GROUND WATER RESOURCES AND DEVELOPMENT POTENTIAL OF
 VELLORE DISTRICT, TAMIL NADU

Vellore District is located in the northwestern part of Tamil Nadu. Its total geographical area is 5920.18 sq.km. and has been subdivided into seven taluks and 20 blocks for administrative purposes. The district has a total population of 30,26,432 as per 1991 census, of which more than 65% resides in rural area. Agriculture is the major occupation of the people in the district with the net area being 40% of the total geographical area. Leather tanning and associated industries are also prominent in the district. Paddy, groundnut, sugarcane and cotton are the major crops grown in the district. Food grains and food crops like jawar, ragi, maize and pulses, cash crops like turmeric and chillies, oil seeds like coconut and sesame are also grown. Nearly 20% of the total geographical area is under irrigation. Ground water is the major source of irrigation, accounting for nearly 75% of the net area irrigated.

The district receives a normal annual rainfall of 916.2 mm. The contribution from southwest monsoon ranges from 45 to 52%, whereas the contribution from northwest monsoon ranges from 30-43% of annual normal rainfall.

Physiographically Vellore district can be broadly divided into (i) hilly terrain in the western and southwestern parts and (ii) Plain regions in the east. Palar and its tributaries viz. the Ponnaiyar, Cheyyar, Pambar and Malattar drain the district. Almost all the major streams are ephemeral in nature and are mostly structurally controlled. The district has more than 1300 tanks and 604 canals, which act as the main sources of surface water. Two irrigation projects vis. Palar Anicut and Ponnaiyar Anicut have been executed for augmenting surface water irrigation facilities.

A major part of district is underlain by crystalline rocks comprising Charnockite and Khondalite groups of rocks of Archaean age, except for Recent Alluvial deposits along major drainage courses and patches and Gondwana sediments. The Crystalline rocks exhibit several structural deformations arising out of polymetamorphism. The predominant trend of lineaments in the eastern and southwestern parts of the district is NE-SW whereas in the central part, both NE-SW and NW-SE trending lineaments have been identified.

Ground water occurring in crystalline rocks, limited to the weathered residuum in the shallow zone and to sheared and fractured zones at depth, is under phreatic to semi-confined conditions. In the sedimentary formations comprising sandstone, clay and shale, phreatic aquifers of limited potential exist. Recent alluvial aquifers also constitute potential aquifers of limited thickness (<15 m) in the district. Depth to water is within 10.0 mbgl in a major part of the district throughout the year. Deeper water levels are observed in isolated pockets in Gudiyatham, Peranambattu, Madanur, Anicut and Vellore blocks. Water levels are shallowest in the area adjoining Palar River.

Comparison of ground water levels during May 1997 and January 1998 indicates a rise in ground water levels in about 84% of wells analysed. Rise in levels is generally in the range of 0-4 m. Decline in water levels during the period has been observed in Gudiyatham, K.V. Kuppam & Kandili blocks.

Analysis of long-term water level data (1987-97) indicates that water levels have a rising trend in more than 90% of the wells analysed. Declining trends have also been observed in isolated cases in Gudiyatham, Alangayam and Kaniyambadi blocks. Geophysical studies, carried out in connection with selection of sites for exploratory drilling in crystalline rocks have given apparent resistivity ranging from 10 ohm.m (top soil) to >900 ohm.m (massive granite/charnockite).

Exploratory bore wells have been constructed at 20 locations by CGWB in the district, ranging in depth from 18.70 to 200 m.bgl. The thickness of weathered zone encountered in these wells ranged from 2.50 to 16.60 m. and the yield of wells from 0.20 to 4.50 lps. Fracture zones were encountered down to a depth of 116 m. during drilling. The yield of bore wells constructed by State Govt. agencies in crystalline rocks ranged from 40 to 200 lpm. The transmissivity of these aquifers ranged from 8 to 80 m²/day. In recent alluvial formations, the yield of wells ranges from 200-400 lpm, transmissivity ranged from 200-300 m²/day and field permeability ranged from 20-30 m/day.

Preliminary evaluation of ground water resources as per GEC norms (1984) indicates that the level of ground water development in the district ranges from 40.84% (Walajapet block) to 110.90% (Kaniyambadi Block). The level of ground water development at year 5 for the district is computed as 79.82%.

Based on the level of development at year 5, three blocks (K.V. Kuppam, Kaniyambadi & Vellore) fall under “Over-exploited” (Development >100%) category, four blocks (Nemili, Madanur, Tiruppathur & Anicut) under Dark (85-100%) category and one block (Peranambattu) under (<65.2) category. All the remaining blocks are classified as “Grey” category (65-85%). Computation of the irrigation available in the district indicates that the potential already created (as in 1998) is about 85% of the utilisable irrigation potential. Considerable potential remains to be tapped in Peranambattu, Walajapet, Sholinghur, Arcot, Alangayam and Timiri blocks.

Ground water in the district, in general, is potable and suitable for domestic and irrigation applications, except in the vicinity of leather tanning units mainly in Ambur, Vaniyambadi, Ranipet, Walajapet and Madhanur blocks, where it is highly mineralised due to pollution from tanneries.

Development of ground water in the district is mainly through dug wells and shallow bore wells. The water requirements of urban habitations are met through water supply scheme designed and executed by TWAD Board, most of which tap the recent alluvial deposits of Palar River or its tributaries. About 98% of the rural habitations have also been provided with protected water supply schemes. In spite of the rather high level of ground water development in the district, considerable scope still exists for development in several block, ideally through dug wells and shallow bore wells, constructed at suitable locations, observing proper spacing criteria.

Several blocks in the district where leather tanning units function are vulnerable to a high degree of pollution and unless suitable remedial measures are initiated, may end up with no source for drinking water supply. Blocks where the development of ground water is above 85% are likely to be vulnerable to the hazards associated with water table decline unless the ground water withdrawal is restricted to sustainable levels.