollution. |