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The area is drained by Palar, Ponnaiyar rivers and its distributaries. The area covered by the studies is 3044 Sq. km. The area is underlain by crystalline of Archaean group of metamorphic rocks. Alluvium of recent age restricted along the river Palar. Recent alluvium consists of sands, clay and silts. The crystalline rocks with granulitic texture and showing characteristic gneissic bending, charnockite are found in patches. Pumping tests were carried out on 10 open irrigation wells in different hydrogeological terrains. 100 key wells have been established during premonsoon period and 222 wells inventoried. The depth of dug wells ranged from 3.65 mbgl (Ayerpadi) to 23.9 mbgl (Mettur). During the premonsoon season the water levels ranged from 0.90 mbgl (Uriyur) to 16.9 mbgl (Balamudur). During the postmonsoon season the water levels ranged from 0.93 mbgl (Ayerpadi) to 17.9 mbgl (Damarapakkam). The fluctuation of water level varied from 0.0 (Artumparuthi) to 3.75 mbgl (Kainur) and -0.05(Sholingur) to -4.85 mbgl (Sumaitangi). The blocks of Anicut, Arcot, Kaniyambadi, Katpadi, Sholongur, Vellore and Timiri are “over-exploited”. The blocks of Arakkonam, Kaveripakkam and Walaja are “semi-critical”. Nemili block is in the “critical” category. Hydrological studies such as field infiltration tests in various soil groups and assessment of water balance in the water shed were carried out for Koilmalai watershed which forms part of Palar river basin. Compared to the previous studies, water levels are in a declining trend. With a view to computing the unit draft one village has been selected from each over-exploited block e.g. Palayanoor village in Timiri Block, Virudhampattu village in Katpadi Block and Perumal kuppam village in Sholingur Block.
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