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Dharmapuri district, located in the northwestern part of Tamil Nadu has a total population of 2833252 as per 2001 Census, about 82% of which resides in rural areas. The district has been subdivided into 10 taluks and 18 blocks for administrative convenience. Agriculture is the main occupation of the rural populace in the district and the net sown area accounts for about 42% of the total geographical area of the district. Groundnut, Paddy, Ragi, Sugarcane, Coconut, Jowar (Cholam), Cotton and Pulses are the important crops grown in the district. Dug wells and dug-cum-bore wells are the major sources of irrigation, followed by tanks and canals. The district receives average annual precipitation ranging from 760 to 910 mm., with the coefficient of variation ranging from 22 to 36%. Rains are received during both Southwest (June to September) and northeast (October to December) monsoon seasons. There is considerable spatial variability in the distribution of rainfall, which shows a gradual decrease from north to south, east and west. Dharmapuri district falls under Ponnaiyar and Cauvery river basins. All the rivers except Cauvery are ephemeral in nature. Prominent geomorphic units identified in the district from Satellite Imagery include shallow and deep buried pediments, pediments, bazada zones and structural hills. The district has 10 reservoirs and 175 tanks, which serve as surface water irrigation sources. Krishnagiri Dam Project is the most important surface water irrigation project in the district, irrigating about 3642 ha. Krishnagiri taluk has the maximum number of tanks (65) in the district, followed by Dharmapuri (25) and Palacode (18) taluks. Geologically, the district is underlain by formations ranging in age from Archaean to Recent. Crystalline rocks comprising Charnockites, gneisses and associated rocks occupy a major part of the district. Recent alluvial and colluvial deposits are restricted to major drainage courses and foothill zones. Geophysical investigations carried out along select major lineaments have established the occurrence of thick weathered zones in gneisses and charnockites. Exploratory bore wells have been constructed at 29 locations by Central Ground Water Board, which has brought out the wide spatial variation in well yields and aquifer parameters. Productive fracture zones have been encountered down to a depth of 188 m. The yield of exploratory wells in the district ranged from 0.2 to 16.44 lps. The important aquifer systems in the district are constituted by weathered and fractured crystalline rocks. Ground water occurs under phreatic conditions in the weathered residuum and under semi-confined to confined conditions in deeper fracture zones. Recent alluvial deposits are found to form localized, discontinuous aquifers with low to moderate yield potentials. Depth to water levels in observation wells of CGWB including piezometers constructed under Hydrology Project tapping the phreatic zone ranged from 1.88 to 18.05 m.bgl. during May 2001 and from 0.50 to 13.80 m.bgl during January 2002. The shallowest water levels in pre-monsoon period were observed in Kaveripattinam block whereas during post-monsoon period, water levels were the shallowest in Kariamangalam, Kaveripattinam, Pappireddipatti, Thally and Krishnagiri blocks. The elevation of water table in phreatic aquifers during January 2002 ranged from 268 to 914 m. above Mean Sea Level. The gradient of ground water table, in general, is towards east and northeast. The fluctuation of water levels during January 2002 in comparison with water levels during May 2001 ranged from a decline of 5.10 m. to a rise of 11.15 m. Rise in water levels were observed in about 80% of wells analysed, indicating recharge sufficient to compensate withdrawal in a major part of the district. Comparison of water levels during May 2001 with the average water levels for the period 1991 – ’00 indicates a rise in 56% wells analysed. Analysis of long term trend of ground water levels during May for the period 1992 – 2001 has shown a rising trend in about 52% of wells analysed. The depth to piezometric surface in the district ranged from 7.16 to 14.20 m.bgl. during May 2001 and from 5.0 to 11.30 m.bgl during January 2002. It was below 10.0 m.bgl in the major part of the area during both these periods. The fluctuation in piezometric levels between May 2001 and January 2002 ranged from a decline of 0.80 m. to a rise of 8.50 m. Computation of the ground water resources available in the district based on GEC 1984 methodology show that the total replenishable ground water resources available in the district is of the order of 108680ha.m/yr. The net utilisable ground water resources available in the district for irrigation have been computed as 88334 ha.m/yr. The net ground water draft through various abstraction structures is of the order of 65190 ha.m/yr. The balance ground water available, computed as the difference between ground water resources available for irrigation and net ground water draft has been computed as 34497 ha.m. The level of ground water development projected to year 5 and assuming an annual increase of 0.6% in ground water draft ranges from 8.05% in Kelamangalam block to 127% in Palacode block. Based on the level of ground water development, Palacode and Bargur blocks have been categorized as ‘OVEREXPLOITED’ (>100%), whereas Dharmapuri, Pappireddipatti and Mattur blocks have been categorized as ‘DARK’ (85–100%). In Krishnagiri, Veppanappalli, Kaveripattinam, Karimangalam, Harur and Uttangarai blocks, the level of ground water development is between 65 and 85% and is hence categorised as ‘GREY’. The remaining blocks, where the level of ground water development is below 65%, have been categorised as ‘WHITE’. The status of irrigation potential from ground water varies considerably from block to block. Considerable potential is available for development in Hosur, Sulagiri, Thally, Kelamangalam and Pennagaram blocks of the district, to be developed through suitable ground water abstraction structures. The balance irrigation potential available in the district can be fully developed by constructing 37474 ground water abstraction structures, each having an average command of 1.0 ha. Considerable spatial variation exists in the quality of ground water in both shallow and deeper aquifers in the district. Ground water in the phreatic zone, in general, is potable but is likely to cause high to very high salinity hazard and medium to high alkali hazard when used for irrigation. Proper soil management strategies are to be adopted in these areas while using these waters for irrigation. Majority of samples collected form the phreatic zone belong to CaHCo3 and CaCl2 type, indicating that various geochemical processes such as cation exchange and base exchange are active in this zone. Occurrence of fluoride and nitrate in excess of permissible limits for drinking use has been noticed in ground water from the fracture zone in the entire district. Presence of iron in excess of permissible limits is also observed in localized areas. Major ground water–related issues in the district include the depletion of ground water levels due to over-exploitation and the presence of fluoride in excess of limits recommended for human consumption in a major part of the district. Industrial pollution in Hosur-Krishnagiri area is likely to become an issue in the near future. In view of the rather high level of ground water development in many of the blocks of the district, further development of ground water has to be carried out in a judicious manner. Artificial recharge through rainwater harvesting also needs to be popularised in the district as a cost-effective method for arresting the decline of ground water levels and water quality deterioration. |