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Namakkal district, having a total geographical area of 3363 Sq.km. has been subdivided into 4 taluks and 15 blocks for administrative convenience. The district has a population of 1495661 (2001 Census) with a population density of about 4.45 persons/ Square Kilometre. About 63 percent of the population resides in rural areas. Agriculture is the mainstay of the rural populace in the district. During 2002-03, the net area sown constituted about 47 percent of the total geographical area of the district. Wells are the major source of irrigation water, accounting for about 89 percent of the area irrigated. Food crops comprising cereals and pulses are cultivated in about 30 percent of the total area under cultivation in the district. Oil seeds like groundnut and coconut are cultivated in about 21 percent and sugarcane in about 5 percent of the area. Namakkal district receives rainfall from both Southwest and Northeast monsoons. The normal annual rainfall in the district ranges from 641 to 881 mm. Physiographically, the district forms a plateau with many hillocks and undulating terrain. Various landforms namely Structural hills, buried pediments, pediments, bazada zone and valley fills have been identified from Satellite imagery. A major part of the district forms part of Cauvery river basin. All the rivers except Cauvery are ephemeral in nature. The Tirumanimuttar is the important tributary of Cauvery River, whereas Vasista and Suvedha are the important tributaries of Vellar river draining the northern part of the district. The district has no major surface water reservoirs. It has about 270 tanks and 46 canals, which are used, as surface water irrigation sources. The district is underlain by geological formations ranging in age from Archaean to Recent. Charnockites, gneisses and associated rocks are the important litho-units exposed. The crystalline rocks exhibit multi-structural and poly-metamorphic complexity. The thickness of weathering is in the range of 2 to >30 m. Recent alluvial deposits are generally localised and are restricted to major drainage courses. A number of folds, faults and shears, developed through at least three phases of tectonic deformation have been identified in the district. Three sets of major lineaments, trending NE-SW, N-S and NW-SE have been identified in the district from Satellite Imagery. Ground water occurs under phreatic conditions in the shallow alluvial aquifers and weathered residuum in crystalline rocks and under semi-confined to confined conditions in deeper fractures. The yield of wells and aquifer parameters show wide variation. Large diameter wells have yields ranging from 100 to 500 lpm. and varies considerably depending on the topographic set-up, lithology and degree of weathering. Bore wells, drilled down to 292m.bgl. by Central Ground Water Board have yields ranging from 0.50 to 15.26 lps. Productive fracture zones have been encountered in the depth range of 8.80 to 292.00 m bgl. Depth to water in phreatic zone was in the range of 1.98 to 41.25 m.bgl. during pre-monsoon season (May 2003) and between 1.60 and 32.40 during post monsoon period (January 2004). Elevation of water table during January 2002 ranged from 110.57 m. to 405.47 m above MSL. The general gradient of water table is toward Cauvery. A Comparison of water levels during May 2003 and January 2004 show that the water levels have shown a rise in about 86 percent of wells analysed. Analysis of long-term fluctuations using Simple linear regression indicate declining trend in 55 percent wells during pre-monsoon period and in 69 percent wells in post-monsoon period. Analysis of long-term water levels by comparing the water levels during 2003 with the average values for the previous decade (1993 – 2002) indicate decline in water levels in about 78 percent wells in pre-monsoon period and in 72 percent wells in post-monsoon period. Depth to piezometric surface in deeper aquifers ranged from 14.00 to 39.00 m.bgl. during May 2003 and from 6.10 to 30.60 m.bgl. during January 2004. The fluctuation of piezometric surface during May2003–January 2004 ranged from 1.34 to 13.40m. Analysis of long-term trends indicates declines in the piezometric heads in all the bore wells analysed in the district. Development of ground water in the district is through dug wells, filter points, dug-cum-bore wells and bore wells. The Net Annual Ground Water availability, computed as per norms recommended by GEC 1997 is of the order of 493.51 M.Cum. The existing ground water draft for all uses in the district as on 31.12.2003 is of the order of 503.82 M.Cum. The balance ground water resources available, computed as the difference between net annual ground water available and the gross ground water draft including the allocation for domestic and industrial uses for the next 25 years has been computed as 69.048 M.Cum for the district as a whole as in January 2003. The stage of ground water development in 2003, computed as the ratio of the net ground water draft to available ground water resources for irrigation is in excess of 100 percent in Erumaipatti, Namagiripet, Namakkal, Pallipalayam, Puduchatram, Rasipuram, Sendamangalam and Vennandur blocks and hence they have been classified as ‘OVEREXPLOITED’. Mallasamudram and Paramathi blocks, in which the development of ground water is between 90 and 100 percent, have been categorised as ‘CRITICAL’, whereas Kabilarmalai, Mohanur and Tiruchengode blocks, where the development is between 70 and 90 percent fall under ‘SEMI CRITICAL’ category. The remaining blocks in the districts fall under ‘SAFE’ category. The irrigation potential created is in excess of utilisable irrigation potential in a major part of the district. Limited potential is available for development in Elachipalayam, Kabilarmalai, Kolli Hills, Mohanur and Tiruchengode blocks. Ground water in the district, in general, is potable both in the phreatic and deeper fractured aquifers. Incidence of high TDS, Fluoride and Nitrate has been reported from parts of the district. Ground water in a major part of the district is likely to cause high to very high salinity hazard when used for irrigation. The major ground water-related problems in the district include decline in ground water levels and the incidence of fluoride in excess of permissible limits in parts of the district. |